Dilatancy Effects on Surface Foundations on Dry Sand

Abstract

This paper presents the results of finite-element analyses of rigid-surface strip foundations on dry cohesionless soil subjected to displacement-controlled vertical loading. A two-surface constitutive model with a non-associated flow rule, representing the full range of pressure-dependent drained shear strength and volume change behavior of dry sand, is employed to model the soil. A range of foundation widths and sand initial relative densities is covered. The results show that, for narrow, rigid-strip foundations, the conventional bearing-capacity calculation provides a reasonable indication of the load-carrying capacity of the foundation. However, there is no peak in the load-carrying capacity for wide foundations, and the load–deformation curve exhibits stiffening behavior, even at large settlements; this is particularly apparent at larger values of the initial relative density. Based on the results, it is observed that with the increase in vertical foundation loading, the vertical stiffness of the foundation increases with each loading increment, due to the tendency of the dense sand to become more dilatant with the increase in confining pressure. At large settlements, the state of the sand beneath the foundation approaches the critical state. Settlement vectors beneath the foundations on dense sand reveal that the displacements approximate one-dimensional compression.