Analytical solution for one-dimensional degradation-consolidation of saturated municipal solid waste

Owing to loss of solid mass of municipal solid waste (MSW), the consolidation under external loading is complex. In order to study the degradation-consolidation behavior of saturated MSW, the universal model for the one-dimensional (1-D) degradation-consolidation is established. A simplified 1-D degradation-consolidation model considering hydrolysis of degradable solid, formation of pore water due to intra-particle water release and degradation-dependent compressibility is derived based on the existing research achievements of degradability, compressibility and permeability of MSW. The top and bottom boundary conditions of waste layer are assumed to be free-draining and impervious, respectively. The analytical solution to a simplified 1-D degradation-consolidation model is derived. Case studies are carried out for the fresh MSW in landfills of China. The results show that the excess pore water pressure being larger than the initial value is found in deeper waste layer during the early stage of consolidation under an instantaneous constant loading. This is mainly due to loosened soild skeleton, increasing compressibility associated with loss of solid mass. The excess pore water pressure is found to be negative in the whole waste during the later stage of consolidation. The reason is that the loss of solid mass causes the increasing void ratio, while the increase of compressibility is relatively smaller. The sensitivity analysis shows that an increase of the secondary compression rate causes the increasing excess pore water pressure during the early stage of consolidation, and its dissipation will be delayed with the increasing preconsolidation pressure.