Advancement in Estimation of Undrained Shear Strength through Fall Cone Tests

Abstract

Fall cone tests provide simple and rapid estimate of undrained shear strength (su) of fine-grained soils at various water contents. The accuracy of such su estimation depends greatly on the selection of a fall cone factor K that relates the final penetration depth hf with su. Available prediction methods for K often fall short of capturing the exact mechanics involved in fall cone penetration. This leads to significant uncertainties in su estimation, particularly for a cone angle of 30°. Finite element analyses (FEAs) employing a coupled Eulerian-Lagrangian technique can successfully simulate the evolution of soil resistance around a cone penetrating through soil. Based on the results obtained from a series of FEAs, this paper presents a fall cone-bearing capacity factor that accounts for strain-rate dependent strength gain in fine-grained soils, soil inertia during undrained cone penetration, and nonzero cone velocity at the start of penetration. The effects of strain rate and cone-soil interface roughness condition on su are quantified. Numerical predictions demonstrate good agreement with results obtained from fall cone and vane shear tests in Kaolin and Marine silt and with the data available in the literature.