Effects of Degradation on Geotechnical Properties of Municipal Solid Waste from Orchard Hills Landfill, USA

Abstract

In bioreactor landfills, geotechnical properties of municipal solid waste (MSW) are believed to be affected by increased moisture content and accelerated biodegra- dation due to leachate recirculation; however, studies to quantify the changes in the MSW properties are scarce. This study quantifies the change in geotechnical properties of field MSW as a function of level of degradation. Fresh MSW samples were collected from the working phase of Orchard Hills landfill (Davis Junction, Illinois, USA) and were subjected to leachate recirculation and enhanced anaerobic degradation in specially designed laboratory bioreactors. Samples were exhumed from the bioreactors at different stages of degradation as determined by the amount and composition of biogas generated, and subse- quently tested for moisture content, organic content, unit weight, hydraulic conductivity, compressibility, and shear strength. Moisture content of MSW increased significantly, while organic content decreased with degradation. Bulk unit weight increased with degradation which led to decrease in saturated hydraulic conductivity. Primary compression ratio showed slight increasing trend with degradation, while the secondary compression ratio was not affected significantly with the degradation. The friction angle decreased from 30� to 12� , but cohesion increased from 29 to 65 kPa with degradation based on direct shear test results. The testing of saturated MSW in triaxial con- solidated undrained conditions resulted in lower shear strength with no distinct correlation of friction angle and cohesion with degradation. Additional large-scale, long- duration testing is recommended using the field MSW samples with the consistent composition to establish the correlations between the engineering properties and degree of degradation. Overall this study showed that the engi- neering properties of field MSW are affected by degrada- tion and these changes should be properly accounted in the analysis and design of bioreactor landfills involving lea- chate recirculation.