Study On Relevant Characteristics Of Deformation And Strength Of Municipal Solid Waste

To investigate the laws and correlation properties of the deformation and shear strength ofthe fresh municipal solid waste (MSW) and degraded waste in the landfills, a series of combinedtests of compression test and direct shear test were carried out by a large–scale laboratory testingequitment. According to the major composition of MSW samples from the Tianziling landfill inHangzhou, China, fresh MSW testing samples (the degraded waste samples are gained from thefresh MSW samples which were degraded in the natural environment.) were prepared ingeo-environment laboratory. A large number of experiments had been carried out. Besides, thetheoretical analysis had also been done.The fresh MSW was devided into there parts which were easily biodegradable material,difficultly biodegradable material, unbiodegradable material. Three mixture proportions wereused to simulate the three stages of urban economic development those were underdeveloped,developing, and developed. The initial void ratios of the samples were selected as2.1,2.5and2.9. Four different vertical pressures, which were25,50,100, and200kPa, were chosen, and thecompression times for every vertical load were0,0.25,0.5,1,2,6,12, and24hours, respectively.The shear strength parameters for ten different shear strain limiting values, which were2%、4%、6%、8%、10%、12%、14%、16%、18%、and20%, were studied. Besides, four different degradationtimes were considered, which were30,60,120and180d.288fresh MSW samples and1152degraded waste samples were prepared to investigate the correlation properties between thedeformation and shear strength.Based on the testing results, following conclusions had been gained for the fresh MSW:①The vertical compression strain increases with the increasing of the compression timeand vertical pressure. And the relationship can be fitted to the form of a logarithmic mode.②The relationship between the void ratio and the logarithm of the vertical pressure is ininverse proportion.③The shear stress increases with the increasing of the shear strain. The relationship is ashear strain hardening curve, which can be described as a form of a hyperbolic line.④The shear strength increases with the increasing of the compression strain at differentcompression time. The relationship can be described as an exponent model.⑤With the increase of the compression strain, the shear strength increases first, thendecreases, and increases again at the end. The relationship can be fitted to the form of amultinomial mode.⑥The relationship between the shear strength and the vertical load applied on the test sample is conformity with the law of Coulomb.⑦The cohesion force and the internal friction angle of the fresh MSW increase with theincreasing of the shear strain limit value, and a logarithmic model can be used to describe theirrelationship.⑧The shear strength parameters of the fresh MSW under various conditions are obtained.Furthermore the following conclusions had been drawn for the degraded waste:①The density of the degraded waste increases with the increasing of the degradation time.And a logarithmic model can be used to describe the relationship.②The total strain increases with the increasing of the vertical pressure. And a logarithmicmodel can be used to describe the relationship, and the logarithmic expression had beenestablished.③The shear strength increases with the increasing of the degradation time. And alogarithmic model can be used to describe the relationship.④The shear strength increases with the increasing of the total strain which was caursed bythe different vertical pressures. An exponent model can be used to describe the relationship.⑤The shear strength increases with the increasing of the total strain which was caursed bythe different degradation time. The relationship could be described as a linear line.⑥The relationship between the shear strength and shear strain limiting values at differentdegradation times, which were30,60,120,180d can be described as a logarithmic model can beused to describe the relationship, and the logarithmic expression had been established.⑦The shear strength parameters of the degraded waste under various conditions areobtained. Those are the cohesion force varies from8.3to28.1kPa, and the internal friction anglevaries from11.9to36.3degree.Both the compression process and the progressive shearing failure process of the municipalsolid waste in landfills have been taken into considered. So the research results are closer toactual operation situation of the landfill. Besides, the conclusions lay a theoretical basis for thestability analysis of the landfills, and can provide the references to the actual landfillengineering.