In-situ and Laboratory Geotechnical Properties of Municipal Solid Waste from South Eastern Johannesburg

The heterogeneous constitution of municipal solid waste and problems associated with the prediction of the stability of landfills require an in-situ assessment of mechanical properties. Dynamic cone penetration (DCP) tests were conducted in-situ in seven test pits in a municipal landfill in south-western Johannesburg, and samples excavated from each test pit were used to determine other laboratory geotechnical properties. The composition of pits involves plastics, textiles, leather, metal, glass, soils, gravel, debris, wood and garden cuts, paper, cardboards and organics. The dynamic cone penetration index (DCPI) results from seven test pits revealed that the DCPI of half of the pits was in the range of 0–10 mm/blow, while the others were in the range of 10–20 mm/blow. The in-situ density of the municipal solid waste (MSW) indicates a predominantly loose to medium-density in-situ compaction state. Fibrous content and construction debris are the two dominant waste compositions. DCPI was found to decrease with a ratio of fibrous to construction debris greater than 1.0. Relationships between DCPI and products of specific gravity (Gs) and dry density from laboratory and in-situ tests are moderately correlated with coefficients of determination (r²) of 0.61 and 0.71, respectively.