Influence of Slope Angle on Water Flow in a Three‐Layer Capillary Barrier Soil Cover under Heavy Rainfall

A three‐layer capillary barrier soil cover has been recently proposed for minimizing rainwater percolation in humid climates. Its performance has been preliminarily investigated by both physical and numerical modeling at a fixed slope angle of 10°. However, the slope angle of soil cover is varied in engineering practice and hence it is an essential design parameter. In this study, the influence of slope angle on water flow in the three‐layer soil cover was investigated via flume model tests subjected to heavy rainfall. A 3‐m long flume model of soil cover was instrumented to monitor matric potential and volumetric moisture content as well as components of water balance at slope angles of 3°, 10° and 18°. Furthermore, numerical simulations of transient seepage were conducted to back‐analyze the experiments. Both experimental and numerical results showed that the infiltration ratio increased as the slope angle increased because of the increase in the soil water potential gradient normal to the slope gradient. Meanwhile, the lateral water flow in the upper two layers was enhanced by the increase of slope angle due to water backfill effect at the top of clay layer. Correspondingly, the steeper the slope, the lower the matric potential, volumetric moisture content and soil water potential in the upper two layers were. Due to low hydraulic conductivity of the bottom clay layer, the percolation through the cover remained virtually nil at each slope angle. The above findings could have significant implications for the design of sloping three‐layer capillary barrier soil cover.