Mechanical Response of Fine-Grained Soil-Solid Waste Composites from Field Scale Direct Shear Tests

The paper reports a study on the reinforcing effect of non-degradable municipal solid waste (MSW) in fine-grained soils with possible applications in reinforced soil construction. A low-plasticity silty soil was randomly mixed with five-year-old, non-degradable MSW at 0.0, 0.5, 1.0, and 2.0% concentrations by dry weight (wt%), and compacted in a large-scale split shear box of approximately one meter cubed volume. Specimens were consolidated under uniform normal stresses across their entire plan area for twenty-four hours and then sheared under drained, displacement-controlled conditions. Strength comparisons were made consistently at a large strain level to capture any reinforcing benefits of the soil-MSW mixtures under field conditions. The consolidation response of the composites exhibited a distinct threshold. Mixtures up to 1.0 wt% MSW showed consolidation behavior similar to that of a comparable unreinforced soil, whereas a 2.0 wt % concentration caused a slower consolidation rate and substantially larger settlements. The concurrent reduction in the virgin compression slope and increase in the recompression slope with reinforcement concentration indicates strain-dependent interactions, where interlocking between the soil and waste material mobilizes the tensile resistance of waste fragments anchored within the soil matrix. Results also show a significant (i.e. by as much as 50%) increase in the drained shear strength of the mixtures at large deformations relative to comparable raw samples. Variations in the shear strength properties of mixtures indicated two distinct trends in that, for up to 1.0% waste concentration, the increase in shear strength was essentially due to an increase in the apparent cohesion with minimal change in the friction angle, whereas at 2.0% concentration, the friction angle increased significantly while cohesion decreased, reflecting a transition to an interlocking-dominated reinforcement mechanism.