Finite element analysis experiments on landfill cover drainage with geosynthetic drainage layer

Landfill cover systems invariably include a drainage layer which is most often a drainage geocomposite. Finite element analysis of seepage in landfill covers with a drainage geocomposite was performed to determine the effect of rainfall rate, slope length, slope angle, anisotropy, multiple materials and three-dimensional slopes on the pressure head above the liner. Simple methods, based on published equations, were found to provide similar maximum pressure head on the liner as the steady state finite element analysis when only the geocomposite was involved in the drainage. Pressure heads for transient, more-than-one-material, three-dimensional and anisotropic cases were found to be very different from simple solutions. The finite element analysis showed the variation of pressure head along the liner to be highly non-linear with the geocomposite and cover soil saturation occurring simultaneously. The seepage analysis was combined with a limit-equilibrium slope stability analysis to determine factors of safety against slope failure and compare the results with simple methods.