Geotechnical Properties of Municipal Solid Waste

A geotechnical testing program was conducted to evaluate the engineering properties of aged solid waste samples retrieved from a landfill that began accepting waste as early as 1940. The conducted tests included water content, specific gravity, Atterberg limits, grain-size distribution, compaction, permeability, consolidation, triaxial, and direct shear. Maximum dry unit weight achieved using the Standard Proctor Test was approximately 9.3 kN/m3 at a water content of 31%. Compression Index values, Cc, derived from small-scale (63.5 mm in diameter), one-dimensional consolidation tests were between 0.4 and 0.9 for a void ratio range of about 1.0 to 3.0. Secondary Compression Index values, Cα, appeared to be less dependent on initial void ratio and more dependent on conditions favorable to microbial activity and were estimated to range between 0.009 and 0.03. Total strength parameters from consolidated undrained (CU) triaxial tests yielded a range of cohesion values, c, of about 100 kPa at w of 55% to 40 kPa at w of 72%. Apparent effective strength parameters were evaluated as an effective friction angle, φ', of 34° and an effective cohesion of 16.8 kPa. Results from direct shear tests at different levels of horizontal displacement indicated that the value of the friction angle increased with the displacement level while cohesion remained essentially constant. Effective friction angles, φ', of 20.5 to 39° with c' of 27.5 to 0 kPa were evaluated from the direct shear tests. In general, results from this study were comparable to those reported in the literature and obtained from laboratory, field, and large-scale unconventional tests. However, the apparent effective strength parameters evaluated from the conventional laboratory tests seem generally higher than those evaluated through back calculations. Apparent effective friction angle values evaluated in this study were as much as 10° higher than those reported in the literature and evaluated from back calculations.