Shear viscosity of clays using the fall cone test

Abstract

A knowledge of shear viscosity is important in understanding the viscous resistance in the dynamic penetration of soils for geotechnical applications such as jacked piles and cone penetrometers. Viscosities of soils with water contents greater than the liquid limit have been investigated using viscometers. There is, however, no standard method to determine shear viscosities of clays at water contents lower than the liquid limit. In this paper, the post failure (critical state) response of fine-grained soils is modelled as if they were visco-plastic fluids. In addition, the theory of the fall cone test, currently used to interpret the index and strength properties of fine-grained soils, is re-evaluated to discern the viscous drag as the cone penetrates the soil. This re-evaluation shows that the shear viscosities of clays at liquidity indices less than 1·5 can be estimated from a continuous record of time-cone penetration depth data. Fall cone test results on kaolin show that the shear viscosity decreases exponentially with increase in liquidity indices.