Rights Reserved. No Part of This Publication May Be

COPYRIGHT All rights reserved. No part of this publication may be reproduced, stored in an automatic database or retrieval system, or published in any form or in any way, electronically, mechanically, by print, photo print, microfilm or any other means without prior written permission of COB. In accordance with article 15a of the Dutch Copyright Law of 1912, information from this publication may be quoted in articles, dissertations and books, provided the source is mentioned clearly as well as indication of the author is given, if mentioned in the source. © COB report K100-06 ‘Second Heinenoord Tunnel Evaluation Report,’ February 2000. Stichting COB, Gouda, the Netherlands.

DISCLAIMER COB and those who worked on this publication have observed as much accuracy, meticulousness and care as possible when composing this publication. Nevertheless, it should not be excluded that errors and omissions may be found in this publication. Therefore, any use of this publication and this information is entirely at the risk of the user. COB, including anyone who worked on this publication, rejects any responsibility and expressly disclaims all liability for damages of any kind arising out of use of, reference to or reliance on this publication and its information, unless the damages proceed from intent or coarse negligence of COB and/or anyone who worked on this publication. PROLOGUE

Knowledge and experience in the field of underground construction in soft soil is important if the Netherlands wish to keep abreast of topical matters and maintain the national and international position of Dutch designers and contractors. A broad panel of parties from the business world, government and knowledge institutes, erected the programme Impulsprogramma Kennisinfrastructuur Ondergronds Bouwen1 in 1994.

The purpose of this stimulation programme was to come to a durable strengthening of the knowledge infrastructure. The core of this infrastructure is formed by the Centre for Underground Construction (COB2), which initiates and co-ordinates research and developments in the field of underground construction. COB makes use of the method and infrastructure of the Centre for Civil Engineering Research and Codes (CUR3) in Gouda. The Technical University Delft has a chair “Underground Construction” which is closely associated to the COB. A broad range of businesses, branch organisations, research institutions, and scientific and governmental institutions participate in COB. Through a contribution to the programme by the Interdepartmentale Commissie voor het Economisch Structuurbeleid (ICES) 4, the government stimulates the realisation of this knowledge infrastructure.

The research and development work of the COB is conducted within the framework of a comprehensive implementation programme. This programme is initially divided into four themes, i.e. “Tunnelling in soft soil,” “Exploring, predicting and monitoring,” “Economical tunnel construction,” and “Constructing, administering and maintaining.” The themes are fleshed out by carrying out research and development projects. An important project within the first theme is the “Pilot Project Bore Tunnels”(COB Commission K100). The essence of this project consists of the intensive monitoring of the Second Heinenoord Tunnel, the first bored large diameter tunnel in the Netherlands. Through this monitoring, existing instrumentation for the exploration of the underground and prediction models for the behaviour of soil and construction is tested.

The activities of this project were started as an initiative of the Bouwdienst van Rijkswaterstaat5 in the beginning of 1994. In November of the same year this commission evolved into the COB implementation commission K100. The report at hand, Evaluation Report Second Heinenoord Tunnel, was achieved under responsibility of this commission.

1 Impulsprogramma Kennisinfrastructuur Ondergronds Bouwen: Dutch for Programme for the Stimulation of Knowledge Infrastructures of Underground Construction. 2 COB is the abbreviation for Centrum Ondergronds Bouwen, Dutch for Centre for Underground Construction . 3 CUR is the abbreviation for Centrum Uitvoering Research en Regelgeving, Dutch for Centre for Civil Engineering Research and Codes. 4 ICES is the abbreviation for Interdepartementale Commissie voor het Economisch Structuurbeleid, Dutch for Interdepartmental Commission for Regional Economic Policy. 5 Bouwdienst van Rijkswaterstaat: Dutch for Civil Engineering Division of the Ministry of Transport, Public

Works and Water Management.

The report describes the evaluation of the measurements that were conducted during the boring of the Second Heinenoord Tunnel. Its objective is to provide a general survey of knowledge developed about the boring of tunnels and about the possibilities and limitations of the measuring systems.

This report is composed of work reports approved by K100. The composition of K100 and a list of work reports are enclosed in the appendices.

The final editing of this report was done by M. Th. J. H. Smits MSc and the translating by M.D.M. van Vliet MA.

COB Commission K100 thanks everybody who has contributed to the realisation of this report.

October 1999 K.J. Bakker MSc Chairman COB Implementation Commission K100

CONTENTS

FOUT! GEEN INHOUDSOPGAVEGEGEVENS GEVONDEN.

SUMMARY AND CONCLUSIONS

This report provides a general survey of the calculations done beforehand and of the measurement evaluations done during the construction of the Second Heinenoord Tunnel. The main objective of these evaluations was to increase the technical knowledge about boring in soft soil in the Netherlands. There was especially insight obtained into the value of present design and calculation models for the description of the boring process, and of the behaviour of the tunnel lining and the surrounding soil. In order to achieve this, the measured values were compared with the predictions and an explanation was sought to explain discrepancies. In several instances these discrepancies were attributed to changed preconditions and circumstances occurring during the measuring, which caused the original ‘input’ of the predictions to be incorrect. In these cases the predictions with altered assumptions have been repeated, and subsequently pronouncements upon the value of the prediction models could be done.

The evaluations were realised in three phases. In order to recognise measuring errors timely and to obtain a first insight into the results, the third order evaluation occurred as soon as the measuring results arrived. The second order evaluation was an in-between evaluation whenever a certain measuring range was passed. It consisted of the assessment and possible correction of the rough measuring data, graphical display of the results, and their comparison with the predictions. The idea was to give recommendations for the monitoring of the passing of the next distance in addition to giving first insight into the quality and accuracy of the predictions. The first order evaluation was the broad and definitive evaluation of the measuring results. These consisted of a critical reflection of the prediction models, supplemented with several recalculations of the measured behaviour in case of altered assumptions and/or calculation models.

In the evaluation phase it appeared that the knowledge acquirement about boring in soft soil, inside and outside of the Commission K100, greatly developed over the course of the project. Therefore, much improved calculation models, compared to the prediction models available at commencement of the project, were used or developed during the first order evaluations.

The evaluations were realised for the fields of bore technology, tunnel construction, and geotechnology. Furthermore, the measuring programme itself was evaluated for the benefit of future monitoring projects. The most important findings of these evaluations have been summarised below.

For tunnels with a small cover the margin between which the minimum and maximum pressure at the face of the TBM6 may vary to prevent instabilities is small. While the cutting wheel rotates, the plastering effect of the slurry at the face of the TBM is continually broken. This causes extra water pressure that negatively influences the stability of the face of the TBM. Calculation models have been developed that take the extra water pressure into account when determining the minimum support pressure. These models are the initial impetus to accentuate design practice.

6 TBM is the abbreviation for Tunnel Boring Machine.

The forces on the main jacks of the TBM are primarily determined by the support pressure at the face of the TBM exercised on the pressure partition. This can be measured well. The reaction forces exercised by the soil on the TBM, i.e. the shield friction and the cutting powers, seem more difficult to quantify. The contributions of these forces are, however, relatively small. Therefore, the equilibrium of forces is hardly influenced by the type of soil that is being bored through. Consequently, the decrease of effectiveness while boring through layers of clay, as observed in practice, is due to other factors such as for instance the lumps of clay that clog the discharge pipes.

Soil deformations and in particular surface settlements cannot be predicted well with the current analytical design models. This is especially caused by the insecurity towards the data input of loss of volume. Moreover, predictions made with finite element calculations, which schematise the loss of volume to concentric contraction of the tunnel diameter, provide unrealistic results. Given a certain loss of volume, the calculated settlement trough is too wide and too shallow.

Measurements indicate that settlements of the surface level mainly occur with passing of the TBM or when grouting the tail of the TBM. There is a virtually linear relation between the volume of the injected grout and the settlement of the surface level. Therefore, the determining factor for the effect on the tunnel surroundings is the behaviour of the grouted annulus of the tunnel lining. Future design calculations need to take this behaviour into account.

The stresses that originate through construction of the lining from lose segments are more or less equal to the stresses that are caused by the soil and the grout around the tunnel at a later time. Further development of the models is necessary to be able to calculate these tensions in future with any success.

At the more detailed level of the tunnel segments, the balance of forces is highly three-dimensional. This is caused, amongst others, because stresses in longitudinal direction also lead to stresses and strains in cross direction. Within K100, three-dimensional calculations have strongly increased insight into local effects of forces.

To determine the global beam reaction, a two-dimensional model of the tunnel (elastic supported beam) is sufficiently accurate.

A good evaluation of measurements and calculations is only possible when measurements at the TBM, in the soil, and in the tunnel lining are co- ordinated to one another and integrally analysed. The fact is that processes occurring at the face of the TBM, in the soil and in the lining of the tunnel influence each other highly.

CHAPTER 1 INTRODUCTION

1.1. ACQUIRING KNOWLEDGE THROUGH PILOT RESEARCH OF SHIELD DRIVEN TUNNELS

To give impetus to the amassing of knowledge about boring of tunnels in soft soil and to gain practical experience, the Minister of Transport, Public Works and Water Management, having conferred with the Ministry of Economic Affairs and the Ministry for Housing, Regional Development and the Environment, decided to execute two pilot projects for bored tunnels. These pilot projects are: − the Second Heinenoord Tunnel underneath the river Oude Maas near Barendrecht, − and the Botlek Railway Tunnel underneath the Oude Maas in the Botlek area.

The amassing of knowledge is accomplished by performing purposive research during and after the construction of these tunnels, recording the operation, and evaluating the obtained results. The research of the Second Heinenoord Tunnel is supervised by the CUR/COB Commission K100 “Pilot Project Research Bore Tunnels.”

Before and during the execution of this research, the Commission K100 has drawn up several reports. From this extensive series, especially the following basic reports are worth mentioning: − the instrumentation and measuring plan [K100-01], − the instrumentation report [K100-02], − the evaluation plan [K100-03], − the prediction report [K100-04], − and the instrumentation and measuring report [K100-05].

evaluation report

PREDICTION REPORT INSTRUMENTATION PROCESS DATA K100-04 AND MEASURING AND PRACTICAL REPORT K100-05 OBSERVATIONS

The value of practical research is increased by making a priori predictions of results of measurements and experiments. For this reason a large number of predictions were made, which are summarised in the prediction report [K100- 04].

The measuring results themselves are summed up in the instrumentation and measuring report [K100-05].

Subsequently, during construction of the tunnel many process and environment parameters were measured and numerous observations were done. These process data and practical observations were not reported separately, but obviously they did play an important role in the evaluation of the measurements.

Various partial evaluations of the measurement data were performed and recorded during construction of the tunnel. In the evaluation report before us, the integral evaluation and assessment of the executed predictions and measurements of the entire pilot project are recorded.

1.2. OBJECTIVE OF THE EVALUATION REPORT

The main objective of the evaluation report is to provide a survey of the acquired technical knowledge about the boring of tunnels, which is developed through the monitoring of the Second Heinenoord Tunnel. It concerns knowledge not only about the fields of bore technology, geotechnology and tunnel construction, but also about measuring systems, implementation aspects of the construction of the tunnel, and the launching of such monitoring projects.

This objective was attained by systematically assessing the design and calculation models that were used to make predictions. Based on an analysis of the possible discrepancies between the predictions and the measurements, it is possible to indicate where exactly these models fall short and therefore need improvement.

1.3. READING INSTRUCTIONS

Chapter 2 discusses the project Second Heinenoord Tunnel, more specifically the monitoring project.

An important role in many prediction calculations is played by parameters of the boring process that are beforehand unknown, such as pressures at the face and losses of volume. Evaluation of these predictions is only useful when these parameters are known. Therefore, chapter 3 lists these parameters and, when relevant, compares these with the expected a priori values.

The core of this evaluation report consists of chapters 4, 5 and 6. These chapters describe the knowledge acquired in the fields of soft soil tunnelling technology, geotechnology and tunnel construction. Chapter 7 contains an evaluation of the measuring instrumentation, which can be of importance to future monitoring projects. Finally, chapter 8 discusses the general ‘educational moments’ that occurred during the construction of the tunnel.

CHAPTER 2 MONITORING THE SECOND HEINENOORD TUNNEL

2.1 THE PROJECT SECOND HEINENOORD TUNNEL

2.1.1 GENERAL REMARKS

South of Rotterdam the intersection of motorway A29 with the river Oude Maas, the Heinenoord Tunnel, causes daily traffic jams in the municipalities Barendrecht and Binnenmaas. Originally the tunnel consisted of four lanes for fast traffic and two lanes for slow traffic. The ever increasing congestion of the A29 near the tunnel leads to the decision to augment the capacity of the tunnel from four to six lanes for fast traffic. Slow traffic - pedestrians, (motor)cyclists, and agricultural traffic - will be re-routed through a new tunnel, the Second Heinenoord Tunnel.

The Second Heinenoord Tunnel consists of two bored tunnel tubes, of which the closed part of the tunnel have an inner and outer diameter of respectively 7.58m and 8.28m. One tunnel tube is accessible to agricultural traffic and the other for cyclists and pedestrians. The access way to the closed part of the tunnel, built with a 1:15 slope, is only accessible to agricultural traffic. Pedestrians and cyclists enter the closed part of the tunnel by escalator or lift. Due to the combined use by agricultural and pedestrian traffic, the maximum inclination of the tunnel is 1:30. The length of the bored part of the tunnel is approximately 950m per tube. Both accesses, including entry shafts, measure approximately 200m.

Figure 2: Impression of the Second Heinenoord Tunnel

The Second Heinenoord Tunnel was deliberately chosen as the first pilot bored tunnel, because the risks of the implementation were relatively limited. There are no buildings in the near vicinity of the tunnel, nor are cross connections between the tunnel tubes necessary. Moreover, the diameter of the tunnel is more than 8 metres, which for a bored tunnel is a relatively small diameter, over a metre smaller than the diameter of the Botlek Railway Tunnel. Furthermore, the fact that the ground was already property of the Ministry of Transport, Public Works and Water Management and therefore complex planning procedures could be avoided played a role in the choice for the Second Heinenoord Tunnel as first pilot project.

2.1.2 SOIL CONDITIONS AT THE SECOND HEINENOORD TUNNEL

The tunnel crosses the river Oude Maas. Through the constantly changing course of the river over the past thousands of years a complex pattern of channels arose in the subsoil, with alternating layers of clay, peat and sand (see figure 3).

Figure 3: Geotechnical profile of longitudinal section

The surface of both riverbanks lie at approximately NAP7 +2m and the top of both dikes at approximately NAP +6m. Just below the surface previously applied layers of soil, of variable composition and stiffness, are found. As a result of these soil supplements, both banks are still to a degree subject to surface settlement. Between NAP -2m and NAP -10m there are layers of sandy soil, which turn into sandy clay on the North bank of the river, whereas on the South bank an intermediate layer of peat is found. Between NAP -10m and NAP -15m there is a moderate to dense Holocene layer of sand. Below this layer the so-called Pleistocene starts. This is the generic term for the layers of soil that have been left behind just before the end of the last ice age. In the area of the Second Heinenoord Tunnel, the Pleistocene contains dense to very dense sand layers. From a depth of NAP -20m these turn into a composition of very rigid clay and sand layers.

The geological texture of the soil in the area of the Second Heinenoord Tunnel is fairly representative of the geological condition of the soil of the Western part of the Netherlands, apart from the fact that there are no soft peat layers in the project area. Most of the bored tunnel is to be found in Pleistocene sands or rigid clay. However, this soil is less stiff (by a factor of 2 to 5) than that in, for instance, German and Japanese projects.

In order to fixate the bottom of the river, stone revetment was applied to the river bed.

2.1.3 BORE TECHNOLOGY

The two tubes of the Second Heinenoord Tunnel have been bored with a Tunnel Boring Machine (TBM) that was designed specifically for this project. It is constructed of a steel cylindrical shield (with a diameter of approximately 8.5m), with a cutting wheel at the face. At the back of the TBM the finished tunnel can be found. Within the shield the tunnel rings are built (see figure 4).

Figure 4: Cross-section of the TBM

7 NAP is the abbreviation for Nieuw Amsterdams Peil, Dutch for New Amsterdam Water Level, a reference

point for water level in the Netherlands.

The technique that is used is called the Slurry Shield Method. The soil is cut by a rotating cutting wheel, consisting of five arms. At the end of these arms overcutters are fixed, which can, if desired, cut outside of the diameter of the shield. The excavated soil is mixed with a fluid that contains a high level of clay, called bentonite slurry. This mixture can be pumped away easily. The bentonite slurry is maintained under pressure by use of air pressure. This prevents water and soil from flowing into the TBM. The mixture of bentonite and soil is transported to a separation plant outside the tunnel where the two components are separated. Afterwards the slurry is pumped back into the system.

The front part of the tunnel can only be accessed while under air pressure. Under certain circumstances the slurry level can be partly or fully lowered in order to, for instance, replace the chisels. The tail of the TBM, the rear end of the shield measuring approximately 5.5m, is kept under atmospheric pressure. This is where the thrust jacks, the air pressure cabin and the erector for placing tunnel segments are located. Whenever a distance of 1.5m has been bored, the tunnel tube is constructed immediately. This newly constructed part of the tunnel is used by the TBM to push off against so it can excavate the next 1.5m.

The TBM has a larger diameter than the tunnel tube. The empty space, that will arise accordingly, is filled with grout.

Per construction day 10 to 15m of tunnel can be bored. However, it has to be noted that the speed of boring is related to the type of soil being bored through. In constructing the Second Heinenoord Tunnel a maximum of 22m per day was accomplished when boring through sand, whereas when boring through stiff clay only 2 to 5m per day could be realised.

2.1.4 TUNNEL CONSTRUCTION

The tunnel lining consists of rings of prefabricated concrete elements of 1.5m wide (see figure 5).

Figure 5: Tunnel construction

These rings have an inner diameter of 7.6m and a lining thickness of 0.35m. The joints between the rings are called ring joints. Every single ring consists of seven segments, as well as one key segment. The joints between the segments are called the longitudinal joints. Two parallel rings have been moved by half a segment in relation to one another so as to create a stacked structure.

Two notches form the contact surface of the ring joints, in order to transfer shear forces. Small plates of material that can be tightly squeezed (made from a rubber bitumen compound, called ‘kaubit’ in German) support easy pressure distribution. Plywood plates have been put in place to distribute the axial forces between the segments. The segmented structure is made waterproof by a rubber sealing profile covering the complete periphery of each segment.

2.2 RESEARCH OBJECTIVES, PREDICTIONS, MEASUREMENTS AND EVALUATIONS

2.2.1 INTRODUCTION

Based on a general inventory of research objectives, the priorities for the Second Heinenoord Tunnel were set and a definitive research programme in the form of an implementation plan was drawn up. The approach comprises in consecutive order: predicting behaviour, measuring behaviour, and evaluating the measuring results.

This chain of predicting-measuring-evaluating was completed for as many research goals as possible. In some cases it was impossible, by definition, to measure. The analysis of failure mechanisms, fortunately not occurring in reality, can be mentioned as an example of this. On the other hand, some observations and measurements were not predicted, for instance because the necessary calculation models were not available at the time. This was the case with measuring the deformation of the tunnel construction.

2.2.2 RESEARCH OBJECTIVES

Bored traffic tunnels with a large diameter had not been previously constructed in the Netherlands. Globally, a large number of similar tunnels have been built, but these were not constructed under the soft soil conditions as found in the Western part of the Netherlands, which are characterised by a relatively low stiffness and a high water table. Accordingly, the aim CUR/COB Commission K100 set itself was ‘to develop knowledge and expertise about tunnelling in the soft Dutch soil.’ This aim was pursued by testing, through means of measuring, calculating and experimenting, whether existing theoretical models could adequately describe deformations occurring during and after the tunnelling process, as well as forces arising in and around the TBM and tunnel lining.

When wishing to keep risks to a minimum and attempting to achieve design optimisation, a need for a deep and accurate understanding of face stability arises. Likewise, there should be understanding of the stresses on the segmented lining over a longer period of time and the influence caused by tunnel construction on adjacency. Apart from these technical aspects, economic aspects are of equal significance, particularly that of the speed by which various layers of soil can be bored through. Finally, usefulness aspects of the tunnel are important to practical research of bore tunnels, especially the vibrations from within the tunnel and the re-use of the excavated soil.

The aspects mentioned above could be divided into four fields of interest: bore technology, geotechnology, tunnel construction, and vibrations and environment. The first three fields have been incorporated in the research objectives of CUR/COB Commission K100 and will be addressed below. These research objectives are described in more detail in Appendix 1. Examination of the fourth field was conducted by other CUR/COB commissions and will not be addressed in this report.

THE FIELD OF BORE TECHNOLOGY - Determining face stability of the TBM In determining face stability there are a few important matters to take into account. Firstly, it is important to know about the upper and lower boundary values of earth pressure. The bentonite pressure must lie between these two values. When lower than the minimum earth pressure, soil and groundwater will flow into the TBM. However, if the bentonite pressure is higher than the total effective earth pressure, the soil will be pushed away from the face, creating an unstable situation as well. When determining this stability, the distribution of pressure in the mixing chamber, which contains a mixture of bentonite and excavated soil, is an important aspect to be taken into account. Because of its influence on stability, awareness of the water overpressure generated by boring in the surrounding soil is also important. When determining face stability, the effects of stagnation of the TBM, possibly combined with a drop in the level of bentonite (in which case the face must be maintained stable by air pressure), should be examined. The same applies to the effect caused by simultaneously boring in porous and non-porous layers of soil. - Equilibrium of forces during the excavation The jacks that push the TBM and the drive of the cutting wheel need enough capacity to prevent jamming of the TBM. Consequently, it is important to be familiar with the magnitude of the jack forces, for example as a function of the characteristics of the soil to be bored through. The lining and the surrounding soil will eventually absorb these jack pressures. Accordingly, it is not only necessary to be familiar with quantifying the jack forces but in particular with the distribution of the forces over the individual jacks. - Determining the effectiveness of the tunnelling process When determining the effectiveness of the tunnelling process, the emphasis lies on the examination of the excavation process and the mixing of bentonite and soil in the mixing chamber. The way in which the excavated soil manifests itself in the mixing chamber, for example as large chunks of clay or as a suspension, influences the pressure distribution in the mixing chamber and accordingly face stability. It also influences the effectiveness of the pumps and pipes that transport slurry and soil. Wear of the cutting teeth, pumps and pipes, which need be examined more thoroughly, also influence the efficiency of the tunnelling process.

THE FIELD OF TUNNEL CONSTRUCTION - Determining the load on the construction and the equilibrium of forces inside the construction When constructing the tunnel, the lining of the tunnel will be the heaviest burden on the budget. Hence, an economical and safe design of the lining is of major importance. The main research objective of tunnel construction is to determine the utility of the calculation models. The effect of forces within the tunnel construction, or rather in the lining, is a complex and time-consuming process. Successively the tunnel, constructed of separate segments, will experience axial and torsion forces which are caused by the jacks that drive the TBM and the cutting head, assembly stresses, radial forces caused by pressure of the grout being pressed into the tail of the TBM, and finally soil pressures that arise after setting of the grout. These earth pressures act mainly perpendicular on the axis of the tunnel but, because of the differences in longitudinal direction, beam reaction will also be of consequence. The load of the soil on top of the tunnel performs a special task, as it serves to support the lining.

Furthermore, constructing the second tunnel tube in close vicinity of the first one will influence the earth pressures and accordingly the load on and the forces within the first tube. This phenomenon has been studied as well.

Finally, leakages can result in changes in earth and water pressures, thus changing the load on the tunnel. Attention has been paid to this aspect, too.

THE FIELD OF GEOTECHNOLOGY - Determining deformations and pressure changes in the surroundings of the tunnel Soil deformations and stress changes in the surrounding area caused by the tunnelling process could lead to surface settlements, and thus damage buildings in the vicinity. Gaining insight in all aspects of this process is the main research objective within the field of geotechnology. This includes extraordinary situations such as long- term stagnation of the TBM and decrease in the level of bentonite in the mixing chamber. In addition, the long-term influence of the presence of the tunnel on the rise of the water table and on the safety in case of possible collapse mechanisms (like buoyancy and breaking of the tunnel) has been examined. - Determining the necessary soil parameters for design and implementation In order to determine these soil parameters, an extensive programme of specific measuring was added to the regular research of the Second Heinenoord Tunnel. Based on this extended study Commission K100 also aimed to examine the reliability of the geotechnical system with respect to both the layer structure and the characteristics per layer.

2.2.3 PREDICTIONS

The value of the measurements and experiments in this pilot project has increased by predicting the results in advance through use of calculation models and occasionally through estimations or assumptions. By comparing the predicted behaviour with the observed behaviour, immediate understanding of the limitations of the existing design and calculation models of bore tunnels could be gained.

A prediction often consists of a range of possible measurements which follow from measuring the sensitivity of certain input parameters. This measuring of sensitivity is particularly important when the measuring result follows from a complex process, in which various initially unknown input parameters play a prominent part. For instance, the force exercised on the cutting wheel in order to make it rotate is dependent on the penetration depth of the cutting chisels and on the behaviour of the soil plug in the middle of the face of the TBM. The measured value of this force, therefore, explains little without considering and possibly quantifying the underlying processes.

In addition to the previously described function, based on knowledge obtained through measuring, predictions have also been used to correct the measuring and instrumentation programmes.

Some predictions could not be validated by measuring, referring to those measurements that ultimately have not been executed or the predictions of the safety margins (upper and lower boundaries) for failure mechanisms (like buoyancy of the tunnel) that, fortunately, did not occur.

The basic assumption of the predictions was that they needed to be founded on existing models used both nationally and internationally. Collecting these models and applying them to the Second Heinenoord Tunnel was already a significant result of this pilot project in itself.

When still in the phase of formulating predictions, little was known about some input parameters. These are the so-called process parameters such as grout pressure, face pressure, and final configuration of the cutting teeth. For the duration of the pilot project these parameters have been registered as often as possible. In some cases, the registered process parameters gave reason for correcting the prediction of the evaluation phase.

The predictions are listed in the prediction report (K100-04).

2.2.4 MEASUREMENTS AND EXPERIMENTS AT THE SECOND HEINENOORD TUNNEL

To meet the above mentioned research objectives a large number of measurements and experiments were conducted at the Second Heinenoord Tunnel. The choice for instrumentation, experiment and measurement setup is described in Instrumentatie en meetplan8 K100-01. Before the instrumentation and data acquisition systems were mounted, elaborate specifications were formulated that ensured that useful measuring results were obtained.

Figure 6: Inventory of measurements

Measurements were conducted on the TBM, in the soil and on the surface in two measuring areas on both banks of the river Oude Maas, and in the tunnel construction itself, especially within two measuring rings fixed in the tunnel lining underneath both the measuring areas. These measurements were divided into: - bore technological measurements, - geotechnical measurements, - tunnel construction measurements, - and other measurements.

BORE TECHNICAL MEASUREMENTS The contractor conducted several standard measurements of, amongst others, jack forces, position of the overcutters, flow rates and thrusts in the pipes, rate of progress, position of the TBM, movement of the cutting wheel, grout pressures, and injected volume of grout in the tail of the TBM.

8 Instrumentatie en meetplan: Dutch for Instrumentation and Measurement Plan.

Figure 7: Instrumentation within the TBM

These standard measurements were combined with the following measurements: - compression of the mixture and the differential pressure in the supply and discharge pipe, - slurry pressure in front of and behind the cutting wheel (in eight different places), - pressure on the baffle wall and inside the air chamber, - position and rpm of the cutting wheel, - height of bentonite level, - actual pressure for driving the cutting wheel (in two places), - and temperature in the mixing chamber. In addition to these, several other measurements were conducted to verify the predictions. These included tidal measurements, samples of inbound and outbound slurry, and measurements of the wear of the cutting teeth.

GEOTECHNICAL MEASUREMENTS On both sides of the Oude Maas an area for conducting geotechnical measurements was set up (see figure 8).

Figure 8: Inventory of Geotechnical instrumentation

The following items were measured: - surface settlements at a large number of locations, - horizontal displacements above and between the tunnel tubes (eight inclinometers), - vertical displacements above and beside both tunnel tubes (eleven extensometers), - earth pressure and water pressure measurements at four places between both tunnel tubes, level with the tunnel axis, all of which are located in the Northern measuring area, - and water pressure measurements before the face of the TBM (six water-pressure gauges).

TUNNEL CONSTRUCTION MEASUREMENTS Underneath both geotechnical measuring areas the tunnel was instrumented with two measuring rings. Both rings were located in the Western tunnel tube. No measuring rings are placed in the Eastern tube.

Figure 9: Survey of measuring areas and position of measuring rings.

Both measuring rings comprise of seven instrumented segments and one key segment (see figure 10). The instrumentation of the measuring rings is identical, except for the key segment in the Southern measuring ring. This still was equipped with six strain gauges as a consequence of the results of the Northern measuring ring. Per measuring ring 70 strain gauges and 14 earth pressure gauges were applied. Else, per measuring ring 18 displacement gauges were installed to measure the displacement differences over the joints.

figure 10: Survey of instrumentation of measuring

On the South bank, within the geotechnical measuring area, in both tunnel tubes the displacement of three just constructed tunnel rings was measured. The purpose was to measure the deformation within and directly behind the TBM. Because the measuring started directly after the first segments were built, so still within the TBM, useful information was obtained about the deformation of the lining occurring during the boring process.

In addition to these measurements, long-term deformations of the tunnel in cross and longitudinal direction were measured by means of levelling and roundness measurements.

OTHER MEASUREMENTS AND EXPERIMENTS Aside from the CUR/COB Commission K100, several other bodies conducted measurements and experiments during the construction of the Second Heinenoord Tunnel. In many cases these took place in close co-operation with K100. - Pile experiment North/South Metro Line: Project organisation ‘North/South Metro Line’ conducted the work for a project involving test piles on the Northern riverbank. Thus, with respect to the construction of the new North/South Metro Line in Amsterdam, the influence of tunnelling on the closely situated piled foundations could be analysed. Moreover, in the tunnel tube a test with a falling weight was conducted, which simulated the nuisance of vibrations caused by metros. - Steel fibre concrete: The pilot project ‘Steel Fibre Concrete in the Second Heinenoord Tunnel’ (conducted by Bouwdienst Rijkswaterstaat and Technical University Delft) designed, produced and implemented 16 steel fibre concrete rings in the second tube. - Re-use of soil: The CUR/COB Commission K200 ‘Re-use of Soil from Bore Tunnels’ looked into the possibilities of re-using the different fractions that were excavated from the tunnels. - Seismic research (by Technical University Delft): With reference to the boring of the Second Heinenoord Tunnel it was investigated whether the vibrations caused by the TBM could be used as a vibration source for seismic research on obstacles. - Measurements of vibrations: CUR/COB Commission L400 measured vibrations when the TBM passed the Southern riverbank. The measurements were simultaneously done in the soil, on the surface and inside the TBM. The purpose of these measurements was to get an idea about the nuisance vibrations, caused by boring, and to search for the most important causes of this nuisance. - Thickness of grout measured with radar: It was attempted to measure the thickness of the shield of grout around the tunnel lining by means of radar. Because of disturbance given by the steel reinforcements in the tunnel segments, these measurements did not give satisfactory results.

2.2.5 METHOD AND SURVEY OF EXECUTED EVALUATIONS

The evaluation of the measuring results mainly consisted of comparing the predictions with the measurements. The main goal of this evaluation was to obtain answers with respect to the posed research questions, in order to increase technical understanding about the tunnelling process. Additionally, by accurately comparing the predictions to the measurements, understanding of the value of current calculation models was gained. Accordingly, models that turned out to be insufficient had to be improved.

