Cone penetration tests in unsaturated silty sands

Abstract

Very little is known about how to interpret cone penetration tests (CPTs) when performed in unsaturated soils. The few published studies on CPTs in unsaturated soils have focused on either clean sands or silt. In this study, new results of laboratory-controlled CPTs in an unsaturated silty sand are presented. Silty sand exhibits hydraulic hysteresis and suction hardening. Suction is observed to have a pronounced effect on measured cone penetration resistance. For an isotropic net confining stress of 60 kPa, it is observed that higher suctions give rise to cone penetration resistances that are 50% larger than those for lower suctions. A semi-theoretical correlation is presented that links measured cone penetration resistances to initial relative density and mean effective stress. Suction has an influence on cone penetration resistances through suction hardening, as well as its contribution to effective stress. For this silty sand, it is shown that failing to account for suction may result in significant overestimations and unsafe predictions of soil properties from measured cone penetration resistances.