An analytical solution for vertical gas flow in layered MSW landfill with depth-dependent permeability

Abstract This study develops a steady-state analytical model for one-dimensional vertical gas flow in layered municipal solid waste (MSW) landfills. The model explicitly considers the stratified landfill configuration and includes a depth-dependent gas permeability coefficient. The analytical solution is derived using the method of undetermined coefficients and validated through model degeneration and comparison with COMSOL 6.0 numerical simulations. Parametric analyses show that the proposed base-e exponential layered model captures the variation of gas pressure gradients across different waste layers. Further investigation indicates an asymmetric influence of permeability parameters in the upper and lower layers on gas pressure distribution. Variations in upper-layer parameters transmit downward. They cause an overall shift in the lower-layer pressure distribution. However, changes in lower-layer parameters do not affect the upper-layer pressure distribution. In addition, the cover-induced pressure response of a double-layer cover system depends on its equivalent permeability coefficient. It is independent of the vertical stacking sequence. These findings provide a theoretical basis for landfill cover design and gas migration risk assessment.