The planning of the evaluation process was linked to the planning of the tunnelling process. Hence, by measuring at different moments and at different levels, the evaluations could be divided up into third order, second order and first order evaluations.

THIRD ORDER EVALUATION A third order evaluation was a quick evaluation the moment the measuring data became available. They were intended to timely recognise failure in the instrumentation and/or data acquisition and to provide a first communication of results. Therefore, they were conducted at the site hut. Third order evaluations were conducted in six longer periods of time, each lasting approximately a week, whenever the TBM passed critical spots or measuring instruments. At these times, when necessary, the site hut was attended 24 hours per day by the project organisation and representatives of the contractors enabling the direct processing of the geotechnical, bore technological and tunnel constructional measurements.

SECOND ORDER EVALUATION A second order evaluation was an intermediate evaluation whenever a certain measuring range was passed. They were conducted a few weeks after every passing and consisted of assessing, and when necessary correcting, rough measuring data, graphical display of the results, and their comparison with the predictions. The idea was to be able to give adequate recommendations for the monitoring of the passing of the next distance in addition to giving first insight into the quality and accuracy of the predictions.

The results of the second order evaluations are recorded in the following work reports:

In the field of bore technology: [K100-W-058]: Eerste passage (westelijke buis) meetgebied noord (First passage (Western tube) measuring area North) [K100-W-069]: Eerste passage (westelijke buis) meetgebied zuid (First passage (Western tube) measuring area South) [K100-W-081]: Tweede passage (oostelijke buis) meetgebied zuid (Second passage (Eastern tube) measuring area South) [K100-W-092]: Tweede passage (oostelijke buis) in meetgebied noord (Second passage (Eastern tube) measuring area North)

In the field of geotechnology: [K100-W-059]: Eerste passage (westelijke buis) meetgebied noord (First passage (Western tube) measuring area North) [K100-W-071]: Eerste passage (westelijke buis) meetgebied zuid (First passage (Western tube) measuring area South)

[K100-W-085]: Tweede passage (oostelijke buis) meetgebied zuid (Second passage (Eastern tube) measuring area South) [K100-W-090]: Tweede passage (oostelijke buis) in meetgebied noord (Second passage (Eastern tube) measuring area North)

In the field of tunnel construction: [K100-W-061]: Eerste passage (westelijke buis) meetgebied noord (First passage (Western tube) measuring area North) [K100-W-066]: Eerste passage (westelijke buis) meetgebied zuid (First passage (Western tube) measuring area South) [K100-W-086]: Tweede passage (oostelijke buis) meetgebied zuid (Second passage (Eastern tube) measuring area South) [K100-W-095]: Tweede passage (oostelijke buis) in meetgebied noord (Second passage (Eastern tube) measuring area North)

These work reports describe the progress of understanding the observed phenomena. Possible explanations for the measuring results are confirmed in some cases, and in other cases contradicted by the results of the next tunnel distance. For instance, the correlation between the jack forces and axial forces in the tunnel lining were initially found to be ‘incorrect’ as a consequence of allegedly inaccurate measurements of the jack force [K100-W-061]. However, because the axial forces adapted themselves to the jack forces over time, eventually they were qualified as ‘correct’ after all. This example illustrates that second order evaluation reports need to be seen as a whole. In first order evaluations it is attempted to create this coherence.

FIRST ORDER EVALUATION The first order evaluation is the broad and definitive evaluation of the measuring results. Per field of interest (bore technology, geotechnology and tunnel construction) it consists of the following three main divisions: 1 Critical reflection on the prediction models by comparing all the measuring results (that is, all four passages) and further research into their validity. During this reflection, the choice of parameter for these predictions in addition to other assumptions and preconditions have been compared to the actual circumstances. From this, it could be concluded whether any post dictions would be necessary. This division of the first order evaluations can be seen as a summary and synthesis of all second order evaluations that were reported for each measuring area without any reciprocal coherence. 2 When necessary, executing post dictions, which consisted of recalculation of the measured behaviour using altered assumptions and/or calculation models. Post dictions have only been conducted when earlier evaluation indicated that insight needed to be increased. 3 Based on these critical reflections and post dictions, making pronouncements about the validity of the various prediction models, indicating where these models need improvement, and making recommendations for future projects.

Assessing the executed measuring programme was also part of the first order evaluation. It assessed whether the measurements were relevant, sufficiently accurate and elaborate enough in frequency, time span and number of locations to attain the research objectives. The evaluation of the entire measuring instrumentation is reported in [K100-W-107]. A review of the soil research is presented in [k100-w-105c].

The critical reflections on the prediction models are presented in the following reports: [K100-W-102]: Reflection on the prediction models of face stability [K100-W-103]: Reflection on the predictions of equilibrium of forces and the effectiveness of boring process [K100-W-104]: Reflection on the predictions of the wear of cutting elements [K100-W-105a]: Reflection on the analytical predictions of stress changes and deformations of the soil, mainly concentrated on predicted and measured settlement troughs [K100-W-105b]: Reflection on the numerical predictions of stress changes and deformations in the underground [K100-W-106]: Reflection on the calculation models for forces within and loads on the tunnel lining

Based on the second order evaluations and the above mentioned critical reflections on the prediction models, the following topics were deemed relevant for further analyses by means of first order evaluation, amongst others through post diction:

In the field of bore technology: [K100-W-102]: Further research of the influence of extra water pressure before the face of the TBM on the minimum required support pressure. Additionally, the minimum and maximum support pressures for fourteen cross-sections were recalculated. These were compared with the measured support pressures along the entire course of the tunnel. [K100-W-103]: Further outlining and analyses of the tangential and axial equilibriums of forces, naming the insecurities in the measurements and in the various components of the equilibrium. Furthermore, these analyses encompassed the resisting slip forces of the non-cutting elements and the eccentricity of the jack forces. [K100-W-103]: Further reflection on the effectiveness of the tunnelling process by assessing the behaviour of the slurry mixed with the excavated soil and the depositing behaviour of the particles. [K100-W-103]: Further research of the effectiveness of pumps and pipes, in particular the closer analyses of measured characteristics of slurry and the measurements in the second tunnel tube during construction of the rings. [K100-W-104]: Post dictions about the wear of cutting elements and comparisons with measured wear. These post dictions were deemed necessary because the cutting teeth geometry, as used in earlier predictions, did not correspond with reality.

In the field of geotechnology: [K100-W-105a]: Further analyses of the loss of volume during boring and its consequences on surface settlements and soil deformations. Especially the grouting in the tail of the TBM, as an important part of the process, was evaluated further. Else, a comparison with various empirical formulas has been made. [K100-W-105b]: Post dictions of the soil deformations in the measuring area South by means of a three- dimensional model, which models, amongst others, the grout pressure (measuring area North has been verified by CUR/COB Commission L520). [K100-W-105b]: Further reflection on the influence of the construction of the second tube on the first tube by means of two- and three-dimensional finite element calculations and comparisons with the measurements. In these reflections that resulted in recommendations for the minimum distance between the tunnels the grouting process (pressures and volumes) was involved as well. [K100-W-105c]: In light of the first order evaluation it was investigated whether the soil research for the Second Heinenoord Tunnel was adequate. This resulted in recommendations for future projects.

In the field of tunnel construction: [K100-W-106]: The researchers opted to concentrate on improving models in the field of tunnel construction, because already during second order evaluation the existing two-dimensional models fell short of explaining certain observed phenomena. These improved models had to be capable of explaining in particular the assembly stresses, the influence of the joint behaviour on the equilibrium of forces, and the interaction between the rings and the beam reaction of the tunnel. Therefore, a three-dimensional shell model was developed that fitted the three-dimensional model used to quantify the interaction with the ground [K100-W-105].

CHAPTER 3 EVALUATION OF BORE PROCESS PARAMETERS

3.1 INTRODUCTION

While executing the predictions for the various aspects of the tunnelling process (geotechnology, bore technology, and tunnel construction), several bore process parameters that were not known when formulating the predictions, proved to be of importance. The following are worth mentioning: - The geological circumstances, which followed from the soil research. Paragraph 5.4 reviews this soil research. For practical reasons a comparison between the characteristics of the excavated soil and the expectations raised by the geotechnical longitudinal profile could not be made. - Pressures on the face of the TBM. Paragraph 4.2 (Stability of the Bore Face) elaborates on the measured face pressures compared with the minimum and maximum pressures on the face of the TBM. In the predictions no detailed expectations of the face pressures were given. In the set of prediction parameters (K100- W-004) a range of 100 to 350kPa is given. It was assumed, when calculating possible surface settlement caused by low face pressure, that the applied face pressure would be equal to 105% of the water pressure plus 20kPa. Presuming a phreatic level of NAP -0.1m and a depth of the tunnel axis at NAP -14.3m, the expected face pressures were 17kPA at measuring area North and 160kPa at measuring area South. In reality, both measuring areas yielded pressures of 200 to 240kPa. - Characteristics of the slurry. These characteristics are, amongst other things, responsible for keeping the excavated soil particles in suspension and for the plastering effect of the bentonite suspension. Paragraph 4.5 (Effectiveness of the Boring Process) describes the measured characteristics of the slurry and compares it to the characteristics that were expected beforehand. - Distribution of the jack forces. Paragraph 4.3 (Equilibrium of Forces in Axial Direction) addresses the expected total force on the main jacks. It may be concluded from the measurements that the pressure on the main jacks is not divided equally over the jacks. Most pressure is measured at the bottom jacks. This is especially caused by the fact that the front part of the TBM is heaviest. Furthermore, the distribution of the forces is also dependent on the curve the TBM makes. The total force in the main jacks and their distribution over the groups of main jacks is not constant in time. It is also of relevance whether the overcutters were used in this matter.

This chapter pays attention to several bore process parameters: - design of the cutting teeth on the face of the TBM, - grout pressures and volumes when injecting the tail of the TBM, - bentonite injection,

- and advancement speed.

3.2 DESIGN OF THE CUTTING TEETH ON THE FACE OF TBM

The cutting wheel of the TBM is equipped with 31 cutting teeth or cutting elements (not counting two overcutters), which are applied in different positions. The positions of the cutting teeth on the used bore face differ from the positions assumed in the predictions. The final configuration of the cutting teeth is shown in Appendix 3.

The predictions assume a knife with a height of 60mm and a width of 120mm. The angle of the knife, which is the angle between the cutting edge of the knife and the horizontal plane, was kept at 90° (see figure 11).

Figure 11: Terminology of cutting elements

After carrying out the predictions, the design of the face elements was drastically altered. For instance, the angle of the knife was decreased to approximately 60° and the length of the wearing surface, defined as the length of the wearing surface in cutting direction, was diminished to a very small size.

Moreover, the predictions assumed that the cutting wheel would always rotate in the same direction. However, in reality the cutting wheel cuts both ways. Therefore, the cutting teeth have a non-cutting character in one of the two cutting directions.

The discrepancies mentioned above have a major influence on the cutting pressure and on the wear of the cutting elements.

3.3 GROUT PRESSURES AND VOLUMES

Grouting process

Directly behind the tail sealing of the TBM the grout injection is applied. This injection can be applied in two different ways - through the segments or through the TBM. When injecting through the TBM, which happened at both passings of measuring area North and the second passing of measuring area South, grout is injected at 0°, 60°, 240°, and 300°. When injecting through the segments, as was done when passing measuring area South, grout was injected at three positions (0°, 120°, and 240°), which caused the grout volumes per injection point to be larger compared to the TBM injections. In addition to the method, the composition of the grout was adapted during work on the tunnel.

Grout pressures and grout volumes Grout pressures are of importance to the equilibrium of forces in the tunnel lining and to the calculation of the surface settlement.

The grout pressures have not been measured in the tail of the TBM itself. Instead the pump pressure at the discharge opening was measured. Hence, (unknown) pressure losses occurred. When grouting through the segments, as was done when passing measuring area South for the first time, the loss of pressure is probably less.

Table 1, below, reflects the predicted and measured values of the grout pressures. The prediction assumes on the one hand a grout density of 22kN/m³ and on the other hand an even composition of the pressure profile caused by grouting. Predicted and measured grout pressures diverge rather much.

Table 1: Prediction and measurement grout pressures in kPa. Measuring ring Prediction Prediction Measuring ring North (78) Measuring ring South (570) North (kPa) South (kPa) (date 04-04-97) (kPa) (date 04-11-97) (kPa) - top 251 226 150 176 - side 346 321 170 286 - base 440 416 200 230

The predicted density of 22kN/m3 was higher than the density measured during the first passing of measuring area North, especially because the share of water was fairly large. The employed injection pressures of the first passing lie approximately on the level of the water pressure at the height of the tunnel axis. The difference between the employed injection pressures between the first and the second passing of measuring area North is remarkable. The employed pressures of the second passing are higher.

The distribution of the grout pressures around the lining of the measuring ring at the first passing of measuring area North is roughly symmetrical around the vertical axis and roughly hydrostatic. The difference between top and base is only 50kPa, which is less than expected with such a very watery mixture. The distribution of grout pressure hardly changes over time.

The difference in grout pressure between both passings of measuring area South is less than between both passings of measuring area North. However, the method of injecting differed, as described above, which may have caused the actual grout pressure in the tail of the TBM to be considerably higher during the first passing than the second passing. When passing the measuring ring in measuring area South for the first time, an uneven pressure is measured - the highest pressure is found near the injection points, i.e. 350kPa at 129°. Because grouting took place in three places, the grout volume per injection point was higher. This led to relatively large pressures in the areas around the injection points.

Grout volumes By comparing measurements of the volume of injected grout (measured with a ruler) with the number of strokes by the pump per ring, the number of strokes does not seem a measure for the volume of injected grout. The reason for this is that the very same plunger pumps also wash the grout pipes clean, and that there may be air in the pipes as well.

3.4 BENTONITE INJECTION

In several places, amongst which the second passing of the piled test field of the North/South Metro Line, a bentonite injection was given at the top of the TBM at approximately three metres from the end of the shield. At this location the bentonite pressure more or less equalled the employed grout pressure. A possible bentonite injection influences the jack forces as it serves as lubrication. Moreover, the bentonite can lessen water egress from the grout shield so the loss of volume is less.

Structural research into the applied bentonite injections and their consequences did not take place.

3.5 SPEED OF PROGRESS

General As a consequence of the discontinuous boring process a difference occurred between the speed of progress of the boring (metre per hour) and the speed of progress of tunnel construction (metres per day).

Progress speed of tunnel construction Per day of boring approximately 10 to 15m were realised. The progression rate of tunnel construction is very much dependent on the type of soil to be bored through. At the Second Heinenoord Tunnel progress in sand was approximately 22m, while progress in stiff clay was only 2 to 5m per day. This is probably the case because boring through clay is complicated by the sticking of the clay to the cutting teeth. Additionally, the discharge of excavated clay is aggravated by the pipes clogging up quicker. For example, on passing measuring area North for the first time the boring through clayey sand was characterised by slow advancement.

Progress speed of boring

Measurements of the first passing of measuring area North showed that the speed of progress of the bore shield and the bore face were more or less equal. Therefore, it was concluded that the TBM advanced as a whole. The values fluctuate around 2.5m/hr, albeit with a fair margin. The speed of progress increased slightly when the TBM advanced further into the ground. The most plausible explanation for this is that the soil to be bored becomes sandier from the beginning to the end of the measuring area. During the second passing of this area the average boring speed was 1.4m/hr, with little fluctuation.

During the first passing of measuring area South the speed of progress rather varied over the measuring area. While boring ring 548, the speed of the shield was higher than the speed of the face of the TBM. Moreover, the speed decreased somewhat as the travelled distance of the measuring area increased. During the second passing the average boring speed was approximately 2m/hr with only limited fluctuation.

CHAPTER 4 EVALUATIONS IN THE FIELD OF BORE TECHNOLOGY

4.1 INTRODUCTION

The main research objectives into the field of bore technology included: - Determining face stability, particularly the upper and lower limits of the support pressure for which the soil surrounding the face does not collapse. Important in these determinations are the occurring support pressure, which is determined by the pressure distribution in the mixing chamber, and the extra water pressure that may arise in front of the face of the TBM. - Determining the axial and tangential equilibriums of forces during excavation. - Determining the effectiveness of the tunnelling process, especially the excavation process and the resulting mixture in the mixing chamber, the wear of the cutting teeth, as well as the effectiveness of pumps and pipes.

This chapter includes a comparison of the predictions made and the values measured. Differences are explained and the prediction models concerned are evaluated. However, not for all cases a full comparison between predictions and measurements could be made: - During the tunnelling process reaching instability obviously was not the intended goal. Nevertheless, maximum face stability has accidentally been determined experimentally, when face instability occurred during boring. - It was impossible to determine all forces on and within all individual parts of the TBM. However, showing the relative importance of the main components was aimed for.

4.2 STABILITY OF THE BORE FACE

When bentonite pressure is lower than the minimum support pressure, soil and groundwater will flow into the TBM. Whereas when the bentonite pressure is higher than the maximum support pressure, soil will be pushed away from the bore face, creating an equally unstable situation.

Pressure distribution in the mixing chamber, which contains a mixture of bentonite and excavated soil, determines the occurring support pressure. In addition, it is important to be familiar with the water overpressure generated by the TBM in the surrounding soil, since it could influence stability.

In case of the Second Heinenoord Tunnel, it turns out that the minimum and maximum values of the support pressure, taking into account the influence of water overpressures due to tunnelling, are not far apart. As a result, the regulation of support pressure lies between narrow margins. This is caused by the shallow depth of the tunnel, particularly underneath the river Oude Maas.

Paragraph 4.2 describes the minimum and maximum permissible support pressure. Next, the pressure distribution in the mixing chamber and the water pressure at the face are concentrated on. Finally, at the end of the paragraph, an extensive evaluation of the measured support pressures is presented by way of two appendices.

4.2.1 MINIMUM SUPPORT PRESSURE

PREDICTION MODELS Predictions of the minimum support pressure were carried out during various phases and using numerous prediction models: - In [K100-W-024] six different analytical models were used for both measuring areas. - In [K100-W-015] analytical calculations of the minimum support pressure were conducted using the analytical calculation model of Jancsecz. Considering the calculations pertain to predictions and not design calculations, the pressure reduction caused by soil arching was taken into account, even though Jancsecz advises against this when calculating designs. - In view of the first order evaluation, the minimum required support pressure was calculated for seven indicative cross- sections (see [K100-W-102]). Since these calculations were conducted after the measurements, they were not predictions in the literal sense. Nevertheless, the applied calculation model and the parameters used in the calculations roughly match the predictions of [K100-W-015]. They used the models of Jancsecz (for sand) and Prater (for clay). Because many cross-sections contain both layers of sand and clay, every calculation was done twice - once using Jancsecz’s model and once using Prater’s model. Subsequently, the lowest of both values was defined as minimum support pressure. - Commission L520 used an algorithm to calculate the minimum permissible support pressure at the face of the TBM for those instances when the bore face consisted of layers of sand and clay (ref. Bibliography [1]). This model was not applied in the ‘predictions.’ - In [K100-W-023] numerical calculations were made by means of PLAXIS, using a two-dimensional plane strain model. - In [K100-W-024] numerical calculations were made by means of PLAXIS, using a two-dimensional axial symmetrical model. - In [K100-W-037] an experimental prediction for both minimum and maximum support pressure of measuring area North was carried out in the geotechnical centrifuge. - CUR/COB Commission L520 conducted a back-analysis of the results of the aforementioned centrifuge tests. These calculations were made by means of the EEM-program DIANA, which uses a three-dimensional model (ref. [2]). They included examining the situation of passive collapse of the face of the TBM.

Table 2 summarises the most important findings of the predictions.

Table 2: Predictions of the minimum support pressure at the height of the tunnel axis Location Prediction model / K100 work report Minimum support or other literature pressure (kPa) Measuring area North, tunnel Jancsecz / [K100-W-023] 165 tube West Centrifuge test / [K100-W-037] 163 PLAXIS 2D plane strain / [K100-W-023] 169 PLAXIS 2D axisymmetrical / [K100-W-024] 145 DIANA 3D / ref. [2] 150 Ring 74 tunnel tube West Jancsecz / [K100-W-102] 145 Ring 175 tunnel tube West Jancsecz / [K100-W-102] 192 Ring 250 tunnel tube West Jancsecz / [K100-W-102] 230 Ring 351 tunnel tube West Jancsecz / [K100-W-102] 247 Ring 381 tunnel tube West Jancsecz / [K100-W-102] 231 Ring 509 tunnel tube West Jancsecz / [K100-W-102] 171 Ring 546 tunnel tube West Jancsecz / [K100-W-102] 152 Measuring area South, tunnel Jancsecz / [K100-W-023] 142 tube West PLAXIS 2D plane strain / [K100-W-023] 133 PLAXIS 2D axisymmetrical / [K100-W-024] 130 Measuring are South, tunnel Jancsecz / [K100-W-023] 142 tube East PLAXIS 2D plane strain / [K100-W-023] 133 PLAXIS 2D axisymmetrical / [K100-W-024] 130 Ring 84 tunnel tube East Jancsecz / [K100-W-102] 148 Ring 121 tunnel tube East Jancsecz / [K100-W-102] 169 Ring 249 tunnel tube East Jancsecz / [K100-W-102] 232 Ring 316 tunnel tube East Jancsecz / [K100-W-102] 258 Ring 364 tunnel tube East Prater / [K100-W-102] 237 Ring 455 tunnel tube East Jancsecz / [K100-W-102] 196 Ring 556 tunnel tube East Jancsecz / [K100-W-102] 143 Measuring area North, tunnel Jancsecz / [K100-W-023] 165 tube West Centrifuge test / [K100-W-037] 163 PLAXIS 2D plane strain / [K100-W-023] 169 PLAXIS 2D axisymmetrical / [K100-W-024] 145 DIANA 3D / ref. [2] 150

EVALUATING THE PREDICTION MODELS - It is remarkable how well the experimental prediction and Jancsecz’s calculation model accord with one another. This is confirmed by centrifuge tests done at a later date (ref. [3]). The model developed by Jancsecz proves to be accurate in sand, provided no water overpressure is present in the sand body. - When using the two-dimensional PLAXIS calculations, schematising the third dimension obviously provides a source of insecurity. Moreover, these calculations do not take groundwater flows into account, which may result in collapse values lower than the water pressure. - The low values found using the three-dimensional DIANA calculations can be explained by the overestimation of the effective cohesion c, as used in the calculations. Therefore, values lower than the water pressure are possible in this case as well.

Figure 12 below shows the underlying idea of the collapse mechanisms according to Jancsecz. When the face of the TBM has been plastered, there will be no groundwater flow in the earth body. The pressure at the face of the TBM is, through the filter cake, transferred onto the (sand) grains. Consideration of the equilibrium, as is the basis of Jancsecz’s model, is valid in this situation.

Figure 12: Collapse mechanism according to Jancsecz.

When the face has not or not sufficiently been plastered, the face pressure will cause a groundwater flow through the bentonite. This pressure will not be carried directly onto the grains, but will be present as hydrostatic pressure even outside of the assumed collapse pattern.

Figure 13: Face stability: when there is water overpressure, the net effective force supporting the face is lower.

As indicated in figure 13, this means that the face pressure is only partly available to stabilise the wedge. Therefore, in case of no or only a partly plastered face, a higher face pressure is necessary in order to keep the sliding wedge in equilibrium. Hence, in the evaluation phase an adapted calculation model was deduced to calculate the minimum face pressure when there is a higher water pressure at the bore face [K100-W-102]. This model was used to recalculate the minimum face pressure of the various cross-sections. The results are listed below in table 3.

Table 3: Predictions of the minimum support pressure at the level of the tunnel axis, comparing situations with and without the influence of water overpressure.

Location Original prediction of minimum Minimum support pressure support pressure (kPa) taking into account the extra water pressure (kPa) Ring 74 tunnel tube West 145 164 Ring 175 tunnel tube West 192 225 Ring 250 tunnel tube West 230 262 Ring 351 tunnel tube West 247 274 Ring 381 tunnel tube West 231 263 Ring 509 tunnel tube West 171 198 Ring 546 tunnel tube West 152 185 Ring 84 tunnel tube East 148 165 Ring 121 tunnel tube East 169 192 Ring 249 tunnel tube East 232 272 Ring 316 tunnel tube East 258 291 Ring 364 tunnel tube East 237 - 1 Ring 455 tunnel tube East 196 233 Ring 556 tunnel tube East 143 161 1 Prater’s model is indicative.

By taking into account the water overpressure at the face of the TBM, the minimum required face pressure increases by 10 to 20% over the entire length of the tunnel, that is 20 to 40kPa. Although the calculations were conducted using a provisional and still insufficiently tested model, the order of the increase of the minimum permissible face pressure when calculating the influence of extra water pressure is probably correct.

4.2.2 MAXIMUM SUPPORT PRESSURE

PREDICTION MODELS The predictions mainly use analytical models, in which the maximum support pressure is determined by the load of the soil on top of the tunnel and the friction of the soil against the adjacent soil which is not being pushed upwards. The predictions give a failure pressure which is considerably higher than the pressure caused by the weight of the soil above. The results of the calculations vary substantially. The most conservative ones calculate a maximum pressure equal to the water pressure plus 1.6 times the horizontal effective earth pressure of the cover of the tunnel measuring once the diameter.

Beside these analytical calculations, numerical calculations of the maximum support pressure were also executed. These results vary substantially as well.

During the centrifuge test, simulating the situation of measuring area North, no maximum support pressure was found. Even at a support pressure of 1300kPa the face remained stable.

COMPARING THE PREDICTIONS TO THE MEASUREMENTS

The Second Heinenoord Tunnel encountered instability of the face of the TBM. This happened on 28 August 1997 when boring ring 351of the Western tunnel tube. The face pressures that were measured when this occurred can be compared with the predicted maximum permissible values. Therefore, the pressure measured near the tunnel axis needs to be recalculated to the pressure on the topside of the tunnel. This recalculated pressure on the top amounts to, on average, 268 to 277kPa, depending on the (unknown) weight of the slurry. This figure more or less corresponds to the vertical earth pressures, that is the total load of the soil layers on top.

However, when not the mean pressure over the entire ring but the measured pressure plotted as function of the time, which is more accurate, is taken as reference point, a totally different picture emerges (see figure 14).

60 0 55 0 P1 5 Measured face pressure at 50 0 tunnel axisx (kPa) 45 0 40 0 35 0 30 0 25 0 20 0 15 0

10 0 Supposed time of face 50 instability 0 0 1 2 3 4 5 6 7 Time after start 28-8-97 00:00:00 (hr)

Figure 14: Pressure measured in the mixing chamber at the level of the tunnel axis while boring on the morning of August 28, 1997.

The fluctuating pressure around one and two o’clock indicate that boring actually took place. It is clear that boring stops around the time of 2:40, as the fluctuations decrease. Then the pressure increases up to 380kPa, without any boring taking place. Possibly, during the preparations for boring the next stretch (there is some noise in the measuring signal, but less than during the boring itself), the pressure increases even further to more than 450kPa, just to decrease rapidly afterwards. For a little while a somewhat higher pressure emerges only to decrease quickly to 260kPa, which is but slightly above the calculated water pressure in that location (239kPa).

The pressure development at the time the instability occurred is shown in Figure 15a.

600

550 P1 5 500 Measured face pressure at tunnel axis (kPa) 450 400 350 300 250 200 150 100 Supposed time of face 50 instability 0 11,000 11,500 12,000 12 , 5 0 0 13 ,000 13,500

Time after start 28-8-97 00:00:00 (s)

Figure 15a: Detailed development of bore pressure on tunnel axis at the time of face instability.

Figure 15 a shows that the pressure in the mixing chamber is already slowly dropping before the instability occurs. Presumably the pressure can be withstood by the layer of plaster that has been formed during the time the boring stopped. However, when the cutting wheel is set in motion, approximately around the time the instability occurs (see figure 15b), the layer of plaster is removed by the knife, which causes a groundwater flow in the earth body. As a consequence, the effective earth pressures above the tunnel diminish and insufficient strength is available. The subsequent momentary pressure peaks could have originated in the collapsing of (part of) the face of the TBM.

Figure 15b: Position of the cutting wheel and pressure development at the time of face instability.

In the few minutes before the instability occurred, the face pressure equalled the water pressure plus 2.4 times the vertical effective earth pressure. According to the predictions, failure due to blow-out could then occur. This may be the case even when there is no weak spot in the soil. These calculation models, however, do not consider the influence of groundwater flow resulting from the removal of the layer of plaster. How this influence should be accounted for was not examined.

ASSESSING THE PREDICTION MODELS Just as the determination of the minimum support pressure, the calculation methods for determining the maximum support pressure assume implicitly that the face of the TBM is entirely plastered by slurry. However, it appears that this is often not the case (see paragraph 4.2.4). While boring, there is a continuous groundwater flow upwards. This may lead to a decrease of the effective earth pressure and a weakening of the soil. This has not been taken into account with reference to the evaluation.

An absolute minimum of the maximum face pressure is found when the groundwater flow directed upwards causes blow-out. This lower limit of the maximum pressure more or less equals the vertical total stress. This method disregards the radial distribution of the upward pressure and thus only gives realistic results for a tunnel with a relatively small cover. With proper plastering it is improbable that this mechanism will occur. However, when boring, proper plastering is out of the question.

The measured face pressures were considerably above the vertical total stress in the soil (at level with the topside of the tunnel tube) without any collapse occurring, in particular when boring the Western tunnel tube.

When collapse of the soil at the bore face is considered as strictly passive collapse, as in the model of Leca and Dormieux (ref. [4]), very high values of the permissible pressure will be found that clearly are not suitable in practice (see also [K-100-w-024]). Similar high values were found in the centrifuge test [K100-W-037].

When there is no boring and the face is plastered, relatively high pressures are possible. A plastered face may be of importance when the face of the TBM must be put under air pressure. When the face is put (partially) under pressure, it is researched beforehand whether the loss of air will be limited. A limited loss of air means that the face is plastered. It is most likely that the maximum permissible face pressure is higher in this situation than during boring.

To conclude, there are many calculation models, which yield strongly diverging results. The face pressure measured at the topside of the tunnel at the time of bore face instability equals the water pressure plus 2.4 times the effective earth pressure.

4.2.3 DISTRIBUTION OF PRESSURE IN MIXING CHAMBER

The average pressure and the pressure distribution in the mixing chamber strongly influence the stability of the face of the TBM. Figure 16 gives an example of the pressures measured in the mixing chamber by means of pressure gauges fixed on the front of the cutting head.

Figure 16: Example of pressures measured in the mixing chamber. Boorfrontdruk (kPa) : Face pressure (kPa)

The pressure distribution measured in the mixing chamber is practically linear. Thus, the density in the mixing chamber is more or less uniform. In this situation the density can be calculated by simply calculating the dilution.

The absolute value of the density in the mixing chamber varies per measuring area and is considerably higher than was assumed in the predictions: - Measuring area North, passing 1: 1450kg/m3 - Measuring area South, passing 1: 1290kg/m3 - Measuring area South, passing 2: 1260kg/m3 - Measuring area North, passing 2: 1390kg/m3 The predictions of the density in the mixing chamber amounted to 1170 to 1200kg/m3 for the measuring areas. The maximum density predicted for boring in sand (1495kg/m3 in a density current on the face of the TBM) actually appears to have been exceeded underneath the river Oude Maas. Thus, the cutting wheel torque increased considerably.

The predictions considered the possibility of a density current occurring along the face of the TBM, with the density being lower in the remainder of the mixing chamber. From the measurements it follows that the density in front of and behind the cutting wheel were roughly the same. This may be because the density current is so thin that it passes in front of the pressure gauges. Moreover, a smaller bentonite discharge was injected into the mixing chamber than expected. Therefore, the differences in density are smaller, which causes the density current to be less strong.

