An Investigation of Factors that Influence the Water Diversion Capacity of Inclined Covers with Capillary Barrier Effects

Abstract

Covers with capillary barrier effects (CCBEs) can be used as an alternative to more traditional covers that rely on materials with a low saturated hydraulic conductivity. A typical CCBE includes a fine-grained soil layer placed on a coarser material. Other layers can also be added to help the cover play its role(s) efficiently. In a cover built on a flat area, the capillary barrier effect at the interface between the fine and coarse materials allows the finer soil layer to store incoming water, which can later be released by evaporation. Such Store-and-Release covers can be quite convenient in arid and semi-arid conditions. In sloping areas, a CCBE also acts as a lateral water diversion system. Part of this diversion occurs along the sloping interface between the two superimposed soils. It can contribute significantly to the reduction of water percolation deeper into the underlying wastes. However, inclined CCBEs are more complex, as they are influenced by many factors that are not yet fully understood. In such layered covers, moisture is not evenly distributed along the length of the slope. Under some conditions, the moisture-retaining layer can reach a critical degree of saturation at a certain down dip location, which increases infiltration of water into the coarse material and reduces the cover efficiency. This paper presents some of the main results of an ongoing investigation of inclined CCBEs that includes testing on a physical model, field work on large scale covers, and numerical analyses of various cover scenarios. Emphasis is placed here on numerical simulations to assess some of the influence factors that affect the diversion capacity and moisture distribution. The numerical results show how the diversion capacity is affected by the saturated hydraulic conductivity of the fine-grained soil, by the precipitation rate and duration, and by the layer thickness. The findings presented here can be useful for the design of inclined CCBEs.