The role of wetting-induced expansion of unsaturated soils in potential shallow landslides

Unsaturated swelling soils expand in volume significantly during a wetting event (for example, rainfall infiltration, snow melting, or irrigation), which can lead to substantial change in the stress regime within and degradation of mechanical properties of the shallow soil mass. These changes can, though not completely, interpret many likelihoods of shallow landslides in swelling soils that has been frequently observed. In this work, an infinite slope formulation is proposed to address the mechanism of the shallow slope failure, where the unsaturated soil is described by the extended Mohr-Coulomb elasto-plastic constitutive law, in particular, the material parameters of the yield surface is altered according to the accumulation plastic deviatoric strain (extended to unsaturated soils from the classic softening), to simulate the degradation of mechanical properties. In this way, the influence of (i) the wetting induced swelling, (ii) the swelling induced stress change, and (iii) the associated softening behavior, on the stability of shallow layer is quantitatively examined. The proposed infinite slope formulation is applied to two typical swelling soil slopes: a synthetized one and a real field case. A good agreement between prediction and available experimental data from a published field study is obtained, illustrating the important implications for the engineering design of swelling soil slopes.