Numerical Analysis of a Municipal Solid Waste Slope Failure

The Zone II slope of Dona Juana Municipal Solid Waste (MSW) Landfill became instable two years after commencing with MSW filling. The slope failure resulted in displacing about 1.5 million ton of municipal solid waste toward the Tunjuelito River. Zone II was designed with a leachate recirculation system. The original failure investigation in 1997, utilized instrumentation data and back calculation of the safety factor using limit equilibrium methods to investigate the possible cause(s) of failure. In this paper, the Dona Juana slope failure was investigated utilizing a coupled hydro-mechanical 2D numerical simulation, which allowed to qualitative understanding on the importance of secondary drainage slots. The analysis results, in terms of safety factor and location of the failure surface, are in general agreement with the data collected from field instrumentation and conclusions presented in previous studies. The results demonstrate that the filter to liner area ratio has significant effect on the factor of safety against slope instability. Recommendations on the proper design and operation of a landfill with a leachate recirculation system are provided.