Finite element simulation of dynamic pile penetration into a saturated porous medium

Numerical modelling of dynamic penetration of objects into soil layers is one of the most challenging problems in computational geomechanics, mainly due to the extreme material nonlinearity, large deformations, and changing boundary conditions. Numerical solution of such problems demands robust algorithms for time stepping as well as integration of the soil constitutive models. This paper presents the dynamic penetration of a pile into a nonlinear saturated porous medium, and addresses the pore water pressure distribution as well as the soil resistance mobilised during the installation phase. The finite element method, in conjunction with Biot's theory of consolidation, is used to model the coupled transient behaviour of the porous medium. The Arbitrary Lagrangian-Eulerian method is employed to avoid mesh distortion throughout the numerical simulation. The pile is treated as a rigid body and the interface between the soil and the pile is modelled using the so-called node-tosegment method of contact mechanics. The generalised-a method is employed to integrate the governing equations in the time domain. Numerical results indicate that the proposed method is able to successfully solve these highly nonlinear problems of geomechanics in which either a saturated or unsaturated soil interacts with another structure.