Shear viscosity of clays in the fall cone test

The purpose of this paper is to investigate the use of a fall cone test to determine the viscosity of clay soils with a liquidity index of less than one. The conventional tool to determine the viscosity of clay soils is a viscometer. But, viscometers are suitable only for determining the viscosity of soils for water contents greater than the liquid limit. Because soil flow can take place within the plastic range, the viscosity has to be determined by means other than viscometers. In this study, eight soils were thoroughly investigated using the fall cone test. The results of the study show that the fall cone test is suitable to determine the shear viscosity of clay soils. Excellent correlations (regression coefficients > 0.95) were found between the final penetration depth and the dynamic equilibrium depth, and between the liquidity index and the viscosity.