Advancement in Estimation of Undrained Shear Strength through Fall Cone Tests

Fall cone tests provide simple and rapid estimate of undrained shear strength (s(u)) of fine-grained soils at various water contents. The accuracy of such s(u) estimation depends greatly on the selection of a fall cone factor K that relates the final penetration depth h(f) with s(u). Available prediction methods for K often fall short of capturing the exact mechanics involved in fall cone penetration. This leads to significant uncertainties in s(u) estimation, particularly for a cone angle of 30 degrees. 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 conesoil interface roughness condition on s(u) 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. (C) 2021 American Society of Civil Engineers.

Automated summary

Fall cone tests provide estimates of undrained shear strength of fine-grained soils, with the accuracy greatly dependent on the selection of a fall cone factor K. Finite element analyses can simulate soil resistance evolution during cone penetration, aiding in quantifying the effects of various factors on undrained shear strength.