Experimental Study On GCL Degradation Characteristics Under The Coupling Of Freeze-thaw Cycling,Wet-dry Cycling And Municipal Solid Waste Leachate

In recent years,GCL has been widely used in the construction of composite bottom liner systems of waste disposal sites with its excellent hydraulic performance,simple and quick installation process,good integrity and adsorption performance.It has also gradually attracted the attention of researchers.Cold and dry in winter and hot and rainy in summer are typical climatic characteristics of the Loess Plateau.Under the influence of natural conditions,small landfills in this area often experience freezing and thawing cycling in winter,and often experience wet and dry cycling in summer.Combined with the flooding of landfill leachate caused by the lack of rain and sewage diversion in the landfill,The GCL composite bottom liner systems of small landfills in the Loess Plateau area often experiences the coupling of freeze-thaw cycling?wet-dry cycling and municipal solid waste leachate,coupling will seriously affect the interception performance of GCL and affect the stability of landfills.In order to explore the mechanism of the degradation of GCL interception performance by freeze-thaw cycling ? wet-dry cycling and municipal solid waste leachate coupling,this paper analyzes the indoor test and test results,from hydraulic performance of GCL,adsorption properties of bentonite in GCL,tensile strength of geotextiles in GCL.Research work has been carried out in three aspects of GCL,and some valuable conclusions and results have been obtained:(1)Based on the preliminary investigation,the penetration test of GCL under the coupling of freeze-thaw cycling and municipal solid waste leachate was carried out to study the deterioration law of GCL hydraulic conductivity under the coupling effect.The results showed that during the 0-20 freeze-thaw cycling,The coupling effect offreeze-thaw cycling and municipal solid waste leachate will increase the hydraulic conductivity of GCL with the increase of the number of freeze-thaw cycles,but the increase is limited.The coupling of the freeze-thaw cycling in distilled water only slightly increases the hydraulic conductivity of GCL during the 0-5 freeze-thaw cycles.During the 5-20 freeze-thaw cycles,the hydraulic conductivity of GCL tends to be stable.(2)Based on the preliminary investigation,the penetration test of GCL under the coupling of wet-dry cycling and municipal solid waste leachate was carried out to study the deterioration law of GCL hydraulic conductivity under the coupling effect.The results show that the coupling of wet-dry cycling and municipal solid waste leachate will infiltrate GCL.The coefficient is significantly increased,and the reason for the increase in the hydraulic conductivity is related to the double-layer thickness of bentonite.When the inhibition of bentonite by the wet-dry cycling and municipal solid waste leachate reaches equilibrium,the permeability coefficient of GCL does not increase with the increase of the number of wet-dry cycling.The coupling between the wet-dry cycling and distilled water can only produce a slight increase in the hydraulic conductivity of GCL under the first wet-dry cycling,and the post-hydraulic conductivity keeps stable.The effective stress has a great influence on the hydraulic conductivity of GCL.When the effective stress is increased from 20 kPa to 150 kPa,the hydraulic conductivity is reduced by about 4 orders of magnitude.(3)Based on the tensile test of geotextile in GCL based on the coupling of freeze-thaw cycling and municipal solid waste leachate,the deterioration law of tensile strength of geotextile under this coupling is studied.The results show that the coupling effect of freeze-thaw cycling and municipal solid waste leachate can reduce the tensile strength of the geotextile in GCL,and the reduction rate of the tensile strength of the braid is higher than that of the nonwoven under the same conditions.(4)Based on the tensile test of geotextile in GCL based on the coupling of wet-dry cycling and municipal solid waste leachate,the deterioration law of the tensile strength of geotextile under this coupling is studied.The results show that the coupling effect of wet-dry cycling and municipal solid waste leachate has a slight decrease in thetensile strength of geotextiles.And the coupling effect on the tensile strength of the braid is higher than the tensile strength of the nonwoven under the same conditions.