Effects of principal stress rotation on the cumulative deformation of normally consolidated soft clay under subway traffic loading

The authors investigated the effects of principal stress rotation (PSR) on the traffic load-induced settlement of subways in soft subsoil. Here, a series of hollow cylinder tests on normally consolidated, medium-plasticity soft clay with and without principal stress rotation were performed along with finite-element modeling and simulation. The results show significant increases in both excess pore-water pressure and cumulative deformation of the normally consolidated soft clay when PSR is present and simulated, and the effects become more pronounced as the maximum effective principal stress ratio or load frequency increases. Under the actual traffic load-induced stress in subsoil below the subway tunnel, the presence of PSR increases the cumulative deformation of soft clay by 9-23% compared with that without PSR. As an approximation, the cumulative deformation of soft clay with the effect of PSR can be estimated by multiplying the deformation derived from the repeated triaxial testing without PSR with the ratio of axial strain between the two tests.