ABSTRACT:

Rainfall-induced landslides are common natural disasters in many cities such as Hong Kong. During rainstorms, infiltration of rainwater reduces suction within an unsaturated soil slope. This leads to a reduction in shear strength of soils and hence landslides. Two-dimensional transient seepage analyses of pore water pressures in unsaturated soil slopes have been carried out. However, the influence of rainfall patterns on pore water pressure induced by infiltration has seldom been reported. In this paper, three-dimensional computer simulations were carried out to investigate the groundwater responses of an unsaturated cut slope subjected to three different rainfall patterns. Depending on the initial pore water pressures in the ground, rainfall patterns can have different degrees of influence on the groundwater responses. When the initial pore water pressures in the ground are low (i.e. high suction values), the advanced type A seems to be the most critical one for slope instability.

INTRODUCTION

Many natural and man-made slopes are susceptible to failures. Rainfall-induced landslides are the most common natural disasters in Hong Kong. During rainstorms, infiltration of rainwater reduces matric suction, i.e. negative pore water pressure, within an unsaturated soil slope. When the shear strength at the potential failure slip is exceeded, slope failure would occur. Therefore, an improved understanding of the variations of matric suction in the ground due to rainfall infiltration is essential for safer slope designs. Two-dimensional (2D) transient seepage analyses in unsaturated soil slopes have been carried out by many researchers and engineers (Lim et al 1996; Rahardjo and Leong, 1997; Wilson, 1997; Kasim et al 1998; Ng and Shi, 1998; Sun et al 1998; Ng and Pang, 2000). Various parameters such as rainfall intensity and duration, return periods, wetting and drying history of soilwater characteristic curves, and water permeability were considered in the 2D analyses.

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