Fall cone behavior of non-plastic silts and undrained shear strength from DSS tests

Fall cone penetration behaviour of clays had been investigated for years, however, very little is known about the fall cone penetration behaviour of silts, especially low to non-plastic ones. Extensive fall cone tests were done on three different non-plastic silts over a broad penetration range. The results were compared with the behaviour of various soils with low and high plasticity. It was observed that the fall cone penetration water content relationship is typically non-linear for most plastic soils. However, it surprisingly becomes linear at the extreme sides of plasticity. More explicitly, the change of penetration depth with water content of non-plastic silts and bentonites are shown to be expressed with the same linear equation with different coefficients. Next, undrained shear strengths of silts were determined from direct simple shear tests performed under at least three vertical consolidation stresses. The simple power relationship between water content and undrained shear strength, proposed for remoulded clays in the literature, is observed to work very well for reconstituted non-plastic silts as well. Finally, undrained shear strengths of silts were predicted based on their liquid limits obtained from fall cone tests by modifying a relationship in the literature, which was developed mainly on clays.