Analysis of Slope Stability in Unsaturated Expansive Soil: A Case Study

To get a better understanding of failure mechanism of slopes in soils that exhibit expansive characteristics subjected to any type of inundations, particularly, when the soils switch from unsaturated to saturated states, the field study may severe as a rather effective method for providing the most representative information. However, field investigation is usually time-consuming and expensive. While, numerical simulation provides a faster way for producing quantitative interpretation of several complicated mechanisms. In this paper, a field experiment is studied numerically, which involves simulation of water flow within the slope profile by finite element method, followed by quantification of the stability of potential failure mass by the classic slices Method. Special emphasis is placed on the effects of cracks on the flow behavior in the shallow layer, which is one of the most essential characteristics in expansive soils. The Bimodal Soil Water Characteristic curve, together with the Bimodal permeability functions, is found to be more effective in reproducing the change of flow regime (pore water pressure and water content) from the finite element water flow analyses, in comparison to the Unimodal functional properties. The stability analyses illustrate that the shear behavior of soils within the shallow layer should be better described by strength parameters measured under lower confining pressure close to the field conditions. This implies the actual mobilized shear strength of expansive soils in shallow layer should be better modeled with a non-linear strength model that is able to accommodate the low stress conditions.