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INTERNATIONAL SOCIETY FOR MECHANICS AND

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This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. Large in-situ tests to investigate the performance of compacted

Des essais in situ en oedomètre à grande échelle sur l'argile compacte non saturée pour étudier sa performance

Yasser El-Mossallamy Department of Civil Engineering, Ain Shams University, Egypt & Arcadis, [email protected]

Gerhard Schulz & Otto Heeres Arcadis, www.arcadis.com

Salih Aksoy GEOMED, Geoteknik Müş. Etüt, Den. ve Tic. A.Ş., Turkey

ABSTRACT: Istanbul New Airport will be located at 40km north of Istanbul, direct at the Black Sea coast. The area is a former open-cast coal mining area. The total area of the project location is about 75.94km2 (7594ha). With a capacity of up to 150mln passengers annually it will be one of the largest airports in the world. The Earthwork is divided into and fill areas. In the fill area, the embankments reach heights up to 70m. Especially in the northern part of the project area, there are large areas filled with mining spoil (remolded) material due to former mining activities. The spoil material is inhomogeneous and it was deposited without any compaction. The available material for construction is mainly the Danişmen Formation, which consists of low to high plastic clay. Large scale shear box tests are conducted to investigate the mechanical performance of the compacted clay. Large scale oedometer in-situ tests are carried out on the unsaturated compacted clay to study its deformation performance. The chosen constitutive laws and design parameters are adopted according to the test results. Verification was carried out via the implementation surface monitoring of constructed embankments.

RÉSUMÉ : Istanbul New Airport sera situé à 40 km au nord d'Istanbul, directement sur la côte de la mer Noire. La région est une ancienne zone de mines à charbon à ciel ouvert. La superficie totale de l'emplacement du projet est d'environ 75,94 km2 (7594 ha). Avec une capacité jusqu'à 150 millions de passagers par an, ce sera l'un des plus grands aéroports du monde. Le travail de terrassement est divisé en zone de coupe et de remplissage. Dans la zone de remplissage, les talus atteignent des hauteurs jusqu'à 70 m. Surtout dans la partie nord de la zone du projet, il y a de grandes surfaces remplies de déchets miniers (remoulés) en raison des anciennes activités minières. Le matériau de dégradation est inhomogène et il a été déposé sans aucun compactage. Le matériau disponible pour la construction de remblais est principalement la formation Danişmen, qui se compose d'argile plastique. Des essais de caisse de cisaillement à grande échelle sont effectués pour étudier les performances mécaniques de l'argile compacte. Des essais in situ en oedomètre à grande échelle sont effectués sur l'argile compacte non saturée pour étudier sa performance. Les lois constitutives choisies et les paramètres de conception sont adoptés en fonction des résultats du test. La vérification a été effectuée par le biais de la surveillance de la mise en œuvre de la surface des digues construites. KEYWORDS: Istanbul New Airport, Danişmen Formation, unsaturated, in situ testing, settlement performance, stability performance 1 INTRODUCTION The challenges for the earthworks are summarized as follows:  Great amount of cut in the south and fill in the north Istanbul New Airport will be located at 40km north of Istanbul, direct at  Thick existing heterogeneous spoil with poor mechanical properties the Black Sea coast. The total area of the project location is about due to previous open-mining activities. 2 75.94km (7594ha). Since 2013, Phase 1 is under construction, see  The presence of at the project area  High seismicity of the area  Stringent requirements regarding reliability, availability, serviceability and safety with tight time schedule for construction The available material for embankment construction is mainly the Danişmen Formation that is excavated in the southern part, which consists of partially saturated low to high plastic clay (approximately 70% is CL, 30% is CH). According to the AASHTO classification Figure 1. Phase 1 consists of Runway A, Runway B, the terminal and system, this material can be classified as clayey soil (group A-6). apron areas and Runway C. Therefore, a testing program was developed for using these materials to construct the embankment: in-situ compaction trials, large scale oedeometer tests and large scale shear tests. As verification, compaction control tests are performed to check the reached relative compaction during construction.