The density measured in the mixing chamber is significantly higher than in the discharge pipe. The density in the mixing chamber is determined by a balance of the inbound and outbound mass. On the one hand, at the bore face excavated soil and groundwater flow into the mixing chamber. On the other hand, this mixture is diluted with bentonite in the mixing chamber. Right in front of the mixing chamber the bentonite supply pipe splits. Through the use of control valves the bentonite can be sent to the front of the cutting wheel, to the supply openings in the working chamber, to the shield of the TBM (to reduce shield friction), and straight into the suction pipe of the discharge pipe. The distribution of the inbound slurry has not been evaluated further. In the predictions it was assumed, albeit incorrectly, that all bentonite pumped into the TBM flowed only into the mixing chamber. The density in the working chamber was kept lower than the mixing chamber, because thus the mixture could be pumped along more easily.

4.2.4 WATER PRESSURE ON THE BORE FACE

In each of two locations on the tunnel course, three water-pressure gauges were applied. These, though, were ‘swallowed’ by the TBM while it was boring. These gauges were originally intended to record the water underpressure that was expected to occur as the cutting teeth cut the soil. However, the predictions showed that the gauges would register a water overpressure in sand caused by groundwater flow from the face [K100-W-015]. Measurements confirmed this, as is demonstrated in figure 17.

Figure 17: Example of measured extra water pressure as function of the distance to the face of the TBM compared to the original prediction.

The water pressure at the bore face increases during boring, whereas when the rings are being placed and no boring is occurring the water pressure at the face decreases to the hydrostatic value. In short, the face pressure was higher than expected in the predictions. Therefore, post dictions were made that use the registered face pressure as precondition (see figure 18). 200 Measurement piezometer 5

190 postdiction 180 170 Pressure (kPa) t un n e l distance piezometer 160 150 140 During boring 130 120 110 During standstill 100 0 5 10 15 20 25 30 35 Distance (m)

Figure 18: measured extra water pressure in front of the face as a function of the distance and the result of post diction.

The prediction and hence also the post diction were conducted for circumstances during boring. For this situation the measurements and post diction agree well. The discrepancies between measurements and post diction at moments no boring occurred can be explained by the plastering effect of the bentonite. Neither the prediction nor the post diction calculated this effect, as it could be demonstrated that it would not occur during boring. During the boring hardly any plastering could occur, because the speed at which the bentonite penetrates the sand body is lower than the progress speed of the TBM. Therefore, the water overpressure in the mixing chamber during boring results in water overpressure at the face of the TBM. During standstill, when a ring is constructed, filter cake can build, which diminishes permeability of the bore face. Consequently, the water pressure at the bore face decreases. How the plastering effect works is discussed in other reports (ref. [3] and [5]). This water overpressure also influences the stability of the face of the TBM, as already discussed above.

When, in sand, the face of the TBM was less than 2.5m away from the water- pressure gauge, the influence of the knives on the cutting wheel could be measured as a fluctuation in the water pressure. Figure 19 compares the results of these predictions and measurements.

figure 19: Measurements and predictions of water pressure just before ‘swallowing’ the water-pressure gauge.

The distance over which fluctuations in the water pressure arise as a consequence of the passing of the knives of the cutting wheel matches the measurements fairly well. However, the predicted negative water pressures, caused by the dilatation as the knife passed, were not recorded. The passing of the knife rather seems to lead to an increase of the water overpressure.

The time span between the peaks corresponds with the passing of the cutting tooth and thus relates to the rotational speed of the cutting wheel (approximately 2 rotations per minute). It is apparent that not all cutting spokes have the same influence. If this were the case, the period between the peaks should have been substantially shorter. This can be explained by the fact that the cutting teeth are located at different distances from the axis of the TBM. Therefore, one cutting tooth passes closer to the water-pressure gauges than the others, which subsequently has a dominating influence.

4.2.5 MEASURED BORE FACE PRESSURES COMPARED WITH MINIMUM AND MAXIMUM SUPPORT PRESSURES

In Appendix 3 the face pressures measured over the distance of the tunnel are plotted on the same scale as the cross-section. As indicated in the figures, the pressures measured above the mixing chamber and the pressure (P15) measured at the level of the axis are what matter. Both gauges are mounted on the pressure partition. The pressure measured at axis height was compared to the results of the post dictions. The average pressure when boring a ring is depicted in this appendix.

The figures in Appendix 3 show that for the duration of approximately 100 rings (rings 250 to 351) boring takes place with a face pressure equal to or substantially higher than the pressure corresponding to the vertical total pressure of the soil and water above the tunnel. Several times the pressure is 40kPa higher than corresponds with the vertical total pressure. In those cases the face pressure accumulates to the water pressure plus approximately 1.5 times the effective earth pressure. Yet no blow-out occurred at these pressures. The last rings that were bored before the instability of the Western tunnel tube underneath Oude Maas occurred were bored with a face pressure that was more or less equal to the vertical total pressure.

The average pressures per ring give insight into the pressures when boring took place but are not suitable to explain the calamity that occurred. Therefore, Appendix 3 gives a detailed time registration of the pressures in the Western tunnel tube at the time of the instability. Assessments of these and other time registrations show that the face pressure does increase to high values but that it is still significantly lower at the start of the tunnel than where the instability occurred. The high pressure at the commencement of boring, combined with the small cover of not very compact layers of soil at that location, may have triggered the instability.

Moreover, Appendix 3 shows that the face pressures used when drilling the second tube were considerably lower. The pressure at the face of the TBM did not exceed the vertical total pressure.

Except for directly after the instability occurred, the face pressure was always higher than the minimum face pressure, regardless of whether the water overpressure was included in the calculations or not. Neither was it a matter of instability of the face by using too low a face pressure. The accuracy of the suggested calculation models of the minimum face pressure, therefore, could not be established by monitoring.

4.3 EQUILIBRIUM OF FORCES IN AXIAL DIRECTION

INTRODUCTION Understanding the equilibrium of forces of the boring process is important to the design and the dimensioning of both the TBM and the tunnel lining. Additionally, through this understanding the efficiency of the boring process may be increased by minimising the forces. In the prediction phase not only the co-ordinating equilibrium of forces but also the sub processes determining these total forces were examined. In the evaluation the total measured forces and moments were, as far as possible, assigned to these subcomponents. Based on this the relative importance of the various sub processes can be shown.

PREDICTION MODELS The total axial jack force required follows from aggregating the following forces (see figure 20): - shield friction, - load on pressure partitions (bentonite pressure), - load on the bearing chamber (bentonite pressure), - load on the seal of the tail, - suppression of the soil plug, - axial cutting forces,

- load due to the slope of the TBM, - and slope load on the backup train

Figure 20: Axial forces on the TBM.

The axial forces exerted on the cutting wheel are part of these and are made up of the axial bentonite forces in the bearing chamber, the axial cutting forces and the forces needed to suppress the soil plug in front of the cutting wheel.

In the predictions the various components of this equilibrium of forces were calculated as best as possible by looking at it from different angles.

CALCULATED EQUILIBRIUM OF FORCES BASED ON THE MEASUREMENTS The measured total forces in the main jacks amounted to 13.5 to 15MN in measuring area South and approximately 18MN in measuring area North. Underneath the river these increased to 22,500kN in both clay and sand. The force on the cutting wheel jacks amounted to approximately 2 to 2.5MN for the evaluated rings, which is approximately 10 to 15% of the main jack force. Underneath the river Oude Maas the axial cutting wheel force amounted to approximately 3.75MN, which is about 15% of the main jack force occurring there.

Figure 21 below shows the relative contributions of the various axial forces for the situation without overcutters. This division is based on the second passing of measuring area South and applies to the fictive total force, which is the sum of the absolute values of all components. The load on the tail sealing and possibly, depending on the gradient, the slope load actually have an opposite sign as compared to the other forces. The soil stratum that was bored underneath measuring area South consisted of sand with thin layers of clay.

A xial E q u ilib riu m o f F o rce s (without overcutters) Clay (38) and sand (32), 50:50

M ain jacks Slop e load of backup train 0% Load on tail sealing Slop e load TBM <5 <5% A xia l cuttin g wheel S hield 15% 20% Cutting wheel jacks

Cutting force & soil wedge (4% ) 30%

Load on p ressure 60% Force on bearing chamber (12%) 70%

Figure 21: Axial equilibrium of forces: Approximate division of forces in percentages, deduced from several measurements conducted when boring the second tunnel tube without using overcutters.

Figure 22 shows the relative contributions of the various axial forces for a situation where overcutters were used. This division is based on the first passing of measuring areas North and South.

Axial E q uilib rium of Forces (with overcutters) Sand (32)

Main jacks Slop e load backup train 0% Slop e load TBM Load on tail sealing <5% <5% A xial cutting wheel 20% S hield friction 15% Cutting wheel jacks

Cutting force & soil wedge (5%) Load on p ressure 30% 60%

Force on pressure chamber (12%) 70%

Figure 22: Axial equilibrium of forces: Approximate division of forces in percentages, deduced from several measurements done while boring with overcutters.

When boring underneath the river Oude Maas additional data were collected in two measuring areas in order to determine the influence of the soil conditions on the equilibrium of forces. Over the distance of the second tunnel tube the following additional equilibriums were determined: - Ring 260-300: This is where the tunnel cuts through two soil layers, each covering approximately 50% of the face of the TBM: • Clay, locally sandy and/or containing thin layers of sand. • Sand, medium to coarse-grained, often gravelly. - Ring 380-420: • The bore face consists of one type of soil: • Sand, medium to coarse-grained, often gravelly. The results are illustrated in figures 23 and 24.

Axial Equilibrium of Forces (without overcutters) Clay (38A) and sand (32), 50:50

Main jacks Slop e load backup train 0% Slop e load TBM Load on tail sealing <5% <5% Shield Axial cutting wheel jacks 20% 15% Cutting w heel jacks

Cutting force & soil wedg e (4%) 30%

Load on p ressure 60% Force on bearing cham ber (12%) 70%

Figure 23: axial balance of forces: approximate division of forces in percentages, deduced from measurements done when boring the second tunnel tube underneath the Oude Maas through a clay/sand profile (ring 260-300).

Axial Equilibrium of Forces (without overcutters) sand (32)

Main jacks Slope load backup train 0% Slope load TBM Load on tail sealing <5 <5 Shield Axial cutting wheel jacks 15% 20% Cutting wheel jacks

Cutting force & soil wedge (5%) 30%

Load on pressure 60% Force on bearing chamber (12%) 70%

Figure 24: Axial equilibrium of forces: Approximate division of forces in percentages, deduced from measurements done while boring the second tunnel tube underneath the Oude Maas through a sand profile (ring 380-420).

COMPARING THE PREDICTIONS WITH THE MEASUREMENTS Report [K100-W-047] presents predictions for the axial and tangential forces on the cutting wheel. In tables 4 and 5 these have been compared with the measurements.

Table 4: Measured and calculated axial equilibrium of forces for rings 260—300, consisting of 50% clay (locally sandy and/or containing thin layers of sand) and 50% sand (medium to coarse-grained, often gravelly).

Main jack force Measured value (MN) Prediction (MN) TOTAL 20 213 174 Pressure partition 13 15 Cutting wheel 3 53 0.24 Friction 5 3 Tail sealing -0.61 -0.8 TBM and backup train -0.22 -0.2

Cutting wheel force Measured value (MN) Prediction (MN) TOTAL 3.3 4.63 0.24 Bearing chamber 2.4 - Cutting force and soil 0.9 Cutting force: 0.15 plug Plug: 0.5-4.53 1 Calculated from the grout pressure measured in the tail of the TBM. 2 Calculated on basis of slope in that location. 3 With soil plug. 4 Without soil plug.

Table 5: Measured and calculated axial equilibrium of forces for rings 380-420, consisting of sand (medium to coarse-grained, often gravelly). Main jack force Measured value (MN) Prediction (MN) TOTAL 18 233 164 Pressure partition 12 13 Cutting wheel 3 73 0.34 Friction 3 3 Tail sealing -0.61 -0.8 TBM and backup train 0.22 0.2

Cutting wheel force Measured value (MN) Prediction (MN) TOTAL 3.2 7.53 0.34 Bearing chamber 2.2 - Cutting force and soil 1.0 Cutting force: 180 plug Plug: 0.6-7.33 1 Calculated from the grout pressure measured in the tail of the TBM. 2 Calculated on basis of slope in that location. 3 With soil plug. 4 Without soil plug.

EXPLANATION OF THE DIFFERENCES BETWEEN PREDICTIONS AND MEASUREMENTS An important cause of the differences between predictions and measurements is using incorrect assumptions about the process parameters such as the face pressure employed, grout pressures used in the tail, and cutting depth. As a result of these differences and unexpected measurements, the predictions of several cross-sections were re-executed, using the measured process parameters as input. The resulting equilibriums of forces were compared with the values measured at the cutting wheel jacks and main jacks. This explanation demonstrates that the total jack force can be calculated relatively accurately, but that it remains difficult to divide this force up into the above- mentioned subcomponents.

The cutting wheel force appears to be the most insecure factor in the predictions. The other forces agree fairly well with the measured values.

Assuming that the prediction model explaining the forces caused by a soil plug is correct, it can be deducted from the measured data whether a soil plug did (partially) arise or not at all. The predictions for the axial cutting wheel force without soil plug were lower than the values that were actually measured. This difference is caused by the bentonite pressure of the bearing chamber, which the predictions disregarded.

Comparing the equilibriums of forces with the different locations (both measuring areas as well as the location underneath the river Oude Maas), the equilibrium of forces does not seem to be influenced that strongly by the type of soil being bored through. This is the case because that part of the forces caused by friction with the soil (i.e. shield friction and cutting forces) is relatively small.

ASSESSMENT OF THE PREDICTION MODELS AND DESCRIPTION OF THE COMPONENTS OF THE EQUILIBRIUM OF FORCES - The largest contribution (approximately 50%) to the total main jack force consists of the load on the pressure partition of the TBM, which is directly related to the maintained support pressure. Because the TBM is top-heavy and the face pressure increases the deeper it gets into the ground, the resultant of the combined main jack forces lies below the middle of the TBM. Moreover, the TBM has a tendency to diverge in the horizontal plane, which causes the resultant to be eccentric not only in vertical but also in horizontal direction (see figure 25).

Figure 25: Asymmetrical main jacks. Drukhoofdvijzels (Mpa): Pressure main jacks (Mpa) Hoofdvijzelgroep: Group of main jacks.

- The load due to the slope of the TBM is minimal and can be relatively accurately calculated. - The load on the tail seal is caused by the injected grout and can be calculated well from the injection pressure and the surface pressure. - In order to predict the lining friction several assumptions were made about the influence of the bentonite. Hence, the predicted values of the lining friction diverge strongly, ranging from 3.8kPa to 49kPa, which corresponds to a friction force of 900 to 11,200kN to be overcome. The measured values amount to approximately 6500kN (which is 30% of the total jack force) without using overcutters. However, it has to be noted that the lining friction could not be established by measurements and is therefore considered to be an (uncertain) element of the equilibrium. During the second passing of measuring area South the influence of the use of overcutters was researched further. Using the overcutters, the corrected main jack force (i.e. the total main jack force minus the load on the pressure partition) decreased by 80% from 12,000 kN to approximately 2,500 kN (see figure 26). Assuming that the axial cutting forces do not diminish when using the overcutters, this means that a strong decrease of

the friction against the shield is responsible.9 The force on the jacks of the cutting wheel and the torque on the cutting wheel did not significantly increase when using the overcutters.

Figure 26: Influence of overcutters.

The friction along the shield of the TBM consists of an axial and a tangential component. The sum of these two components can never exceed the yielding friction. As the TBM experiences a bigger displacement in axial than in tangential direction, the axial shield friction component will almost equal the maximum friction force and the tangential component will be very small. - Most of the exerted cutting wheel force (approximately 70%) is caused by bentonite pressure in the bearing chamber. The predictions do not take this into account. The cutting wheel can rotate in two directions in order to enable correction of rolling of the TBM. Accordingly, both sides of the cutting arms have been equipped with cutting elements. The first chisel cuts away the soil and the second one, which is dragging through the soil, follows at approximately 0.90m. Since the cutting wheel continually slowly moves forward, this dragging component pushes away the soil. Through simple modelling accompanied by post diction [K100-W-103] it appears that the axial forces on the non-cutting elements are approximately one sixth in size of the axial forces on the elements that do actually cut. This mechanism causes the emergence of a clay or sand plug between the cutting elements. Visual examination of the cutting wheel showed this, in addition to the fact that between cutting elements the spoke was less worn than at places not containing cutting elements. From measuring the water pressure it followed that the dragging non-cutting elements scrape the soil (including bentonite).

9 In this location the original equilibrium of forces before applying the overcutters is somewhat different from

the division shown in figure 21.

- In all probability a soil plug has not emerged when boring in sand. This can be partly explained by the low level of forces. Nevertheless, in clay there will have been a soil plug, although this cannot be said for certain as it was not possible to check this. Considering that the cutting wheel force consisted of approximately 10 to 15% of the total main jack force, the combined effect of the possible soil plug, the cutting and the non- cutting elements added up to only 3 to 5% of the total required axial force. - It turned out that it was easier to manage the TBM when using overcutters, which shows from the lessened eccentricity of the jack forces. Improved manageability in the horizontal plane is the result. In addition, when using overcutters the normal force and the bending moment exercised by the jacks on the tunnel lining are smaller, decreasing the likelihood of damaging the tunnel segments.

4.4 EQUILIBRIUM OF FORCES IN TANGENTIAL DIRECTION

PREDICTION MODELS The tangential forces on the TBM consist of four components: - cutting torque of the face, - cutting torque of the overcutters, - soil plug torque, - and mixing torque.

The total torque, i.e. the total tangential force, is the sum of these components and equals the sum of the torque in the groups of main jacks and the shield friction of the TBM. The composition of the total torque is illustrated in figure 27.

Figure 27: Frontal view of TBM (cutting wheel) showing the various torques

COMPARING PREDICTIONS AND MEASUREMENTS The total torque, following from the measurements, is nearly completely distributed onto the lining by the sets of main jacks. The tangential friction along the shield of the TBM is of subordinate importance, as the maximum friction was already ‘spent’ in the axial direction, in which direction the displacements are larger. This was not included in the predictions, though they did include the assumption that the maximum friction along the shield would be more than sufficient to prevent rotation. The total measured cutting wheel torque fluctuates periodically between 400 and 800kNm, with an average of approximately 600kNm. The measurements done in the measuring areas as well as the measurements done underneath the Oude Maas are within this range. The torque is slightly higher than the predictions indicated, which assumed absence of a soil plug in front of the shield. Initially they were of the order of 200 to 700kNm. However, other predictions did include a soil plug. In these predictions the predicted values amounted to 1.5 to 2MNm, which is far above the measured values. Figure 28 shows the relative contributions of the four torques that constitute the cutting wheel torque. Since it was not possible to measure all torques individually, several estimations were done.

Figure 28: Approximate division of the four torques constituting the total cutting wheel torque, deduced from several measurements done when boring the first tunnel tube.

ASSESSMENT OF THE PREDICTION MODELS AND DESCRIPTION OF THE COMPONENTS OF THE EQUILIBRIUM OF FORCES - The mixing torque, caused by the resistance experienced by the rotating cutting wheel in the mixing chamber, is a negligible factor. - Based on measurements, the two remaining factors cannot be differentiated. These are the cutting torque of the cutting elements and the overcutters, and the moment caused by the occurrence of the soil plug. It has to be noted that another important component constitutes the cutting torque, which is the dragging non-cutting elements pushing the soil away. As a soil plug will not occur in sand, the soil plug torque can be dismissed. In clay, however, this phenomenon may indeed occur, but this has not been observed with absolute certainty.

During the second passing of the measuring area North, the relation between the total cutting wheel torque, the cutting wheel force and the cutting depth was examined (cutting depth being the quotient of the progress speed of the TBM and the rpm of the cutting wheel). By boring a number of rings with corrected progress speed and rpm, a set of data was obtained for a wide range of cutting depths. The results of these measurements are given in figure 29.

Figure 29: Three-dimensional projection of the relation between cutting depth, cutting wheel force and cutting wheel torque.

From the measurements it can be concluded that, on approximation, a linear relation exists between the cutting wheel torque, the cutting wheel force and the cutting depth. This linear relation had already been predicted in the prediction phase.

4.5 EFFECTIVENESS OF THE BORING PROCESS

4.5.1 WEARING OF THE CUTTING TEETH

The effectiveness of the tunnelling process is determined, amongst others, by the wear of the cutting teeth on the bore face. The extent of the wear determines whether the elements need to be replaced during the boring process. Replacing the cutting elements prematurely is a time-consuming and risky operation, which needs to be avoided whenever possible.

After replacing the teeth that were used for boring the first tunnel tube, they were measured for wear, in particular their reduction in size. The predictions and post dictions previously made were compared to these results.

‘Archards wear law’ was used to predict the wear of the cutting teeth. It says that the wear of the face elements is dependent on the wear mechanism, the characteristics of the soil, the load (contact pressure), the characteristics of the material, and the design of the elements.

The cutting wheel of the TBM is equipped with 31 cutting teeth (excluding two overcutters), that have been fitted into different positions. These teeth were constructed from a container of steel, in which the sets of teeth made from hard steel (tungsten) were placed. For the first tunnel tube two sets of teeth were used. With the first set the first two metres of the sealing plug of the entry shaft were bored, the second set was used to bore the remainder of the tunnel, including sealing plug South. The wear measurements indicate that the second set of teeth wore on average 11mm (the outer position of the cutting wheel).

Because the positions of the cutting teeth on the cutting wheel and the size of the cutting elements were changed after the predictions of the wear of the cutting elements were formulated, a post diction of the wear was conducted [K100-W-104]. Both the predictions and the post dictions overestimate the wear of the teeth. Firstly, it is believed that this is especially caused by the fact that the calculations assumed a constant cutting depth over the entire length of the tunnel whereas this was not actually the case. Secondly, the wear constant of metal, which was not verified on the employed teeth by means of laboratory tests, was used instead of the wear constant of tungsten. Over the entire tunnel distance the same value of the wear constant was used. In reality it may be expected that in sand there is more wear than in clay. This means that the wear in sand is higher than the ‘average’ wear observed over the course of the tunnel.

4.5.2 FORMING OF MIXTURE

The principle of the slurry shield is based on the supply of fluids (a bentonite suspension) to the face of the TBM, where it is mixed with the excavated soil and formed into a slurry. This mixture is pumped into the separation plant located on the surface. This device separates the slurry from the excavated soil, which subsequently is discharged. The clean bentonite suspension is transported back into the face of the TBM. This suspension is called regenerated bentonite.

The slurry shield boring method uses the specific characteristics of bentonite slurries, in particular their high viscosity and ‘yielding pressure,’ which provide the fluid with a certain strength when in rest. This enables essential functions such as transport and bore face support. The bentonite circulation through the TBM and separation plant is reflected in figure 30. This paragraph limits itself to the physical processes in the mixing chamber.

Figure 30: Bentonite circulation through TBM and separation plant.

BEHAVIOUR OF SLURRY When passing the measuring areas the rheological properties of the slurry were determined. These characteristics determine the flow behaviour of the slurry. Only the flow behaviour of the regenerated bentonite is of importance to the tunnelling process. Measurements show that this behaviour varies. They indicate that the regenerated bentonite is thinner than the predictions assumed (except for two peaks). Most of the measurements show a viscosity of approximately a factor 3 lower, whereas the yielding pressure may be lower by a factor 10. Fresh bentonite is made with a density of approximately 1040kg/m3. Initially the idea was not to let the density of the regenerated bentonite become higher than 1150kg/m3. However, measurements indicate that it increased up to 1200kg/m3. Yet, it was concluded that the essential functions of the slurry as a form of transport still could be fulfilled with the ‘weaker’ rheology.

TYPE OF FLOW AND MIXING IN THE MIXING CHAMBER The type of flow in the mixing chamber is determined by the rpm of the cutting wheel, the geometry of the orifices, and the rheology of the mixture. The flow, as a consequence of the shear stresses caused by the slurry, in the room between the cutting wheel and either the pressure partition or the face of the TBM determines the type of flow (laminar or turbulent). The predictions assumed a turbulent type of mixing. However, if the flow were not turbulent, the mixing can only be accredited to the circulation of the slurry.

Taking the measured rheological characteristics as fact, the flow in the mixing chamber is laminar, except in case of the slurry monsters with the lowest rheological index numbers combined with the highest rpm of the cutting wheel (3 rotations per minute). When calculating the type of flow in this case, in principal a similar model can be applied as to the predictions. However, the influence of rheology needs to be carefully considered.

The soil trapped in the triangular space between the arms is being carried along by the rotating movement of the cutting wheel, which is responsible for the mixing. It followed from the predictions that a non-uniform density emerged when boring in sand (a density flow along the face of the TBM). Yet, from the measurements it was concluded that there is homogeneous mixing in most of the mixing chamber.

Whereas originally it was assumed that the mixing type was turbulent, it showed, against all expectations that the laminar mixing type functioned just as well in distributing and discharging the excavated material through and from the mixing chamber. It did not seem necessary to strive for turbulence in the mixing chamber.

PARTICLES DEPOSITING IN THE MIXING CHAMBER In the mixing chamber a high slurry density needed to be created in order to keep the face of the TBM stable. Nevertheless, high densities are only possible if the particles are intercepted in the slurry and depositing at the bottom of the mixing chamber is prevented.

At the examined depositing speeds, the high viscosity of the bentonite suspension prevents the excavated particles from depositing quickly. However, because the fluid is constantly moving during boring, the internal microscopic structure of clay platelets is continually being broken and the particles deposit slowly but surely (which is called dynamic sedimentation).

Contrary to common beliefs, the yielding pressure of the slurry, in fluid state, is not a threshold value for the depositing of particles. The prediction for the depositing of particles, for that matter, disregarded the above-mentioned dynamic sedimentation. It also used an over schematised rheological description with a constant viscosity. In reality the viscosity increases with the decreasing depositing speed, which holds off depositing even further.

According to dynamic sedimentation theory, the bored sand particles (characteristic diameter 0.4mm) deposit in flowing state. During standstill, however, they will be intercepted in the slurry. Large chunks of clay (diameter 0.1m or more) will deposit both in flowing state and in standstill. Only by producing a high concentration of clay balls, they can form a matrix that can support the bore face.

BORING IN CLAY The bored clay will partly disintegrate and thus be absorbed by the bore fluid. The part not disintegrated will form clay balls, which may clog the orifice of the distribution pipe. When boring through clay layers, clay chunks have indeed been found in the separation plant. Therefore, it was said that the density of the inbound and outbound bentonite stream increased when passing underneath the Oude Maas. This is probably the result of the large quantities of excavated clay particles that ended up in the slurry and could not be completely removed by the separation plant. Compared to bentonite, these excavated clay particles hardly contributed to the flow characteristics of the boring fluid.

4.5.3 EFFECTIVENESS OF PUMPS AND PIPES

Pumps and pipes served to provide the mixing chamber with slurry and to discharge the excavated soil. It is important that the pumps and pipes are geared to one another. In order to achieve this, the specifically non-Newtonian characteristics of these fluid flows need to be considered.

CHARACTERISTICS OF PUMPS AND PIPES The non-Newtonian character of the slurry in principle does not influence the pump curve. Because centrifuge pumps are used, the decisive parameter is the slurry density.

Because of the relatively long, straight flow lengths, the loss of wall friction significantly contributes to the loss of energy. Directly measuring the pipe resistance of a 10m stretch of discharge pipe corresponds well with the tube resistance calculated from the pressure changes at the supply side of the pump near the extension of the pipe. In turbulent stream mechanisms the bentonite suspension shows a decreasing friction coefficient. In the end, the decrease in pressure caused by wall friction is greater than the decrease in pressure when pumping water, as the density of the slurry is higher. Provided the decreased friction coefficient is included in the predictions and no sedimentation of sand occurs, accepted calculation methods can be applied.

TUBE SPEED AND SEDIMENTATION OF SAND For the selected operational setting of the discharge pipe, transportation of the particles was unproblematic. There was no significant sedimentation of sand in the transportation pipes, which would have led to higher drag values than measured. The transportation capacity model as used in the predictions is applied to and verified for sand water mixtures. The resulting current velocities are relatively safe. The impression is that for the same slurry characteristics smaller return discharges could suffice. Then, however, the flow needs to remain within the turbulent regime in order to prevent sedimentation. Possibly the discharge needs to be adapted when too much clay is bored. A potential benefit consists of the reduction of the pump capacity. Moreover, the volume flow to the separation plant decreases but becomes more highly concentrated.

Turbulence in the discharge pipes can be encouraged by using a smaller diameter. However, this has two disadvantages. Firstly, more pump energy is required because of the losses through more friction with the wall of the pipe. Secondly, large clay chunks can clog the pipes.

4.6 SUMMARY: ACQUIRED KNOWLEDGE IN THE FIELD OF BORE TECHNOLOGY

FACE STABILITY The Second Heinenoord Tunnel is characterised by its shallow depth underneath the river. Research shows that for such shallow tunnels the margins between which the minimum and maximum face pressure may fluctuate to prevent instability are fairly small.

As the cutting wheel rotates, the plastering effect of the slurry on the face is continuously broken. This causes a higher water pressure, which negatively influences the stability of the bore face. Consequently, the minimum required face pressure is probably higher than the values calculated in the predictions. The realised face pressures, however, were amply above the minimum values.

Calculation models which, when determining the minimum support pressure, consider the higher water pressure, have not been justified sufficiently enough in order to serve as design models for tunnels. The development of collapse of the bore face and the influence of arching effects have not been researched adequately.

When boring the Second Heinenoord Tunnel the face pressure was remarkably higher than the total earth pressure on top of the tunnel. Once more, there are no tested calculation models available that can calculate the maximum face pressure. Analysis of the measurements demonstrated that perhaps the groundwater flow had influenced this as well. From analysis of the measurements it followed that during the instability that occurred when boring ring 351 the face pressure was so high that, even without weak spots in the soil, collapse of the soil was a real possibility. As the occurrence of weak spots can never be ruled out beforehand, a ‘historical’ research into any disturbance by humans (i.e. piles, spuds, boring and drilling tests) need always have taken place.

There are still many insecurities linked to calculating the maximum permissible face pressure. A safe approach is to limit the maximum face pressure to the total pressure of the water and the soil layers above, and to disregard the extra strength that may still have been present until verified calculation methods have been developed.

At the bore face the slurry and the excavated soil mixed well, which means that the pressure distribution at the face is hydrostatic. The density of the support fluid, however, proved to rather fluctuate over the course of the bored distance. Moreover, this density was higher than expected beforehand. This is explained by diluting the excavated soil with less slurry. The fierce fluctuations of the pressures measured when passing sand underneath de Oude Maas could indicate that the sand concentration in the mixing chamber were so high that effective earth pressure arose. When boring through clay underneath de river Oude Maas the same phenomenon occurred. The clay chunks arising when excavating clay cannot be kept in suspension. By accumulating the clay chunks (effective earth pressures) the mixing chamber can remain filled with excavated clay and become clogged.

Originally it was expected that water underpressure would arise when cutting the soil with the cutting teeth. However, over time these expectations for sand were adjusted - water overpressure would arise through groundwater flow from the bore face. This was confirmed when during actual boring the water pressure increased before the face and decreased to hydrostatic value during standstill (when placing the rings).

In sand, when the face was distanced less than 2.5m from the water-pressure gauge, the influence of the knives on the cutting wheel was measurable as a fluctuation of the water pressure. Passing of a knife did not lead, contrary to expectations, to extra water pressure.

