Shear strength characterization of fresh MBT and MSWI wastes from a Spanish treatment facility.

A laboratory shear strength characterization of the landfilled materials of the Municipal Solid Waste integral treatment plant from the Meruelo Environmental Complex in Cantabria (Spain) was performed. The materials tested come from the rejection of the Mechanical and Biological Treatment (MBT-MSW) and the slags produced in the energy recovery plant (MSWI). Laboratory characterization consisted of direct shear and consolidated drained triaxial testing. Mohr-Coulomb failure criterion parameter values were obtained and compared to reported values in the literature. In some tests, failure was not reached due to the reinforcement effect for fibrous particles; thus, the mobilized shear strength parameters for different values of axial strain were obtained. The triaxial test results showed strain-hardening in MSW-MBT but not in MSWI. Failure was reached on both materials in direct shear testing, with MSWI showing peak and ultimate strengths, whereas MBT-MSW exhibited only ultimate strength. Direct shear test obtained strength can be characterized by a cohesion of 20 kPa and a friction angle of 33° for MBT-MSW ultimate strength, while cohesion and friction angle varies from 13.4 to 29 kPa and from 38.5° to 42.3° for MSWI ultimate and peak strength, respectively. The mobilized cohesion and friction angle obtained for MBT-MSW in consolidated drained triaxial tests ranged from 15.1 to 62.7 kPa and 20° to 28.7°, corresponding to a strain level of 5% and 25%, respectively. In triaxial testing of MSWI specimens, failure was reached, and the material showed a cohesion of 51.3 kPa and a friction angle of 32.8°.