Study On The Permeability Characteristic And Permeability Mechanism Of Degraded MSW Materials

Landfilling has been one of the primary methods for municipal solid waste disposal.Landfill leachate generated during the process is the main cause of environmental pollution.High level leachate is the main reason for the instability of landfill.The permeability characteristic of municipal solid waste is the important property for controlling and managing landfill leachate.The permeability coefficient is the important parameter to measure the permeability characteristics of municipal solid waste.A self-made permeability and compression combined test apparatus was used to 1519 permeability and compression combined tests with 42 degraded municipal solid waste samples.And the permeability characteristic and its variation law of municipal solid waste was systematically studied.According to Hangzhou Tianziling landfill waste composition,municipal solid waste samples were prepared manually and placed in sealed polyvinyl chloride?PVC?barrel for anaerobic degradation.When the municipal solid waste samples reached the specified degradation time,the organic matter content tests,permeability and compression combined tests were carried out.The permeability and compression combined tests were conducted with municipal solid waste under 7 degradation ages?40,60,105,150,195,240,and 285 d?.Six different vertical pressures?25,50,100,150,200,and 300 kPa?were selected,and six compression times 2 min and 1,2,6,12,and 24 h)were applied for each.Hydraulic gradients of 2.25,2.0,1.75,1.5,1.25,and 1.0 were applied for vertical pressures of 25,50,and 100 kPa and hydraulic gradients of 8,7,6,5,4,and 3 were applied for vertical pressures of 150,200,and 300 kPa..Degradation test results show that:?1?With increasing degradation age,the density increased gradually.The relationship between density and degradation age could be formulated as an exponential function with the fitting coefficient = 0.94.?2?With increasing degradation age,the strain increased gradually.The relationship between strain and degradation age could be formulated as an exponential function with the fitting coefficient = 0.94.?3?With increasing degradation age,the organic matter content decreased gradually.The relationship between organic matter content and degradation age could be formulated as an exponential function with the fitting coefficient = 0.99.Permeability and compression test results show that:?1?A critical hydraulic gradient was found for degraded MSW.The relationship between the permeation rate and the hydraulic gradient was formulated as a linear function that conforms to Darcy's law and the fitted coefficients were>0.96;?2?With increasing pressure,the permeability coefficient decreased gradually.The relationship between the permeability coefficient and pressure was formulated as a power function,and the fitted coefficients were>0.90;?3?With increasing compression time,the permeability coefficient decreased gradually.The relationship between the permeability coefficient and compression time was formulated as a power function,and the fitted coefficients were>0.90;?4?With increasing density,the permeability coefficient decreased gradually.The relationship between the permeability coefficient and density was formulated as a power function,and the fitted coefficients were>0.91;?5?With increasing compressive strain,the permeability coefficient decreased gradually.The relationship between the permeability coefficient and compressive strain was formulated as a power function,and the fitted coefficients were>0.82;?6?With increasing degradation age,the permeability coefficient decreased gradually.The relationship between the permeability coefficient and degradation age was formulated as a power function,and the fitted coefficients were>0.86;?7?The permeability coefficient of degraded municipal solid waste is 10^-4-10^-2 cm/s.?8?A Permeability coefficient-Pressure-Density-Degradation age mathematical model is established.This study comprehensively considered the influence of many factors?i.e.,degradation age,pressure,compression time,density,compressive strain,and hydraulic gradient?on the permeability characteristics of MSW.The test results could provide a theoretical basis for landfill leachate production,landfill capacity calculation and drainage system design.