EQUILIBRIUM OF FORCES The force exerted on the main jacks of the TBM is mainly determined by the support pressure at the face, which is exercised on the pressure partition. This can be measured well. However, the shield friction on the machine consisted of a substantial but difficult to quantify share of the jack force. On average, the recalculated share of the shield friction amounted to approximately 30%. When using the overcutters, this force substantially decreased, as did the total main jack force. Moreover, by using the overcutters the eccentricity of the forces decreased, the manoeuvrability improved and the load exerted on the tunnel lining was limited.

The force on the cutting wheel jacks amounted to 15% of the force on the main jacks. This force is mainly determined by the bentonite pressure on the bearing chamber. Comparing the equilibriums of forces for the various locations (both measuring areas and the locations underneath the river), it seems that they are not substantially influenced by the type of soiling being bored through. This is the case because the share of forces causing the soil resistance, i.e. the shield friction and the cutting forces, is relatively small. The decrease of effectiveness observed in practice when boring through layers of clay can thus be attributed to other factors.

Measurements conducted during the second passing of measuring area North prove that there is, on approximation, a linear relation between the cutting wheel torque, the cutting wheel force and the cutting depth. The cutting depth is the difference of the speed of progress of the TBM and the rpm of the cutting wheel.

EFFECTIVENESS OF THE TUNNELLING PROCESS As a consequence of unfamiliarity with the cutting depth and with the wear resistance of the used cutting teeth as a function of the type of soil being bored, the wear of the cutting teeth was overestimated.

The boring fluid added to the mixing chamber was not extremely viscous. By intercepting the fine clay particles which were excavated the density of the slurry increased. Therefore, it is concluded that the flow into the mixing chamber was primarily laminar, that the excavated solid soil components slowly deposit during this flow, but that these components are divided evenly over the mixing chamber by the rotating movement of the cutting wheel after all.

Provided the preconditions for a homogenous forming of mixture are met, the density in the mixing chamber can be calculated easily through a continuity analysis and can be regulated by the operator (albeit with some delay). The pressure in the mixing chamber is determined directly by the operator by means of air pressure in the air pressure cabin.

When dimensioning the pumps and pipes, the characteristics of the mixture in the mixing chamber need to be kept in mind. Moreover, one also has to bear in mind the demands in order to maintain a disruption-free discharge of the bored soil (transport capacity of the pipe).

It follows from analysing the pipe resistance that the influence of the slurry on this resistance can be calculated easily. From discharge and density measurements in the return pipe and the mixing chamber it shows that part of the supplied slurry directly gets discharged again. The discharge of the supply and discharge pipe, therefore, is higher than required in the mixing chamber. It is thought that, with respect to transport capacity, smaller discharge may suffice using the same bore fluid characteristics. Still, the slurry flow must remain in the turbulent regime in order to prevent sedimentation. For clay the hydrodynamic slip forces need to amount to such a size that the individual clay balls cannot come to a standstill against the wall.

CHAPTER 5 EVALUATIONS IN THE FIELD OF GEOTECHNOLOGY

5.1 INTRODUCTION

The main research objective in the field of geotechnology was to gain understanding of (soil) deformations and stress changes around the tunnel. This is important, as they could lead to surface settlements and all their variously related negative consequences. Another research objective was concerned with the reliability of the geological model, including the structure as well as the characteristics per layer.

This chapter will compare the predictions which were made with the actual measured deformations and stress changes in the soil, divided into the following aspects: - surface settlements in cross direction (§ 5.2.2.), - surface settlements in longitudinal direction (§ 5.2.3.), - deformations in the underground (§ 5.2.4.), - and stress changes in the underground (§ 5.2.5).

The differences between predictions and measurements will be explained, and the prediction models in question will be assessed. Most attention will be given to the predictions regarding the surface settlements and their relation to the grouting process. The findings of this research will be summarised in paragraph 5.3. Attention will also be paid to the influence of boring the second tunnel tube on the first tunnel tube (§ 5.2.6.). Finally, this chapter will focus on the soil model by evaluating the way the geotechnical parameters were determined (§ 5.4). Of course the chapter concludes with a summary of the knowledge obtained in this field.

5.2 DEFORMATIONS AND PRESSURE CHANGES IN THE SOIL

5.2.1 CAUSES OF DEFORMATIONS

Deformations around the tunnel are the result of a loss of volume occurring in the construction process. The main causes of this loss of volume and the resulting surface settlements are: - “Face loss”, as a result of the soil unloading at the face of the TBM. This loss of face is mainly dependent on the employed support pressure and on the volume of the excavated soil in relation to the advance rate of the TBM. As concluded from the conducted measurements, the surface settlements caused by this loss of face are relatively small, several millimetres at the most. - The conic shape of the TBM. The diameter of the TBM is larger on the front side than on the backside of the machine (8.55m versus 8.52m), which may cause surface settlements.

- Use of overcutters. Using overcutters, and hence excavating more soil than the diameter of the TBM, may play a part in the surface settlements above the TBM and soil deformations. As concluded from the conducted measurements, the settlements above the machine range from only several millimetres to approximately 15mm. - (Incomplete) filling of the tail of the TBM with grout and shrinking of the grout. Considering that the outer diameter of the tunnel is smaller than the smallest diameter of the TBM (8.30 versus 8.52m), a space around the tunnel lining arises after the TBM passes, the so called tail void. This space is filled with grout in order to limit deformations around the tunnel. Measurements indicate that the extent of grouting ultimately determines the surface settlements. There is a clear relation between, on the one hand, the volume of grout and the grout pressures employed, and on the other hand the measured surface settlements. - The effects mentioned may also minimally influence deformations on the long-term.

These causes cannot be clearly discerned from one another. Therefore, most prediction models assume a total loss of volume, which is the sum of all effects mentioned. Only state-of-the-art finite element models, as used for first order evaluations, may keep the various sub-processes apart, both in quantity and in succession. The following paragraphs mainly describe the total effects of boring and constructing the tunnel, because the prediction models that were used could not distinguish between them. Yet, in order to obtain some knowledge about the relative importance of the various sub-causes, tables 6 and 7 below give the ‘measured’ proportional distributions of the settlements per phase of the boring process for the measuring areas North and South as compared to the predictions given in [K100-W-009]. The measured distributions can be found in [K100-W-073]. [K100-W-105a] also shows a, albeit somewhat diverging, distribution as deduced from the measurements.

Table 6: Proportional distribution of settlements of first passing measuring area North (%). Face loss Passing TBM Grouting tail void Consolidation effects Prediction 20 30 30 20 Measurement section line A 17 40 27 16 Measurement section line C 17 41 31 11 Measurement section line F 16 46 36 03 Average North 17 42 31 10

The settlements due to passing of the TBM proved to be relatively larger than predicted in measuring area North. On the other hand, relatively the time- dependent effects (after-effects) were much smaller as compared to the predictions.

However, in measuring area South, where compressible layers were found in the underground, relatively large time-dependent settlements have been observed.

Table 7: Proportional distribution of settlements second passing measuring area South (%).

Face loss Passing TBM Grouting tail void Consolidation effects Prediction 15 25 25 35

Measurement section line S 31 08 23 38 Measurement section line Q 17 08 58 17 Measurement section line O 15 35 30 20 Average South 21 17 37 25

5.2.2 SURFACE SETTLEMENTS IN CROSS DIRECTION

PREDICTION MODELS Analytical models To predict surface settlements the empirical formula (two-dimensional) as formulated by Peck was used. This formula makes the deformation dependent on the volume of the settlement trough on the one hand, and the bending point coefficient on the other. According to Peck, the surface settlement is:

x2 − 2 i 2 w ( x ) = w max e

V s w max = i 2π

w: Vertical displacement (m)

wmax: Vertical displacement above the tunnel axis (m) x: Horizontal distance to the tunnel axis (transversal) (m) i: Horizontal distance from the tunnel axis to the bending point of the settlement curve (m) 3 Vs: Volume of the settlement curve per stretching metre of tunnel (m /m)

The value of Vs is being equalled to the total tunnelling loss. In the calculations the loss of volume varied between 0.5% , 1.0% and 1.5% of the surface of the tunnel.

The bending point of the settlement curve i determined especially the settlement trough. The bending point coefficient varied between either 5 or 10m. The deformations were determined for the construction of one tunnel tube and for the construction of two tunnel tubes in both measuring areas. ⎡ ⎤ Vs y wz = ⎢1+ ⎥ 2hπ 2 2 ⎣⎢ y + h ⎦⎥

The analytical formula published by Sagaseta in 1987 was used to determine deformation occurring during the construction of one tunnel tube and the deformation caused by the construction of two tunnel tubes as well. The formula for surface settlement straight above the tunnel states the following:

wz: Vertical displacement (m) h: Depth of the tunnel axis below the surface (m) y: Horizontal distance to the face of the TBM (longitudinal) (m) z: Vertical distance to the tunnel axis (m) 3 Vs: Volume of the settlement curve per stretching metre of tunnel (m /m)

This formula can only vary the value for loss of volume but not for the shape of the settlement trough. However, in later publications Sagaseta presented adapted formulas. In the paragraph where the prediction models are assessed, these adapted formulas will be discussed. In the predictions using Sagaseta’s formula, the same two alternating values for the loss of volume were used as in Peck’s model.

Numerical models By means of the finite element program PLAXIS, deformations (of surface and underground) and stress changes in the surroundings have been calculated for the construction of one and two tunnel tubes. Previous to these two- dimensional calculations, a sensitivity analysis was executed to examine the stiffness of the tunnel, the material model, various soil characteristics, the level of the groundwater table, and the total loss of volume. Consequently, it was decided to only vary the total loss of volume in the predictions and to only assume 0.5%, 1.0% or 1.5% of the surface of the tunnel. In the calculations the loss of volume was translated into radial contraction of the lining.

By means of the finite element program DIANA, a three-dimensional prediction was made for pressures and deformations, which would occur when boring the first (Western) tunnel tube in the Southern measuring area. From this calculation a prediction for measuring area North was deduced without using any other numerical analyses. Based on the size of the tail, the total loss of volume when boring was assumed to be 2.7%, leading to a loss of volume of 1.6% on the surface.

COMPARING PREDICTIONS WITH MEASUREMENTS Surface settlements were measured over several section lines in both measuring areas (see Appendix 4).

Initially, in both measuring areas variations in surface settlements were observed, which had not emerged from the predictions. This is because the predictions had presumed, per measuring area, one fixed set of parameters for the geotechnical profile and one for the boring process. Also, contrary to the predictions, in several instances the measured settlements were not symmetrical in relation to the axis of the tunnel. For instance, during the second passing of measuring area North, at the height of section line F, an asymmetrical settlement trough is found. Moreover, in both passings of measuring area South the cross troughs proved not to be completely symmetrical. This may be caused by the presence of a dike body near the measuring area, by a non-uniform layer structure, or by the loss of navigability of the TBM.

To get an idea of the measured variations, tables 8 and 9 provide a short summary of the measured total settlements and volume losses in both measuring areas as a function of the distance to the bore face (expressed in the number of tunnel diameters D).

Table 8: Measured maximum surface settlement (in mm) in relation to the distance behind the bore face (in diameters D). Measuring area Measuring area Measuring area North, second Measuring area South, North, first South, first passing second passing passing passing Section line → C F O Q F G C A Q O 0 D 5 4 4 2 0 4 2 2 2 3

1 D 15 15 2 -3 8 9 5 5 3 10 2 D 27 22 5 -5 11 13 7 6 10 16 4 D 30 - 4 -3 12 14 8 7 12 20

Table 9: Measured volume of settlement trough in relation to the distance behind the bore face (in diameter D), expressed in percentage of tunnel surface (%). Measuring Measuring area Measuring area North, second Measuring area South, area North, South, first passing second passing ** first passing passing Section line → C F O Q * F G C A Q O 2 D 0.7 0.6 - 0.2 - - - - 0.20 0.19 4 D 0.8 - 0.1 0.1 0.4 0.44 0.24 0.23 0.26 0.24 * Rising wall. ** Incomplete trough.

The first passing of measuring area North shows that predictions using Peck

(i = 10m), Sagaseta and PLAXIS (all with trough volume Vs = 1%) underestimate the maximum settlement and the slope of the trough at a distance of four diameters behind the bore face. An example is given in figure 31:

Figure 31: Comparing predictions with measurements of surface settlements measured at section line C, first passing measuring area North.

For the first passing of measuring area South and the second passing of measuring area North all predictions overestimate the maximum settlement. The slope of the cross trough is generally underestimated, whereas its width is overestimated.

For the second passing of measuring area South the maximum settlement on section line Q (at -2D) is strongly overestimated, when using DIANA

calculations (Vs = 1.6%) and Peck (Vs = 1% and i = 5m). By using Sagaseta, Peck

(Vs = 1% and i = 10m) and PLAXIS (Vs = 1%), which assume a smaller boring loss than the DIANA calculation, a reasonably good correspondence with the maximum settlement is obtained. In this case the slope of the transverse trough is also often underestimated, which results in overestimating the width of the trough. For section line O the maximum settlement and the slope of the cross trough were underestimated when using PLAXIS, Sagaseta and Peck

(Vs = 1% and i = 5m).

EXPLAINING THE DISCREPANCIES BETWEEN PREDICTIONS AND MEASUREMENTS Analytical models For Peck’s as well as Sagaseta’s formula, the loss of volume during boring needs to be determined. Generally, this value is overestimated in predictions, leading to an overestimation of the settlement. However, a solid method determining the loss of volume a priori is not available. Moreover, the fact that the bending point coefficient i is hard to determine, or can only be estimated, plays a part in Peck’s model as well. To a large extent this value determines the shape of the settlement trough. Predicting a rise of the surface (as occurred during the first passing of the Southern measuring field) and an asymmetrical settlement curve (for example caused by local soil circumstances and the manoeuvring of the TBM) is not possible when using these models.

By using Peck’s formula a so called ‘fit’ could be established a posteriori, by using the measuring points located on the section lines in the Northern and Southern measuring areas. The results of these ‘fits’ reasonably approximate the shape of the measured settlement troughs in cross direction (see figure 32). Figure 32 shows that back calculation of the measured settlements is not really possible when using Sagaseta’s 1987 formula because the width of the settlement trough cannot be varied in this formula.

Figure 32 : Calibration of measured surface settlement using formulas of Peck and Sagaseta.

Table 10 below shows the input values for various passings and measuring sections in Peck’s model by which the measured trough can be approximated as well as possible.

Table 10: Input values for Peck’s model, lest the outcome agrees with the measured trough.

Passing North 1 South 1 North 2 South 2 Section line 1 2 1 1 2 3 4 1 2 Bending point coefficient 5.6 5.7 8.0 6.8 6.7 6.1 6.1 5.5 5.4 Volume trough (%) 0.76 0.55 0.12 0.38 0.44 0.22 0.21 0.25 0.40

Finite element models In the finite element model, the boring is simulated by enforcing a displacement of soil in the direction of the tunnel axis, which leads to unloading of the soil around the tunnel. This mainly leads to many overestimations of the size of the settlement trough. Whether the soil around the tunnel unloads or arches is strongly dependent on the grouting process, in particular on the grouting volume and the pressure with which the grout is being pumped into the tail of the TBM. This process has not been modelled in the predictions.

ASSESSING THE PREDICTION MODELS Analytical models It can be said that the predictive value of the analytical methods of Peck and Sagaseta is limited, which is due to the insecurity related to the input parameters. The estimated loss of volume during boring amounted to 1%. However, the measured volume of the settlement trough when boring the Second Heinenoord Tunnel varied between 0.1 and 0.8%. The bending point coefficient measured a value ranging from 5.5 to 6.5m, whereas a priori values of 5 and 10m were assumed.

In practice the volume of the settlement curve Vs is not a very usable prediction parameter as it is directly influenced by the size of the occurring loss of slurry at the tunnel. This is very much dependent on the carefulness and accuracy of the implementation and can therefore hardly be predicted.

Based on the measured cross section lines at the Second Heinenoord Tunnel, the following formula to determine the Peck parameter was formulated:

i = α*z + β

In this formula z is the depth of the heart of the tunnel.

In the final report [K100-05], it was indicated that α = 0.21 and β = 2.99. Report [K100-W-105a] states that for α and β the values 0.35 and 1.07 were extrapolated, although this only includes fitting to the second passing in the North. When including all measurements, no meaningful correlations are

found. Report [K100-W-073] poses that i = 2.86 Vs + 2.784 with an excellent correlation coefficient. Such a relation is interesting to establish, albeit less

useful in practice since Vs is unknown. It should be noted that the number of measurements on which the aforementioned relation for the Peck parameter is based is limited, especially compared to formulas known from literature. Report [K100-W-105a] shows that this Peck parameter is dependent on the structure of the soil - in clay and peaty soil wider settlement troughs are to be expected than in sand. Expanding the number of measurements, taken from future tunnel projects, will lead to a more reliable relationship.

Sagaseta and others (see Ref. [7]) developed a new analytical formula to determine the displacements caused by the construction of tunnels. The theory uses a breakdown of the total deformations of the tunnel into the following elements: - omni directional contraction of the tunnel cross-section, usually expressed as a loss of volume, - the tunnel cross-section becoming oval without loss of volume, - and vertical displacement of the tunnel cross-section, without deformation of the cross-section. Firstly, Sagaseta quantified the effect of the loss of volume at certain depths. The formulas following from these quantifications were supplemented with the effects caused by the tunnel cross-section becoming oval. Finally, Sagaseta and Oteo completed the theory by accounting for the effects of compressibility of the soil and plasticity. In imitation of the projects presented by Sagaseta, it was attempted to attain a ‘fit’ of the different passings of the Second Heinenoord Tunnel with the measured displacements of the surface, based on the given formulas. This proved to be reasonably feasible. However, executing predictions using this adapted theory remains difficult because insecurity regarding the correct choice of the different input parameters is still prevailing. Thus, a number of projects need to be analysed under specific Dutch circumstances.

Due to their simplicity, the analytical methods are best suitable for a first estimation of the expected surface settlements and for analysing the measured settlements.

Finite element models If, when applying the finite element method, the loss of volume is schematised to concentric contraction of the tunnel cross-section, no realistic results are yielded. Even when the measured and therefore exact loss of volume is entered as concentric contraction, the calculated settlement troughs are too shallow and too wide (see figure 33).

Figure 33: Differences between contraction model and grout pressure model.

In order to obtain a more realistic description of the tunnelling process a more accurate modelling of the grouting process is desired. To fill up the tail of the TBM grout is injected under high pressure. The pressure distribution of the grout determines the pressure changes and the deformations around the bored tunnel. This pressure distribution is dependent on the injection pressure, the characteristics of the grout, the number of injection points, the locations of these points, and the size of the tail.

Within CUR/COB Commission L500 a finite element model was developed which included the pressure distribution of the grout around the tunnel. The model was used to recalculate the measured deformations of the Second Heinenoord Tunnel. The shape of the settlement trough was approached fairly well using this model (see figure 33) although the grout pressure distribution used in the model did not correspond to reality. This was mainly caused by the fact that the three-dimensional soil arching in longitudinal direction could not be discounted in a two-dimensional model. Therefore, for the first order evaluation Commission K100 worked on a three-dimensional grout pressure model for the purpose of post dictions. Paragraph 5.3.2 elaborates on this model and the post dictions executed using this model.

Applying a grout pressure model is considered a precondition in order to meaningfully analyse deformations and pressure changes during boring.

5.2.3 SURFACE SETTLEMENTS IN LONGITUDINAL DIRECTION

PREDICTION MODELS The analytical model of Peck and the two-dimensional finite element model (see § 5.2.2.) used in the predictions do not provide information about the development of the surface settlements in longitudinal direction. These two- dimensional models, however, do calculate the maximum settlement above the tunnel axis at some distance (>4D) behind the face of the TBM. Presuming the settlement is still minor at the bore face (§ 5.2.1.), a basic idea about the development of the surface settlement in longitudinal direction can be obtained. Using the three-dimensional models (Sagaseta’s analytical model or finite element analysis by means of DIANA), qualitatively valid predictions of the longitudinal trough may be obtained.

COMPARING PREDICTIONS WITH MEASUREMENTS In figures 34 and 35 the measured surface settlements above the tunnel axis are shown.

Figure 34: Measured surface settlement above tunnel axis, measuring area North.

Figure 35: Measured surface settlement above tunnel axis, measuring area South.

- When passing measuring area North for the first time, hardly any settlements were measured up to approximately 7m in front of the face of the TBM. This indicates that the deformations in the underground were dominated by tail effects. - The measured shape of the longitudinal trough, when passing measuring area North for the second time, agrees with this. This explains why the soil behaves little to not at all time-dependent. The variations of the settlements of the measuring area and at a large distance behind the bore face are caused by fluctuations in the boring process. There is no relation between the course of the settlements and the volume of injected grout, which is fairly constant. - Even during the first passing of measuring area South the surface settlements in front of the bore face were limited to a few millimetres. Above the TBM generally minor surface settlements did occur. Above the tail of the TBM the surface heaved. The maximum heave of the surface was 5mm. These surface rises most probably are caused by a large quantity of grout, which is pumped into the tail of the TBM. After a while surface heaves decreased and surface settlements appeared.

- During the second passing of measuring area South the surface settlements in front of the TBM were limited to only approximately 2mm. Generally these settlements occurred immediately after the TBM had passed, after which the slope of the longitudinal trough diminished from 15m behind the face onwards. Nevertheless, a complete stabilisation of the surface settlements did not occur, which is probably caused by time- dependent effects. Once more there is no clear relationship between the settlements and the volume of the injected grout.

Figures 34 and 35 show that variations in surface settlement are rather substantial over the whole measuring area, which the predictions did not expect. Table 11 summarises the minimum and maximum values per measuring area.

Table 11: Variation maximum measured settlements per measuring area in mm above the tunnel axis. North, passing 1 North, passing 2 South, passing 1 South, passing 2 Highest value 37 17 13 21 Lowest value 22 7 2 5

- During the first passing of measuring area North, the slope of the longitudinal trough above the TBM was being underestimated due to the underestimation of the settlements occurring there (Peck, Vs = 1%, i = 10m, Sagaseta and Plaxis). At a larger distance from the tunnel axis the settlements, however, were overestimated. With Peck being Vs = 1% and i = 5m, the settlement above the tunnel axis was overestimated. Further away from the tunnel axis the calculated settlements agreed fairly well with the measured settlements, and therefore also with the longitudinal settlements. - When passing measuring area South for the first time, the predictions seem to have overrated the maximum settlement and thus the slope of the longitudinal trough above the tunnel axis. At some distance behind the TBM the difference between prediction and measurement was actually very substantial. The predictions underestimated the bore performance (too large a loss of slurry), which resulted in all the surface settlements being overestimated. - For the second passing of measuring area South the predictions overestimated the maximum settlement and hence also the slope of the longitudinal trough above the TBM. The predictions underestimated the bore performance, which lead to overestimation of

the surface settlements. Using PLAXIS, Sagaseta, and Peck (Vs = 1%, i = 5m), at the height of section line O the settlements above the

tunnel axis were somewhat underestimated. Using DIANA (Vs = 1.6%)

and Peck (Vs = 1%, i = 5m) the displacements on this location had been overestimated. - For the second passing of measuring area North the maximum settlement and/or the width of the cross trough, and therefore also the slope of the longitudinal trough above the TBM, were overestimated. Directly above the tunnel the development of the settlements as function of the position of the TBM (as calculated by using Sagaseta and PLAXIS for section lines F and G) agreed fairly well with the measured course of settlement. The predictions appeared to underestimate the bore performance and hence overestimate the surface settlements.

EXPLANATION OF THE DIFFERENCES BETWEEN PREDICTIONS AND MEASUREMENTS AND ASSESSMENT OF PREDICTION MODELS The limitations of the employed prediction models, as discussed in § 5.2.2., and the ensuing explanation of the discrepancies between the predictions and the measurements fully apply to the predictions of the surface settlements in longitudinal direction. The predictions based on Sagaseta’s formulas explaining the shape of the longitudinal trough can also be used to predict the speed at which settlements in the vicinity of the boring occur, given a certain progress speed of the tunnelling process. When Sagaseta’s formulas are ‘fitted’ to the measured maximum settlement through the value for loss of volume that has to be entered, the steepness of the longitudinal trough is underestimated and therefore too slow a settlement speed is predicted.

5.2.4 DEFORMATIONS IN THE SOIL

PREDICTION MODELS The deformations in the underground were determined amongst others by using the finite element program Plaxis. An imposed loss of volume Vs of 1% was assumed. Because it involves a two-dimensional analysis in a plane perpendicular to the tunnel axis, no predictions of longitudinal displacements in the underground were carried out. The DIANA analyses mentioned above (§ 5.2.2.) could have explained such deformations, which could have been compared to the measurements. However, such evaluation did not take place.

COMPARING THE PREDICTIONS WITH THE MEASUREMENTS Vertical displacements in the underground

Figure 36: Vertical soil deformations 4-D behind the face, Northern measuring area.

Figure 37: Vertical soil deformations 4-D behind the face, Northern measuring area.

Table 12 shows the volumes of the measured ‘settlement troughs’ at surface level and at two depths in the underground.

Table 12: Volume of vertical soil displacements in percentage of tunnel surface. Measuring area Measuring area Measuring area Measuring area North, first passing South, first passing North, second South, second passing passing Section line 0.76 0.04 0.23 0.19 NAP —3.4/-3.55m 0.84 0.09 0.23 0.17 NAP —6.5m 0.85 0.14 0.24 0.11

At the first passing of measuring area North, the predictions generally underestimated the ground settlements and the slopes of the trough. The differences between the predicted and measured settlements are largest above the tunnel. Beside of and transverse underneath the tunnel the predicted settlements more or less match the measured settlements. The additional, upwards directed ground movements, located transversely underneath the tunnel positioned at 4D behind the TBM, are manifested both in the measurements and in the predictions.

For the other measuring areas it applies that the predicted vertical displacements differ enormously from the measured displacements due to incorrect modelling of the boring process in PLAXIS and DIANA (concentric contraction). The displacements were either overestimated in the predictions or indicated collapse instead of heave of the soil. The overestimation is largest using DIANA calculations, which assume a larger loss of slurry than PLAXIS calculations.

Horizontal displacements in the underground

Figure 38: Horizontal soil displacement located 4D behind the TBM, measuring area North.

Figure 39: Horizontal soil displacement located 4D behind the TBM, measuring area South.

When predicting the first passing of the measuring area North, the horizontal displacements at larger depth near the tunnel were overestimated. The PLAXIS calculations pointed to an almost uniform development of the horizontal displacements, whereas the measurements showed settlement decreasing along with depth.

When predicting the other passings, at different distances to the bore face the displacements away from the tunnel were measured instead of the predicted displacements in the direction of the tunnel. Both the PLAXIS and the DIANA calculations assume concentric contraction. The measurements do not show that bore loss and hence soil unloading occur but that the soil is arched by for instance the injecting of grout into the tail void. In DIANA a larger bore loss is given, resulting in a larger deviation from the measuring results.

The predictions of the horizontal displacements presume that the soil conditions and the influence of the boring process are symmetrical with regard to the vertical plane through the heart of the tunnel. This means that the horizontal displacements above the tunnel should amount to zero. Nevertheless, measurements show that small displacements in this direction do occur, for instance by non-uniform soil conditions or by steering of the TBM. The measured displacements, however, approximate the measuring inaccuracy so no far-reaching conclusions can be drawn from this.

EXPLANATION OF THE DISCREPANCIES BETWEEN PREDICTIONS AND MEASUREMENTS, AND ASSESSMENT OF THE PREDICTION MODELS The limitations of the employed prediction models, mentioned in § 5.2.2., and the ensuing explanation of the discrepancies between predictions and measurements fully apply to the predictions about deformations in the underground.

5.2.5 PRESSURE CHANGES IN THE SOIL

PREDICTION MODELS Using the finite element program PLAXIS, predictions were made for the vertical and horizontal effective earth pressures at the height of the tunnel axis between both tunnel tubes in a plane perpendicular to this tunnel axis. For each phase of the boring process these vertical and horizontal effective earth pressures caused by the construction of either one or two tunnels were indicated.

COMPARING THE PREDICTIONS WITH THE MEASUREMENTS The calculated vertical effective earth pressures in measuring area North, caused by the construction of the first tunnel, are demonstrated in figure 40. The results are determined for the employed volume loss of 1%.

Figure 40: Calculated vertical effective earth pressure occurring at tunnel axis level in measuring area North.

The earth pressure boxes are located at 2m (SMS 1 and 3) and 4m (SMS 2 and 4) from the side of the tunnel at tunnel axis level.

For the passings of measuring area North, PLAXIS predictions prove that the vertical effective earth pressure increases after each passing. At 4m beside the tunnel the predicted increase amounts to approximately 30kPa. The measured pressure increase, however, is considerably smaller. The predictions hardly show any change in the effective normal pressure in horizontal direction. However, during the measurements an apparent pressure increase was generally observed. This is probably caused by the fact that the predictions, by using the contraction model, overestimated the loss of tail on the side of the tunnel.

No predictions were done for stresses in the longitudinal direction of the tunnel, nor for measuring area South.

EXPLANATION OF THE DISCREPANCIES BETWEEN PREDICTIONS AND MEASUREMENTS, AND ASSESSMENT OF THE PREDICTION MODELS The limitations of the employed prediction models, as mentioned in § 5.2.2., and the ensuing explanation of the discrepancies between predictions and measurements are fully applicable to the prediction of stress changes in the underground.

5.2.6 INFLUENCE OF CONSTRUCTION OF THE SECOND TUNNEL ON FIRST TUNNEL

KEY QUESTION In present design practice of bored tunnels it is feared (even internationally) that the soil around the tunnel that was bored earlier unloads by the passing of the TBM boring the tunnel next to it. This may cause the first tunnel to suffer from additional horizontal ovalisation. If boring the second tunnel causes soil arching, e.g. as a consequence of a high grout pressure, the first tunnel may suffer an additional vertical ovalisation.

Besides the potential disruption at the TBM’s face, the unloading or arching of the soil may be caused by the conic shape of the TBM and by the grout pressures in the tail of the TBM.

The unloading or arching of the soil near the first tunnel initially increases as the distance between the two tunnels decreases, as goes without saying. Consequently, the question that arises is what is the minimum distance to be maintained between the two tunnels. In practice the minimum distance of at least half to once the tunnel diameter is usually used by rule of thumb.

In design practice there is a need for well-argued and preferably differentiated design guidelines in order to be able to build tunnels closer together, more specifically to be able to realise a more economical design of shafts.

FIRST ORDER EVALUATION OF MEASUREMENTS DONE AT THE SECOND HEINENOORD TUNNEL The objective of the first order evaluation was to examine on the one hand whether the measurements conducted in the measuring ring of the first tunnel tube showed any influence of the second passing of measuring area South and to search on the other hand for a founded recommendation for the minimum tunnel distance.

Measurements indicated that the boring of the second tube did not influence the deformations of the already existing tunnel tube.

In order to determine the minimum tunnel distance the results of deformation measurements and post dictions (see § 5.3.2.) were linked to the conclusions of similar studies conducted by COB Commission L500, which were based on fictive geotechnical profiles.

MINIMUM TUNNEL DISTANCE The deformation measurements show that at a short horizontal distance from the tunnel lining (approximately 2m) a horizontal displacement, directed away from the first tunnel towards the future tunnel tube, occurred when first passing measuring area South. Still, at 7m distance of the lining no significant horizontal displacement occurred anymore. Considering that at the measuring ring the distance between both tunnels is approximately 8m, it may be concluded that the second tunnel tube would have fallen outside of the influence of the soil deformations caused by the construction process of the first tunnel.

