Finite Element Modelling of Seismic Performance of an Excavation Supported by Propped Diaphragm Walls in a Natural Structured Clay Soil

A series of non-linear FE simulations of the behavior of excavations in natural structured clays supported by diaphragm walls under seismic loading conditions has been performed to investigate the effects of the initial degree of structure and of the destructuration rate on the performance of the structure, quantified in terms of permanent displacements and rotations of the walls. In order to reproduce the main characteristics of the cyclic/dynamic soil response at very small to medium-large strain levels, a recently proposed hypoplastic model for clay has been used to describe the soil behavior. In the model, an additional scalar state variable (sensitivity s) allows to incorporate the effects of soil structure. The results show that, while destructuration effects are almost negligible during the static excavation stage, the progressive degradation induced by the earthquake shaking may induce a significant increase in the accumulated permanent displacements, mostly controlled by the destructuration rate of the material.