Bearing Capacity of Shallow Foundations on Unsaturated Soils: Analytical Approach with 3D Numerical Simulations and Experimental Validations

Abstract

The ultimate bearing capacity of shallow foundations on unsaturated soils is investigated through the concept of suction-dependent effective stress. The first approach is a new analytical solution considering the influence of matric suction on ultimate bearing capacity by extending Vesic’s solution for saturated soils. Accordingly, a modification factor has been introduced as a nonlinear function of matric suction for tuning the cohesion-dependent component in the bearing capacity equation. The second approach is incorporating the unsaturated effective stress state in conjunction with the suction-dependent cohesion into a three-dimensional (3D) finite-difference code. In developing the 3D simulations, the variation in matric suction versus the depth of the soil was considered as well as the dependency of the degree of saturation on the soil suction. In addition, in three-dimensional numerical analyses, the input material parameters were modified to take into account the suction-stress concept in unsaturated soils. To assess the validity of the analytical and numerical approaches, four series of experimental data from physical plate load tests conducted under different matric suctions and embedment depths of the footing were selected. Accordingly, water retention curves of different test materials were considered as key input parameters used in both approaches to improve model predictions. Results from the analytical approach show the dependency of the presented correction factor on the soil properties, geometrical aspects of the foundation, and its embedding depth. In addition, the 3D numerical simulation revealed the suitable functionality of the effective stress approach on predicting the load-displacement behavior of shallow foundations on unsaturated soils. Moreover, the comparison between analytical, numerical, and experimental data shows a good conformance between the experimental test results, analytical solutions, and numerical predictions, especially for sandy soils.