Figure 41 depicts the calculated behaviour of the horizontal displacement at tunnel axis height for several locations along the tunnel axis. The calculations were conducted using a three-dimensional finite element model (see § 5.3.2.).

0 -2 -4 -6 Unset grout zone -8 -10 -12 8.6 m -14 17.6 m -16 23.6 m Horizontal0 displacement2 (mm)4 6 8 10 0 D 1/8 D 1/4 D 1/2 D 1 D 38.6 m Distance to tunnel (m) 47.6 m

Figure 41: Measured horizontal soil displacements as function of the distance to the tunnel lining and the distance to the face of the TBM.

The measured grout pressures are so small that in the unset grout zone at tunnel axis level a horizontal displacement of 15mm, directed towards the tunnel, is calculated. This equals the initially imposed conicity of the TBM. Therefore, unloading of the soil as caused by this conicity is hardly compensated for by the grout pressures in the tail of the TBM. Figure 41 illustrates that the extent of the horizontal displacement strongly decreases with the distance to the tunnel lining. From a distance of ¼D (2m) onwards the decrease is only very small. The horizontal soil deformation at a distance of 2m from the tunnel amounts to approximately 2mm. Furthermore, it shows from figure 41 that the calculated horizontal displacements at the height of the tunnel axis decreases somewhat after the grout has set.

The aforementioned COB Commission L500 executed two-dimensional calculations using two depths (1D, 2D) and two fictive geotechnical profiles for three different grout pressure developments (high pressures, average pressures, low pressures), four conicity values (0mm, 10mm, 20mm, 30mm), and three distances between the tubes (¼D, ½ D, 1D). These calculations showed that the conicity of the TBM can lead to a significant unloading of the surrounding soil, which, when at a short distance from the second tunnel, is felt by the first tunnel (see figure 42 below).

1-D

FEMGV 5.2-02.B Witteveen & Bos 24 SEP 1999

½D

FEMGV 5.2-02.B Witteveen & Bos 24 SEP 1999

¼D

Figure 42: Influence of conicity of passing TBM on the first tunnel.

Furthermore, the calculations showed that, even at low grout pressures (corresponding to a loss of volume of 3%) with an equilibrium at tunnel axis level and unloading of the soil around the rest of the circumference, the influence of the tunnel located at ¼D distance from the other tunnel was insignificant.

To summarise, the minimum required distance between the two tubes is dependent on several situation-dependent factors: - depth of tunnel and geotechnical profile of ground, - conicity of TBM, - grout pressures, - strength of the lining, - and forces on the first tunnel before the passing of the second tunnel.10 Therefore, for each situation it needs to be determined which minimum distance between the tubes should be used. As a conservative recommendation for the time being a minimum distance of ½D could be applied. Provided the grout pressures are controlled and continually measured in the tail, shorter distances up to ¼D are attainable.

10 If the first constructed tunnel initially suffers horizontal ovalisation, an unloading of the soil at the height of the tunnel axis will not be beneficial to the forces within this tunnel. However, if the first tunnel initially

suffers vertical ovalisation, the unloading of the soil at the height of the tunnel axis will be beneficial.

5.3 FURTHER REFLECTION ON THE GROUTING PROCESS AND ITS INFLUENCE ON SURFACE SETTLEMENT

5.3.1 INTRODUCTION

Evaluation of the surface settlements showed that many of the settlements arose after passing of the TBM. This indicates that filling the tail void of the TBM with grout is essential.

In figures 43 and 44 a survey of the employed injection pressures is given for both passings of both measuring areas. In these figures the average grout pressure per placed ring was plotted against the position of the bore face on the local x’-axis. The figures also depict the prevailing water pressure at the topside as well as the bottom side of the tunnel.

figure 43: Grout pressure measured on passing measuring area North.

Figure 44 : Grout pressure measured on passing measuring area North.

Comparing the grout pressure measurements inside the TBM with the measuring rings, it appeared that during the injecting through the pipes in the shield the measuring results of the instruments in the grout pipe could differ from the grout pressure in the tail of the TBM. The grout pressure measurements done at the time of injecting through the segments (first passing measuring area South) were probably more representative of the actual grout pressure occurring in the tail of the TBM.

The differences between the measured pressures during the first and the second passing of measuring area North are huge (see figure 43). The prevailing pressures of the first passing are approximately equal to the height of the water pressure at tunnel axis level. During the second passing the prevailing pressures are substantially higher, which therefore have resulted in minor surface settlements.

For the passing of measuring area South the difference in the employed pressure is minor (see figure 44). However, the injection method differed (see § 3.3.), hence the actual grout pressure in the tail of the TBM may have been considerably higher during the first passing than during the second passing. Moreover, the volume of injected grout may have differed. During the first passing of measuring area South there is a lavish injecting of the tail void up to approximately 6 to 6.5m3 per placed ring. This means that, without the use of overcutters, approximately 20 to 30% excess grout was injected compared to the theoretical volume of the tail void. For the second passing this difference is considerably smaller - approximately 5.8m3 grout was injected per ring placed, which is approximately 7% more than the theoretical volume of the tail void including the use of overcutters.

Based on these measurements, there appears to be an almost linear relation between the volume of injected grout and the surface settlement (see figure 45).

Figure 45: Relation between surface settlement and volume of injected grout per passing of the measuring area.

Based on these measurements, per measuring area there is a nearly linear relation between the volume of injected grout and the surface settlements. Yet this linear relation varies per passing, which may be caused by the use of overcutters during the second passing of both measuring area North and South.

Furthermore, it may be concluded from the measurements that there is no reliable relation between the prevailing average grout pressure and the total injected volume. Measuring the volume of injected grout by means of counting the number of strokes of the pump proved to be not very reliable as the volume per stroke varied.

The models calculating the influence of the bore tunnel on its surroundings use the injection pressure as one of the input parameters (see § 5.3.2.). In practice such control of pressure is hard to maintain. Therefore, it should be recommended to pay attention to the actual displacements and thus the injected volumes around the borehole when executing model calculations.

5.3.2 NUMERICAL SIMULATION OF THE GROUTING PROCESS

On behalf of the first order evaluation of the measurements conducted at the Second Heinenoord Tunnel, numerical simulations were done using a specially designed three-dimensional finite element model (see [K100-W- 105b]). With these it was attempted to relate the boring process to the pressure changes and the deformations in the vicinity of the bore tunnel. The evaluations limit themselves to measuring area South, whereas measuring area North was analysed by Commission L520 using the same model (Ref. [6]). The model was given input of not only grout pressures, but also for example conicity of the TBM, face pressure, jack forces and the weight of the backup trains (see figure 46).

vloeibare uithardende uitgeharde groutzone groutzone groutzone

belasting volgwagens

bentonietdruk

6 m 3 m 30 m vijzelkracht 4 ringen 2 ringen 20 ringen

Figure 46: Longitudinal section of the three-dimensional grout pressure model.

The numerical model formed the basis for modelling the tunnel construction (see § 6.4.). Below the modelling of the grout pressure model itself is discussed, including the post dictions executed using this model and the ensuing conclusions.

THE FINITE ELEMENT MODEL The finite element model (DIANA) models the TBM and the surrounding soil in three dimensions.

+2,5

GWS +0,3 toplaag

-3,25 3 -4,5 4 -7,25

-10,5

18 -13,0 -14,0 -14,75 31

-21,5

38A -24,5 38E/F -27,0

Figure 47: Generated mesh of elements used for the post diction of the first passing of measuring area South. toplaag: Top layer.

The TBM was simulated by scaling the elements using the correct stiffness and weight distribution. In measuring area South bentonite with unknown pressure was injected around the shield. This bentonite pressure arches the soil and thus compensates the conicity of the shield. The influence of any possible change of course were not included for it probably does not exceed the influence of the conicity of the TBM.

By means of an internal overpressure in the elements concerned both the face pressure and the grout pressure in the tail were simulated. On the bottom side of the tunnel a grout pressure was measured that was lower than the water pressure. Because this is not physically possible, these measurements were corrected. Based on an average advance of the boring process of 12 rings per 24 hours and an estimated setting time of 12 hours for the grout, the length of the zone of setting grout was discovered to be 6 rings (approximately 9m). This zone was schematised in the model into a zone of 4 rings of completely unset grout and a zone of 2 rings of partly set grout. There are no data available on the shrinkage of the used grout. It is estimated that the grout will shrink approximately 5% during the setting. In the partly set grout zone and the completely set grout zone the model claims that the grout shrinks approximately 5%.

The main jacks were modelled using bar shaped elements, which could provide the deformation or the pressure. The distribution of the jack forces over the height of the tunnel was included as well.

The tunnel lining was modelled as coupled monolithic rings with a ring stiffness approaching the actual stiffness of the segmented lining. The results of the three-dimensional lining calculations, which will be discussed in paragraph 6.4., were used in the modelling. This lining calculation also provided the stiffness of the joints linking the rings.

For the behaviour of the soil linear elastic behaviour with a Mohr-Coulomb collapse line was assumed. The sand layers were calculated to be drained and the clay layers to be undrained.

EXECUTED POSTDICTIONS OF PRESSURE CHANGES AND DEFORMATIONS IN THE VICINITY Using the rough model discussed above the measured deformations in the soil were recalculated for the first passing of measuring area South. Unfortunately the measuring ring in the tunnel lining was located on the edge of the measuring area, where hardly any geotechnical measuring instruments were situated. Therefore, it was impossible to recalculate the geotechnical measurements and measurements in the lining of one cross-section, also due to the difference in height of the measuring ring and the tunnel ring in the heart of the measuring area. The tunnel cross-section in the middle of the measuring area was used as basic principle for the ‘geotechnical’ post dictions, even though no measurements of the grout pressure in the tail were available for this cross-section. The grout pressure measured at the measuring ring was initially increased by a constant value of 5kPa at the cross-section concerned. This increased value was not based on measurements but on observations that the surface heaved in the middle of the measuring area during boring while on the edge of the measuring area at the height of the measuring ring the surface collapsed. Later on, the grout pressure (distribution) was varied as well.

Extra calculations were carried out for the finite element calculations of the tunnel lining (§ 6.4.), imitating the situation at the measuring ring as well as possible without altering the geometry of the original calculation for the middle of the measuring area.

Four relevant calculation versions were carried out for the post dictions: Version: Description of version: 4 Calculation for purpose of tunnel construction calculation (see § 6.4.) at height of measuring ring (ring 571). 5 Calculation for purpose of geotechnical evaluation at the middle of measuring area South (ring 550). 8 The same, with different grout pressure, final calculation for purpose of geotechnical evaluation. Calculation with two different grout pressures in order to examine the effect of different grout 9 pressures on ovalisation of the tunnel lining (see § 6.4.).

For the geotechnical evaluation no reliable measurements of the grout pressure in the tail were available. Therefore, the distribution of the grout pressure was manipulated to such an extent (versions 5 and 8) that a reasonable correspondence with the measured deformations around the tunnel was calculated. In figure 48 the assumed grout pressures as well as the pressures for versions 5 and 8 have been presented.

Second Heinenoord Tunnel - Measuring Area South -5 Initial vertical earth pressures -6 Initial horizontal earth pressures -7 Initial radial pressures -8 Initial water pressure Grout pressure version 5 -9 Grout pressure version 8 Depth (m NAP) -10 -11 -12 -13 -14 -15 -16 -17 -18 -19 -20 000E+0 050E+3 100E+3 150E+3 200E+3 250E+3 300E+3 350E+3 400E+3 Pressure (Pa)

Figure 48: Assumed distribution of earth and grout pressures.

Version 8 saw the best correspondence between the measurements and simulations (see figures 49 - 51).

Figure 49: Calculated and measured vertical displacements at 20m behind the face of the TBM.

Figure 50: Calculated and measured horizontal displacements at 20m behind the face of the TBM.

Figure 51: Calculated and measured longitudinal trough (surface heave) in front of the bore face.

The measured heave of the surface starts several metres in front of the face of the TBM. The heave in the calculations, however, begins only after the bore face passed approximately 5m. Therefore, in figure 51 the calculated longitudinal trough has been moved forwards 5m. Consequently, the shifted line agrees fairly well with the measured values. Moving the longitudinal trough can mean that already from the face of the TBM there was slurry pressure present in the borehole, possibly caused by the bentonite injection along the shield.

An analysis of the geotechnical measuring results shows that in the first weekend of November 1997, after building ring 568 (at the end of the measuring area), the measuring area as a whole collapsed 2 to 3mm. This is illustrated in figure 51 by the abrupt measured collapse of the surface at approximately 23m behind the face of the TBM, the cause of which is unclear. Possible causes may be:

- settlement of the total area as a consequence of earlier heaves, - water egress from the grout, - disappearance of extra water pressure as a consequence of the boring process, - and measurement errors made. It is known that in measuring area South the reference point shifted several millimetres. In this respect it should be noted that the absolute values of the measured and calculated deformations at the first passing of measuring area South were extremely small. Therefore, small deviations caused by inaccuracies in the measurements or models seem very large in terms of percentage.

POSTDICTIONS CONDUCTED WITH RESPECT TO THE APPROXIMATE EQUILIBRIUM OF FORCES IN THE TUNNEL CONSTRUCTION Versions 4 and 6 of the calculations have mainly been drawn up in order to examine the approximate equilibrium of forces on the tunnel construction in more detail. Furthermore, these calculation versions serve as basis for further analysis of the local equilibrium of forces in the tunnel. The results will be discussed in § 6.4.

CONCLUSIONS TO BE DRAWN FROM NUMERICAL SIMULATIONS OF THE GROUTING PROCESS By means of two-dimensional finite element calculations the measured deformations in the soil can be recalculated, provided a grout pressure is applied around the tunnel lining. This grout pressure does not correspond with the expected values based on the measurements. The cause of this is thought to be the soil arching occurring at the zone containing fluid grout. In a three-dimensional finite element calculation this soil arching is considered. Post dictions using such a grout pressure model do provide a reasonable agreement between measurements and calculations. However, due to a lack of reliable measuring data, the grout pressure distribution was calculated back (through trial and error) to the measured deformations around the tunnel. Hence, this three-dimensional grout pressure model could not be properly validated. Because the calculation results are very much dependent on the entered grout pressure, which probably varies substantially during boring, measurement of the grout pressure in the tail void is essential to a proper validation.

5.4 EVALUATION OF GEOTECHNICAL RESEARCH

The geotechnical soil examination for the Second Heinenoord Tunnel consisted of: - 107 soil-drilling tests, 18 boreholes, of which four Begemann-borings11 and five piezometers, - in-situ tests, consisting of four vane tests, three pressiometer tests, six dilatometer tests, two monopole tests, and electrical density tests in two verticals, - a large number of classification tests and 79 determinations of grain size distribution, - 56 determinations of the plasticity index, - 23 compression tests, 24 undrained and 16 drained triaxial tests,

11 Dutch test examining the soil structure by lifting a column of soil from the earth.

- direct shear tests of clay samples, - 22 determinations of the activity of clay monsters according to Skempton, - and several determinations of the percentage of humus and calcium, pH, shape of the grain, and minimum and maximum density.

The soil mechanical site and laboratory testing that was done proved to have been adequate after completion of this project. The use of in-situ techniques in order to determine the stiffness and porous characteristics of the soil proved to be of great value. In conventional triaxial testing pressure changes as a result of boring are not simulated. Moreover, the accuracy of such tests is minimal for small strain levels, such as seems the case in reality. These effects have to be taken into account when interpreting triaxial tests, otherwise adjusted test procedures or test erections need to be used, such as triaxial extension tests. Seismic techniques may provide a more continuous picture of the soil. These techniques are being examined and evaluated further within the framework of other COB research. Because two-dimensional reproduction by means of geotechnical longitudinal and cross-sections prove to be too limited, generating a three-dimensional profile of the soil is advisable.

5.5 SUMMARY: ACQUIRED KNOWLEDGE IN THE FIELD OF GEOTECHNOLOGY

- Quantifying the influence of boring on the surrounding soil was almost impossible using the current analytical design models. These models were too pessimistic, which was in particular caused by the insecurity about the loss of volume to be entered. - Furthermore, the predictions of the surface settlements formulated through finite element calculations, schematising the loss of volume to concentric contraction of the tunnel cross-section, yield unrealistic results. - The vertical displacements of the surface in front of the face of the TBM remain limited to 15 to 20% of the maximum settlement. This suggests a good support of the bore face. Most of the maximum settlement occurs directly above the TBM and its tail, and amounts to 75% of the ultimate settlement. - Looking at the measurements, there is an almost linear relation between the volume of injected grout and the surface settlement. - Therefore, the determining factor for the influence on the surroundings is the behaviour of the grout cover around the tunnel lining. Future design calculations need to be tuned to this behaviour.

CHAPTER 6 EVALUATIONS IN THE FIELD OF TUNNEL CONSTRUCTION

6.1 INTRODUCTION

The main objective of this pilot project in the field of tunnel construction is assessing the usefulness of the existing calculation models for the design of the tunnel lining. These existing models are two-dimensional - one should differentiate between models describing the balance of forces for the cross- section and those describing it for the longitudinal section. The measuring programme has taken this into account. Therefore, two measuring rings have been implemented (see §5.1.2) to provide cross-sectional information, while additional deformation measurements were conducted for the tunnel as a whole, providing information about longitudinal behaviour. However, evaluations showed difficulty in differentiating these two directions when dealing with a tunnel constructed of segments. The balance of forces within the tunnel segments is mainly three-dimensional. This is amongst others caused by stresses in longitudinal direction, for instance due to the jack forces, which also lead to stresses and strains in cross direction. Additionally, there is a disruption of the plane stress situation as a result of building the segments in the TBM and particularly of pressure concentrations at the key segment when it does not make full contact.

Despite the limitations, as described above, this chapter will follow the broad outline of the prediction models, including a separate reflection on the longitudinal and cross directions in order to satisfactorily compare predictions and measurements. The end of this chapter will elaborated on the three- dimensional balance of forces within the tunnel lining, based on state-of-the- art calculation models which were used by K100 in order to explain the measured balance of forces in the lining.

The chapter will be concluded with a summary of the knowledge developed in the field of tunnel construction during the Second Heinenoord Tunnel project.

6.2 PRESSURE CHANGES AND DEFORMATIONS IN CROSS DIRECTION

PREDICTION MODELS For the prediction of the forces in cross direction (perpendicular to the longitudinal axis of the tunnel) 34 prediction models were used. These can be divided into three groups: - models with a single ring, - models with a double ring, - and continuum models.

Figure 52: Example of a single ring model.

Single ring models schematise the tunnel lining into a circular shaped bending beam, whereas the embedding of the tunnel in the soil is described by linear radial springs. For the predictions twelve versions of this model have been employed. These versions differ from one another in the way the ring is constructed (complete ring of seven segments, with or without counting their own weight), the characteristics of the longitudinal joints (hinges, rotation stiff hinges, or contact elements), the way the soil is modelled (using solely radial springs, or combined with tangential springs), and the way the soil load is applied (radial or also tangential).

Figure 53: Example of a double ring model.

In single ring models the co-operation of the segments in longitudinal direction is disregarded, whereas in double ring models the co-operation between the rings is accomplished by some coupling. This connection may either be rigid or flexible, or achieved by contact pressures in volume elements. Because for instance the longitudinal joints are stacked in relation to each other, a different stiffness arises than when using a single ring model. Fifteen versions of this model were used for the predictions.

Continuum model

Figure 54: Example of a continuum model.

Several predictions were carried out using the continuum models. These models do not schematise the soil around the tunnel as springs but as a continuous medium. The seven versions of this model differ mainly in the way the interaction between the tunnel lining and the surrounding soil is modelled.

COMPARING THE PREDICTIONS WITH THE MEASUREMENTS Normal force The measured maximum normal force amounts to 2610kN at 154° (and 2460kN at 103°) in measuring ring North and 4000kN at 116° in measuring ring South. All models underestimate the occurring normal forces for both measuring rings. In figure 55 a comparison is made for measuring ring South, although the corresponding figure for measuring ring North would be almost identical.

Figure 55: Measured and pre-calculated normal force in the lining, per model. Numbers 1.01-1.12 are single ring models, numbers 2.01-2.15 are double ring models, and numbers 3.01-3.07 are continuum models.

Moreover, it is remarkable that the measured variation in normal force is much wider than expected. In measuring ring North the minimum tangential normal force was 120kN at 334°, while the expectation was higher.

Bending moment The maximum bending moment in measuring ring North amounted to 224kNm at 129° and 350kNm at 116° in measuring ring South. All models underestimate the moments occurring in both measuring rings. In figure 56 a comparison is made for measuring ring South, although the corresponding figure for measuring ring North is almost identical.

Figure 56: Measured and pre-calculated maximum bending moment in the lining, per model. Numbers 1.01-1.12 are single ring models, numbers 2.01-2.15 are double ring models, and numbers 3.01-3.07 are continuum models.

The predictions generally overestimate the negative moment. The measured values developed to -127 and -105kNM at respectively 116° and 283°.

EXPLAINING THE DIFFERENCES BETWEEN PREDICTIONS AND MEASUREMENTS The differences between predictions and measurements are mainly caused by the pressures that arise during construction of the lining within the TBM. In both measuring rings significant pressures were observed at the time the rings were still inside the TBM, and therefore did not experience load from the soil or grout yet.

It is striking that the predictions for these moments agree better with reality than the predictions for normal forces. This may be the case because the bending moments in the ring are less sensitive than the assembly forces.

Figure 57 below compares the predictions with the measurements after the measured values were deposed of assembly forces.

Figure 57: Measured and pre-calculated maximum bending moment in the lining, per model, excluding the moment caused by assembly forces. Numbers 1.01-1.12 are single ring models, numbers 2.01-2,15 are double ring models, and numbers 3.01-3.07 are continuum models.

ASSESSING THE PREDICTION MODELS The employed prediction models (models with a single ring, models with a double ring and continuum models) can only assess load and forces in radial and tangential direction. The interaction of successive rings, as occurring according to the conducted measurements, cannot be described by all models.

The assembly stresses, which are of similar magnitude as the stresses caused by the external loads on the tunnel, cannot be described by the employed models. Only a three-dimensional finite element model can do this. Moreover, none of the models included (the effects of) the key segment and the grout.

When excluding the assembly stresses from the measured forces, the cross- section forces and the load on the tunnel can be described fairly well by empirical models and two-dimensional finite element models. Still, it is necessary to calculate the pressure distribution over the tunnel in compliance with the volume loss during boring. This effect can be quantified by assuming the soil embracing the tunnel to be a continuum, for example through use of a two-dimensional finite element calculation. However, this quantification was not used for the predictions, with the exception of one model which overrated the stiffness of the lining.

Furthermore, the analytical and two-dimensional models were only valid with soil stiffness ranging from 5 to 120MPa, as could be concluded from previous literature study. For Dutch soil this criterion almost always holds.

6.3 PRESSURE CHANGES AND DEFORMATIONS IN LONGITUDINAL DIRECTION

PREDICTION MODELS Two prediction models were used to describe the forces in longitudinal directional. Both models correspond in modelling the joint movement in the ring joints and in calculating the deformations and cross-section forces in longitudinal direction of the tunnel. However, their main difference rests in the analysis of the loading situation. Whereas one model mainly concentrates on the consequences of the (unequal distribution of the) jack forces, the other model focuses on the load caused by the stiffness differences of the soil in longitudinal direction of the tunnel.

Model 1: Axial interaction between segments of a tunnel lining A linear beam model of a length of 225 metres was used for the tunnel. One side of this tunnel model experiences an eccentric and not completely horizontal load from the jacks in the TBM. Deformations in the ring joints were taken into account for the bending stiffness of the beam. This includes the behaviour of the kaubit joint plates, which lead to non-linear elastic behaviour. The beam rests on soil springs, except for a small part directly behind the TBM, which is situated in liquid grout. Hence, this part is unsupported but experiences an upward load. Using this model a sensitivity analysis was conducted for various loads from within the TBM and for the length of the non-supported part in the liquid grout.

Model 2: Beam reaction of the tunnel tube The second prediction model consists of linear beams of a length of 1.5 metres clustered by means of non-linear rotation springs and shear springs. These springs discount the effects of the ring joints in the tunnel construction. The beam model is supported by soil springs simulating the elastic embedding.

The model examines the beam reaction that occurs as a consequence of the upward load on the tunnel tube, the different types of soil with different embedding constants in the longitudinal profile, and the fact that the tunnel tube is connected to the shaft on the one end and to the TBM at the other end (see figure 58).

Figure 58: Modelling of beam reaction of tunnel tube.

COMPARING PREDICTIONS WITH MEASUREMENTS As a result of the location of the measuring rings with respect to the shafts a comparison between measurements and predictions is only possible for predictions of axial normal forces and longitudinal bending moments directly behind the TBM using the prediction model (of a length of 225m) as mentioned above. The predictions hugely overestimated the longitudinal moment. The predicted bending moment amounted to 60 to 75MNm for a measured value of 10 to 20MNm. Predictions using other models, particularly focusing on the bending moments in longitudinal direction near the starting shafts, could not be verified by measuring.

EXPLAINING THE DIFFERENCES BETWEEN PREDICTIONS AND MEASUREMENTS Overestimation of the moment is mainly caused by overestimation of the moment the jack exerts on the tunnel, taken to be 62.6MNm (upward), whereas approximately 20MNm was measured. The fact that the moment executed by the jacks is not constant in time and that it accidentally may not have been at its maximum at the specific measuring rings, has to be mentioned. The assumptions predicting the influence of the grouting seal proved to be incorrect. It was assumed that the length of liquid grout would be between 3.75 and 7.5m and that the grout shell would not be thick enough to cause hydrostatic grout pressure. Measurements done at the Southern measuring ring indicated that the tunnel was situated in hardened grout over a distance of approximately 30 metres.

The axial jack forces, that had been assumed in the predictions, actually were approximately 20MN. However, these values were not measured in the lining as a result of local effects (three-dimensional force transfer through the joints to grout and soil) and beam reaction. The employed prediction models do not explain this difference very well.

ASSESSING THE PREDICTION MODELS Evaluation of the measurements shows that substantial beam reaction occurs directly behind the TBM in combination with local effects, for example the absorption of the jack forces. As a result, the calculated axial force in the lining does not match the aggregate of the jack forces. In order to be able to describe this behaviour properly, a calculation model is needed that not only consists of segmented rings (three-dimensional local forces effects) but that also possesses a sufficient length of connected rings to describe a rough balance of forces. Such models were not available when the predictions were formulated.

Figure 59: Beam reaction behind the TBM.

It was observed that the axial normal pressure right behind the TBM increases somewhat on the top side of the tunnel and decreases again as the distance to the TBM grows. This indicates that the part of the tunnel directly behind the TBM experiences an upward load due to the grout still being fluid. At a larger distance behind the TBM the grout shell has set, which causes the tunnel to co- operate with the surrounding soil. It is remarkable that ultimately the measured decrease of the axial normal pressure high in the tunnel is greater at measuring ring South than measuring ring North. Possible causes are: - direction of boring (upward versus downward), - structure of soil, - grout process (four injection points through the tail sealing versus three injection points through the segments), positions of the injection points, and the grout volume, - and progress speed (larger at measuring ring South than measuring ring North).

A correct modelling of the aforementioned forces needs to embrace the forces in longitudinal direction of the tunnel (jack forces) but also the different preconditions and loads perpendicular to the longitudinal direction. The first ring and a half of the lining is radially unloaded as this part is still located within the TBM. The part behind this, still in the unset grout, is loaded by grout pressures but is not supported. Further back the grout shield is set, which causes the lining to support the surrounding soil. These different areas need to be considered in this model (see figure 60).

End situation 15-20 Rings

Figure 60: Model required to describe beam reaction.

6.4 EQUILIBRIUM OF FORCES IN THE TUNNEL: A THREE-DIMENSIONAL MODEL

6.4.1 INTRODUCTION

In a segmented bore tunnel there is a three-dimensional equilibrium of forces at a global as well as a local level, which develops from the construction phase to the end phase. At the global level ring reaction and beam reaction of the bored tunnel should be distinguished. To some extent these two mechanisms show interaction which cannot be modelled by applying two separate models for ring and beam reaction.

At local level there is a three-dimensional distribution of strains and stresses in the segments combined with assembly stresses, which prevent the local force play at the joint plates in the ring joint planes.

In order to increase insight of the three-dimensional equilibrium post dictions were conducted in the first order evaluations, using two closely fitting three- dimensional finite element models: - The first model [K100-W-105b] comprises a simplified model of the tunnel tube in combination with a detailed model of the boring process, including the grouting of the tail void. This model provides understanding of the global equilibrium in the tunnel tube, which is caused by influences from the TBM, unset grout zone, set grout zone, and surrounding soil. Moreover, this model was used to determine pressure changes and deformations in the soil around the tunnel (see § 5.3.2.). - The forces on the tunnel tube and accompanying global deformations, which were calculated using the first model, were used as preconditions for the second model [K100-W-106]. This second model comprises a more detailed model of the tunnel tube with segmented shield elements. This gives insight into the local forces. Therefore, the consequences of placing the key segment were determined using this second model.

The choice for two closely fitting models was based on practical considerations. An integral model, which models both the tunnel in great detail as well as the boring processes and the behaviour of the soil around the tunnel, is not yet feasible. Furthermore, results of such an integral model would probably be difficult to interpret.

6.4.2 THREE-DIMENSIONAL FINITE ELEMENT MODEL OF THE GLOBAL EQUILIBRIUM OF FORCES

FINITE ELEMENT MODEL The employed finite element models have already been treated in paragraph 5.3.2.

CONDUCTED POSTDICTIONS OF PRESSURE CHANGES AND DEFORMATIONS IN THE ENVIRONS Using this model the pressure changes and deformations in the environs were recalculated. The post dictions showed a reasonable correspondence between measurements and calculations for the first passing of measuring area South (see § 5.3.2. and [K100-W-105b]).

CONDUCTED POSTDICTIONS OF THE GLOBAL EQUILIBRIUM OF FORCES IN THE TUNNEL CONSTRUCTION Two of the calculation versions, which were conducted using the model, mainly served to examine the global forces in the tunnel construction more closely. In addition, these versions were assumptions for further analysis of the local forces acting in the tunnel. These calculations were done for the cross-section in which measuring ring South is located. The grout pressures measured in that cross-section were therefore assumed to be the load on the unset grout zone (see figure 61).

250 200 150 100 50 0

Figure 61: Employed grout pressure development.

The partly set section of the grout shield (measuring three metres or two tunnel rings) has obtained a stiffness comparable to the sand layer underneath the tunnel. The stiffness of the set grout is stiffer by a factor 10, which however is still negligible compared to the stiffness of the tunnel lining.

The axial jack force amounted to 18.7MN and provided an external moment of 11MNM. Additionally, the grout pressure on the tail sealing was considered.

In the vertical equilibrium of the tunnel tube not only its own weight, soil (and groundwater) and grout loads but also the axle loads of the backup trains play a part.

