Dynamic Characteristics of Municipal Solid Waste with Degradation in Bioreactor Landfills

Bioreactor landfills are operated to enhance refuse decomposition, gas production, and waste stabilization. The major aspect of bioreactor landfill operation is the recirculation of collected leachate back through the refuse mass. Due to the presence of additional leachate and accelerated decomposition, the dynamic characteristics of MSW in bioreactor landfills are expected to change. Assessment of dynamic properties of landfills is one of the major geotechnical tasks in landfill engineering. In order to understand the changes in dynamic properties of bioreactor waste mass with time and decomposition, eight small scale bioreactor landfills were built in laboratory and samples were prepared to represent each phase of decomposition. The state of decomposition was quantified by methane yield, pH, and volatile organic content (VOC). A number of Resonant Column (RC) tests were performed to evaluate the dynamic properties (stiffness and damping) of MSW. The test results indicated that the normalized shear modulus reduction and damping curves are significantly affected by the degree of decomposition. The shear modulus increased from 2.11 MPa in Phase I to 12.56 MPa in Phase IV. The increase was attributed to the breakdown of fibrous nature of solid waste particles as it degrades. Therefore, the shear modulus reduction curves should be evaluated based on the degree of decomposition, rather than just the sample composition itself.