Eperimental Study Of Gas Leakage Characteristics Of Geosynthetic Clay Liner Overlap

In the covering barrier system of organic contaminated site,GCL overlap may have the dominant circulation channel of organic pollution gas leakage;to solve this problem,Na-bentonite paste is used to seal GCL overlap at home and abroad,but the research on gas resistance performance of GCL overlap is missing.Financially supported by the National Key R&D Program of China（No.2018YFC1803100）and the state Natural Science Foundation"Research on the Mechanism and Performance of Polyphosphorus-based Dispersant Modified Bentonite Vertical Engineering Barrier to Block High-risk Heavy Metal Pollutants"（41877248）,the dissertation presents modified fluid loss test,rigid wall liquid permeability test,hydration test,rigid wall gas permeability test and theoretical analysis,the variation of gas permeability coefficient of the intact GCL and its overlap with water content of GCL,overlap width,overlap thickness of Na-bentonite paste,the soil-to-water ratio of Na-bentonite paste and overlying pressure have been studied.Based on the experimental results,the following conclusions can be obtained:（1）Through the modified fluid loss test,the influence of soil-water ratio of Na-bentonite paste on the tap water permeability coefficient was studied,it demonstrated that the soil-water ratio of 1:6 is better in anti-seepage performance.The effectiveness of the independently developed device was studied through the modified fluid loss test of the intact GCL and the independently developed rigid wall liquid permeability test,it showed that the tap water permeability coefficient of the intact GCL was only 10.75%larger than that of the modified fluid loss test,which was relatively safe.Through rigid wall liquid permeability test of GCL overlap,it was determined that the liquid permeability coefficient of overlap was lower and anti-seepage performance was better when the soil-water ratio was 1:6.（2）Based on hydration test,the influence of overlying pressure on w of the intact GCL was studied,it exhibited that,with the increase of overlying pressure,w decreased from 221.26%to 188.75%after complete hydration.Through GCL rigid wall gas permeability test,it found that w was the main controlling factor of k_g0of the intact GCL.It revealed that when the overburden pressure was 0 k Pa and w≤85%,k_g0 was basically unchanged at 1×10^-7m/s.When w continued to increase,it decreased rapidly with a maximum decrease of 2 orders of magnitude.It also illustrated that when the overlying pressure was 20 k Pa and w≤72%,k_g0had the same trend.As w continued to increase,k_g0decreased by 3 orders of magnitude.（3）Combined with the conclusions of liquid permeability test of GCL rigid wall and gas penetration test of GCL rigid wall,the soil-water ratio was determined to be 1:6,the gas resistance at the GCL overlap was better.The concept of relative gas permeability coefficient was introduced,that is,normalized treatment,GCL overlap gas permeability coefficient（k_g）was divided by intact GCL gas permeability coefficient(k_g0),to quantitatively compare the gas resistance performance at the overlap part and non-overlap part.It indicated that the higher the moisture content of GCL,the larger the overlap width of GCL,the thicker the lap thickness of Na-bentonite paste,the larger the overburden stress,the better the gas resistance of GCL overlap.