A case study on the behaviour of a deep excavation in sand

A complete case record of an excavation in sand is explored in this study. Numerical analyses were conducted to evaluate the influences of soil elasticity, creep and soil–wall interface. Back-analyses indicate small strain parameters should be used if an elastic–perfect plastic model is selected. In addition, excavation-induced seepage has only a limited effect on vertical displacements. Delayed installation of 3rd level struts and base slab construction caused significant time-dependent (creep) movements during the excavation. Back-analyses show that the dynamic viscosity (Dv) used in the visco-elastic model for creep simulation is in the range of 1.5 × 1015–2.0 × 1015 Pa, but there are still inconsistencies in movements both near to and far from the excavation. Interpreting from observation data, the creep rate of wall movement caused in the non-supported stage of the excavation varies between 0.14 and 0.38 mm/day. Finally, parametric studies of interface elements indicate that the most sensitive parameters are the normal (Kn) and shear stiffness (Ks) of the interface. Back-analyses using an elastic–perfect plastic model indicate that using 3 × 106 Pa for Kn and Ks produces more acceptable results.