EFFECTS OF MODELING SOIL NONLINEARITY AND WALL INSTALLATION ON BACK-ANALYSIS OF DEEP EXCAVATION IN STIFF CLAY

This paper describes the application of two relatively simple models: a linear elastic-perfectly plastic Mohr-Coulomb and a nonlinear ''brick'' model for simulating the top-down construction of a multipropped excavation in the overconsolidated stiff fissured Gault clay at Lion Yard, Cambridge, with and without wall installation effects modeled. Numerical results are evaluated through comparisons with the comprehensive case record at Lion Yard. The objectives of the comparisons are to illustrate the effects of modeling wall installation and soil nonlinearity inside the yield surface on geotechnical designs. These comparisons are thus focused on aspects in which the practicing engineers are most interested, including the bending moments and deflections of the diaphragm wall, the strut loads, and the ground movements around the excavation. The results of the comparison demonstrate that the use of a Mohr-Coulomb model with a ''wished-in-place'' wall can reasonably predict the maximum bending moments and deflections of the wall for design purposes once the input soil parameters are correctly estimated. However, it significantly overestimates strut loads and fails to estimate the general ground deformation pattern.