A case study analysis of a landslide considering the residual shear strength of unsaturated soil

ABSTRACT: Several of the natural and compacted fine-grained soils slopes that are in either saturated or unsaturated condition typically undergo a large deformation prior to reaching failure conditions. Such slopes should be designed taking account of their strain-softening behavior based on their residual shear strength parameters. In this paper, a recently reactivated Outang landslide near the Three Gorges Dam in China is interpreted using the residual shear strength parameters of unsaturated soils. A series of site investigations (i.e., boreholes, exploratory wells and trenches, footrill) and direct shear tests results were used to study the progressive failure behavior of this landslide. Slope stability analyses were conducted using Geoslope considering the combined influence of the precipitation and Yangtze River water level variation, based on the residual shear strength parameters. This study might be of significant interest to the geotechnical engineers to understand the unsaturated soil slope behavior at residual state.