A simple method to assess the effects of soil spatial variability on the performance of a shallow foundation

The performance of a geotechnical structure is controlled not by the properties of soil at a point but by the average over a certain line, area, or volume, as pointed out by Vanmarcke (1977) who proposed the variance function. This paper develops his idea and attempts to specify the size of the local averaging of soil parameters to evaluate the resulting variability in performance of a geotechnical structure. In other words, the mean and variance of a local average of a geotechnical parameter for an appropriate volume are used to evaluate the effects of soil spatial variability on the performance of a geotechnical structure. The size seems to be highly dependent on the type of geotechnical problem under consideration. This paper examines the deformation and stability of a shallow foundation to specify the averaging volume size. The results suggest that the concept can be extended to many other geotechnical reliability analyses.