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Nº 8 - JULY 1999 Editorial Editorial staff: Nisa Nurmohamed, chief editor We are very pleased to present this special Marco Hutteman, Plaxis Users Association (NL) edition of the PLAXIS bulletin. Besides the Peter Brand, Plaxis bv normal contents part of this bulletin is devoted to the PLAXIS symposium held last Scientific committee: March in Amsterdam. As requested by Prof. Pieter Vermeer, Stuttgart University participants the opening speech by Dr. Ronald Brinkgreve, Plaxis bv Margriet Janzs and a publication on creep by the Dutch Ministry of Public Works and Water management are published. In addition, a summary of the discussions is provided. Column Vermeer FIELD SITUATION WITH OCR ≈ 1 he first international PLAXIS symposium was Ta big success, nearly 100 participants from Very young soil deposits have experienced 20 different countries participated. The only vertical stresses due to self weight, Experienced Users Course directly after the without additional deformations due to conference was very well attended with 40 previous overburden or ageing, i.e. creep. Bulletin of the participants. Such soil may be truly normally PLAXIS Users Association (NL) consolidated with an over-consolidation Other courses included a PLAXIS short course factor of nearly one. PLAXIS bulletin P.O. Box 3302 in Egypt, and the course “Introduction to To my experience such situations are rare 2601 DH Delft The Netherlands Computational Geotechnics” organised as a and even alluvial deposits are mostly E-mail: post-conference activity to the XIIth “European characterised by a pre-overburden pressure, [email protected] Conference on Soil Mechanics and Foundation either caused by real pre-loading, ageing Engineering” in Amsterdam. or structuring. This may be true for natural IN THIS ISSUE: soil deposits with a geological age, but it Editorial ᕡ The course in Egypt, presented in both Arabic does not hold for man-made soil deposits. and English, showed that the PLAXIS program Extremely young soil layers stem for Column Vermeer ᕡ is used more and more globally. This is again instance from human mining activities. Plaxis Practice ᕢ shown by the overwhelming interest at the Mining remnants of all soils have been PLAXIS booth on the exhibitions at the created. They range from gravely slugs to New developments ᕦ Amsterdam conference and the 3rd National sandy soils up to soft tailings, as created ᕦ Recent activities Conference of the Geo-Institute in Illinois, after treatments of iron ore. Plaxis Version 7.11 ᕧ U.S.A. he first tailing problem I got involved in ᕨ New Plaxis office All the above shows that the PLAXIS company Tconcerned a deposit with a thickness of Agenda 20 is on the move, which brings us to the last about 30 m over an area of some square topic. The PLAXIS company will move to a kilometres. On top of it there was nothing like SPECIAL: Plaxis symposium new office situated in Delft. More information a crust so that one could not walk on it. The The prehistroy of Plaxis on the office location is provided in this undrained shear strength simply vanished at Experiences with a viscoplastic model bulletin. the surface; it increased with depth according Summary of discussions 1 ≈ to rule Cc 2/4 , as may be expected from a model (SS-model), but in this case I had no soil with OCR ≈ 1.0. The clayey silt was classified preference. Indeed, our problem happens to by the parameters as listed in Table 1: be dominated by one-dimensional compression and both models will follow the Table 1 Soil parameters logarithmic compression law. Instead of *, as 2 Saturated weight ≈ 17 kN/m used as an input parameter for the SS-model, ∝ Porosity n ≈ 60 % the HS-model requires: Plasticity index I ≈ 40 % σ p ref ref Eoed = = 1000 kPa ≈ –9 λ* Vertical permeability kf 10 m/s ≈ Compression index CC 0,6 at least when choosing σ ref = 100 kPa. The These are averaged values as the deposit was HS-model also requires the input m = 1 as far from being homogeneous. Together with otherwise it does not yield the logarithmic other such “moorlands” the area had to be compression. The question rises whether or made stable and passable by adding a granular not we could have analysed that problem by fill on top. Calculations were not just needed means of the simple Mohr-Coulomb model for estimating the settlement, but also for (MC-model). Indeed, one might select a predicting the period of consolidation. In fact constant value of the stiffness modulus such the amount of water being squeezed out was that the final settlements comply to analyses important as the cleaning of this water would with more advanced models. The present entail substantial costs. To this end oedometer problem, however, is not only on the final tests were carried out and for the oedometer settlements, but also on the settlements module it was found that: during