Numerical investigation of the performance of covers with capillary barrier effects in South China

A cover with capillary barrier effects (CCBEs) is a promising final cover for controlling water infiltration into a waste containment system. A CCBE consisting of a layer of fine soil and a layer of coarse soil relies on the particle size contrast of the two soils. Although CCBEs have been successfully used in dry climate, their performance under high precipitation intensities and high evaporation conditions (e.g., in South China) is still unclear. This paper aims to evaluate the performance of the CCBE in high-precipitation areas and propose appropriate combinations of local soils for constructing a CCBE in South China. Several combinations of lean clay, clayed sand, and silty sand with gravel are examined using saturated/unsaturated seepage analysis. Two contrasting conditions, i.e., a drizzle lasting for a long time and an intense storm lasting for a short time, are applied to the covers. The covers perform well when subject to prolonged small rainfall at an initial maximum suction of 150 kPa. When subject to a short-time heavy rainfall, breakthrough occurs in the cover consisting of clayed sand overlying silty sand with gravel. Of the three covers, a CCBE consisting of lean clay overlying silty sand with gravel performs well under both prolonged light rainfall and short time heavy rainfall conditions. This CCBE has the longest period of time before breakthrough and the least amount of percolated water under prolonged heavy rainfall.