Effect of characteristics of unsaturated soils on the stability of slopes subject to rainfall

Abstract

This research aims to investigate the influence of characteristics of unsaturated soils on the stability of slopes subject to rainfall by using a coupled hydro-mechanical approach. In practice, distribution of the soil suction and moisture content at the shallow depth of a slope is considerably affected by the near-ground environment and climate change, e.g. vegetation, precipitation, evapotranspiration, and exposure to sun light, etc, and shallow slope failures are mainly governed by the unsaturated soil behavior at the shallow depth. The relationship between the soil suction and soil moisture content is important in characterizing the mechanical behavior of unsaturated soils. Parameters quantifying the soil-water characteristic curve (SWCC) are used to represent the characteristics of unsaturated soils. In addition, the degree of saturation at the residual state in the soil also affects SWCC, and the subsurface flow in a slope is governed by the hydraulic conductivity of the soil. Thus, influence of parameters (α g n) in SWCC, the hydraulic conductivity of the soil (Ksat) in saturated conditions, and the degree of saturation (Sr) at the residual state on the stability of slopes subject to rainfall is investigated. Major findings summarized from this research are: (1) α, n, and Sr values of the soil considerably affect the variation of the factor of safety (FS) of the slope with time during rainfall, specifically at the later stage of the rainfall activity. (2) Influence of m values on the stability of a slope during rainfall is minor. (3) The hydraulic conductivity at saturated conditions (Ksat) plays an important role in the stability of a slope during rainfall. Variation of the factor of safety of the slope with time during rainfall is not noticeable if the Ksat value of the soil is low.