Geotechnical Evaluation of Consolidation and Conductivity of Synthetic Municipal Solid Waste

Municipal solid wastes are contained in landfills that occupy large areas over several decades and have a significant environmental footprint. The deformation and flow through properties of these materials are important for infrastructure construction on and leachate migration in municipal landfills. However, these properties are not regularly determined because of material heterogeneity, variable constituents, lengthy testing, and pungent odor. The main contribution of this research is the application of consolidation theory to understand the geotechnical behavior of synthetic municipal solid wastes. For this purpose, a synthetic material was prepared in a large cell and incrementally loaded with hydraulic conductivity measured after each load. Test results indicated that void ratio decreased from 0.90 to 0.78 during consolidation as the applied stress increased from 70 to 1225 kPa. The compression index of 0.20 (similar to degraded municipal solid wastes) bounced back with a swell index of 0.022; both indices fell within the range for silt and clay. Likewise, the measured hydraulic conductivity decreased by two orders of magnitude from 10^–6 to 10^–8 m/s and closely matched those of fine-grained soils. It is concluded that compression of municipal solid wastes follows the consolidation theory and this property is affected by initial void ratio (arising from composition, saturation, and sample disturbance) and particle rearrangement (due to pore water expulsion of during loading). In contrast, the measured conductivity is marginally affected by compression and is quite different from that estimated using the consolidation theory primarily due to alterations in the pore network.