The Effect of Leachate Recirculation on the Slope Stability of Bioreactor Landfills

Leachate recirculation in bioreactor landfills provides appropriate conditions for rapid decomposition of waste. On the other hand, this operation increases the pore water pressure and consequently increases risk of bioreactor failure, especially on the side slopes. In the present study, according to the waste conditions, a two-dimensional (2D) model was proposed through GeoStudio software for investigating the effects of leachate recirculation (by considering vertical injection pipes in two areas A1 and A2 at distances of 20 and 40 m from the side slope of the landfill, respectively) in a bioreactor landfill with a slope of 3:1 H: V at a height of 20m from the base and at two injection pressures (150 and 200 kPa) on stability of bioreactor. Also, six different waste layers with various charecteriastics (including different cohesion, internal friction angle, specific gravity, and hydraulic conductivity were considered.  The results revealed that Factor of Safety (FS) values were lower when the leachate injection was located at the area A1 in comparison to the area A2. This could be due to the higher pore water pressure generated when leachate injection was located at A1. Moreover, the higher values of injection pressure (200 kPa) and greater distance from the side slope (A2) cause more areas to be affected by the leachate recirculation and provide stable conditions for bioreactor landfills in a shorter time. The findings of the current research help to better understandthe influence of leachate recirculation on the FS value and enhance the design of biorector landfills.