2 SITE CONDITIONS

Due to the previous mining activities, the area of Istanbul New Airport is very heterogeneous. The site topography is strongly affected by the Figure 1 Left: project location. Right: situation in 2013. Blue line: activities of the open-mining. The project area has variable elevations total project, white line: Phase 1. ranging from 150 meters in the South to fewer meters above the sea level in the North. There are stream valleys with alluvial deposits. The The area is a former open-cast coal mining. Due to the topography, the northern and north-eastern part of the site is bounded by the Black Sea site is divided into areas. In the fill area, especially in the shoreline. Elevations along the site vary from approximately El. ± 0.0 to northern part of the project area, there are large areas filled with mining +150 meters Several artificial lakes of various sizes and depths have spoil (remolded) material due to former mining activities. The spoil been formed in the spoil area. material is inhomogeneous and it was deposited without any compaction. The embankment height reaches up to a height of 70m.

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3 , AND SEISMICITY

The main geological units at the project site are the Ceylan, Danişmen, Belgrad Formations and mining spoil. The Ceylan formation is composed of sandy-limestone, marl, silty limestone, clayey-limestone, and limestone alternation. The Danişman formation is a dominant unit of the project area and is widely exposed all around the site and located over the Ceylan formation. It is composed of claystone, marl, sandstone alternation with 1-5m thick lignite layers, and sandstone-gravelstone Figure 3 Basic design concept with embankment fill, buffer fill lenses. The units are dipping about 5-10° to the north. and landscaping fill The Belgrad formation locally overlays the Danişman formation and With this combination of sealing and drainage, water into consists of sandstones, and . The spoil consists of a the embankment body is completely avoided. The evaluation of heterogeneous mixture of clays, sands, marls and lignite of Danişmen geotechnical parameters regarding embankment performance is carried formation. out considering this design principle.

5 SETTLEMENT PERFORMANCE CRITERIA

Serviceability requirements are given in ICAO Appendix 14. Differential settlements as as longitudinal and transverse slopes govern the serviceability requirements of different areas (runways, taxiways and aprons). Figure 4 shows the runway roughness criteria to guarantee surface evenness and to avoid water pools on the surface for bump lengths between 0m and 60m.

Figure 2 Geology and 3d model

Based on the available data, a 3D geotechnical model was created that served as a basis for the earthwork design, see Figure 2. The 3D model contains CPT’s and data, the lithology, the geological map of the site, groundwater data, the topology before mining operations started, the topology before airport construction started and the 3D masterplan of the airport.

Groundwater measurements were performed in 318 open boreholes. Figure 4 ICAO Settlement performance criteria Based on these measurements it is assumed that the groundwater can be found at ground level, or even above (artesian levels). For the Due to the high serviceability requirements, the residual settlements earthworks design and also groundwater modeling an estimation of need to be limited. maximum groundwater levels has been calculated to design an adequate drainage system between the native soil and the embankment. 6 TESTING PROGRAM ON DANIŞMEN CLAY

According to the Turkish Ministry of Public Works and Settlement, the The requirements to the Danişmen fill material are beyond the usual due project site is located within the 3rd degree zone corresponding to PGA to huge cut and fill volumes, embankment heights up to about 70m, the levels of 0.2g. A seismic study of the site was performed based on a water sensitivity of Danişmen and due to the seismic conditions. analyses of the site. After estimation of the magnitude of Therefore a testing program was developed as follows: the design , the design earthquake characteristics at the rock 1. Suitability testing in which grains size distribution, , outcrops were determined. Next, the epicenter distances for the design Proctor curves, moisture content, volumetric weight and earthquake source zones were estimated. The geotechnical conditions permeability were assessed. Compaction trials were performed at were assessed using 5 deep drillings in which cross logging suitable materials. was performed. 2. Large scale in situ shear tests on compacted unsaturated material to Input acceleration time histories were scaled for different design levels. investigate the at natural moisture content and under 21 real acceleration time histories compatible with the earthquake water inundation. hazard in terms of the probable magnitude, epicenter distance, and fault 3. Large scale in situ oedometer tests on compacted unsaturated mechanism recorded on stiff (soft rock-rock) site conditions with material at natural moisture content to determine immediate average shear wave velocities larger than Vs30 > 600m/s were selected settlements, detect whether consolidation occurs at high stress as a set of possible input motion for site response analysis. The selected levels, assess creep properties at high stress levels and investigate acceleration time histories were scaled with respect to PGA estimated whether the material saturates at high stress levels. based on the hazard assessment.

