Latest revision as of 12:57, 6 June 2024

Abstract

The current cone factor of piezocone penetration tests is derived based on the assumption of elastic-perfectly plastic soil, and the soil rigidity index in the formula is empirically determined. This study introduces a novel in-situ testing equipment for determining both undrained shear strength and soil rigidity index of clays. The presented technique combines cone penetration test (CPT) and in-situ expansion. Indoor experiments are conducted to test the equipment. Corresponding theoretical analysis is carried out to interpret the experimental results. A hyperbolic hardening soil model for undrained clay is used throughout the derivation process so that the nonlinear stress-strain relation is taken into account. The ALE (Arbitrary Lagrangian Eulerian) large deformation finite element method is first employed to analyse the influence factors such as rigidity index, cone roughness, and in-situ stress anisotropy during the penetration process. The formula of cone factor is then proposed and correlated with the limit expanding pressure of the spherical cavity. The rationality of the cone factor is verified by comparing with the ALE analysis results and those published studies. Besides, the limit pressure of in-situ expansion tests is determined based on the load-displacement curve of cylindrical cavity expansion, Specific bearing capacity formula is derived and revised based on finite element analyses. Finally, undrained shear strength and soil rigidity index are solved based on the penetration and expansion results. Interpretation of experimental results shows that the proposed method in conjunction with the newly developed CPT can reasonably predict the undrained strength and rigidity index of soft soils.

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