Analytical solution for infiltration and deep percolation of rainwater into a monolithic cover subjected to different patterns of rainfall

Monolithic cover is increasingly considered for use at landfills of solid wastes in arid and semi-arid areas. The evaluation of the deep percolation of rainwater through the monolithic cover is required for the cover design. An analytical solution is developed in this study for evaluating the infiltration and deep percolation of rainwater into a monolithic cover, subject to different patterns of rainfall events. The analytical solution is derived from the simplified one-dimensional governing equation of unsaturated flow for an infinitely long monolithic cover by taking the exponential forms of the soil–water characteristic curve and the hydraulic conductivity curve into account. A unit gradient boundary (UG) is considered at the bottom boundary of the monolithic cover. The patterns of rainfall considered include uniform type (U), advanced type (A1 and A2), central-peaked type (C), and delayed type (D1 and D2). The delayed percolation after the completion of a rainfall event can be captured by the analytical solution. Numerical simulation is conducted to compare the results with the analytical solution and to demonstrate that the analytical solution is acceptable for describing a silty soil, which is commonly used as the material for a monolithic cover. The analytical solution is used to investigate the influence of the rainfall pattern on the infiltration process and the occurrence of deep percolation. The analytical solution is used to evaluate the total percolation of a monolithic cover subjected to a sequence of non-continuous rainfall events within a wet season. The evaluation accounts for the influence of the initial water storage in the cover on the percolation by using the antecedent rainfall method proposed by Crozier and Eyles in 1980. A case study is performed to demonstrate the evaluation approach by using the water balance monitoring data of a model test on a silty soil cover reported in the literature. The case study indicated that the total percolation from the analytical solution is 34% greater than the measurement, which was on the conservative side for practical application.