Factors Influencing Rainfall-Induced Slope Failures

Abstract

A major trigger for shallow slope failures is rainfall, whose infiltration results in a reduction in the factor of safety from an increase in pore water pressures, increases in the degree of saturation and reductions in the shear strength of the slope material. In this study, model slopes were prepared in a Plexiglas box from a clayey soil obtained from a housing development site at CSU Fullerton and used to examine the influence of the variations in the slope forming material properties and the applied rainfall. Specifically, model slopes were prepared to have four different relative compaction levels between 60 and 74% at an inclination of 40°. The slopes were instrumented with tensiometers and copper wires to evaluate the pore pressure response and deformation when 30 mm/h of rainfall was applied using a rain simulator system. The variation of seepage velocity with rainfall duration, spatial distribution of suction and the deformation of the slope were recorded. The rainfall was stopped when complete saturation of the slope was obtained, as determined from visual inspection of the wetting front and the real‐time tensiometer recordings. From the results obtained, increase in the initial void ratio and intensity of the rainfall resulted in an increase in the pore water pressure as well as the velocity of the wetting front. The study result was useful to obtain relationship between relative compaction, seepage velocity, and deformation characteristics of the slope.