Numerical study on undrained cone penetration in structured soil using G-PFEM

This paper presents a model for the numerical simulation of cone penetration in structured soil under undrained conditions based on the Particle Finite Element Method. An extended version of the Clay and Sand Model (CASM), allowing microstructural bonding and its degradation to be taken into account, was implemented into the application G-PFEM and compared to the analytical solution for undrained spherical cavity expansion. A robust model for cone penetration is obtained using a nonlocal stress-integration combined with the IMPLEX integration scheme. A parametric study on the shape of the yield surface – which is adaptable for the CASM – and the degree of initial bonding, as well as the rate of destructuration, was conducted to investigate the influence on the obtained normalized parameters Q_t, B_Q, U, and the cone factors N_kt, N_Δu, N_ke used for the determination of the undrained shear strength. It was found that the highest cone factors, leading to conservative estimations of the peak undrained shear strength, are obtained for unbonded material. Both, the shear strength and the tip resistance increase due to soil structure, however, N_kt and N_ke are not significantly influenced as long as no destructuration takes place during penetration.