| Mechanical biological treatment(MBT)can greatly reduce the amount of municipal solid waste(MSW)and has become a hot topic in environmental geotechnical engineering.The research data on hydraulic characteristics of MBT waste was relatively inadequate,and that in China was even more scarce.The works in this paper were funded by the National Natural Science Foundation of China "Study on the strength characteristics and mechanism of waste based on MBT technology"(51678532)and "Study on the correlation and interaction mechanism of MBT waste permeability and deformation"(51978625).Considering the effects of pressure,compression time under pressure,dry density,compressive strain,hydraulic gradient,particle size,and void ratio.Permeability tests of samples M1-1,M1-2,M2-1 and M2-2 with smaller particle sizes were carried out by a compression and permeability combined apparatus;permeability tests of samples M1-3 and M2-3 with larger particle sizes were carried out by a large-scale vertical permeability apparatus.The permeability tests on the sample M2-2 was conducted under the pressures of 50,100,150,200,300,400 kPa.The compression times under each pressure was set to 0.03(2 min),3,6,12,24,and 48 h with six hydraulic gradients.A hydraulic gradient of 2,1.75,1.5,1.25,1,and 0.5 was used for pressure of 50,100,150 kPa,and a hydraulic gradient of 5,4.5,4,3.5,3,and 2.5 was used for pressure of 200,300,and 400 kPa.The compression times under a pressure of 100 kPa was set to 0.03(2 min),3,6,12,24,48,72,96,120,144,and 168 h.The permeability tests on the samples M1-1,M1-2 and M2-1 were conducted under five pressures,and the compression time under each pressure was set to 24 h with six hydraulic gradients.The permeability tests on the samples M1-3 and M2-3 were conducted at five dry densities,a hydraulic gradient of 1.25,1,0.75,0.5,0.25,and 0.1 was used for each dry density.The results of compression and permeability and large-scale vertical permeability tests of MBT waste show that:(1)The relationship between the penetration rate of MBT waste and the hydraulic gradient was fitted to a linear relationship,which was in accordance with Darcy's law.(2)With the increase of pressure,the permeability coefficient of MBT waste reduced.The relationship between the logarithmic permeability coefficient and pressure was fitted to a linear relationship.(3)With the increase of dry density,the permeability coefficient of MBT waste reduced.The relationship between the logarithmic permeability coefficient and dry density was fitted to a linear relationship.(4)With the increase of compression time under pressure,the permeability coefficient of MBT waste decreased.The relationship between the logarithmic permeability coefficient and the logarithmic compression time was fitted into a linear relationship.As compression time was larger than 24 h,the reduction of void ratio and permeability coefficient was relatively small.(5)With the increase of compressive strain,the permeability coefficient of MBT waste reduced.The relationship between the logarithmic permeability coefficient and compressive strain was fitted to a linear relationship.The results of permeability tests of MBT waste with different particle sizes show that:(1)Under the same pressure and compontent content,the permeability coefficient of samples(0-10 mm)was smaller than that of samples(0-20 mm).(2)As the dry density increased,the reductions of the permeability coefficient of samples with particle size of 0-10,0-20 and 0-40 mm decreased in order.(3)With the decrease of void ratio,the permeability coefficient decreased.The relationship between the logarithmic permeability coefficient and the logarithmic void ratio was fitted to a linear relationship.(4)As the average particle diameters of samples with the particle size of 0-10,0-20 and 0-40 mm were different,the distributions of void ratio and permeability coefficient were different.(5)The permeability coefficient was changed with the increase of the void ratio and the average particle diameter.The relationships between the logarithmic permeability coefficient and the void ratio and the average particle diameter were established.Based on the SPSS software simulation,the physical equation of stress and strain,and the one-dimensional consolidation theory of Terzaghi,the prediction equations of permeability coefficient were obtained.According to the prediction equation of permeability coefficient and pressure and compression time under pressure,the relationship between the permeability coefficient and the buried depth of MBT waste in Hangzhou was obtained.The results of MBT waste in this paper were compared with municipal solid waste and MBT waste in related countries to provide reference for the permeability analysis of MBT landfill. |
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