Bearing capacity of foundations resting on a spatially random soil

The paper presents the effect of the spatial variability of the soil properties on the ultimate bearing capacity of a vertically loaded shallow strip footing. The deterministic model used is based on numerical simulations using the Lagrangian explicit finite difference code FLAC 3D. The cohesion and the angle of internal friction of the soil are modelled as non normal anisotropic random fields. The methodology used for the discretization of the random fields is based on the spectral representation method proposed by Yamazaki and Shinozuka (1988). The results have shown that the average bearing capacity of a spatially random soil is lower than the deterministic value obtained for a homogeneous soil. A critical case appears when the autocorrelation distances are equal to the footing breadth. The average value of the ultimate footing load is more sensitive to the horizontal autocorrelation distance than the vertical one. Finally, it has been shown that accounting for the spatial variability of the soil properties gives a higher reliability index of the foundation than the one obtained with the assumption of random variables.