Anti-seepage And High Strength Improved Loess Liner Test And Numerical Simulation Research

The scientific treatment of domestic waste is a serious challenge facing the world.At present,the treatment of domestic waste in Northwest China mainly adopts incineration and landfill.When the landfill method is applied,the landfilled waste will inevitably produce a large amount of leachate during the long-term accumulation process.Once the leachate penetrates the landfill and enters the surrounding soil,it will cause major harm to the surrounding ecological environment and residents.In areas rich in clay resources,compacted clay is usually used to construct an anti-seepage liner system at the bottom and surrounding of the landfill to prevent the landfill leachate from spreading around.In the northwest region of China,the low permeability clay resources are scarce,but the loess is abundant.If the permeability and strength of natural loess can be improved by scientific means,the strength can be improved,and the permeability can also meet the anti-seepage requirements of landfill liners,so as to adjust measures to local conditions and reduce engineering costs,then the improved loess liner can be used as an economic and effective engineering measure in the construction of landfills.In this paper,based on the analysis and summary of previous research results on loess improvement and liner system,the research object is loess on a site in Lanzhou,in which bentonite,gypsum and dura fiber are mixed in certain proportions,and the cohesion,internal friction angle,shear strength and permeability coefficient of the improved loess are investigated by direct shear test and variable head permeability test.The results of the indoor tests were also used as the basis for numerical simulation research to simulate the feasibility of impermeable and high-strength improved loess liner,and the application research of improved loess liner was systematically carried out.The main research results achieved in this paper are:1.The basic physical properties of the loess used in the research were studied,including particle analysis test,natural moisture content test,liquid-plastic limit test and compaction test,and the test results obtained provided data reference for the design of subsequent test schemes.The basic mechanism of bentonite and gypsum-improved loess was analysed and summarised to provide a theoretical basis for subsequent indoor experimental research and numerical simulation studies on bentonite and gypsumimproved loess.2.Respectively on the bentonite,gypsum,dura fiber single material improvement loess and bentonite,gypsum,dura fiber composite improvement loess direct shear test research.The specific effects of bentonite incorporation ratio,gypsum incorporation ratio,dura fiber incorporation ratio and moisture content of soil samples on the changes of cohesion,internal friction angle and shear strength of the improved loess were analysed.The study shows that in the study of shear strength of single material improved loess,the optimum mixing ratio of bentonite is 8%,gypsum is 12% and dura fiber is 0.5%;in the study of shear strength of multi-material improved loess,the optimum mixing ratio of bentonite-gypsum-dura fiber is: bentonite 8%,gypsum 10%,dura fiber 0.5%.3.Respectively on the bentonite,gypsum single material improved loess and bentonite,gypsum,dura fiber composite improved loess for variable head penetration test research.The influence of the mixing ratio of bentonite,gypsum and dura fiber,the compaction degree of the soil sample and the age of the soil sample on the permeability coefficient of the improved loess was analysed.The study on the impermeability of the composite improved loess showed that the best ratio of bentonite-gypsum-dura fiber composite improved loess was 9% bentonite,12%gypsum,0.1% dura fiber,94% compaction and 3 days maintenance age.After the test,the permeability coefficient of the composite improved loess under this ratio meets the impermeability requirements of the sanitary landfill liner.4.Considering the influence of bentonite,gypsum and dura fibre on the shear strength and impermeability of the composite improved loess,the final composite improved loess ratio was determined as follows: 9% bentonite,12% gypsum,0.1% dura fibre,18% moisture content,3 days maintenance period and 94% compaction.The cohesion,internal friction angle and permeability coefficient of the composite modified loess were obtained through the test.5.Based on the above improved loess test results,a numerical simulation model was established to study the feasibility of the application of the composite improved loess liner.The study shows that: under the limit condition of leachate filling the landfill,the infiltration line of leachate still remains inside the modified loess liner,which shows that the modified loess liner meets the requirements of the landfill liner structure for leachate interception and barrier;under the condition of medium rain or heavy rain lasting for 10 days,the leachate of the landfill still does not penetrate the modified loess liner and does not cause pollution to the soil around the landfill;under the condition of sudden drop of leachate The safety of the slope of the modified loess liner meets the requirements;under the pressure of the waste body,the displacement and deformation of the composite modified loess liner is smaller and the pressurebearing effect is better than that of the ordinary loess liner.Therefore,the feasibility of the composite modified loess liner has been verified in terms of both impermeability and high strength.