Shear Strength of Municipal Solid Waste

While the engineering profession's understanding of the response of municipal solid waste (MSW) to monotonic and cyclic loadings has improved over the past two decades, several important issues remain unresolved. Characterization of the shear strength of MSW is a critical step in performing reliable static and seismic stability analyses of landfills. Landfill stability analyses can be no more reliable than the reliability of the engineer's estimate of the shear strength of the waste. Furthermore, the stress-strain response of MSW needs to be considered to provide compatibility between the mobilized shear strength and the level of deformation along potential failure surfaces. Relevant studies of MSW shear strength are summarized in this state-of-knowledge chapter. Large-scale laboratory test data, which includes direct shear (DS), triaxial (TX), and simple shear (SS) test results, and back-analyses of failed and stable landfill slopes in the field are considered. Findings from a recent comprehensive study by Zekkos (2005) are emphasized. There is large variability in the shear strength of MSW reported in the literature. Obstacles to characterizing the shear strength of MSW include its age, heterogeneity and the difficulty in recovering and testing representative waste samples due to the large size of some waste constituents. Differences in testing procedures employed and in the assumptions made when interpreting the test results also contribute to the variability of the shear strength of MSW. A consistent conceptual framework to perform and to evaluate the results of the laboratory and in-situ tests performed on MSW is required. It is hoped that the recommendations provided as part of the first "International Waste Mechanics Symposium" will address this issue and work toward providing a common framework for advancing the profession's understanding of waste properties and mechanics through developing consensus on the performance and reporting of laboratory and field testing procedures. Published data reported in the literature on the shear strength of MSW are discussed in sections on large-scale tests and back-analyzed assessments. This literature review does not provide complete descriptions of the works completed by researchers, as this information is available in detail in the referenced papers. Instead, key findings are summarized. Following the literature review, a summary of the state-of-knowledge of MSW stress-strain response and strength is presented and recommendations are made for developing a consistent framework for performing and reporting shear strength data on MSW. Currently unresolved issues are also identified.