Evaluation of Lateral Earth Pressure Coefficients for Municipal Solid Waste

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ABSTRACTIn this project, laboratory testing will be conducted using unique large scale waste testing equipment to evaluate at rest, active, and passive lateral earth pressures in municipal solid waste (MSW). The magnitude of lateral earth pressures in municipal solid waste (MSW), including active, passive, and at-rest pressures, and the factors that influence these lateral pressures are largely unknown, despite their importance to a broad range of design problems. The lack of information on MSW lateral stresses affects not only design of landfill structures but also the evaluation of MSW shear strength, and hence landfill stability. To address this knowledge gap, at rest, active, and passive earth pressures will be measured on 0.75 m-long, 0.2 m-wide, 0.22 m-tall reconstituted specimens using a new lateral pressure measurement device. Lateral pressures will also be measured in simple shear tests on 0.45 m diameter specimens. The lateral pressure tests will provide lateral earth pressure coefficients for MSW as a function initial density, maximum particle size, and confining pressure. The testing program will also yield data on the development and evolution of normal stresses in simple shear testing. Interpretation of the data will provide insight as to how MSW shear strength and lateral stresses depend on stress state and compositional factors, including fibrous reinforcement and degradation of the MSW. Synergies between this testing program and previous testing programs will provide additional valuable fundamental information on the mechanical behavior of MSW, including important new insights on stress strain behavior, anisotropy, the influence of waste composition, and the influence of initial density.Broader impacts of the proposed test program include more economical and more protective landfill containment system design, an enhanced understanding of the potential impacts of waste pre-processing and waste degradation on shear strength and lateral earth pressures, more cost effective methods for increasing landfill capacity, improved landfill remediation strategies, and improved engineering methods for post-closure development on landfills using deep foundations. An enhanced understanding of waste shear strength will enable more accurate evaluation of landfill stability, providing for safer designs and possibly allowing for increased capacity at some sites, extending the life of facilities and thus minimizing the need for new sites. Enhanced understanding of the lateral stresses can also help identify conditions that impact liner integrity. The information developed in this research program will also help address the implications of the emerging technologies of bioreactors and waste pre-processing on the engineering behavior of the waste. The lateral pressure coefficients developed in this study will be invaluable in designing retaining wall system for vertical expansion of landfills, for landfill remediation, and for landfill closure design. This work will also facilitate post-closure landfill development for beneficial reuse of old landfills, as piles supporting buildings on top of closed landfills must carry the downdrag loads from the settling waste and lateral pressure coefficients as well as waste shear strength estimates are required to estimate downdrag.