Finite element analysis of time-dependent behavior in deep excavations

This study investigated the time-dependent behavior of a diaphragm wall and ground surface for a typical excavation in soft clay using two-dimensional finite element analysis. During excavation, deformations normally increase with time, both in the soil excavation time and the elapsed time between excavation stages. The increase may be due to consolidation and/or creep but the mechanism has never been studied comprehensively before. The hardening soil, hardening soil small strain, soft soil, and soft soil creep model were used depending on analysis requirements. Compared to the measurement, the soft soil creep model could simulate the time-dependent wall deflection and maximum ground settlement properly. Creep had a significant contribution to increasing the wall deflection while consolidation had little effect. Creep also caused a significant increase in the ground settlement both in excavation stages and elapsed times while consolidation caused the ground settlement to rebound slightly during elapsed times. The maximum wall deflection and ground settlement induced by the bottom-up method were 0.79 and 0.80 times as large as those by the top-down method, respectively. This was a contribution of a three times smaller support stiffness, elapsed time and unsupported length of the bottom-up method compared to those of the top-down method.