Hysteretic seepage analysis in unsaturated soil covers

![CDATA[This paper aims to study numerically the effect of hysteresis on the hydraulic behaviour of unsaturated soil covers. The Richards equation is coupled with the hysteretic soil water retention curve (SWRC), to describe the flow in unsaturated soils. A linear scanning curve is used to describe the hydraulic behaviour within the main hysteretic loop in unsaturated seepage problems. The proposed approach is implemented with the finite difference method. A comparison of the proposed hysteretic model with the traditional non-hysteretic model is carried out first. The non-hysteretic model using the main drying SWRC leads to significantly different results than the hysteretic model, further demonstrating the necessity of accounting for hysteresis in seepage analysis. A sensitivity analysis on the hysteresis ratio and the slope of the scanning curve is then carried out with the hysteretic model. Results show that hydraulic hysteresis cannot be neglected in the seepage analysis of soil covers composed of soils exhibiting significant hydraulic hysteresis. The proper determination of both the scanning curve and the initial hydraulic state plays a crucial role in the reliability of numerical simulations of soil covers subjected to cyclic drying and wetting. It is suggested that the proposed hysteretic model may be applied in the design and evaluation of the hydraulic performance of soil covers.]]