Stability analyses of quick clay using FEM and an anisotropic strain softening model with internal length scale

Abstract

Sensitive soft clays generally display a significant post peak strain softening response under undrained deformation. A consequence of this behavior is that the safety factor during undrained stress changes cannot be calculated by conventional limiting equilibrium methods and when using numerical methods as the finite element method the solution is mesh dependent. In finite element analyses a shear band generally develops in the strain-softening regime. However, without a proper regularization technique the thickness and generally also the orientation of the shear band are governed by the finite element discretization. To overcome this problem of mesh dependency an internal length scale, that controls the shear band thickness without prescribing the orientation, must be introduced. One method is to use the non-local strain approach. This approach may be implemented into any non-linear finite element programs without reformulating the governing finite element equations. In this paper the NGI-ADPSoft model with a non-local strain approach is used to investigate the stability of a filling in a quick clay slope. The case studied is a slope at Vestfossen that failed due to construction work 11th of September 1984. The slide involved approximately 150 thousand m3, where the terrain in the backside of the slide was lowered with about 5 meters. The back-calculation of the construction of the fill and the following slide event was done using a large deformation finite element analysis with the PLAXIS 2D code.

Stability analyses of quick clay using FEM and an anisotropic strain softening model with internal length scale