ASSESSMENT OF THE SHEAR STRENGH IN THE MSW REJECTS OF THE MATERIALS RECOVERY FACILITIES OF THE SÃO PAULO CITY
In the coming years, the composition and the geomechanical behavior of sanitary landfills are expected to change due to the management hierarchy proposed by Brazilian National Solid Waste Policy. This study aimed to evaluate the shear strength of municipal solid waste collected from the output of the two Material Recovery Facilities of São Paulo city. Assuming that volume minimization techniques will also be necessary face of the scarcity of suitable areas for disposal, the material was shredded and compacted. Standard Proctor tests were previously performed with four samples, indicating maximum dry unit weight values between 6.6 kN/m³ and 10.0 kN/m³ and optimum moisture contents between 20% and 42%. The small-scale direct shear tests revealed increasing stress-displacement curves for all the specimens molded with ten samples, thus the Mohr-Coulomb failure envelopes were established at the horizontal displacement equivalent to 15% of cell width (60 x 60 mm). Cohesion ranged from 1.3 kPa to 31.3 kPa and friction angle from 3.2° to 42.9°, both consistent with the literature. Even after mechanical and manual sorting and particle size reduction processes, the effect of reinforcement produced by fibrous elements could still be seen in the total shearing resistance and the cohesive intercept. Frictional resistance seemed to be affected by the glass and plastic contents – the first increasing it and the second decreasing it –, the dry unit weight and the moisture, requiring more detailed research to quantify such correlations.