Rain-induced slope instability in Hong Kong

Abstract

Slope failures are common in Hong Kong. A wide spectrum of slope failures have been noted. Failures may differ in respect of thickness of failed mass, time of failure occurrence, rotational inclination, failure movement rate, mobility of debris, etc. Small failures significantly outnumber large ones. Due to their close proximity to buildings, however, small failures that collapse catastrophically without prior warning are of concern. Intense rainfall, soils that are largely non-cohesive upon saturation, steep terrain, and intense development are considered to be the major causes of the failures. Loss of pore-water suction, erosion, and pore-water pressure build-up at shallow depths are the most common ways through which rainwater affects the slope stability, as short-burst rainstorms are common. The scale of a failure event depends on the intensity, areal extent, position and duration of the triggering rainstorm. Antecedent rainfall has relatively little influence. The prediction of slope stability in Hong Kong is difficult because of the highly erratic nature of the hydrological influences and the inherent heterogeneity of local soils. While some of the hydrological and geological attributes cannot be accurately predicted and effectively controlled, the hazard can be mitigated by appropriate geotechnical control.