Bearing capacity of strip footings in unsaturated soils reinforced with layered geogrid sheets using upper bound method

A frequently overlooked aspect in previous research on bearing capacity of reinforced foundations is the prevalent unsaturated properties of soils. This paper provides an analytical framework for evaluating the bearing capacity of strip footings with single-layer and double-layer reinforcement in unsaturated soils. Four classical nonlinear expressions are used to determine the additional cohesion induced by matric suction. Solutions for the reinforcement layer undergoing tensile failure and sliding failure are provided separately. In the former case, where the bearing capacity depends on the reinforcement's tensile strength, the Prandtl mechanism is employed. In the latter case, where the bearing capacity is influenced by the characteristics of the reinforcement-soil interface, a multi-block mechanism is adopted. Additionally, sliding failure exhibits different mechanisms depending on the reinforcement's embedded depth. By comparing the results of different failure mechanisms, accurate upper bound solutions for bearing capacity are obtained. In the case of sliding failure, the optimal reinforcement depths that maximize the bearing capacity are identified for both single-layer and double-layer reinforcement. To facilitate engineering use, the optimum depths and corresponding bearing capacity factors are given in tabular form. The effectiveness of the framework is demonstrated through comparisons with previous theories, experiments, and finite element simulation results.