Slope stability of landfills considering leachate recirculation using vertical wells

In bioreactor landfills, leachate recirculation system can significantly promote moisture distribution, thereby enhancing the biodegradation of municipal solid waste (MSW). However, it increases pore pressure inside landfills, which can greatly affect slope stability. In this study, a three-dimensional numerical model is established to study the landfill slope stability under leachate recirculation through Vertical Wells (VWs). A leachate flow model is adopted to describe the migration of leachate, and the distribution of pore pressure is then used to calculate the Factor of Safety (FS) using strength reduction method. A large number of simulations are conducted using the proposed model to investigate the influences of injection pressure, hydraulic and mechanical properties, slope gradient, VW location and group-well configuration on slope stability. Large injection pressure or anisotropy of MSW is adverse to the slope stability. FS changes almost linearly with the variation of friction angle and cohesion. The horizontal distance between the VWs and the slope surface (d) and well spacing (D) are two important factors for slope stability. Design charts of the minimum safe distance (ds) and the minimum safe well spacing (Ds) are proposed considering various conditions. Finally, a design method of leachate recirculation system using VWs is proposed considering both recirculation efficiency and slope stability. The proposed model can well accommodate practical landfills with leachate recirculation system using VWs. The method and the results are promising to be used as a reference in engineering practice.