Effects of hysteresis ink-S-p relationships on the performance of minewaste soil covers

Abstract

Soil covers are widely used in mine waste and landfill applications to protect the environment. The finite-element based model was used to simulate the vertical flow of water through unsaturated cover soils. A hysteretic model for two-phase permeability-saturation-pressure (k-S-p) relations is implemented in unsaturated flow model to predict temporal and spatial fluid distributions in a soil cover. A representation of hysteretic soil hydraulic properties is based on a combination of van Genutchen’s equation and statistical model for relative permeability. Predictions ofk-S-p relations along major flow paths are presented for fine sand, silt, and coarse sand. Employing hysteretic and nonhysteretic relationships, this study also presents a comparison of saturation profiles in four different cover soils: fine sand, silt, and coarse sand as single covers and multi-layered soils. A number of simulations were performed to analyze the saturation profile in the cover soils subject to downward drainage due to gravity and infiltration under various conditions of at the top and bottom. The numerical results indicate that simulation of water flow involving saturation path reversals may produce significant differences between hysteretic and nonhysteretic results. Considerations should be given to effects of hysteresis in hydraulic properties to accurately predict fluid distributions in a cover soil.