Stability Analysis of Unsaturated Soil Slope Considering the Variability of Soil-water Characteristic Curve

Soil slopes are generally unsaturated in which the soil-water characteristic curve (SWCC) plays an important role in its hydro-mechanical response. The commonly used Mohr-Coulomb failure criterion in saturated soil mechanics could be extended to take SWCC into account which is then able to determine the shear strength of unsaturated soil. Like many other soil properties, spatial variation of SWCC within a soil domain is expected. It therefore gives a spectrum of varying shear strength across the unsaturated soil slope. In this study, the effect of this spatial variability on slope stability will be investigated. As a first trial, the true cohesion, friction angle and degree of saturation of the unsaturated ground are assumed to be deterministic. SWCC of the soil is described by the van Genuchten model parameters, which are assumed to follow a prescribed probability density function. Therefore, a random field of apparent cohesion due to unsaturation can then be generated using the Cholesky decomposition method. The necessary statistical information for the random fields could be obtained by the Monte Carlo approach based the varied SWCC. The slope stability analysis is carried out using the finite element analysis method. For a given saturation degree, thousands of realizations of the random fields will be generated and the probability of failure is then evaluated. The relationship between the degree of saturation and probability of failure will be examined. Besides, the influence of correlation length of soil shear strength on the probability of failure will also be analyzed.