CONCLUSIONS AND RECOMMENDATIONS BASED ON THE POSTDICTIONS - The resulting vertical load on the tunnel lining leads to an upward displacement (‘buoyancy’). The calculated buoyancy is more than 10mm at the TBM decreasing to several millimetres at a distance of approximately 40m from the TBM. In reality these displacements are compensated during the construction without significantly influencing the equilibrium of forces. - The forces within the tunnel in longitudinal direction are very sensitive to the employed grout pressure distribution. Based on the measured grout pressures a vertical ovalisation is calculated directly behind the TBM. As a consequence of buoyancy load, this ovalisation decreases somewhat after the (partial) setting of the grout shell. Vertical ovalisation means that the top and bottom side of the tunnel become further removed from one another. When the soil deformations measured in the middle of measuring area South are used to recalculate the grout pressure distribution and this grout pressure is entered in the calculation, horizontal ovalisation is the result. - The tunnel behaves as a slender beam in longitudinal direction. The tunnel tube mainly deforms through bending with the even cross- sections remaining even. Only at the ends of the model (at the TBM and at the edge of the model) this behaviour is disrupted. This means that a two-dimensional model (elastic supported beam) is sufficiently accurate to determine beam reaction. - Despite the above, the distance from the edge of the three- dimensional model to the TBM, measuring approximately 40m, has probably been too limited to eliminate the influence of the edge. The immense stiffness of the tunnel tube in longitudinal direction in proportion to the stiffness of the surrounding (partly unset) grout and soil causes the length over which the precondition dominating one side is cushioned out to be relatively long, according to calculations approximately 60m. This explains the discrepancy between the results of this three-dimensional modelling and the more realistic results of simple beam models. - Beside the limited length of the three-dimensional model, the phasing of the model is important. The advancing boring process is simulated by each time lengthening the model slightly (applying a new set of tunnel rings) and recalculating the moment distribution and deformations. As opposed to the simple non-phased models, this method evokes questions about the way the restraint of the edge of the model affects the calculation and how possibly in reality continuously small dimensional corrections are applied when constructing the tunnel rings. Therefore, it cannot be unambiguously said how the beam moment will ultimately develop between the TBM and the edge of the model.

6.4.3 THREE-DIMENSIONAL MODEL OF A SEGMENTED TUNNEL TUBE

FINITE ELEMENT MODEL This model comprises a segmented tunnel tube of 26 rings (see figure 62). The 26th ring is located entirely within the TBM, whereas the 25th ring is positioned half in and half out of the TBM. The interaction with the environs is expressed by the net load which is imposed on the model. The effect of this net load, deriving from the aforementioned model to determine the global forces (§ 6.4.2.), makes it unnecessary to put the tunnel on springs in this model.

Z X

Figure 62: Three-dimensional segmented shell model.

The net load is applied to the segmented shell model in phases, in which the lining is constructed ring by ring. Next, the assembly load resulting from the (forced) application of the key segment is applied. The magnitude of this assembly load is determined by the measuring results of the key segment in measuring ring South. Therefore, the key segment is schematised in this model as a peculiar longitudinal joint. The characteristics of this ‘joint’ are adjusted to the strain distribution measured in the key segment. As was demonstrated by the second order evaluations, this key segment, via its corners, transfers concentrated forces to the adjacent segments.

The behaviour of the ring and longitudinal joints in the segmented shell model is also based on the results of the laboratory tests carried out within the K100 framework. Concentrated transfer of forces in the ring joints through plywood plates was calculated in, as well as a reduction of the stiffness characteristics of the tunnel tube as a consequence of the concentrated pressure intake by the segments. For the latter an examination conducted by CUR/COB Commission L530 was made use of.

POSTDICTIONS CONDUCTED USING THE SEGMENTED SHELL MODEL The segmented shell model was first used to calculate the correct equivalent stiffness for the monolithic model of paragraph 6.4.2. Therefore, four cases were calculated using four different loads. For the post dictions only two of these calculation versions were done using the shell model: - Version 1 determines the soil loads based on deformation calibrations of the monolithic lining. - Version 2 determines the soil loads based on deformation behaviour of the complete segmented model.

In order to compare the results of both versions with the measurements conducted in measuring ring South of the Second Heinenoord Tunnel the measuring ring was moved through the employed finite element model, so to speak, to four different positions behind the TBM, i.e. approximately 8m, 17m, 26m, or 35m from the face of the TBM. These positions correspond to rings 6, 12, 18, and 24 in the model. The average measuring results over the duration of one hour, directly after the TBM had stopped boring, were considered to be the ‘measuring values.’ The following aspects of the measurements and calculations were compared: - axial and tangential strain distribution in the middle of the segments, - axial and tangential pressure distribution within the segments, - and tangential ring moments within the segments.

COMPARING THE POSTDICTIONS WITH THE MEASUREMENTS Axial strains and beam reaction Figure 63 shows the measured and calculated axial strains. The calculation results for the axial strains are virtually identical for the versions 1 and 2. Figure 63 demonstrates a clear influence of the concentrated intake of the forces at the ring joints. The amplitude of the strains calculated within one segment amount to 25µm/m up to 50µm/m, which is comparable in size to the average strain. However, measurements do not verify this spread. This is the case because per segment only two points are available for measuring the axial strain, with the measuring points corresponding more or less to the positions containing the maximum strain. Considering that the strains were measured exactly where the maxima were located, it was concluded that the measurements agree well with the calculations.

Figure 63 also demonstrates that the calculated distribution of the average axial strain is mainly determined by the global beam moment. Due to the moment caused by the jacks, near the TBM (ring 24) the strain is minimal at the bottom of the cross-section (at ϕ = ±π) and maximal at ϕ = 0. For subsequent rings the size of the moment decreases until it approaches 0 at ring 18. This is expressed in the calculations by a virtually horizontal course of the average strain. In rings 12 and 6 the moment has reversed, and the strain is minimal at the top (ϕ = 0) and maximal at the bottom (at ϕ = ±π).

Figure 63: Average axial strains in the rings considered and measuring results at the corresponding times.

In the measuring ring the calculated trend mentioned above has not been observed. In fact, the measurements show a reverse trend. At ring 6 the moment seems directed in the same direction as and larger than at ring 24, even when other measuring times are considered. In effect, this means that the (calculated) bending shape of the tunnel tube does not correspond to the measured bending. Based on the line of moments the tunnel has a more or less

constant but at least similarly directed bending (κz), according to the second order evaluation [K100-W-066]. Nevertheless, the calculations indicate that the bending moment at the TBM decreases as function of the distance and even changes sign. Therefore, it must be concluded that there is a plain discrepancy between the model and the measurements in the field of the predicted moment line and the connected global distribution of the axial normal pressures in the different cross-sections of the lining.

Comparing the calculated moment line with the one presented in the second order evaluation [K100-W-066], it should be noted that a (more or less) constant difference is observed between the moments caused by the jacks and the moments which are determined on the basis of measurements. Immediately after the measuring ring had been applied, right behind the TBM, the moments should still have been similar. However, the second order evaluation [K100-W-066] shows that the measured jack moment is ±11MNm, whereas the measuring ring measurements yield a moment of ±5MNm. The finite element calculations assume the measured jack forces to be a precondition and therefore yield a beam moment of ±11MNm directly behind the TBM. The evaluation report also explains the difference between jack moment and moment calculated from strain measurements because different positions of the points of application of the jacks were assumed during the calibration of the segments of the measuring ring than during construction. If it is assumed that the positions were as during construction, the jack force following from the measuring ring corresponds to the directly measured jack forces.

Tangential strains

The calculated and measured average tangential strains are depicted in figure 64. The average strain level of version 2 seems lower than that of version 1 (figures 64b and 64a). Whereas version 2 experiences an average tangential strain of -75µm/m for ϕ = 0, version 1 shows a strain of approximately -50µm/m.

Figure 64: Average tangential strains in the examined rings according to version 1 (figure a) and version 2 (figure b) and the measuring results at corresponding times. A possible explanation of the different strain levels of both versions may be that the (longitudinal) joints do not have a reducing effect on the stiffness of the tunnel tube when the cross-section is uniformly reduced. Using the monolithic tunnel model and an elasticity modulus of 24.6GPa a load is determined which yields a uniform strain of approximately -75µm/m (version 2, figure 64b). However, in the segmented shell model for a similar load a uniform strain of -47µm/m was found (figure 64a). The spread in the measuring results makes it difficult to judge which of the two versions best approaches reality. To compare the measurements with the calculations version 1 (calibration through monolithic tunnel model) should be taken as reference point. After all, the load (and not the deformation) is put on in the unset grout. However, the truth will be somewhere in the middle.

The characteristic peaks and dips of calculation results are also expressed in the measuring values. In the calculations there is strain at several longitudinal joints (the dashed lines in figure 64), which indicates that the assumed linear elastic behaviour of the longitudinal joints is actually not correct.

The measured strain levels correspond reasonably well with the calculated values. As with the axial strains, the calculations show that strong fluctuations are to be expected. On the one hand these fluctuations are the result of the locally present ring joint plates. On the other hand these fluctuations are increased because the load on the tunnel is based on the monolithic tunnel model of evaluation report [K100-W-105b], which shows a remarkably coarser distribution of elements than the segmented shell model.

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Where the calculations results are concerned, it has to be noted that the influence of the assembly stresses as a consequence of the forced application of the key segment is hardly perceptible. This is because the assembly stresses are extreme for ϕ = -0.05π ( the key segment is located just left of ϕ = 0). A comparison of the resulting strains with the measured results, however, proves that the calculated strains correspond with the measured values. This indicates that the average level of tangential strain is mainly determined by the axial normal force and the load on the tunnel. The forced application of the key segment is a local phenomenon and hardly influences this.

Curvatures The calculated and measured bendings are represented in figure 65. A positive bending exerts strain on the inside and pressure on the outside of the segments. Based on the continuity of the (closed) ring it may be expected that the average curvature is approximately zero. If the (small) influence of the forced application of the key segment were to be disregarded, this is indeed the case in the calculations. However, the results of the measuring ring measurements do show a resulting curvature, as opposed to the calculation results. Since the segmented ring remains closed as well, the curvatures in the segments, summed along the circumference, need to be compensated by the total angular deflection in the longitudinal joints. This could not be determined in the measuring ring, as no rotations were measured in the longitudinal joints.

Figure 65: Curvature in the examined rings and the measuring results at the corresponding times.

The fact that the calculated bendings show rather strong fluctuations along the circumference is probably (mainly) caused by the way the monolithic tunnel model and the shell model are linked. The (absolute) level of the measured maximum curvatures, however, corresponds reasonably well with that of the calculated curvatures.

Deformation measurements

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The curvatures in the segments and the angular deflections in the longitudinal joints have a direct relation with the shape of the ovalisation. The ovalisation deformations found in the calculations actually originate from the results of the calculations using the monolithic tunnel model. The shape of the ovalisation of rings 6 and 24 is shown for versions 1 and 2 in figure 66. In both cases it is a matter of vertical ovalisation, with the top side of the cross-section being relatively little deformed. This shows from the calculated and measured bendings as well, which are relatively small in the top part of the tunnel cross- section.

The ovalisation is caused by the sides of the tunnel cross-section pushing inwards, which causes an increase in diameter in vertical direction. Obviously this is related to the employed grout pressure distribution around the periphery of the tunnel and the concentrated load on the bottom caused by the backup train. The sides being pushed in leads locally to strain (less pressure) on the inside and (more) pressure on the outside of the segments, which agrees with the measured bendings. Exactly the opposite happens according to the calculations at the bottom, which, however, is not confirmed by the measured bendings at the bottom of the cross-section. Where negative bendings were found in the calculations, bendings measured in the segments were clearly positive. ring 24

ring 6 Y Y Z Z

(a) (b) Figure 66: Deformation (scale factor 300) of rings 6 and 24 of the model for versions 1 (a) and 2 (b).

It follows from figure 66 that the ovalisation for ring 6 is smaller than for ring 24, which is located closer to the TBM. Otherwise, the radial load at some distance behind the TBM is the initial grout pressure.

As indicated before, the shape of the ovalisation, except for the bendings in the segments, is also determined by the angle deflection at the longitudinal joints. The measurements done in the measuring ring, however, do not exemplify this, as no rotations were measured in the longitudinal joints. To get an impression of the ovalisation shape as it occurred in practice the results of the deformation measurements conducted in the first tube in measuring area South were assessed further. These results are described in [K100-W-075]. This report shows that already during the assembly of the three calibrated measuring rings (ring numbers 568, 569, and 570) an ovality arose, with the diameter being smaller in vertical direction than in horizontal direction (low ovalisation). This deviation from the circular shape during construction, which amounts up to 6mm added to the diameter, may have been caused by the weight of the segments themselves, possibly in combination with a certain ovality of the shield. If a ring with such a deviation comes outside of the shield,

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a strengthening of the low ovalisation could occur at uniform pressure distribution along the periphery. The calculations assumed a perfect circle in unloaded state for the cross-section. Consequently, the effect of the construction deviation could not emerge. Provided the pressure differences are sufficiently large, a previously low ovalisation could still change into high ovalisation. The deformation measurements of ring 568 showed that the average diameter, which was used to determine the ovality, became smaller after the ring had left the shield. If this is taken into account, the low ovalisation of ring 568, which is present immediately after construction of the shield, becomes smaller outside the shield. Although ultimately still low ovalisation will arise, high ovalisation apparently was caused by the load exerted on the ring, which corresponds to the conducted calculations. This picture is similar for ring 569. After having left the shield the low ovalisation increased somewhat. However, the change was so small that it fell within the measuring accuracy. In the case of ring 570 (the measuring ring) measurements were conducted along approximately half the periphery, which makes the deviations from the circular shape as calculated in the reports not very reliable. Assuming the reported values, the conclusion is reached that the construction deviations were relatively small for this ring, whereas the change outside of the shield is also within the measuring accuracy for this ring.

Based on the above, it could be concluded that the deformation measurements do not give a clear picture of the actual shape of the ovalisation. As far as ovalisation was clearly present, this was already the case within the shield as a consequence of the measure deviations when constructing the rings.

CONCLUSIONS AND RECOMMENDATIONS BASED ON THE POSTDICTIONS - A strong interaction exists between the forces in ring direction and in longitudinal direction. The conducted calculations show that a three- dimensional modelling can describe this interaction, whereas this is not possible using simple ring models. - The concentrated intake of the axial jack forces and their concentrated transfer onto rings lying further away result in strong fluctuations of the axial and tangential strains along the periphery of the tunnel. The occurring amplitude is similar in size to the average occurring strain. - The sizes of the calculated axial and tangential strains in the middle plane of the tunnel lining corresponds reasonably well with the measured values. - Considering this report’s assumption that the segments (except for the key segment) are constructed round and without any stresses, the effect of the forced application of the key segment is limited and only perceptible in the immediate surroundings of the key segment. Therefore, it may be concluded that this effect plays a subordinate role in the calculated pressure distribution in the tunnel tube. - The sign and the size of the calculated bendings in the segments, caused by ring moments along the periphery, correspond reasonably well with the measured values as far as the top and the sides of the tunnel cross-section are concerned. However, at the bottom of the cross-section the calculated and measured bendings did not match. As there is no information available on the longitudinal joint rotations occurring in practice, a complete comparison between the measuring results of measuring ring South and the calculation results is not possible.

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- It follows from the calculations that high ovalisation of the tunnel cross-section occurs, whereas low ovalisation was reported for the conducted deformation measurements of rings 568, 569 and 570. The calculated (high) ovalisation appears to decrease as the distance to the TBM grows. This actually means that the changed radial load in relation to the initial grout pressure causes low ovalisation. In fact, the conducted deformation measurements show that low ovalisation is still present immediately after construction (even before the rings have left the shield). One ring experiences decreasing low ovalisation after leaving the shield, which implies high ovalisation as a consequence of external load. For the other rings this is unclear as the measuring results are within the measuring accuracy. It was assumed in the calculations that the rings initially were built pressureless and perfectly round. The effect of measuring deviations during assembly was therefore not contemplated. - The calculated beam moment caused by eccentric applied jack load corresponds to the measurements directly behind the TBM, but reverses sign at some distance behind the TBM. The strain measurements show, however, that the beam moment does not change sign and remains more or less constant. Thus the beam reaction is not described adequately by the calculation model. Nevertheless, the ring effect is not substantially affected. - For future measurements done at the measuring rings the expected strong strain fluctuations along the periphery of the tunnel ring need to be considered when positioning the measure instruments. - To gain understanding of the assembly pressures occurring through the construction of the segments in the ring, it is recommended to start possible future measurements prior to actually constructing and loading the segments. - Because a change of radial load influences the ovalisation of the rings, it is recommended that for future measurements the grout pressure on the lining is measured over a larger distance, which will provide a three-dimensional picture. - Looking at the measuring results, the impression may arise that the forces in both ring direction and longitudinal direction do not change at a short distance behind the TBM. The setting of the grout may play an important role in this. In order to examine to what extent the forces in the lining change over the long-term, it is recommended to continue the measurements in the measuring rings of the Second Heinenoord Tunnel for as long as possible. - If it is correct that the forces at a short distance behind the TBM do not change, the calculation of the forces could be done by using a model consisting of fewer rings. This offers the possibility of determining the pressure effects in the tunnel lining by means of a fully integrated model, with soil, grout and tunnel lining being modelled by volume elements. - The method chosen in the first order evaluation to relate a monolithic tunnel model to a segmented shell model worked satisfactorily, although it was a bit laborious. Given the current possibilities existing in the field of finite element modelling, the chosen approach was the best attainable for the time being.

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- Based on calculation results, it is recommended that the distribution of forces in the tunnel construction is determined in both ring direction and longitudinal direction, both in terms of normal forces and moment. Consequently, it can be assessed to what extent the dimensioning of the size of the segments and the reinforcement as used in the tunnel are adequate.

6.5 SUMMARY: ACQUIRED KNOWLEDGE IN THE FIELD OF TUNNEL CONSTRUCTION

ASSEMBLY STRESSES AND APPLICABILITY OF TWO-DIMENSIONAL MODELS - The most remarkable observation of the measurements of the tunnel lining was that the pressures arising during construction of the lining from loose segments were of similar size to the pressures exerted by the soil and the grout around the tunnel. Further model development is required to a priori calculate these pressures in future with any success. - The effect of the forced application of the key segment on the total force play in the tunnel is limited and only perceptible in the immediate surroundings of the key segment. - When the assembly pressures are eliminated from the measured force effects, the tunnel loads and the cross-section forces can be described reasonably well with empirical models and two-dimensional element models. However, it is necessary to calculate the pressure distribution around the tunnel, including the loss of volume during boring. This effect can be quantified by describing the tunnel as a continuum, for instance using a two-dimensional finite element calculation.

USEFULNESS, NECESSITY AND LIMITATIONS OF THREE-DIMENSIONAL MODELS - For local forces, at the level of the tunnel segments, it is difficult to differentiate between longitudinal direction and cross direction as the force effect is very much three-dimensional. This is caused, among other things, by the pressures in longitudinal direction leading to strains and stresses in cross direction. The concentrated intake of the axial jack forces and the concentrated transfer to rings lying further away leads to strong fluctuations in axial and tangential strains along the periphery of the tunnel. Additionally, there is disruption of the even pressure situation caused by placement of the segments and in particular by pressure concentrations in case of incomplete contact of the key segment. The executed calculations demonstrate that a three- dimensional modelling can describe this interaction, which is not possible using simple ring models. - The tunnel behaves as a slender beam in longitudinal direction. The tunnel tube mainly deforms through bending, with the even cross- sections remaining even. Only at the ends of the model (at the TBM and at the edge of the model) this behaviour is disrupted. This means that a two-dimensional model (elastic supported beam) is sufficiently accurate to determine the global beam reaction.

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- When applying a three-dimensional model which calculates the construction of the lining in phases, it needs to be considered how the support at the edge of the model makes itself felt in the calculation and how the construction of the tunnel rings may actually be accompanied by minor measurement corrections. Moreover, the model needs to be long enough (contain a sufficient number of rings) to eliminate the influence of the edges of the model. - The calculated beam moment caused by the eccentric applied jack load corresponds with the measurements done directly behind the TBM, but reverses of sign some distance behind it. Strain measurements, however, show that the beam moment does not change sign but stays more or less constant. Therefore, the beam reaction is not described properly by the three-dimensional model. The ring effect is not substantially influenced by this. - If the forces at a short distance behind the TBM do not change anymore, as will be shown by the measurements, a model of a smaller number of rings could suffice to calculate the force effect. This offers the possibility to determine the forces in the tunnel lining using a fully integrated model, which models soil, grout and tunnel lining with volume elements. - The method of relating the monolithic tunnel model to the segmented shell model, as was chosen in the first order evaluation, worked satisfactorily although laboriously. Given the current possibilities in the field of finite element modelling the chosen approach is the best attainable at the moment.

LIMITATIONS DUE TO INSECURITIES IN PROCESS PARAMETERS AND MODEL CHARACTERISTICS Even in case of an optimally detailed model some relatively big insecurities remain with regard to the process parameters and characteristics. The most important are: - setting time of the grout, the mechanical characteristics of the unset and setting grout shell, and the distribution of the grout pressures, - soil characteristics and especially the pressure-dependent stiffness, - jack forces as function of time and place, - and construction tolerances and hence placement inaccuracies. Therefore, models that can describe the measured behaviour well do not necessarily result in better predictions.

This report restricts itself to the evaluation of the tunnel lining models in relation to the measurements conducted at the Second Heinenoord Tunnel. Whether these models are suitable to implement a detailed design of the tunnel lining, including detailed joint constructions, was not examined. For this, we refer you to the results of CUR/COB Commission L500.

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CHAPTER 7 EVALUATION OF EDUCATIONAL MOMENTS

7.1 INTRODUCTION

In addition to developing knowledge from previously set objectives, a few educational moments occurred during the tunnelling process. In principle, these fall outside of the territory of CUR/COB Commission K100. It was impossible for the Commission to instrument and monitor the complete project area so intensively as to enable registration of every single incident at any location at any time of the day. K100 mainly evaluated the ‘normal’ tunnelling process, in order to improve the generic models for the design of bored tunnels. Various COB newsletters pay attention to the educational moments. The summary below was borrowed from these.

7.2 LEAKAGE IN THE SEALING OF THE TAIL

Having bored approximately 500m of the Second Heinenoord Tunnel with hardly any problem, the steering card of the PLC navigation system broke on 29 May 1997. This caused one of the jack groups to break down. During the programming of the new card, the TBM moved approximately 20cm backward. After having bored 60cm at two places leakages occurred and a mixture of approximately 12 cubic metres of soil and water flowed into the machine. Using the emergency sealing stopped the leaking. Moreover, the influx caused the soil surrounding the tunnel to become unstable. Injecting this soil with bentonite and mortar stopped further leakage during boring. Also, formwork was applied between the last segment ring and the jacks as extra safety. In case the emergency sealing would stop functioning as well, this formwork could reverse the prevailing soil and water pressure.

By means of a mini camera it could be established that the sealing profile located at the grout pipes sagged approximately 1 to 5cm. At the six grout openings the rubber sealing profile had locally been reduced to enable grouting. Therefore, the profile was weaker in those spots. The sagging of the sealing profile was so severe that the fastening of the profile on the tunnel shield did not suffice. In case of a sagged profile the grouting through the grout pipes resulted in such high pressures on the profile that a leakage path arose.

In order to prevent further leakages along the way the formwork was replaced by a steel partition fixed to the jacks, which increased bore production. Secondly, it was opted to grout through the boreholes in the segments, which exercised less pressure on the sealing profile.

When on Monday 30 June the emergency sealing started leaking, it was decided to apply steel brush sealing in place of the emergency sealing. The spaces between the brushes and the tail sealing were filled with grease. This type of sealing does not require emergency sealing nor formwork. To benefit the refitting of the sealing the soil around the shield was injected.

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Figure 67: Leakage of TBM.

7.3 FACE INSTABILITY

On 28 August 1997 a bore face instability occurred during the boring process of the Western tunnel tube. Because the slurry flowed into the soil, the bentonite level in the bore chamber lowered. In order to maintain the level deemed necessary bentonite was pumped into the mixing chamber. After the bentonite supply was used, air and water were pumped to the front. In addition, support plates were put in to support the bore face. Nevertheless, the face collapsed and the cutting wheel of the TBM stood still in the soil.

By means of depth sounding of the river bedding a circular shaped hole with a diameter of 6m and a depth of 2m was found. Cone penetration tests around the TBM showed that at a distance of 6m and more the soil was not or hardly disturbed anymore.

As already written in paragraph 4.2.2. of this evaluation report, the applied face pressure right before the occurring instability was far higher than the earth pressure on the top side of the tunnel. Based on existing theories instability may be expected with such a face pressure. Possibly a weak spot in the soil contributed to the instability, which may have been caused by a removed spud used for the sinking process of the implementation of the First Heinenoord Tunnel. These spuds were driven into the soil approximately every 8 metres and were removed afterwards.

For the boring process of the second tunnel tube several measures were taken against face instability. For instance, further analysis of soil historic research was undertaken in order to map the soil disturbances through the use of spuds. Furthermore, the face pressures at these locations were kept an eye on. The employed face pressures at the second (Eastern) tunnel tube were importantly lower than when boring the first tunnel tube (see Appendix 3).

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7.4 DAMAGED LINING SEGMENTS

When inspecting the tunnel lining of the Second Heinenoord Tunnel, it was found damaged in several places. This damage has been categorised as follows: A. concrete damage at the joint of the key segment, B. concrete damage at the bolt pocket, C. concrete damage of the segment corner, D. difference in ring borders exceeding the notch tolerance, E. longitudinal rips in the elements, F. and leaking joints.

Figure 68: Damage to segments.

Only difference in ring borders, mentioned under D, may have influence on the constructive reliability of the construction, in particular the extent to which the notches fulfil their tasks. The categories C, D and F with possible damage to the exterior of the lining may have influence on the durability of the construction, in particular the increased ripping and additional ripping. These categories may cause increased leakage (and colouring) during their life time.

Four things may have caused the damage: - The occurrence of damage when building the elements into a ring. The concrete elements are produced with a minimum tolerance and therefore have to be placed with great accuracy. In case of insufficient tolerance extra pressure on the diagonal planes of the notch may arise when the key segment is pushed in, which may cause the edge to slip. - Displacement of the TBM. This may be caused by pressure concentration due to prevented displacement when placing the elements, or by the elements coming in contact with the TBM shield (insufficient air size). Additionally, high jack forces, usually accompanying sharp turns with small curve radii, may cause longitudinal cracks. The elements are put in statically undetermined, which causes relatively large load concentrations with small deformations. Flexural strains and torsional stresses are the consequence of the curved shape of the elements.

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- When the tail sealing reaches past a ring of the lining, the ring is being compressed by the grout pressure. Consequently, pressure concentrations arise at the adjacent notches and the pressure planes in the longitudinal joints will be loaded eccentrically. This may result in corners sliding in relation to one other. - The deformation of the ring outside the shield is caused by the occurrence of cross displacements of the rings when the TBM moves with small curve radii. The cross force that arises because the jacks are slightly angled is initially absorbed by the pressure planes through friction and then through the notches.

These causes result in several measures that can be taken to reduce the damage: - building in the key segment without pressure, - tuning the placement accuracy to the available tolerance, - avoiding small curve radii, - enlarging the air size, - centric (in relation to the tunnel shield) and conic (in relation to the last ring) building of rings, - and restriction of the ring deformation by adapting the bolt connection.

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CHAPTER 8 EVALUATION OF THE MEASURING INSTRUMENTS

8.1 INTRODUCTION

Report [K100-W-107] elaborately evaluates the used instrumentation. Per field of interest (bore technology, geotechnology and tunnel construction) the measure instrumentation was assessed using the following criteria: - the formulated specifications, - the installed measuring system, - estimated and spent budgets, - positioning of instruments, - execution of measurements, - and conclusions and recommendations.

Evaluation of the measure instrumentation is deemed important for future monitoring projects, if only because the instrumentation and measurements have absorbed approximately 50% of the total K100 research budget. In this chapter the most important findings per measuring instrument are summarised, grouped per field of interest.

8.2 MEASURING EQUIPMENT BORE TECHNOLOGY

GENERAL REMARKS The following research objectives were central to the field of bore technology: 1. Stability of the bore face: - minimum and maximum support pressure - pressure distribution in the mixing chamber - water pressures in front of the bore face (see § 8.3 on geotechnology) 2. Equilibrium of forces in the TBM: - in axial direction - in tangential direction 3. Effectiveness of the boring process: - wear of the cutting elements - mixture forming - effectiveness of pumps and pipes

Generally, it can be said that the measurements in the field of bore technology are especially of importance to the first research objective of increasing understanding of the stability of the bore face. Obtaining insight into the equilibrium of forces was made difficult by the fact that not all individual components of this equilibrium could be established. For different reasons the measurements only contributed partly to the increased understanding of the effectiveness of the boring process.

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FORMULATING SPECIFICATIONS The following circumstances complicated the formulation of specifications for the COB instrumentation, which was to complement the measurements to be conducted by the contractors Tunnel Combinatie Heinenoord12 and Herrenknecht. - The COB research objectives were highly abstract and therefore first needed to be translated to a concrete measuring programme. - During the formulation of the specifications no predictions were yet available. Had these been available, the choice of the parameters to be measured could have been tuned to the parameters already used in the (calculation) models of the predictions. - Part of the instrumentation was specified by the supplier of the TBM (Herrenknecht). - There was great pressure of time on formulating the specifications. It is recommended to pay more attention to these things in future projects.

EVALUATION OF INDIVIDUAL INSTRUMENTS AND MEASUREMENTS Pressure gauges in the mixing chamber - Measuring objective: Determining the pressure distribution in the mixing chamber. - Measuring method: Pressure gauges. Method proved to be suitable. - Number/position: Number and position of gauges proved to be suitable. - Type of instrument: The type of gauges chosen did not answer to expectations as, in particular, it was observed that the reference point moved. It has to be concluded that such pressure gauges must meet higher demands in future. - Realisation of measurements: The pressure gauges were connected to the data acquisition system. The employed measuring frequency sufficed. - Total result: The measurements were corrected over the course of the project by executing calibrations. It must be concluded that pressure distribution in the mixing chamber could indeed be determined reliably. This contributed substantially to understanding of the employed face pressures. - Recommendation for future projects: The specifications need to be adapted.

Measuring the equilibrium of forces of the TBM in axial and tangential direction - Measuring objective: Determining axial and tangential forces. - Measuring method: Derived from measuring pressure distribution in mixing chamber and jack forces. - Result/recommendation for future projects: It is difficult to determine the equilibrium of forces in axial and tangential direction. This is caused by the fact that less parameters were measured than the number occurring in the equilibriums. Only based on analyses of specific circumstances, such as application of the overcutters [k100-w-081] and experimentation with rpm and progress speed [K100- w-092], can the most important components of the equilibriums be determined. For future projects the measuring instrumentation needs to be reconsidered and specific experiments need to be used in order to measure all components unambiguously - think for instance of measuring the axial cutting forces and elaborating on the experiments with overcutters, separate motion of the cutting wheel and the TBM, and variations in rpm and progress speed.

12 Tunnel Combinatie Heinenoord: Dutch for Tunnel Combination Heinenoord.

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Measuring size and stiffness, and weighing the cutting elements - Measuring objective: Determining the wear of the cutting elements as a result of the boring process. - Measuring method: Measuring and weighing the cutting teeth. - Number/position: Measurements were conducted after the first passing of the sealing wall of the entry shaft and after finishing the first tunnel tube. Both measurements concerned 6 cutting teeth. - Type of measurement: The cutting teeth were measured, photographed, and weighed and Vickers-hardness was determined. - Result/recommendation for future projects: Assessment of the measuring result was realised in report [K100-W-104]. This report recommends to measure cutting depth over the entire tunnel distance, which means that progress speed and rpm (and direction) of the bore face need to be registered. Furthermore, the interpretation of the measurements assumed that wear is even over the entire distance, whereas wear in sand is (far) above average. It is recommended to argue this through laboratory tests.

