Relationships that Govern Changes in Permeability and Microstructure of Leachate Drainage Layer Under Loading

To examine the changes in the permeability and the microstructure of the gravel layer under different overburden stresses, samples of leachate are taken from the Yanqun landfill in Xuzhou, China, which are used as the seepage fluid in an experiment in a physical model established by using similarity theory. A mathematical model of the relationship between the permeability coefficient gradient per unit stress of overburden stress and seepage time is established. The results show that the porosity and permeability coefficient of the drainage layer, the occupied pore space after clogging, rate of reduction in porosity, pore surface area and pore volume of the gravel (drainage medium) all decrease with an increase in the overburden stress. Increases in the overburden stress can lead to a substantial reduction in the permeability and porosity of the drainage layer, and as the permeability of the drainage layer gradually decreases, there is an increase in occupied pore space after clogging as the seepage time is increased, while the drainage porosity of the seepage section near the inlet where the leachate is poured in the lowest under the same overburden stress. The findings of this study can act as a reference source for analyses on the changes in the permeability of the drainage layer in engineering barriers for municipal solid waste landfills and for the optimal environmental operation of landfills.