Effect Of Temperature-Stress-Concentration On Barrier Permeability Of Sand-doped Clay

At present,sanitary landfill is an important means and main way to treat municipal waste.Sand-bentonite is a common anti-pollution barrier,and attapulgite has better stability and strong adsorption,so it has become a substitute material for bentonite.During the operation of the landfill,the load increases continuously.The decomposition of garbage causes the internal temperature to rise.The leachate contains a large number of highly concentrated pollutants and heavy metal ions which further threaten the health and safety of the people around the landfill site and the operation safety of the landfill site.A single factor cannot truly reflect the internal environment of the liner system during the operation of the landfill.In order to explore the anti-pollution performance of the anti-seepage liner of the landfill under multiple sites,the permeability of sand-doped clay under multi-field coupling was studied in this paper.Firstly,the single factor permeability test is carried out to analyze the influence of each single factor on the permeability coefficient and initial hydraulic gradient of sand-doped clay.Then the orthogonal test was carried out to analyze the influence of multiple field coupling factors on the permeability coefficient and initial hydraulic gradient,and the relationship between the multiple field parameters,permeability coefficient and initial hydraulic gradient was established.Through mercury injection and thermogravimetric experiments,the effective porosity was obtained,and the K-C equation was modified from the perspective of effective porosity and effective specific surface area(Kozeny-Carman equation:A formula representing the relationship between rock permeability,porosity and rock specific surface),and comparing the predicted values of the K-C equation with the measured values to prove the feasibility of using multiple field parameters to predict the permeability coefficient,and analyzing the influence of non-Darcy seepage on the service life of the anti-pollution barrier according to the obtained permeability coefficient and initial hydraulic gradient.Specific conclusions are as follows:(1)The influences of confining pressure field,temperature field and concentration field on the permeability coefficient and initial hydraulic gradient of sand-doped attapulgite were analyzed by single factor analysis test.With the increase of confining pressure,the permeability coefficient decreases and the initial hydraulic gradient increases.The increase of temperature and osmotic solution concentration leads to the increase of permeability coefficient and the decrease of initial hydraulic gradient.(2)Through orthogonal experiment,the influences of multiple field coupling factors on permeability coefficient and initial hydraulic gradient were analyzed.According to variance analysis and range analysis of experimental data,the primary and secondary relationships of the influences of temperature,confining pressure andosmotic fluid concentration on permeability coefficient were as follows:Confining pressure>temperature>concentration,that is,the permeability coefficient and initial hydraulic gradient of sand-doped attapulgite are most affected by confining pressure.The optimal combination of permeability coefficient is as follows:temperature 25℃,confining pressure 400kPa and concentration Omg/L.(3)The multi-field parameter expressions of the permeability coefficient and initial hydraulic gradient of sand-doped clay were obtained by multiple regression analysis,and the multi-field parameters were substituted into the calculated predicted values and measured values for comparison.The measured values were distributed on both sides of the predicted values.The results show that the permeability coefficient expressed by the multi-field parameters and the initial hydraulic gradient can well predict the permeability coefficient.(4)The expression of effective porosity with respect to multiple field parameters was obtained by multiple regression analysis,and substituted into the K-C equation.The relationship between the multiple field parameters and the K-C equation was established,and the predicted value of the permeability coefficient was obtained.Comparing with the measured value,it was found that the modified K-C equation could well predict the permeability coefficient.In other words,the K-C equation expressed by multi-field parameters has practical application value and provides reference value for the actual impermeability of sand-doped clay.(5)The antifouling barrier service life of composite gasket is significantly longer than that of single gasket,mainly because the geomembrane in composite gasket has a very low permeability coefficient,which can effectively block the migration of pollutants.With the increase of initial hydraulic gradient,the service life of antipollution barrier increases obviously.The initial hydraulic gradient in the compacted sand clay layer can effectively reduce the water head of leachate and block the migration of pollutants.