Design of inclined covers with capillary barrier effect
Parent, Serge-Étienne; Cabral, Alexandre
Abstract: A design procedure is proposed to minimize water infiltration into landfills in optimizing the water diversion length of inclined covers with capillary barrier effect (CCBE). This design procedure aims at selecting materials and optimizing layer thickness. Selection among candidate materials is made based on their hydraulic conductivity functions and on a threshold infiltration rate imposed on the designer. The capillary break layer (CBL; bottom layer) is characterized by a weak capillarity, while the moisture retention layer (MRL; upper layer) is characterized by a stronger capillarity. The thickness of the CBL corresponds to the height where suction reaches its maximum value for a given infiltration rate. This height can be calculated using the Kisch (1959) model. The optimal thickness of the MRL is determined by applying an adaptation of the Ross (1990) model. The results obtained using the proposed design procedure were compared to those obtained from numerical simulations performed using a finite element unsaturated seepage software. The procedure was applied for two cover systems; one where deinking by-products (DBP) were used as MRL and sand as CBL and another where sand was used as MRL and gravel as CBL. Using this procedure, it has been shown that an infiltration control system composed of thin layers of sand over gravel is highly efficient in terms of diversion length and that its efficiency can be enhanced by placing a hydraulic barrier - such as a layer of DBP - above the MRL.
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