Numerical simulation of pile driving in the passive earth pressure zone of excavation support walls: Fid-Bau Portal

Numerical simulation of pile driving in the passive earth pressure zone of excavation support walls

Grabe, Jürgen / Henke, Sascha / Schümann, Björn

In situ measurements, carried out in deep excavations during construction, show that the installation of anchor piles to prevent uplift of the formation level slab leads to large deformations in the excavation support works. Currently, it is hardly possible to predict these installation-related additional loads and they are often quite astonishing. A first numerical model is presented, to predict the additional loads on the subsoil and the excavation works in the vicinity ofpiling works. The importance of the numerical investigations is described, using the example of the additional deformations measured at Potsdamer Platz during the vibratory driving of anchor piles. The examples and calculations described above illustrate that construction influences, for example due to pile driving, need to be taken into account in certain cases. Using the example of the excavation at Potsdamer Platz in Berlin, the vibratory driving of grouted piles, to prevent the hydrostatic uplift of an underwater concrete slab at formation level, could be simulated numerically by way of a 2D model. According to this, the vibratory driving of the piles essentially led to a redistribution of the stresses in the passive earth pressure zone, with the result that the support provided by the passive earth pressure yields. In contrast to the calculations, the measurement data shows, that the upper anchorage of the wall also yields. The soil liquefaction supposed by Tnantafyllidis and the rise in the pore water pressure proved by measurements are obviously not necessarily essential conditions for the occurrence of the diaphragm wall deformations observed. Nevertheless, efforts should be made in the future, to include soil liquefaction effects due to dynamic loads into the simulation model. If further development and validation of the simulation models is successful, then in the future it may be possible to draw up recommendations for the clearances necessary for dynamic construction processes in the vicinity of excavations. Furthermore, it is necessary to check, whether the construction-related changes to the soil condition parameters have a significant influence on the loadbearing behaviour of the diaphragm wall, with respect to serviceability and ultimate load capacity, because up until now neither conventional nor FEM analyses have included these effects. It is to be expected, that the changed soil condition parameters influence the behaviour at the serviceability limit state in particular. At the ultimate limit state, it is well known that the memory of the soil is generally lost.