Study On Compressibility Of Municipal Solid Waste And Settlement Models Of Landfill

Research of municipal solid waste (MSW) is a hot topic of geo-environmental engineering. Estimation of settlement for MSW landfills is critical to the storage capacity,the stability,the successful site operation as well as to the future development of the landfill sites.In this paper, systematical research of the compressibility of MSW,settlement mechanics and settlement models of landfill were executed through laboratory tests and theoretical analysis. The problems of MSW landfills that was induced by settlement and settlement mechanics were discussed, and some classical settlement models of landfill were also presented.Compression tests of fresh and degraded MSW samples were conducted in laboratory to investigate compressibility characteristic of MSW with different initial ratio and various components. The test results demonstrated that MSW samples with larger initial void ratio have bigger primary compression index. Primary compression index of fresh MSW samples is larger than degraded MSW samples with the same initial void ratio. The void ratio of all MSW samples subjected to vertical pressure 24h is approximately linear with logarithmic of pressure.In order to investigate the long-term deformation properties of MSW subjected to different vertical pressure, three biodegradation-compression test apparatuses for MSW samples were specially developed, whose functions include loading, temperature controlling, leachate recirculating and gas collecting. The test results showed that the total settlement of MSW was determined by components of MSW and pressure. the primary settlement increased and the long-term settlement decreased respectively as vertical pressure that loading to the MSW samples increased, so the effect of vertical pressure on total settlement showed a decreasing trend with elapsed time. The strain-logarithmic time curves for the samples are approximately linear with a relatively flat slope in the early stage of compression, the slope increased dramatically as biodegradation of MSW was accelerated. Proper temperature and leachate recirculation can accelerate the biodegradation rate of MSW, while vertical pressure almost has no effect on biodegradation of MSW.Daters of biodegradation-compression tests were used to analysis some classical settlement models. The results indicated that some models such as Sowers (1973) models with no consideration of degradation settlement can not simulate settlement processes of landfills when MSW was under appropriate composition condition. Some models such as Bjarngard et al (1990) models,Park et al (2002) models and Chen et al (2008) models can successfully predicted long-term settlement as accelerated compression due to decomposition of MSW was calculated in the settlement prediction of MSW landfills.