Coupled hydro-mechanical modelling of a 1995 Hong Kong landslide

Abstract

The paper deals with the modelling of the instability mechanism induced by rainfall in an unsaturated cut-slope. A large-sized landslide occurred in 1995 in Hong Kong (the so-called “Fei Tsui Road landslide”). It was here analysed because it was characterized by unusual dimensions and very large runout distance for the study area. The slope failure was attributed to a decrease in soil shear strength due to the rise of a perched water table above a weak kaolin-rich layer, together with the loss of suction caused by water infiltration during a heavy rainfall event. The hydro-mechanical coupled analyses made through the commercial software Plaxis 2D aimed to investigate the relations between the hydrological variables (i.e., rainfall infiltration, suction, saturation) and the slope response in terms of changes in soil resistance and soil plastic deformations. The study demonstrates that the evaluation of the hydro-mechanical coupling effects on the hydraulic slope response as well as on the stability of the whole slope is a crucial issue to well capture the mechanical behaviour of the unsaturated cut-slope. Different failure scenarios have been also considered in order to match the field observations and to back-analyse the initial condition of the slope before landslide.