In general, relative compaction RC ≥ 95 %, referring to modified 4 EARTHWORK CONCEPT proctor test results, must be reached for all materials. To verify the limiting values, prior to the use of any soil on site, its suitability is Figure 3 shows a principle cross section of the embankments that are checked based on test results in the laboratory. An in-situ compaction being constructed. Since the fill materials of the embankment consists trial is executed to prove the results of the lab tests. This compaction mainly of Dani men clay (high to low plastic clay), they are sensitive to ş trial served to determine earthworks operation parameters for placing water. Therefore the embankment is designed to be protected from and compaction of each material. During execution of the compaction water ingress. A sophisticated subbase drainage system has been trial the suitability tests were repeated and extended with density designed and implemented to avoid raise of groundwater inside the measurements; static plate loading tests, and dynamic plate loading test. embankment. At its upper surface, the embankment will be sealed with During earthworks construction quality of each compacted layer was a top sealing layer. The embankment slopes must also be protected monitored by application of a roller based Continuous Compaction against infiltration of water. This was done by applying a sealing layer Control system (CCC) in combination with conventional in-situ spot or a drainage layer on top of the slopes, with connection to the sub base tests. drainage and protected by a buffer fill. At many locations, a landscape counterweight fill was designed on top of the slopes.

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7 LARGE SCALE IN SITU SHEAR TESTS high stress level. Therefore, large in-situ Oedometer test with dimensions 80x80x60cm was developed and applied. Large scale in situ shear tests with dimensions of 32cm x 32cm with The aim of the oedometer tests was to assess the stress-strain relation height of 20 cm have been performed to determine realistic shear detected in Danişmen Clay regarding time- settlement behavior for strength parameters for embankment material consisting of compacted construction phase and service life of embankments under real site Danişmen clay. Figure 5 shows the test set-up. conditions. The test program consisted of 3 tests on compacted CL 7 tests were performed on their natural in situ of 21.1%. Danişmen clay and 3 tests on compacted CH Danişmen clay. To 2 tests were performed after a 5 days soaking period, that leads to an consider the real site conditions, the samples were compacted in the increase of the water content of about 3%. The applied vertical stresses same manner as real embankment material (same lift height, no. of varied between approximately 100 and 400 kPa. In order to guarantee passes, weight of compactor, and shape of drum). Realistic load levels drained conditions a shear speed of 0.1mm/min was applied. Figure up to about 2000 kPa were applied to simulate embankments up to a shows measurements obtained during the tests in comparison with back height of more than 70m. Laboratory tests were carried out before and calculation using 3D finite element analyses. after the oedometer tests in which amongst other the moisture content was determined. The test area was excavated down to 1.4m below the ground surface between two bored concrete reaction piles, a concrete slab was constructed on which Danişmen clay was spread and compacted with a 26 tons sheep foot roller to 95% relative compaction (RC) (Modified Proctor). The tested soil was constructed in three layers each 35cm thick and compacted applying six passes. Quality control tests were performed on each layer. After completion of the compaction, the soil specimen was trimmed to 80x80x60cm. A steel box was placed around the soil specimen. A thin load distribution layer of dried was placed on top of soil block specimen and the steel loading plates were horizontally adjusted on the sand bed. The loading system consisted of a hydraulic jack and a Figure 5 Large scale in-situ shear test set-up beam that was welded to the vertical reinforcement of the two large diameter bored piles (figure 10).

Figure 6 Measured shear stress (kPa) vs. displacement (mm) For the tests performed at natural water content a angle of 15° Figure 6 In situ large shear Oedometer test set-up and a of 80kN/m² were obtained. Two soaked samples delivered the same friction angle but the cohesion was reduced to Displacements were measured in each test by 4 displacement gauges on 15kN/m². The results are summarized in Figure 5. the corners of the loading plate. In 3 tests pore water pressures were measured in the sample with a vibrating wire . Figure 7 gives typical measurements obtained during the tests.

Figure 5 Measurements and interpreted yield locus of compacted Danişmen clay.

