Finite Deformation Modelling of Cone Penetration Tests in Saturated Structured Clays

In this work, the complex coupled deformation and flow processes occurring in the soil around a CPTu penetrometer during a test in structured natural clays are investigated by means of the Geotechnical Particle Finite Element Method (GPFEM) code. The GPFEM implementation adopted incorporates a fully coupled hydro-mechanical formulation, based on regularized, mixed low-order linear strain triangles. To capture the relevant features of the mechanical response of natural structured clays, the soil behaviour is described using a finite deformation, non-associative elastic-plastic model for this class of geomaterials, referred as FD_Milan model. The model formulation is based on a multiplicative decomposition of the deformation gradient and on the adoption of an elastic response based on the existence of a suitable free energy function. Two bonding-related internal variables, quantifying the effects of structure on the yield locus, are incorporated to provide a macroscopic description of mechanical destructuration effects. To deal with strain localization phenomena, the model is equipped with a non-local version of the hardening laws. The numerical model has demonstrated capable of capturing the destructuration associated with plastic deformations around the cone tip; the space and time evolution of pore water pressure as the cone tip advances; the effect of soil permeability on predicted excess pore water pressures, and the effect of soil bonding on predicted values of cone tip resistance.