Density and pressure difference measurements in pipes - Measuring objective: Determining flow characteristics, pressure loss, and the extent of sedimentation in the pipes. - Measuring method: Radioactive density measurements in supply and discharge pipes and pressure difference measurements over 10m of discharge pipe. - Result: Both measurements have not functioned adequately. Beforehand not enough attention was paid to the required calibration of the system after placing the instruments. The predictions, therefore, could hardly be tested which meant that the measurements yielded little insight. - Recommendations for future projects: It is recommended to pay a lot of attention to the measuring set up and calibration of the instrumentation in specifications for future projects.

Data acquisition system - Measuring objective: Automatic registration of measuring data. - Number/position: Two separate data acquisition systems were installed. - Realisation of measurements: The instruments installed by the contractor (data supplied by Herrenknecht) were only used during boring periods while the COB-instrumentation was used continuously. It would have been very useful for the evaluation of the measurements if the HK-data would have been measured continually as well. The data transfer through the slip ring functioned without interruption, whereas the radio transmission incidentally was disrupted. - Result: It may be concluded that the data acquisition system as a data processing system functioned excellently.

Grout pressure measurement - Measuring objective: Determining the grout pressure in the tail void and around the lining. - Measuring method: Grout pressure measurements on the pump at the injection points. - Number/position: The contractor measured the grout pressure at every injection point.

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- Result/recommendation for future projects: The measurements were done at the grout pumps. Discharge losses around the injection point are unknown. It must be concluded that in this manner insecurity exists about the actual grout pressure in the tail of the TBM. It is recommended to measure grout pressure in the tail void during future projects.

8.3 GEOTECHNOLOGY

GENERAL REMARKS Two measuring areas were instrumented in order to assess geotechnical objectives, in particular determining pressure changes and deformations in the surroundings. These objectives have been attained for the most part. However, the measured pressure changes in the surroundings could be used more qualitatively than quantitatively.

EVALUATION OF INDIVIDUAL INSTRUMENTS AND MEASUREMENTS Markers and fixed points - Measuring objective: Measuring vertical surface deformation. - Measuring method: Precision levelling. The chosen measuring method (manual levelling of markers) worked properly. The inaccuracy of the levelling, however, was approximately 1mm, which did not meet the specifications. It is caused by weather influences and vibrations from the TBM. Recently systems automatically aligning and referencing each other have become operational. These systems may be preferred in future applications as such equipment enables a higher measuring frequency and allows expanding on the number of measuring points. - One reference point per measuring area was used, placed at a relatively short distance from the tunnel tube. In the Southern measuring area a significant fluctuation of approximately 2mm away from the reference point was observed. Therefore, it would be advisable to place at least two reference points per measuring area and to relate these to at least three NAP water levels. - Number/position: Approximately 50 markers and one reference point per measuring area. This number was reasonable, although along the way number and position have been adapted somewhat. - Type of instrument: DINI 10 levelling apparatus. Range and accuracy of this instrument were conform specifications, although the total accuracy was less than expected due to environmental influences. - Realisation of measurements: This was conform expectations, although the fluctuation of the reference point in measuring area South necessitated corrections. The measurements were influenced by weather effects and vibrations of the TBM. - Total result: Based on the measurements understanding was gained about the occurring deformations, which contributed to the realisation of the research goals. - Recommendation for future projects: Application of at least two reference points per measuring area, related to at least three NAP water marks.

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Figure 69: Installation piezometers in measuring area North.

Inclinometers - Measuring objective: Determining horizontal deformations of the soil as function of the depth. - Measuring method: Using inclinometers, which sufficed well. - Number/position: Four inclinometer tubes per measuring area. This number seemed reasonable, although the tubes above the tunnel axis proved to be useless. - Type of instrument: Digitilt Inclinometer. The range and accuracy of the instrument were conform specifications. However, the occurring deformations were much smaller than expected, which influenced the results of the inclinometers above the tunnel negatively. - Realisation of measurements: This was conform expectations. - Total result: Based on the measurements understanding was gained about the occurring deformations. This contributed to the realisation of the research objectives. - Recommendation for future projects: Measurements above the tunnel proved insufficiently accurate, because determining the position of the top of the inclinometers introduced an inaccuracy of the same order as the occurring horizontal deformations. In order to eliminate risks concerning the progress of the boring process, the specifications state a minimum distance of 2m to the tunnel tube. Considering the positive experiences with this distance, it could perhaps even be diminished. In fact, this applies to vertical deformation measurements as well.

Extensometers - Measuring objective: Determining vertical deformations of the soil as function of the depth. - Measuring method: Extensometers. This measuring method worked excellently - range and accuracy were conform specifications. - Number/position: Four to five extensometers per measuring area were placed. Although this was sufficient, the number could be increased. - Type of instrument: Bar extensometer with displacement sensors. Range and accuracy of instrument were conform specifications.

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- Realisation of measurements: This was conform expectations, the data acquisition system functioned well. - Total result: Based on the measurements insight was obtained about the occurring deformations, which contributed to the realisation of the research objectives. - Recommendation for future projects: The chosen system, which determined the vertical deformation of the anchored rods automatically, answered the demands. Between the tunnel tubes measurements were conducted at six depths, which in retrospect was a bit much. Above the tunnel tubes measurements were conducted at two depths. These measurements enormously benefited the gaining of understanding about the volume losses during boring and the relation with the surface settlements. Enlarging the number of instruments (currently four or five), therefore, seems useful for future projects.

Figure 70: Stress monitoring stations.

Stress monitoring stations - Measuring objective: Determining soil and water pressures and stress changes. - Measuring method: Earth pressure cells and water-pressure gauges. The measuring method leads to mediocre results, e.g. unrealistic negative effective pressures were measured. - Number/position: Three stations in measuring area North. This proved reasonable as more than one measurement is needed in one location in order to obtain a reasonably reliable picture of the pressure changes. - Type of instrument: Stress monitoring stations. Although range and accuracy were conform specifications, they were strongly influenced by the method of installing. - Realisation of measurements: This was conform expectations, the data acquisition system functioned well.

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- Result: Based on the measurements a qualitative insight was acquired about the occurring changes of soil and water pressures, which contributed to the realisation of the research objectives. Measuring grout pressures is especially tricky, because the installation of the instrumentation disrupts the soil structure. This is caused both by boring the hole for the instruments, which leads to arching of the surrounding soil, as well as filling the borehole after placing the instruments, in this case with bentonite suspension. Disruption by soil displacement also occurs with earth pressure cells, which are pushed away. Although the earth pressure cells for the Second Heinenoord Tunnel were calibrated by the supplier, these manufacture specifications have little relation with the accuracy attained after installation in the soil. Therefore, it must be presumed that the absolute values of the measured earth pressures are unreliable. On the other hand, measured changes of earth pressures, as caused by the boring process, are consistent with other measurements such as horizontal deformation measurements and grout pressure measurements. These observations proved important for the increased insight into the effect of boring on surrounding soil. Skipping the earth pressure measurements in measuring area South to cut costs was a sensible decision. - Recommendation for future projects: It needs to be considered whether application of, for instance, ‘spade cells’ will give less disruption during displacement, which in order leads to more reliable measuring results. On the other hand, the disadvantage of not being able to measure vertical earth pressure with these instruments is of minor importance. It is recommended to conduct the measurements in threefold for every intended location. Despite the mediocre results of the earth pressure measurements, it is recommended to use them anyhow.

Water-pressure gauges at the bore face - Measuring objective: Determining the influence of the boring process on the water pressure in front of the bore face. - Measuring method: Water-pressure gauges at the bore face. This method functioned very well. - Number/position: Three water-pressure gauges were installed in measuring area North as well as South. In retrospect only one water- pressure gauge per measuring area would have sufficed. - Type of instrument: Electrical water-pressure gauges were used. Initially these worked with a measuring frequency of once per second. In order to allow better analysis the frequency was increased to thrice per second. The range and accuracy of the gauges sufficed. - Realisation of measurements: For these measurements, with the water- pressure gauges being ‘swallowed by the TBM, much attention was paid to taking measures to prevent blow-out or the TBM stranding on the gauges and cables. The instruments in the borehole were tuned using a special procedure and sealed carefully. The measuring method functioned excellently and could be realised again in the same way under similar circumstances. The instruments were connected to the data acquisition system of the measuring areas, which functioned very well. - Total result: The water-pressure measurements at the face functioned well at the passing of the TBM and contributed to understanding of the processes occurring at the face of the TBM.

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- Recommendation for future projects: Conducting water-pressure measurements at the bore face is useful and can be limited to one measurement per normative cross-section. The gauges must be able to measure a maximum frequency of thrice per second.

Data acquisition system - Measuring objective: Registration measurements. - Measuring method: Data logger containing GSM modem connection or cable connection to measuring computer. This functioned well. - Type of instrument: CR 10 data logger. The instrument met the demands. - Total result: Indirectly the data acquisition system contributed to the realisation of the objectives. The data acquisition system on the North and South riverbank functioned well. Due to external factors (e.g. power failure) some repairs were necessary. The modem connection of the South bank to the measuring computer on the North bank functioned unsatisfactorily due to bad coverage of the GSM network at the Southern measuring area. However, this did not result in loss of measuring data. - Recommendation for future projects: Application of an automatic measuring system with a fixed telephone connection is preferred. However, given the fast development of wireless telecommunication techniques, it is expected that GSM connections nowadays are more reliable.

8.4 TUNNEL CONSTRUCTION

GENERAL REMARKS In two tunnel rings instruments were applied to determine in particular the load on and the forces within the tunnel construction. This is further differentiated into: - determining the internal forces in the segments, - determining the total earth pressure on the segments, - determining the deformations over the joints of the segments. The specifications prescribed to apply three measuring rings. Due to economy considerations eventually only two rings were instrumented. For the second ring use was made of the experience gained with the first ring, for instance by additional instrumentation of the key segment. Two measuring rings are in principle insufficient to associate the changing bore parameters with the depth of the tunnel, soil conditions and the measured ring parameters. Nevertheless, given the enormous effort demanded to process and interpret the measuring results, it can be concluded that a total of two instrumented rings sufficed to increase understanding. The measuring rings were originally projected at the locations with concentrations of geotechnical measurements in the measuring areas. However, for construction technical reasons the measuring ring in measuring area South was moved, which disrupted the relation between ring measurements and measurements of the surroundings. It must be concluded that this should not have happened.

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Figure 71: Strain gauge embedded in concrete.

EVALUATION OF INDIVIDUAL INSTRUMENTS AND MEASUREMENTS Embedded strain gauges - Measuring objective: Determining axial and tangential forces in the lining. - Measuring method: Embedded strain gauges. The employed measuring method was in principle a good choice. Given the fact that there is no even pressure situation in the elements, the strain measurement was insufficient only at a few places. Based on the elaborate additional three-dimensional analysis the strain measurements could be interpreted correctly. For measuring the total axial and tangential normal force, pressure boxes at the contact surfaces between the segments could be interpreted easier. However, for determining the moments in periphery direction no real alternatives are available. - Number/position: In hindsight a larger density of gauges was desired due to the uneven pressure situation in the segments. This asks for dense instrumentation. Additionally, around the key segment a more intensive instrumentation was desired to research the occurrence of pressure concentrations. - Type of instrument: The string strain gauges proved very stable and accurate. Still, temperature influences occurred which could not be corrected on the basis of the temperature corrections given by the manufacturer. This is the case because the temperature correction in the factory is only valid for ideal circumstances (free expansion of concrete). The range of the gauges was more than sufficient. - Realisation of measurements: The measurements have been and are still conducted using four data loggers, which are centrally read by a measuring PC. The cables making this possible proved to be vulnerable, especially on the long-term. This caused the measuring system to break down several times. Nevertheless, measurements have been done approximately 85% of the time. This percentage is fully acceptable, considering that the monitoring of the measuring system from a distance, as was planned, was not feasible. This made immediate intervention during incidents impossible. With regard to the measuring frequency, it has to be noted that only in the first few days after installation measurements were done with a frequency of once per minute. Later the changes in strains and stresses were so small that a substantially lower sample time could be used, for instance

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once per 15 minutes. - Total result: The measurements resulted in more understanding of the forces in the segmented lining. In this respect the research objective was fulfilled.

Embedded pressure boxes - Measuring objective: Determining total earth pressure on the segments. - Measuring method: Pressure boxes embedded in concrete. Interpretation of the readings of pressure boxes proved not as simple as temperature- dependent reading. This is the case because the mercury in the pressure boxes can freely change shape due to its enclosure between concrete and grout. Consequently, an apparent increase of the pressure occurs when the temperature rises. This effect is especially important on the long-term as the tunnel slowly heats up. However, before this effect can be corrected, it has to be measured over a longer period of time. This enclosing effect does not play a role in the fluid phase of the grout. Hence, the employed pressure boxes are suitable for measuring the grout pressures directly after injecting with grout. - Number/position: Two pressure boxes per segment were used, which gave a reasonable impression of the pressure development. The location of the injection points proved to have influence on the measured pressures. Thus near the injection points a more intensive measuring could be considered. - Type of instrument: The pressure boxes work according to the string strain gauge principle and are therefore very stable. The enclosure effect, as mentioned, severely limits the use, because it can only be compensated by long-term measurements. The accuracy after correction for temperature effects amounted to approximately 1 kPa. - Realisation of measurements: The same measuring system as for the string strain gauges was used. - Result: The objective was to follow the development of the radial load on the lining over time. This proved extremely difficult, especially because it seems as if the grout shield freezes the measurements in the pressure boxes. This makes it difficult to interpret the pressures after setting of the grout. Therefore, the objective was only partly attained.

Tachymeters - Measuring objective: Determining the ovalisation of a ring. - Measuring method: Tachymetrics. Opted was for an automatic measuring system with a fixed tachograph. Several measuring points were equipped with prisms. Generally this system functions very well, though it does know limitations because the measuring points cannot be calibrated and referenced due to the presence of backup trains. Thus, this applies especially to the bottom half of the tunnel. It is recommended to conduct additional measurements in future ovalisation measurements. - Number/position: For a global impression of the ovalisation the chosen places for the prisms (on the corners of a segment) functioned sufficiently. For a more accurate picture of the ovalisation at least the middle of a segment needs to be measured as well. - Type of instrument: The chosen set up offered an accuracy of approximately 0.5mm in determining the ovality. The measured ovalities were of the order of 1mm to 5mm, so that the accuracy in hindsight would have been better at 0.1mm. The ovalisation expected beforehand was much greater and the accuracy was tuned to that.

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- Realisation of measurements: The measurements were conducted automatically from 1 November to 7 November 1997. The measuring system proved to function reliably during this period. However, the prisms proved to be vulnerable in spite of a protection brace. - Result: The measurements provided a global picture of the ovalisation, as was the original idea.

Sub-surface soil radar measurements - Measuring objective: Determining the thickness of the grout shield at the three rings, amongst which measuring ring North. - Measuring method: Sub-surface soil radar. The measuring results proved difficult to interpret and are in fact still subject to discussion. - Type of instrument: There is still little experience with using sub-surface soil radar for these type of measurements. Amongst others, the influence of reinforcement on the measurements has been qualified insufficiently. - Result: The research objective was actually not met, since there is still insecurity about the interpretation of the measuring results.

Displacement gauges - Measuring objective: Determining the reciprocal displacement of the segments in axial and tangential direction. - Measuring method: Displacement gauges. The measuring method functioned very well. - Number/position: In both measuring rings the reciprocal displacement between the rings was measured at six places in three main directions. - Type of instrument: Electrical displacement gauges with a measuring accuracy of approximately 0.01mm were applied. These instruments functioned well. - Realisation of measurements: No problems occurred. - Result: The chosen application of joint displacement gauges was insufficient to obtain a good idea of the joint behaviour, considering the three-dimensional character of the force effects. It would be preferred to conduct axial and tangential joint displacement measurements on all corners of the segments. However, this would lead to disproportionate costs increases. Application of additional tachy measurements proved to be useful.

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BIBLIOGRAPHY

[1] CUR/COB commissie L520, Richtlijnen boorfrontstabiliteit, version 1, GD-report CO-372590/197. [2] K100/BTL report ‘Validatie 3D numerieke rekenmodellen aan de hand van centrifugeproeven,’ Geodelft report CO372590/45, October 1997. [3] Stichting van Tunnels en Leidingen, ‘Theorie en proeven statische afpleistering,’ BTL report 34, January 1998. [4] Leca, E. and E. Dormieux, ‘Upper and lower bound solutions for the face stability of shallow circular tunnels in frictional material,’ Géotechnique, 40, no 4, 581-606. [5] Stichting Boren van Tunnels en Leidingen, ‘Afpleistering en Mudspurt tijdens boren,’ BTL report 27, April 1997. [6] CUR/COB commissie L520, report L520-16, ‘3D Validatie groutdrukmodel meetveld noord,’ concept 1, August 1999. [7] Sagaseta, C., ‘Prediction of patterns of soil deformation around shield tunnels,’ PGT 7 Syllabus PAO-cursus ‘Praktijkonderzoek geboorde tunnels en ontwerpmethoden,’ 1999. [8] Verruijt, A. and J.R. Booker, ‘Surface settlements due to deformation of a tunnel in an elastic half plane,’ Géotechnique 46:4, 1996, 753-757. [9] Oteo, C.S. and C. Sagaseta, ‘Some Spanish experiences on measurement and evaluation of ground displacements around urban tunnels,’ in: Geotechnical Aspects of Underground Construction in Soft Ground (R.J. Mair and R.N. Taylor, eds), London, 1996, 731-736.

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REPORTS PUBLISHED BY CUR/COB COMMISSION K100

K100 BASIC DOCUMENTS

COB K100 – 01 K100 Members Instrumentation and Measuring Plan COB K100 – 02 K100 Members Prediction Plan COB K100 – 03 K100 Members Evaluation Plan COB K100 – 04 K100 Members Prediction Report COB K100 – 05 K100 Members Instrumentation and Measuring Report COB K100 – 06 K100 Members Evaluation Report COB K100 – 07 K100 Members Final Report

COB/K111-W-001 Experimental Research of Slipping Behaviour of Ring Joints

K100 WORK REPORTS

K100-W-001 Work Document for Instrumentation and Measuring Plan K100-W-002 Work Document for Prediction Plan K100-W-003 Conceptual Specification of Instruments for TBM Second Heinenoord Tunnel K100-W-004 Set of Parameters for Predictions

K100-W-005 TBM Second Heinenoord Tunnel - Specification and Procurement Plan for the Instrument and Data Acquisition System K100-W-006 Additional Soil Research Second Heinenoord Tunnel: Phase 1

K100-W-007 NEN-plots Triaxial Tests Second Heinenoord Tunnel K100-W-008 Bored Railway Tunnels in the Netherlands K100-W-009 Deformation in Soil, Stress Changes in the Surroundings, Pressures of the Soil on the

Tunnel Lining K100-W-010 Tangential Interaction between Segments K100-W-011 Axial Interaction between Segments of the Lining

K100-W-012 Ring Deformations in Relation to Second Order Effects K100-W-013 Influence of the Grout on the Behaviour of the Tunnel: Prediction Programme for the Pilot Project Bored Tunnels

K100-W-014 Predictions for Bore Technology B-01 and B-02 K100-W-015 Influence of the Water Pressure on Face Stability, Prediction B01D K100-W-016 Pilot Project Bored Tunnels K100, Cluster 1: Wear of Cutting Elements - Prediction B-

06a K100-W-017 Determining the Axial and Tangential Friction of the TBM K100-W-018 Statistical Analysis of Cone Resistance: Predictions of Monitoring by K100 K100-W-019 Beam Reaction of Tunnel Tube K100-W-020 Buoyancy and Breaking of Tunnels K100-W-021 Soil Deformations, Pressure Changes in the Surroundings and Pressure on the Two Tunnels K100-W-022 Ring Behaviour of a Segmented Lining K100-W-023 2D Predictions Face Stability K100-W-024 Prediction Cluster 3 K100-W-025 Specification of the Instrumentation of the Measuring Rings for the Second Heinenoord Tunnel K100-W-026 Laboratory Testing of Tunnel Segments K100-W-027 Additional Soil Examination II: Slurry K100-W-028 3D Predictions for the Southern Measuring Area K100-W-029 Specification and Scenario for the Measuring Areas of Second Heinenoord Tunnel K100-W-030 Disturbance of the Local Groundwater Flow

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K100-W-031 3D Predictions for the Northern Measuring Area K100-W-032 Experimental Research of the Behaviour of Bordering Layer of Construction vs. Soil K100-W-033 Predictions of Slurry Fluids B08 and B13 Second Heinenoord Tunnel K100-W-034 Flow Processes in the Mixing Chamber of the TBM K100-W-035 Pilot Project Bored Tunnels: Determining the Efficiency of Pumps and Transportation Pipes K100-W-036 Specification of Deformation Measuring K100-W-037 Influence of Face Stability; Experimental Prediction V10 of the Northern Measuring Field K100-W-038 Plan for Predictions for Bore Technology K100-W-039 More Precise Determination of Loss of Volume at the Second Heinenoord Tunnel K100-W-040 Prediction Cluster 8 K100-W-041 Prediction Cluster 8: Statistical Analysis of Soil Examination K100-W-042 Pre-evaluation of Research in Bored Tunnels K100-W-043 Geotechnology K100-W-044 Pre-evaluation of the Research Programme of the Tunnel Construction at the Second Heinenoord Tunnel K100-W-045 Quality Analysis for Complex Measuring Programmes for Underground Construction K100-W-046 TBM Second Heinenoord Tunnel: Functional Checks on the Instrumentation and Data Acquisition System K100-W-047 Prediction of Torque and Thrust Forces

K100-W-048 Strain Gauges and Earth Pressure Boxes Instrumentation of Measuring Rings of the Second Heinenoord Tunnel K100-W-049 Project Proposition for Static Pressure Test

K100-W-050 Complete Scenario: Testing and Measuring Programmes COB at the Second Heinenoord Tunnel K100-W-051 Instrumentation of the Second Heinenoord Tunnel at Measuring Area North

K100-W-052 Measuring Plan Monitoring Environmental Effects K100-W-053 Measuring Cutting Teeth, First Tunnel Tube K100-W-054 Calibration Measuring Rings

K100-W-055 TBM Second Heinenoord Tunnel: Functional Checks on the Instrumentation and Data Acquisition System at Barendrecht K100-W-056 Manual of Data Files

K100-W-057 Presentation of TBM Measurements done at the First Passing of Measuring Area North K100-W-058 Evaluation Bore Technology: Section 1 Measuring Area North K100-W-059 Evaluation Geotechnical Measuring of Measuring Area North (First Passing)

K100-W-060 Measuring Report Measuring Ring North of the Second Heinenoord Tunnel, Period of 3 - 17 April 1997 K100-W-061 Second Order Evaluation Tunnel Construction Second Heinenoord Tunnel -Part 1

K100-W-062 Instrumentation Measuring Area South Second Heinenoord Tunnel K100-W-063 Measuring Report Measuring Ring North of the Second Heinenoord Tunnel, Period of 17 April - 13 June 1997 K100-W-064 Passing of Western Tube through Measuring Area North of Second Heinenoord Tunnel K100-W-065 Presentation TBM Measurements of the Second Passing (through Sand Layer) K100-W-066 Second Order Evaluation Tunnel Construction Second Heinenoord Tunnel -Part 2 K100-W-067 Presentation of TBM Measurements for the Third Passing (50% Clay) and Appendixes K100-W-068 Presentation of the TBM Measurements for the First Passing of Measuring Area South and Appendixes K100-W-069 Second Order Evaluation Bore Technology First Passing Measuring Area South and Appendixes K100-W-070 Passing of the Western Tube through Measuring Area South of the Second Heinenoord Tunnel K100-W-071 Evaluation Geotechnical Measuring of Measuring Area South (First Section)

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K100-W-072 Measuring Report Measuring Ring South of the Second Heinenoord Tunnel, Period of 3 - 27 November 1997 K100-W-073 Performance of the TBM at the Surface K100-W-074 Deformation Measurements of Tunnel Rings in and directly behind the TBM in the Second Heinenoord Tunnel, First Tube Measuring Area South K100-W-075 Evaluation of Deformations of the Tunnel Lining in and directly behind the TBM at the Second Heinenoord Tunnel K100-W-076 The Tunnel Boring Machine as a Source of Seismic Signals and Stress Measuring during the Boring of the Second Heinenoord Tunnel K100-W-077 Predictions of the Environmental Effects of the Slurry and the Excavated Soil Fractions of Pilot Research Bore Tunnels K100-W-078 Sample Analysis of Bentonite and Soil Fractions K100-W-079 Deformation Measurements of Tunnel Rings in and directly behind the TBM in Second Heinenoord Tunnel, Second Tube Measuring Area South K100-W-080 TBM Measurements in Measuring Area South II; 24-Hour Presentation K100-W-081 Second Order Evaluation Bore Technology, Second Section Measuring Area South K100-W-082 Prediction of Static Load Test Second Heinenoord Tunnel K100-W-083 Section Eastern Tube Measuring Area South Second Heinenoord Tunnel K100-W-084 Measuring Report Measuring Ring South in the Second Heinenoord Tunnel, Period of 17 - 28 March 1998 K100-W-085 Evaluation Geotechnical Measurements in Measuring Area South, Second Passing

K100-W-086 Second Order Evaluation of the Tunnel Construction of the Second Heinenoord Tunnel – Part 3 K100-W-087 Plan of Experiments TBM

K100-W-088 Evaluation of Deformation of the Lining in and directly behind the TBM at the Second Heinenoord Tunnel, Period of 21 - 28 March 1998 K100-W-089 Eastern Tube Measuring Area North of Second Heinenoord Tunnel

K100-W-090 Evaluation of Geotechnical Measurements Measuring Area North, Second Passing K100-W-091 Presentation of TBM Measurements of Second Passing Measuring Area North K100-W-092 Second Order Evaluation Bore Technology of Second Passing of Measuring Area North

K100-W-093 Report on Radar Research Second Heinenoord Tunnel (Cyclist Section): Measuring the Thickness of the Grout Shield K100-W-094 Measuring Report Measuring Ring North of the Second Heinenoord Tunnel, Period of

1 January - 30 June 1998 K100-W-095 Second Order Evaluation Tunnel Construction of the Second Heinenoord Tunnel - Part 4 K100-W-096 Deformations Measurements Part A: Long-Term and Macro Deformations

K100-W-097 Final Report B446 Calibration Bentonite Tube K100-W-098 TBM: The Second Heinenoord Tunnel - Evaluation of Experience with the Integral Measuring System

K100-W-099 Development of Pressures, Forces and Torques on and inside the Lining of the Second Heinenoord Tunnel Part 1: Analysis K100-W-100 Development of Pressures, Forces and Torques on and inside the Lining of the Second Heinenoord Tunnel Part 2: Measuring Report K100-W-101 Experimentally Determining Dependence on Temperature of Pressure Boxes Used in the Second Heinenoord Tunnel K100-W-102 First Order Evaluation K100 BT-A Bore Face Stability K100-W-103 First Order Evaluation Bore Technology of Second Heinenoord Tunnel K100-W-104 Post diction Wear of the Cutting Teeth K100-W-105 First Order Evaluation: Deformations and Soil Examination K100-W-106 First Order Evaluation: Influence of Boring of the Second Tube on the First Tube K100-W-107 First Order Evaluation: Tunnel Construction K100-W-108 Evaluation Instrumentation Second Heinenoord Tunnel K100-W-109 First Order Evaluation: Plan

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Appendix 1 RESEARCH OBJECTIVES K100

EXPLORATION AND MONITORING OF THE UNDERGROUND (G-00) In order to explore and monitor the underground, the following research objectives were defined.

G-01 Determining the underground situation In order to determine the soil in the tunnel surroundings to benefit the design of the tunnel, conventional soil research is necessary.

G-02 Recording additional information about the soil Additional soil research is necessary for the design of the bored tunnel which will function as pilot project. In addition to cone penetration tests and borings (Begemann 66mm), which are required for a standard design, the following researches need also be conducted: triaxial tests (triaxial compression and extension), and free torsion vibration test (for vibration measurements).

G-03 Detection of foreign objects in the underground In this particular case, erratic boulders and remnants of primeval forest are considered to be foreign objects. Elsewhere foreign objects such as shipwrecks may also be found. Detection of such foreign objects is difficult. The idea is to conduct such research by means of sub-surface soil radar or other non-destructive techniques (NDT). In order to do this, a thin borehole casing needs to be bored along the distance of the bored tunnel. From this casing non-destructive techniques can be used to detect obstacles. The costs are high. Therefore, research is initiated by estimating the chances of encountering foreign objects by means of geological analysis.

G-04 Measuring the effect of the tunnel on the ‘regional’ flow field of groundwater It has to be measured in what way the presence of the tunnel influences the regional flow pattern of the groundwater. This can be researched by placing piezometers left and right of the tunnel over its entire distance and monitoring these before and after construction.

The data are compared to prediction calculations. Any disruption of the regional flow field can cause an increased load on the tunnel tube. Environmental effects can also occur (see M-01).

waar is M-01?????

G-05 Determining the influence of the groundwater potential on deformations during the boring process Increasing water pressures as a consequence of the boring process may lead to ‘swelling’ of the soil. Moreover, drainage as a consequence of the boring process may lead to consolidation. Both have influence on the deformation of the surface, the strength of the soil and the earth pressure at the face of the TBM.

Both can be monitored by placing piezometers in the sand and in weaker layers of soil close to the face of the TBM.

The suggestion for this research is to fit out one section line as a monitoring section line. The tunnelling process must be able to take place undisturbed at 50m from both sides. Monitoring occurs by measuring the water pressure in every soil layer on both sides of the tunnel (at least two per layer) using pressure gauges and inclinometers/ extensometers. The data will be used to verify calculation (prediction) models.

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G-06 Determining the influence of stagnation on the groundwater pressures Only during stagnation are the generated overpressures consolidated away into the groundwater. Only remaining overpressures from the boring chamber remain intact. Monitoring these is possible by applying water-pressure gauges in the vicinity of the locations where stagnation occurs. However, this must be done in all locally present layers.

G-07 Determining the behaviour of groundwater/air during a ‘level drop’ of the bentonite (Absenkung) When replacing the bentonite in the boring chamber by air under increased pressure, air can permeate the soil body from the boring chamber. This may cause: pressure loss in the chamber, blow-out, and pressure building underneath badly permeable layers above the tunnel (buoyancy, loss of stability, etc.). Therefore, it is necessary to monitor the permeable layers above the boring location by measuring the pressures with water-pressure gauges. Deviances from the hydrostatic pressure indicate penetration of air into the soil body.

G-08 Searching for deformations during a ‘level drop’ of the bentonite During a bentonite-level drop, much happens to the pore pressures in the body. During the building and reducing of air pressure in the chamber, deformations in the soil body may arise. This process can be monitored using: water-pressure gauges, earth pressure gauges, and extensometers.

A3 BORING AND TUNNEL TECHNIQUES (B-00) Wat is A3? En waarom staan er wel nog A4, maar geen A2 en A1 eerder in dit stuk….? From bore-tunnel-pipes-research (BTL), the following research objectives were extracted: B-01 Determining the influence of the excavation process on the reaction forces of the cutting wheel on the soil body The reaction forces of the cutting wheel, also called the pressure changes, cause deformations in the surroundings of the bore face. In order to predict pressure changes knowledge about the collapse mechanism and the correlated cutting forces is a precondition. Therefore, known collapse mechanisms need to be tested, such as the occurrence of water overpressures or underpressures, the emergence of cracks or the slipping of surfaces. Moreover, the correlated forces on the cutting elements and the cutting wheel need to be tested. The latter can be done on the basis of existing models predicting the cutting forces of the individual cutting elements. In order to determine the soil parameters for the description and prediction of the collapse behaviour, an additional soil examination has already been defined. This research will answer the question to what extent the water pressure (overpressure or underpressure) generated by the cutting teeth change the characteristics of the soil body. From this answer, the influence of the water pressure on the stability of the soil body can be determined.

