| Landfill is the most common disposal method for municipal solid waste(MSW).At present,the leachate level is high in various landfills in China,which may directly cause problems such as instability of the slope,pollution of leachate and suppression of landfill gas.In addition,the usual dewatering methods can't effectively control the leachate level.These problems are closely related to the permeability characteristics of MSW.MSW has diverse components and sizes.The operation of layered landfill and the presence of flat particles such as plastic and paper make the MSW exhibit obvious layering and anisotropy;In addition the multi-size pores coexist and the seepage has a distinct preferential flow effect.As a kind of heterogeneous porous medium,the permeability coefficient is a function of the characteristics of the medium.The characteristics of the medium mainly include the particle shape and size,the pore size and the pore distribution,etc.The diversity of the medium causes the diversity of the internal structure,so the permeability coefficient of MSW is also a function of the internal structure.Based on this,this thesis focuses on waste structure and permeability coefficient,and reveals the internal seepage mechanism and the permeability characteristics of MSW mainly through testing and theoretical analysis.The main research works and conclusions are followed:(1)Samples are taken from different depths of a Landfill in Hangzhou.Through screening and sorting of MSW,the variation of MSW composition with the burial depth is obtained.It is found that the proportion of fine particles(0D,ie,particle size<2cm)is almost over 50%,and the proportion of 2D particles in coarse grains is the highest.(2)According to the "The Component Data of MSW in Hangzhou",the samples weighed It are manually prepared and put into a self-degrading instrument for degradation.The sample is taken every 3 months to determine the sedimentation,component content and the ratio of lignin to cellulose,which can characterize the degree of MSW degradation.(3)Three methods of single-point injection,staining and CT scanning are used to describe the MSW structure.Basing on the results of CT scanning and the saturated seepage model considering preferential flow and anisotropy,the vertical and horizontal permeability coefficient are calculated.It is found that the methods of staining section and CT scanning can better reveal the characteristics of MSW structure.There are obvious large pores and layered structures inside MSW.The permeability coefficients predicted by the saturated seepage model are well fitted to the triaxial test results.(4)The vertical and horizontal permeability coefficients of MSW under different ages and different loads are measured by self-made permeation instrument.The results show that the permeability coefficient decreases with the increase of the effective stress and degradation age.Compared to the overburden pressure,the degradation age has little effect on the permeability coefficient,which is basically within an order of magnitude.The anisotropy value decreases with the increase of the effective stress.when the load increases from 0 kPa to 400 kPa,the anisotropy value is in the range of 0-12.(5)Based on the permeability coefficient obtained,the leachate production evaluation of Laogang Phase V landfill is carried out.The results show that the leachate production and the ratio of leachate production to landfill volume is increasing.Compared with the leachate production caused by rainfall infiltration,the landfill leachate production accounts for a large proportion of the total leachate production,which is about 52%(rainy season)-96%(dry season). |
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