Deterministic and probabilistic analysis of the response of shallow footings on unsaturated soils due to rainfall

Abstract

Due to rainfall, footings are usually subjected to effects of water table fluctuations which results in the variation of ultimate bearing capacity in unsaturated soils. However, the conventional bearing capacity theories don’t account for the variation of suction as the water table position changes. In this paper, an equation based on Terzaghi theory is proposed to evaluate the variation of bearing capacity due to suction variations due to rainfall. The proposed equation results in higher bearing capacity values compared to the conventional Terzaghi equation. Further, a comparison of the bearing capacity obtained using the proposed equation is made with those obtained from Barcelona Basic model (BBM), Mohr-Coulomb model and Terzaghi equation. It is observed that BBM results in lower values of bearing capacity compared to Mohr-Coulomb model as the former considers the loss of suction upon infiltration. Soil properties like porosity, permeability and soil water characteristic (SWCC) influence the bearing capacity in unsaturated soils. Thus, probabilistic analysis is carried out by using an efficient kriging surrogate model in order to analyze the impact of variation of the associated parameters on the bearing capacity. The surrogate model can predict the surface displacements of footing upon infiltration with enhanced accuracy and computational efficiency. Considering the uncertainty associated with rainfall loads, it is observed that as the return period of rainfall increases, failure probability increases.