Effects of spatial variability of soil properties on surface ground motion

The effects of spatial variability of soil properties on the behaviour of a cohesive and a cohesionless soil profile subjected to seismic excitation are analysed. The input data for the random fields are derived from existing, extensive soil investigations, and Monte Carlo simulation technique, combining digital generation of non-Gaussian stochastic vector fields with dynamic, equivalent linear and nonlinear finite element analyses, is used for this purpose. It is found that the variability of shear wave velocity has small effect on the ground surface response spectrum. The motion intensity and the variation of soil properties in the deterministic description of the profile considerably affect the standard deviation of the surface spectral acceleration, which is successively compared to the uncertainty introduced in attenuation relationships, used for the construction of hazard-consistent design spectra.