Abstract: As a reliable method to determine the liquid limit of finegrained soils, the falling cone test is widely used in soil laboratory testing. At the same time, the undrained shear strength of the soil can be determined from the cone factor K. By studying the theoretical and experimental values of K, combined with concepts of quasi-static and dynamic infiltration, the mechanism of the cone entering into the soil sample is analyzed in this paper. By using the analytical method, the expression of the dynamic undrained shear strength is proposed, and the cone surface roughness, the shear strain rate and the soil heave are considered, so the theoretical expression of the cone factor K can be obtained. Throughout the comparison, it is found that the cone factor K of a 30° cone has a large dispersion. Finally, based on the theoretical analysis results, it is suggested that the 60° cone is more suitable for determining the liquid limit than the 30° cone.

Key words: Falling Cone Test, Cone Factors, Theoretical Approach