Material Point Method for Cone Penetration in Clays

This study presents a coupled material point method (MPM) formulation for the analysis of cone penetration in clays. The formulation is based on the generalized interpolation material point method (GIMP) variant of MPM. A single material point is used to represent both the soil matrix and water. The governing equations are solved using an explicit scheme with the velocity of the soil matrix and the velocity of water as the primary variables. Incompressibility constraints in the soil matrix are resolved using the nonlinear B-bar method, and pore pressures are computed at element centers. The formulation is validated through problems for which analytical or numerical solutions are available. Cone penetration resistances measured at a Boston Blue Clay (BBC) test site are then computed using the coupled MPM formulation with the constitutive response of BBC captured using an advanced bounding surface model based on critical state soil mechanics. Based on the cone penetration simulation, the penetration resistances under undrained, partially drained, and drained conditions are computed by varying the hydraulic conductivity of the clay. The cone factor for undrained penetration is also calculated. Verification and validation exercises demonstrate the efficacy and robustness of the adopted formulation in the realistic simulation of cone penetration in clay.