Unified solution of Meyerhof’s ultimate bearing capacity for strip foundation resting on unsaturated soils

Based on the unified solution of shear strength for unsaturated soils, a unified solution of Meyerhof’s ultimate bearing capacity for strip foundation is obtained by considering the effects of intermediate principal stress, matric suction and strength nonlinearity. The validity and applicability of the obtained unified solution are demonstrated by comprising it with the results of the slip-line theory and upper-bound theory available in literatures. The differences of the ultimate bearing capacity between the Terzaghi’s theory and Meyerhof’s theory and the roughness effect of foundation base are discussed. The influences of the intermediate principal stress, high/low matric suction and effective strength parameters are investigated. The findings show that the Terzaghi’s ultimate bearing capacity simplifies the shear strength of lateral soils as uniform load, which exaggerates the real effect of lateral soils and leads to a larger result. The roughness of foundation base is critical for determining the bearing capacity factors. Meyerhof’s ultimate bearing capacity increases significantly with the intermediate principal stress effect, and the results of Mohr-Coulomb criterion are too conservative due to no consideration of the intermediate principal stress. The matric suction has a dual-effect: the ultimate bearing capacity increases linearly in the low suction region, meanwhile it gradually decreases and eventually stabilizes in the high suction region, which is caused by the nonlinear strength of unsaturated soils. The effects of the effective strength parameters are also important, and furthermore the effect of the effective internal friction angle is more obvious than that of the effective cohesion. Due to considering many practical engineering conditions, such as the intermediate principal stress effect, unsaturated characteristics as well as shear strength of lateral soils, this study can provide useful references for the optimization of foundation design and construction.