Study On The Mechanical And Biodegradation Settlement Properties Of Municipal Solid Waste

In recent decades, industrial and Municipal Solid Waste (MSW) production hasrapidly increased as a result of significant population growth in the global. As aeconomical disposal way of MSW, most of urban waste production were land filled intoregulated centers both in china and aborad. However, with the continuing increase ofMSW in the city, which can pose important environmental disasters. Based on themechanism evolution of landslides for the landfills, Chongqing landfill was selected forthe research and the the mechanical behavior of MSW was elaborately studied in thispaper as follows:1) In order to study the effect of biodegradation on the shearstrength as well asother related factors such as moisture content, organic content, shear strain standard onthe shear strength of MSW. Laboratory tests were applied during the process of organicmatter degradation in the specimens, which was collected from landfills located inChongqing area. The shear tests results during the240days shows that the shear strengthof shredded fresh samples in the initial phase (0d～30d) depends on initial structure andpre-compressive pressure, the effects of organic content and moisture content on shearstrength are not obvious; In the second phase(30d～240d), the shear strength ofcohesion c increases steadily from3.54kPa to22.24kPa while internal friction angle φincreased from14.41°to27.84°during the0~30days and then decreased gradually from27.86°to20.35°. Direct Shear tests results for landfills sample shows that the increaseof moisture content in the waste may caused the decreased of shear strength.Consolidated drained tri-axial tests result shows that the shear strength increasesprogressively as defined axial strain increases from5%to20%, corresponding cohesionc varies from0kPa to66.42kPa and internal friction angle φ ranges from29°to38°.2) In order to study the creep–degradation settlement properties of municipal solidwaste, the change of static-creep-settlement for fresh municipal solid wastes whichcollected from the Chongqing landfill were observed elaborately during the360daysLaboratory test. By analyzing leachate-degradation-strain-time relational curves, thenumber of total creep settlement caused by external load and inner degradation in thewaste can reach33.2%of the sample height, and the leachate production can becontrolled by the external load and organic content; the tests results indicated that thedegradation rule of MSW can be expressed as the Richards model，the relation of cumulative settlenment with cumulative leachate fitting the exponential function model;The corresponding section for organic content that suit for the initial compressiondeformation and the creep-degradation settlement could be ranged from29.1%to36.47%. During the monitoring for settlement and internal temperature field in theanaerobic reaction stage, a optimum temperature zones that varied from22℃to45℃were found and which could accelerate degradation speed of organic matters in thewaste, and it becoming more fasterwhen the temperature reached to41℃.With thepreliminary study for degradation-settlement and temperature field, the tests result willprovide some theoretical help for further settlement analysis in the waste and landfilldesign.3) The creep-settlement properties of municipal solid waste are investigated usingthe compressive experiments indoor. According to the experiment results, deformationof waste sample under respective loading condition is recorded and it can be expressedas elastic-plastic biodegradation induced model in both aerobic and anaerobic phases.Based on creep theory and monitored dates, a creep models called Burgers model isproposed which could better describe the deformation properties of landfills. Based onone dimension compression experiments and data available from published literature,the model parameters are obtained. In order to illustrate the applicability of proposedmodel, settlements due to respective loading of waste with time are predicted for typicallandfill conditions. The proposed Burgers models is capable of reproducing quite wellthe results obtained from tests performed in the laboratory as well as the settlementrecorded in sanitary landfills, both of creep model are valuable for predicting thecapacity calculation and settlement research of landfills.4) Based on the Mitchell’s three-Element conductive model and tests dates, A newlandfill resitivity model was estabilished after the structure and properties parameters oflandfill sample were determined and which was better suitable for ChongQing areas. Byanalysis the effect factors (temperature, moisture density, leachate concentration,porosity), Tests results shows (only one parameter is variable but the other parametersare unchanged): The resistivity of landfill decreased as the increase of porosity in thelandfill and their relationships could be represented by power equations. With morepollutants adding to the specimen, great change has been happened to oil pollutant thanadding NaCl、ZnCl2leachate with increasing porosity of landfill. Suppose the porosityof landfill is fixed, The effect of leachate on the resisitivity can mainly controlled by thedilution process of landfill, and which decreased with the rising of moisture content. The resistivity is liner against the temperature andwhich increased as the increase oftemperature during the aerobic and anaerobic phase in landfills. When assume themoisture content is constants, three kinds of conductive model may be changed due tothe change of porosity in the waste, and it could even cause a change for the electricalresistivity of MSW. Finally, a high-density resistivity chromatography is applied in thefield tests, and the comparison of electrical resistivity between tested value andcalculated was conducted the the results prove that the proposed electrical resistivitymodel is reasonable. These study results could better predict the leachate content in thewaste and evaluate the mechanic behavior in the landfill.