Coupled phenomena in soil: Examples of insights gained from multi-physics particle-scale simulations

Arguably the most important idea in modern soil mechanics is the principle of effective stress put forward by Karl Terzaghi just over a century ago in 1923. The transformational impact of this principle on soil mechanics and geotechnical engineering reflects both the importance and challenge of accounting for the interaction between the solid and liquid phases in soil and other particulate materials. Apart from the multi-phase nature of soil, the influence of temperature changes and chemistry may also be significant. A comprehensive model should account for thermal, hydraulic, mechanical and chemical couplings. Despite significant advances our fundamental understanding of the interaction between the phases and phenomena remains incomplete, compromising our ability to accurately model or predict behaviour for engineering design analyses. Discrete element method (DEM) simulations, coarse-grained molecular dynamics, porenetwork- modelling, and finite volume method computational fluid dynamics simulations together can advance understanding of key coupled phenomena in sand and clay. Emerging challenges include liquidparticle interactions considering both Newtonian and non-Newtonian fluids, the impact of pore-fluid chemistry on clay behaviour, the response of granular materials to changes in temperature, and the challenge of accurately modelling the pressure field when the pore-space includes multiple fluid phases. This paper demonstrates the value of particle and sub-particle scale simulations, while also introducing some of the numerical techniques that can be adopted to develop fully coupled simulation tools.