These results are consistent with in situ observations where most of the slope stability problems in Danişmen clay appear in combination with water. The results prove the necessity to avoid any water ingress into the embankment body by means of a sub base drainage layer, a slope sealing and a sealing layer at the top of the embankments, as shown in Figure 3.

8 LARGE SCALE IN SITU OEDOMETER TESTS

Due to the high stress levels, test embankments are not feasible. The approach was to investigate realistic soil parameters and constitutive laws for the numerical analysis based on realistic in-situ tests that simulate both the construction methodology as well as the expected

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Figure 7 Time settlements in the large scale oedeometer test

Figure 8 shows typical stress strain measurements on short term after 1min and long term. Long term strains were determined via a hyperbolic extrapolation of the measurements. The test results by using low plastic and high plastic Danişmen clay (CL and CH) show that a large part of the deformations of the embankment is immediate settlement that will occur during the embankment construction time. The time dependent part of the settlement is mainly due to creep and is relatively small compared with the immediate settlement. Further, laboratory tests have shown that the samples are unsaturated before and after the tests.

Figure 10 Creep coefficient as a function of the stress level

The time strain performance has shown that there is no evidence of consolidation under all loading steps (up to about 2000kPa). This was confirmed with piezometric measurements during two of the tests. The same results were obtained via triaxial tests on undisturbed samples. The same evident was also proved via PCT dissipation tests. A numerical back analysis was performed with the double hardening as well as the soft soil models to simulate the measured stress strain

performance. A good agreement between measured and back-calculated performance was achieved, see Figure 8 Stress strain measurements.

The preconsolidation pressure was determined according to Casagrande’s procedure. Preconsolidation pressure of 800kPa due to the huge impact of compaction with 26 tons sheep foot rollers was detected. The results of the oedometer tests showed a clear distinction between the properties above and below this stress level, see Figure 9 and Figure 10. In the settlement analyses, a much lower preconsolidation pressure was adopted to be at the safe side and account for uncertainties and relaxation with time.

Figure 11.

Figure 9 Stress dependent stiffness for CH Danişmen

Figure 11 Back analysis of measurements with the double hardening and soft soil model

starting construction in less critical areas, monitor the settlemnts, improve the knowledge and adjust (if needed) for the more critical areas

9 SETTLEMENT PERFORMANCE

The settlement of the embankment platform consists of settlement of the embankments and native layers. Compacted Danişmen undergo immediate settlements and time dependent settlements due to creep. As derived from the results of the performed large scale oedometer tests there is no evidence of consolidation. Settlement of native Danişmen layers consists of immediate settlements, consolidation and creep. The distortion angles due to the residual settlements along the longitudinal

