Stability Analysis According to Different Shear Strength Concepts Exemplified by Two Case Studies

Stability analysis for landfills of municipal solid waste can be conducted according to different analytical calculation methods. The conventional calculation method has been transferred from soil mechanics. The method was invented in the 1920s by Bishop. An advanced method was presented in the 1990s in Germany. It is basically an extended Bishop method which has been adjusted to some specific strength properties of MSW. Meanwhile, the advanced method became technical standard in Germany. Both methods lead to different results in stability analysis regarding the factor of safety as well as the failure mechanism. Due to those differences, engineers may find different conclusions for mitigation and safety measures. Stability analysis is basically a modelling process. Subsequently, only the comparison of calculation results and empiric observations allow a validation of the physical models behind the analysis. Concerning the validation, failures are the most useful events, since they enable back calculation. The following presentation introduces the advanced strength concepts and the stability analysis exemplified at two landfill failures, the back-calculation of the most recent landfill failure which happened in February 2005 on Leuwigajah dumpsite in Bandung, Indonesia. Regarding the number of casualties and the volume of waste, it was the heaviest failure, which ever happened. The second slope failure case to be reviewed occurred in June 1991 on the Bandeirantes landfill located in São Paulo, Brazil. The following article presents the results of the forensic analysis of both cases and the back-calculation of the events. Both alternative calculation methods were used. The results will demonstrate significant differences between the two methods.