Impermeability Of GCL Under The Action Of Solution Environment And Aquatic Plant Root System

Due to its excellent properties,the Geosynthetic Clay Liner GCL（Geosynthetic Clay Liner）is increasingly used in lake ecological seepage control.In the ecological environment of lakes,pollution mainly comes from domestic sewage.The metal ions with high ion content in domestic sewage mainly include potassium,calcium,sodium,magnesium,etc.,and have the characteristics of high TN and TP.At the same time,in order to purify water quality and ecological landscape,a large number of plants will be planted in the lake environment.The presence of these metal ions and organic compounds,as well as the effect of plant roots,will affect the performance of GCL,thus affecting its impermeability.In this dissertation,taking sodium bentonite waterproof blanket as the research object,the effects of solution environment and root action on GCL permeability were investigated through indoor simulation test and outdoor model test,and the conclusions were as follows:（1）Cations in solution will affect the free expansion index of bentonite and the permeability coefficient of GCL.Whether in a single solution or mixture,with the increase of solution concentration,the free expansion index decreases,while the permeability coefficient increases.Meanwhile,the free expansion index of bentonite and the permeability coefficient of GCL are both affected by the concentration of solution and the type of cations in the solution,and there is a limit solution concentration（0.1mol/L）.When the concentration is less than 0.1mol/L,the free expansion index and permeability coefficient change faster,and are greatly affected by the type of cations in the solution.However,when the concentration is greater than0.1mol/L,the rate of free expansion index and permeability coefficient gradually slows down until it reaches a plateau.At this time,the cationic species in the solution has little influence on GCL,which is mainly controlled by concentration.When the concentration of solution reached 1 mol/L,GCL basically lost impermeability.（2）At the same concentration,NH₄⁺solution has less influence on the free expansion index of bentonite and the permeability coefficient of GCL than K⁺solution,while K⁺solution has less influence on the free expansion index of bentonite and the permeability coefficient of GCL than Ca²⁺solution.（3）The combined action of solution environment and plant root system will further increase the permeability of GCL.At this time,the permeability coefficient of GCL reaches 10^-6cm/s,which is three orders of magnitude larger than that of GCL in deionized water.（4）Under the solution environment,the change of anti-permeability of GCL is mainly caused by the ion exchange between cations in solution and Na⁺in bentonite,which leads to the decrease of Na₂O content in bentonite and the thinner bound water film,thus reducing the anti-permeability of GCL.The percentage change of different elements in GCL leads to the change of impermeability of GCL,which is not only related to the growth amount,but also related to the type of the element,and the type of the element occupies a dominant position,so comprehensive evaluation should be paid attention to.