Slope stability of bioreactor landfills during leachate injection: Effects of unsaturated hydraulic properties of municipal solid waste

In bioreactor landfill, the leachate flow and moisture distribution depend upon saturated and unsaturated hydraulic properties of municipal solid waste (MSW). The effects of unsaturated parameters have not been studied because of scarcity of the data and variation in unsaturated parameters due to MSW heterogeneity, degree of decomposition, and pore structure. In this study, a numerical two-phase flow model was used to examine the effects of unsaturated hydraulic properties on the moisture distribution, pore fluid pressures, and the stability of a bioreactor landfill slope with horizontal trench as leachate recirculation system. Unsaturated hydraulic parameters were based on the van Genuchten model and obtained from previously published laboratory studies. The unsaturated hydraulic properties of MSW are found to significantly influence the leachate distribution, pore water and capillary pressures, and landfill slope stability during the operations of leachate injection and subsequent gravity drainage. Further research is needed for better understanding and accurate measurement of hydraulic properties and shear strength parameters of unsaturated MSW.