Estimation of Maximum Liquid Depth in Layered Drainage Blankets over Landfill Barriers

Based on an extended form of the Dupuit assumption, this technical note proposes a computational solution for calculating the maximum liquid depth $\left(D_{\max }\right)$ in layered porous media (e.g., geosynthetic and/or soil drainage blankets of landfills) under free discharge condition. The liquid profile and the location of $D_{\max }$ for either homogeneous media or layered media can be provided from the approach presented in this technical note. In comparison with the results obtained by application of other methods, the presented approach is verified. Most approaches other than the presented method may lead to considerable error, especially when applied to the drainage system, which consists of a drainage geocomposite overlain by a sand layer with low hydraulic conductivity. The variations of $D_{\max }$ in two-layered drainage media with varying geometrical parameters and varying hydraulic properties are studied by a parametric analysis. The results demonstrate for a medium consisting of two sand layers, if the hydraulic conductivity of the upper layer is smaller than that of the lower layer and the maximum liquid thickness above the barrier exceeds the thickness of the lower layer, $D_{\max }$ is very sensitive to the hydraulic conductivity of the upper layer. For a medium consisting of a drainage geocomposite overlain by a sand layer, $D_{\max }$ is significantly influenced by inflow rate, transmissivity of the geocomposite, and the hydraulic conductivity of the sand when they are not extraordinarily low, and $D_{\max }$ is much more sensitive to the slope of the drainage layer compared with the system consisting of two sand layers. It is of great advantage to increase the inclination when geocomposites are applied as drainage material.