Ground Movement Prediction for Deep Excavations in Soft Clay

This paper presents results of a series of numerical experiments, using nonlinear finite-element analyses, which investigate the effects of wall embedment depth, support conditions, and stress history profile on the undrained deformations around a braced diaphragm wall in a deep clay deposit. The analyses use a comprehensive effective stress soil model (MIT-E3) to describe important aspects of clay behavior, including small-strain nonlinearity and anisotropic stress-strain-strength, and focus on soil profiles with constant overconsolidation ratio, where the shear strength and stiffness are proportional to the depth. The results are combined in prototype “design” charts for estimating ground movements as functions of the excavation depth and support conditions, and incorporate the effects of wall length on base stability. Similar techniques are applied for a typical soil profile in Boston where a stiff overconsolidated crust overlies much softer clay. The results show the importance of the underlying clay on predicted wall deflections and ground movements.