Combinations of soil materials for granular capillary barriers for minimizing rainfall infiltration and gas emission

This paper presents a coupled air-water flow analysis to evaluate the performance of a three-layer capillary barrier for controlling water infiltration into and gas emission from a waste containment system in a high precipitation environment, and to optimize combinations of local soil layers for barrier construction. A multi-phase flow model is proposed considering the movements of the gas and water phases simultaneously. The governing partial differential equations are solved in COMSOL Multiphysics software. Several combinations of lean clay with sand (CL), clayey sand with gravel (SC), silty sand with gravel (SM), sandy silt (ML), and well-graded gravel with silt (GW-GM) are examined. The rates of percolation water and gas emission are used as indicators to compare the performance of different combinations. A fine-grained surface soil layer reduces both water infiltration and gas emission due to its low desaturation rate and high water-retention capacity. The coarse middle layer plays a critical role, promoting capillary effects and hindering water infiltration during rainfall as well as draining any infiltrated water or percolated gas.