Geotechnical characterization of municipal solid waste via cone penetration testing – A case study from landfills in Delhi, India

Abstract

Hydro-mechanical properties of emplaced municipal solid waste (MSW) are key design parameters from operation to post-closure phases of landfills. Field techniques are invaluable to evaluate these properties reliably and safely by minimizing health hazards associated with testing large quantities of MSW physically. In the present study, potential of cone penetration test with pore pressure measurement (CPTu) in landfill engineering is demonstrated through a series of CPTu tests at two MSW landfills in Delhi, India, along with comprehensive laboratory testing. CPTu tests were useful in locating the depth to leachate, in knowing whether it is continuously connected over the depth and whether pore pressure (u₂) is hydrostatic or exists at high-pressure conditions. This information is crucial for slope stability assessment of landfills. The CPTu data revealed that in-situ behavior of MSW would be similar to that of sandy-silt and silty-sand and is in good agreement with that revealed by grain size distributions of MSW samples collected close to CPTu locations. Most cone tip resistance and sleeve friction are less than 4 MPa and less than 100 kPa, respectively, and friction ratio is between 1 % and 4 %. Average friction angle (ϕ′) estimated from CPTu data ranged between 34° and 38°. These values agree with measured ϕ′ from large direct shear and triaxial tests on MSW. CPT data from this study and from 22 MSW landfills in 12 countries suggests the potential of CPTu to provide rapid, safe, and conservative estimates of shear strength and pore pressure conditions for stability analysis of landfills.