Stochastic analysis of hydraulic hysteresis in multi-layer unsaturated soil covers under random flux boundary conditions

The effect of hydraulic hysteresis inherent in soil water characteristic curves is explored stochastically in seepage analysis of engineered soil covers. A multi-layer soil cover with random top boundary flux conditions is simulated with the First Order Second Moment method. Water inflow and outflow at the top boundary are chosen as two random variables. The capillary barrier mechanism is taken into account, and the breakthrough hydraulic head at the bottom boundary of the soil cover is adopted as the performance function. Results show that the hysteretic hydraulic model predicts a more conservative result than does the traditional nonhysteretic hydraulic model when simulating seepage in unsaturated, multi-layer soil covers. The dependence of the soil cover performance on its exterior environment during construction is also identified, with a relatively arid season significantly improving the soil cover's functionality. Furthermore, multi-layer soil covers with a proper selection of geotechnical materials provide better performance than a single layer of soil cover of the same thickness. The importance of hydraulic hysteresis in soil covers subjected to alternative climatic actions is emphasized.