B-02 Determining the influence of the excavation process on the size and the degree of deformation of the product units The collapse mechanism, the progress speed of the TBM and the rpm influence the size and the degree of deformation of the product units. This excavation process is important for testing of the existing segregation and disintegration models of soil.

B-03 Description of the process of mixture forming as transfer between excavation and transport

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In order to maintain an optimal boring speed, the mixture forming needs to be tuned to the excavation and transport. For a correct tuning, modelling of the mixture forming is necessary. This is done on the basis of models pronouncing upon: the flow conditions in the mixing chamber. The results will be tested on existing models in the field of turbulent and viscous flows. the influence of disintegration (by dilatation, softening or collisions) on the size of the production units. Description of mechanical and erosional behaviour will be done on the basis of existing failure and ripping sensitivity and softening models. and the segregation of the production units in the mixture resulting from the density difference between production unit and slurry. The results serve to test existing segregation models. These models also consider the effects of the concentration of solid material in the mixture (hindering effect) and the rheological characteristics of the mixture.

B-04 Determining the influence of the slurry pressure on the stability of the bore face In order to control settlements of the surface and to prevent calamities, the interaction between the slurry (mixture of bentonite and soil) and the bore face needs to be described. Grondmechanica Delft13 determines the condition of the soil before the TBM disrupts it. During the boring process measurements need to be conducted that determine the ‘in-situ’ condition of the soil. These measurements must pronounce upon the size of deformations, changed water pressures, groundwater flows and penetration of bentonite in the vicinity of the face in relation to slurry pressure and consistency of the mixture. These data are tested on existing models for the calculation of the stability of the soil body (‘active’ or ‘passive’).

B-05 Determining the effectiveness of the pumps and transport pipes In order to transport the heterogeneous mixture as effectively as possible, the pump pressures need to be adjusted to each other. Therefore, measurements are required. These measurements will be tested on experiences already existing in the dredging world. This way sedimentations and the occurrence of clay balls can be prevented.

B-06 Determining wear of bore face, pumps and pipelines In order to calculate production well, knowledge about the lifespan of the equipment, which is being exposed to abrasive wear, is essential. This way the lifespan of the cutting elements can be predicted. Replacing these elements is a time-consuming and dangerous operation. Therefore, it must be prevented that the elements are worn before the entire distance has been bored. The measurements of the elements serve to determine the wear mechanism, in particular whether it concerns two or three bodies wear. Based on the subsequent testing on existing formulas the weight difference of the cutting element will be calculated.

B-07 Determining the stability of the bore face when boring simultaneously through drained and undrained layers of soil This point connects to B-04. The problem with boring in a layered underground is that the mixing system (slurry shield) only partly meets the demanded functions, especially in non-draining layers. Generally an EPB-shield (Earth Pressure Balance Shield) is used in case of non-draining layers. Variation of the consistency of the mixture must bring to light which is the best mixture composition when boring through a layered soil structure.

B-08 Determining the consequences of standstill of the TBM on the stability of the bore face During the interruptions of the boring process the consistency of the mixture must change in such a way (think for instance of thixotropic characteristics) that the stability of the face remains guaranteed. The change in consistency of the mixture (behaviour of strength vs. strain, and strength vs. rate of strain) is being measured during the interruption and tested on the existing rheological models, which are based on the behaviour of Bingham’s fluids.

13 Dutch company, renamed Geo Delft.

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B-09 Determining the axial and tangential friction along the periphery of the TBM In order to determine axial and tangential friction along the periphery of the TBM the torque on the cutting wheel is measured to determine the torsion. In addition, the jack forces are measured to determine the axial friction along the periphery of the TBM.

B-10 Determining the volume change of the soil at the face During boring the amount of excavated soil needs to equal the product of the progress speed and the surface of the TBM. If this is not the case, deformations in the soil will occur because the extra created cavity around the TBM is being filled up with soil.

B-11 Determining the cyclic behaviour of the soil under influence of vibrations The TBM causes vibrations in the soil during boring. This gives problems with the stability of the bore face because liquefaction of the soil body can occur.

B-12 Determining the influence of the boring process on the mechanical characteristics of the soil Directly in front of the face plastic deformation of the soil body occurs. The shape in which this deformation occurs depends on the type of soil. There are different calculation models written to describe this deformation. These calculation models also describe with which minimum and maximum slurry pressure a stable face is still possible.

Due to plastic deformation of the packed granular material the density of the sand and water underpressures change. Plastic deformation of clay and packed sand leads to water overpressures. By carrying out soil-drilling tests over several meters (roughly half the tunnel diameter) using a piezocone with an electrical density measurement, it can be determined at which distance from the face of the TBM plastic deformation occurs. It goes without saying that such soil-drilling is done from the bore shield. Therefore, the design of the TBM needs to provide for this.

B-13 Determining the influence of the boring process of the pressure distribution in the groundwater It must be determined how the boring process influences the pressure distribution of the groundwater at the bore face in relation to the stability of the face.

A4 CALCULATION MODELS FOR DEFORMATION AND VIBRATIONS (V-00) A number of the following research objectives was deduced from questions posed by the designers. V-01 Researching the behaviour of the rubber sealing profile The tunnel is closed by means of a rubber sealing profile. How does this profile behave in a loading phase and over time (relaxation)? Are optimisations possible? Research needs to be conducted into how the profile behaves in the loading phase and over time. Much quantitative research has already been done into sealing profiles. Therefore, a large part of this research will comprise of literature research.

V-02 Detection of the changes in soil structure To get an impression of the disrupted zone around the tunnel and to determine the soil structure in order to predict deformations, it is useful to conduct cone penetration tests from the tunnel. It can be considered to conduct this research both from the side of the tunnel (through the segments) as well as moving ahead before the face of the TBM.

V-03 Determining the dynamic interaction between tunnel and soil The facility of soil-drilling from the tunnel can also be used to conduct vibration measurements in the soil close to the tunnel. Such measurements provide information about dynamic tunnel-soil interaction and about the relation between the emission model and the transmission model. Such measurements have never been conducted previously, as far as known.

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V-04 Determining boring vibrations in the tunnel The vibrations in the tunnel must be measured during the boring process to determine the axial decrease of these vibrations. The measurements are conducted on the TBM.

V-05 Validation of the vibration model of vibration transmission in the soil (implementation phase) The vibrations in the surroundings are measured during the boring process at: various distances on the surface, a depth in a layer that can intercept the vibration, and at an adjacent instrumented pile.

These measurements must be conducted both before and after a long standstill in order to measure the influence of the setting of the grout.

V-06 Validation of the vibration model of vibration transmission in the tunnel (phase of use) The vibrations will have to be measured in the completed tunnel as well. The tunnel will be made to vibrate by means of a falling weight or an eccentric. Both the radial and the axial vibrations must be measured and the decrease of the vibrations in axial direction.

V-07 Validation of the vibration model of vibration transmissions in the soil (phase of use) The vibrations have to be measured when the complete tunnel will be made to vibrate, which will be done by means of a falling weight or an eccentric. The vibrations will be measured in the surroundings on the surface at several distances, at a depth in a layer which can intercept the vibration, and at an adjacent instrumented pile.

V-08 Determining deformation of the tunnel The position, settlement and deformation of the tunnel need to be determined from the moment of construction until even when the tunnel is already in use. This can be accomplished by means of an automated measuring system. This kind of measuring is especially interesting when boring the second tunnel next to the first. When conducting these measurements, the displacement and rotation of the tunnel over several joints in the to be tested cross-sections as well as ovalisation of the tunnel in several cross-sections need to be considered over a longer time, too. It is desirable to use an automated measuring system for this. This way the measurements can be carried out more or less routinely on fixed times.

V-09 Determining deformation in the surroundings Measurements must yield a three-dimensional image of the deformation in the surroundings of the boring process. More precise, these measurements need to be taken at the moment the TBM shield approaches, the moment the shield passes and several times (in the course of time) after it has passed. Information is not only needed about deformation of the surface, but also about deformation vertical in depth. In short, a complete three-dimensional picture must be formed. To execute this research a three-dimensional network of synthetic tubes would work as any change in its position can accurately be determined.

The deformation is caused by the influence of the support of the TBM’s face and the influence of the tail effect. Both influences are addressed in V-10, respectively V-11.

V-10 Determining the influence of the support of the TBM’s face The relation between the size and the shape of the pressure distribution, which is exerted by the TBM, and the influence of the boring process on the surroundings needs to be determined. It is useful to vary the pressure and measure its influence on the surroundings, of course only within still to be determined boundaries such as ‘water pressure + active effective earth pressure’ and ‘water pressure + passive effective earth pressure.’ Decrease of the pressure caused by a calamity can have major consequences, i.e. instability of the face. Evaluation of the measured results using a three-

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dimensional calculation model can provide understanding about the three-dimensional effect. This effect could then possibly be translated into a three-dimensional factor which can be used in combination with two-dimensional analyses.

V-11 Determining the influence of the tail effect The transfer from the TBM unto the lining is also a cause of deformations. When boring, ‘over cutting’ occurs, which means that the bore shield excavates more material than can be filled by the circumference of the lining. This space has to be filled by means of a grout injection. It is important to know what the effect is of applying the grout in this way, of the height of the grout pressure on the settlements in the surroundings and of the loads on the tunnel.

V-12 Determining the pressures in the surroundings The initial vertical pressure can be determined accurately from drillings. From a combination of the results of a cone penetration test and a pressiometer test a reasonable estimation of the initial horizontal pressure can be given.

Changes of the pressure in the soil as a consequence of an approaching bore tunnel can be registered by gauges being pushed away. In addition, it can be considered to carry out cone penetration tests during and after the boring process.

Water pressures generated in the vicinity can be registered by means of water-pressure gauges.

V-13 Determining the influence of boring on pile foundations in the vicinity In order to predict the models which describe what the influence of the boring process is on the constructions in the vicinity, it is useful to drive some piles into the soil in the vicinity of the tunnel and load these to a certain level of use. During and after passing of the bore shield the settlement of the piles and the change in the relationship between (pile) point resistance and shield friction can be registered as well as the bending moments occurring in the piles, which are the result of horizontal ground movements. It is important to inventory the differences between the different types of piles (e.g. displacing and not displacing soil).

V-14 Determining the ring stiffness of the tunnel construction (constructive aspects) To get an idea of the total ring stiffness of the construction, it is useful to measure the displacement of the tunnel lining as caused by the thrusting of the jacks in the tunnel. In a calculation model this ‘overall’ stiffness must more or less match reality. This type of measurement is not only of importance to the evaluation of the stiffness of the tunnel lining but also to the determination of the bed constant (for the benefit of the ‘spring models’ often used in practice). This measurement can be conducted at several locations, in several directions and over different segments.

V-15 Determining the influence of the shape of the grout shield around the tunnel construction Using non-destructive techniques it is possible to get an idea of the shape and the thickness of the set grout layer around the tunnel construction. When the measuring signal of the ‘tunnel-grout-soil’ total is being compared to the reference signal of just the sum of ‘tunnel-grout’ a reasonable estimation of the thickness of the grout layer can be obtained. Understanding of the distribution of the grout layer around the tunnel is useful for things such as water density, but also for understanding of the friction behaviour of the tunnel in axial direction (decrease of prestress in longitudinal direction of the tunnel).

V-16 Determining the interaction between soil-grout-tunnel construction The interaction between soil-grout-tunnel construction can be determined by validation of the modelling of the interfaces between construction and the soil. In the laboratory shear tests (‘direct shear’) can be conducted on interfaces consisting of ‘tunnel-grout’ and ‘grout-soil’ in order to gain understanding of the transfer of shear stresses between materials.

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V-17 Determining the soil pressures on the tunnel construction Knowledge of the soil pressures are important for several design models for the tunnel construction. Soil pressure boxes can be built into the tunnel segments to register the pressure on the tunnel construction, both during construction and use of the tunnel.

V-18 Determining deformations due to leakage These measurements determine the settlement, consolidation and creep due to drainage of the soil through leakage of the tunnel lining.

V-19 Determining the tangential interaction between the segments The tangential interaction between the segments involves four aspects. The first aspect concerns the moment capacity of the connection between the segments. During construction the segments can be connected with bolts. In a later phase these can be removed. The simplest schematisation for the connections is a hinge, which is used in the calculation. Question is to what extent this hinge is too much of an adverse schematisation of reality. The bolts may add to the moment capacity of the connection. This also applies, possibly even more so, to the normal force in the connection, which works as prestressing force, and to the effect of the adjacent ring, which is stiff at the hinge. Thus, the measurements answer the question ‘What is the size of the moment capacity of the connection between the two segments?’

The second aspect of this research concerns the size of the contact surface between the segments. Currently it is assumed in the calculations that the contact surface amounts to approximately 0.5 to 0.3 times the size of the entire cross-section. Is this schematisation a good approximation?

A third aspect concerns the stiffness of the tunnel ring as a whole. The hinges lead to weakening of the ring and hence a reduction of the stiffness. However, calculations assume a stiffness of 0.8 times the undisturbed stiffness.

A fourth aspect concerns the occurrence and size of possible pressure concentrations as a result of the presence of bolts. As mentioned before, the bolts may provide moment capacity but they may also lead to (unwanted?) shear force capacity. It must be examined how the connection between the segments (shells) behaves under influence of: bolts (moment and shear force capacity), normal force (eccentric), and adjacent rings.

Furthermore, it needs to be determined which part of the complete cross-section transfers the force (size of contact surface).

Thirdly, the occurring stiffness of the rings needs to be determined.

(a) (b) (c) The research can be conducted for the composition of two segments in one ring (a) and for the

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composition of four segments (b) or eight (c) segments in three rings (respective configuration 1-2-1 or 3-2-3). This research could be done in a laboratory and by use of numerical models, after verification.

The ring stiffness must be determined in-situ for the complete ring.

V-20 Determining the axial interaction between the segments The axial interaction between the segments involves three aspects. Firstly, an axial force is initiated in longitudinal direction from the TBM into the segments. This axial force contributes to the connection between the rings because a friction force can be developed between the segments in longitudinal direction, which possibly absorbs an uneven shear force. This force is also of importance for possible cross-connections, where rings are partly or completely transected. As a consequence of creep and relaxation part of this force flows away.

A second aspect concerns the size of the axial forces in the curves. The TBM is steered by varying the jack forces on the already placed segments. Therefore, the TBM is pushed around the corner, as it were. The jack forces can lead to cracking of the concrete of the segments.

Thirdly, there is the question whether rubber support strips need to be applied between the rings to absorb the jack forces from the TBM. When these support strips are applied, what is their influence on the axial force (creep, relaxation)? When these strips are not applied, what is the size of the contact surface between the segments? It needs to be examined to what extent the distance to the face influences the decrease of the axial force and how this force is divided over the ring (at the hinges). This should also take the distribution of forces over the ring in the bends into account.

In addition, the influence of the support strips need to be considered. Is it possible to assemble the segments on each other coldly, and if so, what type of contact surface needs to be looked at?

The research must be conducted over several rings (straight, vertical and horizontal curve, possibly several curve radii) and per ring over the entire periphery. The contact surface research could be combined with research of the tangential interaction between the segments. Part of the research can be done in a laboratory and after verification by means of numerical models.

V-21 Determining the relation between vertical ovalisation and vertical equilibrium The bore tunnel should in principle comply with three equilibrium criteria, that is blow-out, vertical equilibrium and breaking. The criterion of breaking is relevant when a tunnel of shallow depth wants to vertically ovalise as a result of relatively large horizontal forces. The soil above the tunnel then is not interpreted as a supporting construction but as equalising load. The mechanism was used in a model (Wayss and Freytag). It needs to be examined whether there is a real chance that this collapse mechanism will occur in the Netherlands, for this has consequences on the ring stiffness of the tunnel tube. To what extent are existing foreign models applicable to Dutch circumstances? The model can be tested by putting a vertical ovalisation on the tunnel and then measuring the behaviour of the soil. This testing may also be executed in a geocentrifuge.

V-22 Determining the influence of the distance between the tunnel tubes When a second tunnel tube is being bored next to a previously bored tunnel tube, does the boring process of this second tube influence the force distribution on the first tube by means of soil arching? In addition to the foundation, the influence of this boring process also depends on the distance between the tubes. It needs to be examined to what extent the second tube influences the first tube. The distance between the tubes needs to be varied during this research. From how far in front of the TBM to how far behind the TBM occurs this influence, i.e. change of load? When does the arching disappear? Must in the end phase (which is the start of use of the tunnel) an extra load due to arching still be considered? The influence of the distance must be measured at several locations in the first tunnel tube. In addition to this distance, the foundation needs to be accounted for in this calculation

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as well.

V-23 Determining the tangential friction (soil-construction-interaction) The segments of the tunnel tube are supported by soil. In the calculations the soil is schematised as a two-dimensional bar model with radial support. The friction between the soil and the lining is being neglected in this calculation. Question is whether this schematisation is allowable. The soil could possibly support tangentially but could also exert an extra load tangentially. It needs to be researched whether tangential friction is a real influence. How large is the possible added tangential load/support and how big is the mistake made by this neglect? This research could be done in a laboratory.

V-24 Research into ring deformations in relation to second order effects The tunnel tube deforms as a result of the loads. The extent of deformation depends also on the stiffness of the tunnel ring. The deformations could lead to second order effects. These effects are currently neglected in the calculations. Therefore, the problem is two-part: What kind of deformations must be expected and what are the second order effects? On the basis of the measured deformations it must be determined whether the second order effects can be neglected. Therefore, the deformations must be measured at several places in the ring.

V-25 Researching eccentricities The segments are manufactured in a very accurately tuned or fabricated mould. Nevertheless, possible inaccuracies should be taken into account. It concerns inaccuracies which occur in the mould, while placing the segments, and the moment the segments leave the TBM. At these moments an uneven load occurs. To what extent do these inaccuracies influence the force distribution in the segments? Should these occurring eccentricities be taken into account and which of them have the greatest influence? What size are these eccentricities and are they dependent on the place of the segment in the ring? Part of this research consists of literature research.

V-26 Determining the influence of temperature on the segments The tube suffers temperature fluctuations. The temperature gradient is currently determined in these calculations over the thickness of the segments plus the thickness of the grout body. Is this assumption correct or should the gradient be determined only over the segment thickness?

The temperature influence is usually only marginal, but in case of fire an increased temperature should be considered. More precise, one should account for a temperature increase over the top part of the tunnel cross-section. In addition to construction-technical insecurity (such as increase of normal force and moment), there is also insecurity about the safety of the rubber sealing profile on the outside of the segments. To what extent are these profiles threatened by heat? Can a fire have such an influence that the temperature gradient should be considered in the calculation (duration of fire, heat)?

Secondly, it must be examined whether a fire can cause a threat to the rubber sealing.

Which segment thickness must be used as temperature gradient? How great is the influence of an (asymmetrical) fire on the force distribution in the ring? This examination mainly consists of literature research.

V-27 Determining the influence of cross connections For reasons of safety cross connections can be created between two adjacent tunnel tubes. At the location of a (future) cross connection the rings of the tunnel tube are partly or entirely interrupted in order to get a passage. The normal force in the ring concerned is ‘diverted’ around the interruption by means of extra reinforcement or steel segments. Therefore, the interruption leads to pressure concentrations and change of the loading circumstances on the main tube.

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In addition to cross connections, the tunnel may also be extended for electro-mechanic facilities. The same questions arise as for cross connections. It needs to be investigated: how the load and forces in the cross-section are distributed (over adjacent rings)at the cross connection, and what the influence is of another force distribution on the deformation of the interrupted ring and the adjacent rings.

It needs to be investigated how great the pressure concentrations can build up to be.

Beside cross connections it may also be a case of extending the tunnel for electro-mechanical facilities, which raise the exact same questions as for cross connections.

V-28 Determining the influence of the number of segments in a ring For the Second Heinenoord Tunnel was opted for a ring of seven segments and a key segment. The number and dimensions of the segments are determined by practical considerations. In particular the manageability of the segments plays an important part in these considerations. It may be possible to chose more or less segments in order to influence the size of the deformations and the force distribution. It needs to be examined whether choosing a different configuration influences the deformation and force distribution.

It may be researched what the effects is of, for instance, a ring with seven segments and a ring with ten segments. The total weight of a segment can be kept the same, only the dimensions need to change. How great is the influence of another configuration? Using the information stemming from research of joint interactions, a numerical model may suffice.

V-29 Researching the minimal segment thickness by application of a higher concrete strength class The concrete strength class applied to segments currently amounts to B55. Considering the present state of technique it is possible to apply higher concrete strength classes. This may reduce the thickness of the segments. Question is to what extent it is possible to reduce the thickness of the segments when considering durability and all the forces that are exerted on a segment (a.o. splitting force). Beside a higher concrete strength class, other types of concrete could be tested, such as fibre concrete.

By applying a different concrete strength class, the reinforcement may also be adapted. Possibly alternative reinforcement materials such as aramide fibres could be applied, which reduces the influence of corrosion.

It needs to be investigated how great the reduction of the thickness of the segments may be. In other words - What is the minimum thickness of the segments? Part of this investigation consists of literature research.

V-30 Researching segment types The shape of the segments can vary. The type which is most often applied has rectangular angles. However, conic variants are possible as well and have indeed already been applied. Conic types are particularly suitable to curvy tracks. Question is, however, whether segments other than with rectangular angles are accompanied by different (unfavourable) distribution of forces. It needs to be researched whether a deviation in the force distribution occurs as a result of applying a different segment type and if so, how great this deviation is.

V-31 Researching shapes of joints In addition to different types of segments, different types of joints are also possible, such as straight, bent, with or without an aligning key, and all in axial and/or tangential direction. The joint shape is also of importance to the water sealing. It needs to be researched what the constructive effect is of different types of joints. For this research a similar set-up as for V-19 can be used.

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V-32 Researching beam reaction of the tunnel tube When passing inhomogeneous soil, uneven settlements may cause the phenomenon of the tunnel tube acting as beam. This phenomenon mainly plays a part at the beginning and the end of the tunnel tube, where the TBM begins and ends in a pile founded transition construction. It must be researched to what extent the soil and the transition constructions influence the possible beam reaction. What are the consequences for the tunnel tube? Moreover, it needs to be examined whether it is feasible to increase the shear force capacity of the tunnel tube by means of external prestress. Finally, it needs to be examined to what distance the beam reaction can extend and how great its influence is. Part of this research will be literature research.

V-33 Researching new developments In addition to current conventional solutions, are there alternatives to be devised which can optimise the construction? The objective of such research is, for instance, to gain better interaction between segments and grout in order to achieve a thicker construction as it were, or to apply the ECL-method (Extruded Concrete Lining) to the Netherlands, or to develop other segments. Possible alternatives need to be examined.

Types of research The research suggested above in order to determine constructive aspects (that is questions posed by designers), consist of three types: 1. Measurements. The following actions are needed to conduct these: - applying a number of instrumented measuring rings, - applying a mesh of measuring points on the interior of the tunnel, - measuring the mutual deformations of the ring segments, - measuring all deformations by means of laser triangulation, - and measuring pressure boxes in the measuring rings over a longer period of time. These measurements concern instrumentations and experiments with codes I-06, I-07, E-05, E-08, and E-09. 2. Experimental research. Firstly, a test set up of one or more instrumented tunnel rings is erected in a laboratory. Then experimental research is conducted. It concerns an experiment with the code E-05. 3. Literature study.

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APPENDIX 2A POSITION CUTTING TEETH ON FACE OF TBM

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APPENDIX 2B POSITION CUTTING TEETH ON FACE OF TBM

POSITION PRESSURE GAUGES ON BAFFLE WALL

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APPENDIX 3 MEASURED FACE PRESSURE AND CALCULATED BOUNDARY VALUES

Tube 1 1101 Maximum Tube 1 1001 Average Tube 2 1002 Maximum Tube 2 1102 Average

Drawings added separately at the back of this report.

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APPENDIX 4A MEASURING SECTION LINES OF SURFACE SETTLEMENTS

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APPENDIX 4B MEASURING SECTION LINES OF SURFACE SETTLEMENTS

SURVEY OF MEASURING AREA NORTH DURING SECOND PASSING boorrichting tunnel 1: Bore direction tunnel 1 hart: heart boorrichting tunnel 2: Bore direction tunnel 2 x positie opnemer: x position measurement

NB MOET X NIET ° OF IETS DERGELIJKS ZIJN? En waarom staat deze niet aangegeven in bijlage 4A? !!!! (zie ook Appendix 4C)

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APPENDIX 4C MEASURING SECTION LINES OF SURFACE SETTLEMENTS

SURVEY OF MEASURING AREA SOUTH DURING FIRST AND SECOND PASSING boorrichting tunnel 1: Bore direction tunnel 1 hart: heart boorrichting tunnel 2: Bore direction tunnel 2 x positie opnemer: x position measurement

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Nederlands Engels 3d groudrukmodel three-dimensional grout pressure model A aandrukvijzels thrust jacks afstand (m) distance (m) afstand tot boorfront (m) distance to face of TBM (m) afstand tot de tunnelas en de verplaatsing distance to the tunnel axis and settlements afstand vanaf hart tunnel distance from heart of the tunnel Afzetvijzels Thrust jacks measurements Axiale verplaatsing en kanteling snijrad Axial displacement and tilting of the cutting wheel B belasting load belasting op de staartafdichting load on the seal of the tail belasting op drukschot load on the pressure partition belasting volgwagens load of backup trains Bentoniet bentonite Bentoniet toevoer bentonite supply bentonietdruk bentoniet pressure berekende en gemeten langstrog calculated and measured longitudinal trough berekende warden DIANA 3D three-dimensional calculated DIANA values Boorfront face of TBM Boorrichting direction of the TBM borstelafdichting brush sealing Bovenaanzicht view from above C centrifuge centrifuge contractiemodel contraction model D Data-acquisitiesysteem met een meetfrequentie van 1Hz data acquisitions system with a measuring frequency of 1Hz Debietmeting discharge Deformatie metingen Deformation measurements Dichtheidsmeting density dient te worden aangepast wedge. Jancsecz has to be adjusted diepte en verplaatsing depth (m+NAP) and displacements (m+100) Draairichting rotation direction druk (kPa) pressure (kPa) druk hoofdvijzels (MPa) pressure main jacks (MPa) Drukmetingen pressure Drukschot pressure partition Drukverschilmeting Pressure drukwand pressure partition duikwand baffle wall E eerste passage first passing effectieve korrelspanning effective earth pressure Elastisch voegmateriaal elastic joint material erector erector Extensometers Extensometer F fase in tunnelboorproces tunnel 1 phase of tunnel boring process tunnel 1 fijne zeef fine sieve G Gebied met waterspanning is kleiner dan de wig. Jancsecz is area with water pressre is smaller than the wedge. geldig Jancsecz holds geen overcutters not using overcutters gemeten boordruk bij tunnelas measured face pressure at tunnel axis (kPa) gemeten waarde measured value gemeten zettingen measured settlements gemiddelde groutdruk per ‘Vortrieb’tegen de positie van Average grout pressure per places ring

144 graafwiel cutting wheel grond soil Gronddrukdozen Earth pressure boxes grondpropkoppel soil plug torque grote cycloon large cyclone Grout grout grout aanvoer grout supply Grout injectie grout injection groutdrukmodel grout pressure model Grout injectie meting Grout injection measurements groutvilling grout filling/compensation grout grove zeef riddle (voarse sieve) H hellingbelasting op TBM en volgtrein load on the slope of the TBM and the backup train Hellingmeetbuizen Inclinometers het boorfornt in x’-richting plotted against the position of the faxe of the TBM in x’-direction hoek snijrad (graden) angle of cutting wheel (degrees) Holoceen Holocene Hoofdaansluitkast main System hoofdvijzelgroep group of main jacks hoofdvijzelkracht (MN) main jack force (MN) horizontale afstand tot as van de tunnel horizontal distance to the tunnel axis K kleine cycloon small cyclone Koppel torque koppel frontelementen torque of face elements koppel overgebracht door vijzels torque exerted by jacks kracht Force (kN) Kracht door boorfrontdruk force caused by face pressure kracht door wateroverspanning op schuine zijde van driehoek force caused by water overpressure on the hypotenuse of the soil wegde kracht op snijrad force on the cutting wheel Kracht op wig door boordruk force by face pressure on the soil wegde kromming curvature L Langsvoeg longitudinal joint lekkage leakage Luchtkamer air chamber luchtkussen air cushion luchtsluit air pressure cabin M maaiveldverzakking (m) surface settlement (m) maaiveldzettingen (mm) surface settlements (mm) mantelwrijving shield friction Meetring noord Northern measuring ring Meetring zuid Southern measuring ring Mengkamer mixing chamber Mengkamermetingen Mixing chamber measurements mengkoppel mixing torque Mengsel afvoer mixture discharge Meshoek angle of the cutting teeth Meshoogte cutting knife height meting (wsm5) measurement (water-pressure gauge 5) Metingen scheidingsinstallatie measurements separation plant Metingen tunnelboormachine measurements TBM Montagenok in ringvoeg assembly notch in the ring joint N netto effectieve kracht op wig net effective force on the wedge nieuw aangemaakte slurry fresh slurry noodafdichting emergency sealing Noordzijde North O ondersteuning support Oude Maas The river Oude Maas Overcutter overcutter P

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Peilbuizen Piezometers Pleistoceen Pleistocene pomp pump positie boorfront op x’-as position of bore face on x’-axis predictie prediction R Referentiepunt point of reference Rekopnemers Strain gauges ringnummer Ring number Ringvoeg ring joint rotatie rotation Rotatiesnelheid rotation speed S Samenstelling content Schild shield Schilddikte thickness of shield Segment segment segmenten segments slappe grond soft soil slib mud Snijdiepte cutting dept Snijelement cutting element snijkoppel frontelementen torque of the cutting elements of the face snijkoppel overcutters cutting torque of overcutters Snijrad cutting wheel Snijradmeting cutting weheel measurements Snijvlaklengte lengt of cutting face Spaak spoke Spaanvlak cutting edge of the knife staartafdichting tail sealing Staartspleet en afdichting tail and seal of the TBM Stand en krachtmeting position and force Stand snijrad position of the cutting wheel startschacht entry shaft stijvegrond stiff soil T Temperatuuropnemers temperature Teodolietmeting deformatie tunnel heodolite measurements of deformations of the tunnel tijd na begin time after start tijdelijke bekisting temporary formwork Toevoerleiding supply pope measurements toplaag top layer totaal koppel total torque Transportleiding transport pipe measurements tunnelwand tunnel lining tweede passage second passing U uitgeharde grouzone zone containing set grout uithardende groutzone zone containing setting grout Uitkomende grond Excavated soil V vergelijking meting met ‘fits’-raai comparing measurement to ‘fits’-section line vermoedelijk tijdstip blow-out supposed time of face instability vertikale deformatie 100 maal vergroot vertical deformation 1000x enlarged verzameltank vollection tank Vijzel jack Vijzelkracht jack force Vijzelstand position of the jacks vloeibare groutzone zone containing fluid grout Vloeistofniveaumeting slurry level Volgtrein backup train volgwagen backup train volume geinjecteerd grout vs maaiveld zakking volume of injected grout versus surface settlement voorspelde zakking predicted settlement W wandwrijving aan mantel shield friction Wateroverspanning water overpressure

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Waterspanningsmeters voor boorfront water-pressure gauges in front of the face of the TBM wel overcutters using overcutters wsm water-pressure gauge Z Zakbaken Markers zakking settlement z-as z-axis Zuidzijde South zuigmond, afvoer bentoniet/grond suction mouth, discharge bentonite/soil

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