Effect of Spatial Variability on Buried Footings

Natural soil is one of the most variable materials as a result of physical and chemical changes. The variation in soil properties significantly affects the failure mechanism and bearing capacity of a footing. This effect is further complicated by considering the spatial correlation of the soil properties. The purpose of this study is to investigate the influence of the spatial variability of a clay on the bearing capacity of a buried footing. The spatial variation of undrained shear strength of a clay is modelled by random fields. The random fields are generated and mapped into a non-linear finite element analysis. The failure mechanism and bearing capacity of a footing in a spatially random soil can then be revealed. Finally a Monte Carlo simulation is employed to investigate the effect of spatial variability on the buried footing. The random fields with different scales of fluctuation are modelled to reveal the effects of spatial variability. It is found that the mean values of bearing capacity of the foundation are the smallest when the scale of fluctuation is 0.1-1 times of foundation width. The coefficient of variation of the bearing capacity increases with increasing scale of fluctuation. When the scale of fluctuation is on the order of the foundation width the variation in bearing capacity is mainly due to the different shear paths developed in the random soil. When the scale of fluctuation is much larger than the foundation width, the variation in bearing capacity is mainly due to the distinct soil strength in different realizations.