This paper presents a computational framework for the numerical analysis of fluid-saturated porous media at large strains. The proposal relies, on one hand, on the particle finite element method (PFEM), known for its capability to tackle large deformations and rapid changing boundaries, and, on the other hand, on constitutive descriptions well established in current geotechnical analyses (Darcy’s law; Modified Cam Clay; Houlsby hyperelasticity). An important feature of this kind of problem is that incompressibility may arise either from undrained conditions or as a consequence of material behaviour; incompressibility may lead to volumetric locking of the low-order elements that are typically used in PFEM. In this work, two different three-field mixed formulations for the coupled hydromechanical problem are presented, in which either the effective pressure or the Jacobian are considered as nodal variables, in addition to the solid skeleton displacement and water pressure. Additionally, several mixed formulations are described for the simplified single-phase problem due to its formal similitude to the poromechanical case and its relevance in geotechnics, since it may approximate the saturated soil behaviour under undrained conditions. In order to use equal-order interpolants in displacements and scalar fields, stabilization techniques are used in the mass conservation equation of the biphasic medium and in the rest of scalar equations. Finally, all mixed formulations are assessed in some benchmark problems and their performances are compared. It is found that mixed formulations that have the Jacobian as a nodal variable perform better.

Borehole tube sampling is a key process of geotechnical engineering. The paper presents numerical analyses of smooth tube sampling in clay using the particle finite-element method. The soil is described by a conventional elasto-plastic constitutive model (Tresca plasticity and a quasi-incompressible elastic law). The sampler is advanced by several diameters into the soil until a steady state is observed. The elasto-plastic numerical solution for a round-tipped sampler clearly identifies a localised shear failure mechanism at the entrance of the tube. Relevant strain path method (SPM) solutions are numerically evaluated to facilitate full field comparison. For a given thickness ratio elasto-plastic simulation predicts far less compression but much larger extensions at the centreline than SPM. The results also show how including a bevelled sampler tip or a stationary piston changes the failure mechanism and significantly reduces induced peak extension strains. The results agree with available experimental data and well-established empirical observations. The methodology presented may open the way to a soil mechanics-based rational approach to soil sampling simulation.