Pore-scale simulation of soil water retention curves using DEM-derived pore networks

Abstract

This study presents a pore-scale modelling approach for simulating the soil–water retention curves (SWRCs) of silty sands and sands using a pore network model (PNM) applied to artificially generated non-uniform sphere packs. The adopted approach enables detailed analysis of pore size distribution (PSD) and its dependency on key soil properties, including void ratio, grain size distribution (GSD), and soil fabric, thereby offering mechanistic insights into the observed SWRC behaviour. Compared to experimental techniques, this method offers a superior ability to isolate the effects of individual parameters. Furthermore, coupling the PNM with a constructed sphere pack provides a framework for future investigations into the influence of soil moisture on micro-mechanical interactions among particles.

In the proposed method, soil samples are represented as sphere packings generated using a discrete element method (DEM) platform, with their pore spaces idealised as networks of pore bodies connected by pore throats. SWRCs are then derived by applying varying capillary pressures to the pore network. The approach is thoroughly validated against experimental data from the literature before being employed to investigate the effects of void ratio, GSD, and soil fabric on soil water retention behaviour.

It is shown that the model successfully reproduces the hysteresis effect in SWRCs, highlighting the impact of capillary forces and pore connectivity on wetting and drying cycles. The effects of particle size and GSD on the retention behaviour is also examined. Finally, the influence of soil fabric is briefly explored by comparing samples prepared to the same void ratio but subject to different loading paths, namely, one-dimensional and isotropic compressions.