Analytical solutions for rainfall infiltration into monolithic covers considering arbitrary initial conditions

As an isolation barrier between landfill and atmospheric environment, monolithic covers are used to control rain water infiltration and deep percolation into landfill. In recent years, the covers are proved to be effective in some arid and semi-arid areas in North America. An analytical solution for rain water infiltration into a monolithic cover is presented on the basis of the two-dimensional governing equation for unsaturated flows. The analytical solution can take arbitrary initial conditions into consideration. To obtain the analytical solution, it is assumed that both the soil-water characteristic curve and the permeability function can be described by using the exponential functions considering entry air value and the bottom boundary of the monolithic cover is set as the unit gradient boundary. The analytical results are compared with those measured results reported in literatures, indicating that the analytical solution is effective. The influence on rain water infiltration into a monolithic cover and its percolation of using three boundaries including unit gradient boundary, seepage face boundary and fixed pore water pressure boundary as its bottom boundary are analyzed. The results indicate that compared with the other two boundaries, the unit gradient boundary is more suitable for the monolithic covers to calculate the percolation. The influence of various initial conditions on accumulated percolation of monolithic covers is analyzed using the analytical solution. The research indicates that the accumulated percolation increases with the increase of the initial volumetric water content near the bottom of the covers. This study provides a simple and practical method for evaluating the performance of monolithic covers to control rain water percolation through a soil cover.