Effect of hydraulic hysteresis on seepage analysis for unsaturated soils

Abstract

This paper describes a study into the effects of hysteresis on the hydraulic behaviour of unsaturated soil covers. The Richards equation is coupled with the hysteretic soil water characteristic curves (SWCCs), to describe water flow in unsaturated soils. A linear scanning curve on semi-logarithmic scales is used to describe the hydraulic behaviour within the main hysteretic loop in unsaturated seepage problems. The proposed approach is implemented for one-dimensional flow problems using the finite difference method. A comparison of predictions of the proposed hysteretic model with those of the traditional non-hysteretic model is carried out first. For the assumed scenario of a compacted clay cover, the non-hysteretic model using the main drying SWCC leads to significantly different results than the hysteretic model, further demonstrating the necessity of accounting for hysteresis in unsaturated seepage analysis. Moreover, three infiltration tests on layered soil columns are simulated with the proposed hysteretic model. Results show that hysteresis plays an important role in the seepage analysis of unsaturated soils subjected to cyclic drying and wetting. The hysteretic model is suggested for use in the design and evaluation of the hydraulic performance of soil covers.