Experimental Research On Flexible Wall Seepage Test Of Modified Loess Soil Of Landfill Bottom Liner

The impervious barrier of lines system is used to isolate the leachate and landfill gas inthe process of closure, as a barrier to control the pollutant diffusion in region of interest whichis located at the bottom and slope in the landfill, it is also an guarantee for safe operation oflandfill. In a region rich in natural clay resources, usually using compacted clay layer asimpervious liner as the first choice, after a long—term laboratory experiment, fieldexperiment to test the performance of compacted clay layer to prove it could be used as agood impermeable material in landfill. However, in Northwest China, the resources of naturalclay is scarce and loess is very widely distributed. How to change loess for fulfilling landfillseepage performance requirement, suiting measures to local conditions, thereby reducingconstruction costs, is the direction in the research of the numerous scholars now.There are some intrinsic drawbacks in conventional seepage testing permeabilitycoefficient of the impervious lines, such as long test time, poor sealing effects, specimenscould not be fit closely with side—wall, all of those would be affect the results. Therefore,this paper using improved conventional triaxial apparatus to test the permeability coefficientof loess and modified loess, it will have a better simulating the force state of natural soilsample, and obtained more accurate results of permeability coefficient..Based on analyzing and summarizing the predecessors’ study results of loesspermeability of laboratory test, this paper focuses on taking loess of Lanzhou areas as theresearch object, carries the loess soil sample for a good deal of physical and mechanical indextest and triaxial permeability test research, then compares and analyzes the influence factorsparticularly the confining pressure, initial dry density and ratio of modifiers on thepermeability influence rules, so as to provide the technical support for the modified loess asimpervious barrier of lines in landfill design and construction.First, by standard compaction test of proposed landfill remolded loess, determines themaximum dry density and optimum moisture content of loess. Under these conditions, makesspecimens of permeability test, uses a graduated compression permeability test at differentconfining pressures and different densities. Results indicate that for the saturated loess,permeability coefficient is decreasing with the confining pressure increasing, it alsodecreasing with the initial dry density increasing. Second, mixes with different proportionlime、cement and bentonite clay into loess, does the compaction test of modified loess, obtainsthe maximum dry density and optimum moisture content of modified loess in differentproportion of different material, analysis indicates that the change of a certain degree takesplace in compaction property, mixes lime or cement into loess, the maximum dry density decreases obviously, while the optimum moisture content increases a certain extent; and thatmixes bentonite clay into loess, the maximum dry density increases first and then decreases,and optimum moisture content is in continued increases. Then reveals the permeabilitycoefficient must be reduce after mixes different proportions of lime、cement and bentoniteclay in triaxial permeability test, but its range and optimal mixing ratio depending on thematerial have significant differences. Finally, the two types of cement modified loessspecimens of different mixing ratios for different conservation periods, results indicate thatthrough the conservation of the cement modified loess, the permeability coefficient decreasesin the same order of magnitude, illustrate the age of cement modified loess has little effect tothe permeability coefficient.After the permeability of laboratory test, combined the test results with the geologyconditions in landfill of new area in Lanzhou, the results from ANSYS software analysis canverify that a certain thickness of modified loess which is meet the specifications fulfill therequirements for landfill seepage liner.In this paper through the research on triaxial permeability test of modified loess, obtainssome initial rules and results which have a meaningful indicator and the project applicationvalue for the modified loess as impervious barrier of lines in landfill research and application.