Profiles of suction stress of layered soils under infiltration conditions and its applications

Suction stress is critical for understanding the hydrological and mechanical behavior of unsaturated soils in construction and engineering. Many soils encountered in these fields exhibit layering due to geological sedimentation or artificial reinforcement. This study establishes the vertical distributions of matric suction and degree of saturation for layered soils under one-dimensional (1D) steady-state seepage, using the Darcy law and constitutive relationships of unsaturated soils. A closed-form suction stress is derived for an arbitrary number of layers and soil types. Hypothetical layered soils with varying hydraulic properties at four infiltration rates are assessed. Results show that soil stratification affects the suction stress profiles, with the impact depending on infiltration rates, soil configuration, and layer thickness. Abrupt variations in suction stress occur at most layered interfaces due to differences in permeability between adjacent layers. The suction stress profiles can be used to evaluate the earth pressure and stability of layered slopes under seepage conditions. Several case studies of multi-layered slope failures in Southern Italy are presented to demonstrate the suitability of the proposed framework for evaluating the stability of layered slopes under rainfall conditions.