Two-phase two-layer SNS-PFEM for hydromechanical geotechnical large deformation problems

A two-phase one-layer stabilised node-based strain-smoothing Particle Finite Element Method (SNS-PFEM) was previously proposed, but it lacked the capability to simulate water-soil coupling. To address this limitation, this study presents an improved approach called the two-phase two-layer SNS-PFEM, specifically designed to handle such problems. In this method, two overlapping mesh layers are employed to independently represent the two phases. Within this framework, the water phase is characterised as an incompressible Newtonian fluid solved using the PFEM-T3 method, while the soil phase is described using an elastoplastic constitutive model, effectively addressed through a modified SNS-PFEM. To obtain the solution for the proposed two-phase two-layer approach, a fractional step algorithm is utilised, allowing efficient and accurate computations. To validate the proposed method, it is applied to various soil-water coupling problems, encompassing both quasi-static and large deformation scenarios. The first set of simulations are (1) simulation of 1D Terzaghi's consolidation test and (2) simulation of fully submerged soil subjected to gravitational load. Next, the proposed method is applied to simulate cases involving large deformation problems: (1) flow passing through a porous dam, (2) a submerged granular landslide and its induced waves and (3) a submarine progressive landslide. The results of all simulations demonstrate the robustness and versatility of the proposed method in effectively analysing large deformation multi-phase problems in the field of geotechnical engineering. This advancement is a significant step forward in accurately simulating complex interactions between water and soil, opening up new possibilities for research and analysis in geotechnical applications.