intermediate construction stages. The σ σ advanced models predict quite correctly E = d '= ' oed dε λ* relative large settlements for the first loading stage and relatively low settlements, for the with: C final stage, as indicated in Fig. 1. In order to λ* = c ≈ 0.1 (1+e)1n10 simulate such a phenomenon by using the MC- model, one would have to select appropriate This linear increase of the soil stiffness with stiffnesses for each stage of loading. No doubt stress, implies a nice logarithmic compression a cumbersome way of proceeding. law, as may be expected for soft soils. For many problems, especially excavation P.A. Vermeer, Stuttgart University problems, I would use the Hardening-Soil model (HS-model) rather then the Soft-Soil PLAXIS Practice FINITE ELEMENT SIMULATION OF THE SOIL-STRUCTURE INTERACTION FOR A NAVIGABLE LOCK Hanover-Anderten, Uelzen and Suelfeld locks are the corner points of the crest water race of the ‘Mittelland’ and ‘Elbeseiten’ channels in Germany. At present Sülfeld represents a needle eye for the ship passage between Hamburg, Figure 1 Comparison of the Time-Settlement Dortmund or Hanover and Berlin, which have curves between MC-model and advanced models. to be kept independent of the water level in 2 Elbe river [1]. The southern Suelfeld lock has to structure and the old existing constructions. be adapted to the rising traffic and to a new ship generation. For this purpose a modern and Lock structure efficient structure needs to be constructed on The length of the new lock is about 345 m, the old lock place, however on new location. including the inlet and outlet structures. The chamber walls are separated in 11 blocks (each block has a length of 15 m). Two or three blocks have a common foundation plate. For water saving purposes two stepped economizing basins will be constructed beside the lock, which will save about 50% of the water pumping demand. The foundation is located at + 46.4 m MSL, more as 20 m below ground surface in upper water area. The first economizing basin is founded at + 56.7 m MSL and the second at + 58.9 m MSL (Figure 1). Soil profile Figure 1 The Suelfeld lock. 1 old lock; 2 new lock; retaining wall of the A characteristic soil profile of the site is northern economizing basin; northern economizing basin; 5 new economizing basin; 6 diaphragm wall; 7 anchors presented in Figure 1. The bedrock consists of Lias sandstone layers and marls of Malm age, The new structure consists of blocks, founded separated by a 40 - 50 m wide fault system, on massive concrete plates. Each plate which runs nearly perpendicular to the lock supports several blocks and is separated by axis. The location of the faults and the joints from the adjacent plates. The finite geometry of the rock surface was investigated element prognosis of the soil - structure using geophysical methods [2]. While the 2 behavior plays a decisive role in the design excavation pit is very large (about 27000 m ), process for two reasons: the soil conditions the impermeability of the diaphragm wall in are highly non-uniform and the evaluation of the disturbed rock area and the possibility of the settlements produced by the fluctuating water leakage through faults pose a major water level in the lock and in economizing problem for the construction. The influence basins controls the design of the joints. A series of a possible fault blocks movement on the of 2D and 3D simulations performed by BGS structure behavior was also simulated using Hanover and BAW is under way. The aim of this 3D nonlinear finite element analyses. paper is to present the results of some 2D The bedrock is overlain by overconsolidated finite element analyses performed using PLAXIS glacial deposits: clayey silt, sand and glacial till. Version 7.1 in order to evaluate the structure For the evaluation of the sand layer properties, loading and the interaction between the new correlations with the results of heavy dynamic penetration tests were used. The cohesive layers, silt and glacial till, were characterized using laboratory tests on undisturbed samples (12 oedometer and 18 CIU triaxial tests). Since the soil is inhomogeneous a two step calibration procedure was used: (1) statistically averaged parameters were obtained from the tests results and (2) the tests were back-analyzed and compared with the measured behavior of selected samples. The fitting was fairly good Figure 2 Calibration of lab tests on glacial till; a CIU triax; b oedometer for the significant strain domain (Figure 2). 3 This ‘common sense’ approach seems the lock, an active earth pressure is mobilized reasonable, but some work needs still to be in the upper part of the backfill, a quasi-K0 done in order to reduce the uncertainties distribution in the middle and a silo effect related to the selection of calibration samples appears in the lower part.

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