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alignment of runways have been evaluated at different time intervals 1: 600 was defined as acceptability limit criterion. Beyond this value, a after the end of construction to check the serviceability requirements temporary acceptable condition is defined in ICAO, which means that according to ICAO. One dimensional settlement calculations have been maintenance must be planned and applied. performed in a grid of 50m x 50m. Due to the huge size of the project The ICAO acceptability limit criterion was fulfilled for all calculated area in Phase 1, about 16,000 settlement calculation points were sections up to 10 years after EOC. The ICAO design criterion is performed. A special and partially automated spreadsheet was fulfilled for Runway A, Runway B and the apron area up to 5 to 10 developed for this purpose. The geometrical input in the settlement years after EOC. Due to thick and weak Danişmen layers in the area of calculations was delivered by the created geological 3D model. Based Runway C, special measures have been developed to fulfill the ICAO on analyses the influence depth of the embankments was 3 times the criteria, e.g. a longer waiting time or development of a special embankment height and not less than 50m. maintenance plan. The ground water elevation was assumed to coincide with subbase Also, the settlements of the base drainage system after the lifetime of drainage elevation. Next, the calculation model assumes that all spoil 100 years were calculated and presented in a contour map to evaluate its material beneath the subbase drainage layer is excavated and replaced long term functionality. To do so, the change of the gradients and the with water resistant material. The double hardening model was applied change of discharge capacity of the main discharge ditches were to develop the deformation modulus of the embankment material and verified. It was concluded that the settlements do not lead to critical different layers depending on the stress level and stress path. The effect decrease of hydraulic capacity. of over consolidation is taken into account. Terzaghi’s theory for one Considering the results of the conducted analyses, the site construction dimensional consolidation is applied to consider the primary settlement schedule is updated and modified. It was decided starting the (consolidation) of the Danişmen formation. Finally, creep is calculated construction in less critical areas where small values of settlement are according to Bjerrum (1967) for both embankment and Danişmen expected. Meanwhile, monitor the settlements via multipoint magnetic formations. For creep in embankment fill, distinction is made between settlement columns are carried out. The gained information and normally consolidated conditions and over consolidated conditions. knowledge were analyzed. The construction sequence as well as The residual settlements after construction of the pavement on the construction methodology were adjusted. The gained experience was embankments will affect the pavement performance with time. As applied in more critical areas shown in Figure , the construction time of the embankment is assumed to be 9 months. A constant construction rate was assumed in the 10 MONITORING analyses. A waiting (delay time) of 3 months was assumed before the construction of the airfield pavement. A combination of geotechnical, geodetic and hydrogeological monitoring was designed and implemented to verify the derived design assumptions, prove the stability and acceptable behavior of earthworks and obtain reliable information about the time dependent deformations during and after the construction stages. The results can be used to verify the ICAO requirements and develop maintenance plans. Further, an ad-hoc monitoring program was implemented during the rainy season 2015/2016, in which construction activities were paused. These months were used to observe the deformation performance of already completed and/or partly completed embankment sections in the north of Runways A/B and the Apron Area. Figure 12 shows monitoring results of the applied multi points magnetic settlement columns that were obtained in the north of Runways A/B. The measurements were extrapolated via the logarithmic and hyperbolic techniques and a comparison was made with the calculated settlements. It was concluded that the calculations and the design are at the safe side. The logarithmic Figure 16 Construction stages and settlements in time extrapolation is chosen for the final evaluation. The residual settlements affecting the pavement are calculated after the end of construction (EOC). Contour lines of residual settlements after the end of construction are developed and shown at End of Construction (EOC) and at EOC + 1, 2, 3, 5, 10, 20 and 100 years. As an example, Figure shows the calculated residual settlement map at EOC + 5years.

Figure 12 Monitoring measurements and hyperbolic and logarithmic settlement predictions

CPT’s were made in constructed embankments to verify the average cone resistance. The results were correlated with the suitability tests, the compaction trials, the large-scale in situ oedometer and shear tests.

Figure 17 Calculated residual settlement map at EOC + 5years

The embankment surface distortion angles were developed along Runways A, B, C and along a section through the apron area. According to ICAO the following 2 criteria were checked. A distortion angle of 1:1500 was defined as design criterion, while a distortion angle of

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Figure 13 CPT results in embankments constructed with remoulded and recompacted Danişmen

Figure 19 shows an example of the CPT test results. The CPT tests on the constructed embankment are applied as a basic element of the quality control and quality assurance program of the earthwork.

11 CONCLUSION

Istanbul New Airport will be constructed in a former open mining area. The construction of embankments up to 70m high with mainly Danişmen CL and CH clays in a highly seismic active area posed a real challenge. A testing program was developed to assess the suitability and the parameters of Danişmen CH and CL clay. The program consisted of suitability tests, geological investigations and large-scale in-situ oedometer and shear tests. Design parameters and constitutive laws were developed for Danişmen material, which were used in the earthwork design. The compliance with the ICAO airfield surface performance was verified. A monitoring program was designed and implemented. The first results are promising.

12 ACKNOWLEDGEMENTS

The cooperation with IGA Havalimanlari Inşaati Adi Ortakliği Ticari Işletmesi and GEOMED, Geoteknik Müş. Etüt, Den. ve Tic. A.Ş. is gratefully acknowledged.

13 REFERENCES

ICAO 2009. International Civil Aviation Organization International Standards and Recommended Practices. Aerodromes, Annex 14, Volume 1, Aerodrome Design and Operations. (ICAO, 5th Edition 2009) Turkish Ministry of Public Works and Settlement 2007. “Specifications for Buildings to be Built in Disaster Areas” PEER Strong Motion Data Bank, http:// peer.berkeley.edu

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