Experimental Study On Engineering Properties Of Loess Improved By Calcium Lignosulfonate Under The Environmental Effect Of Landfill Leachate

Sanitary landfills are currently one of the most significant methods for disposing of household waste in cities due to the limitations of economy,technology,and applicability.A significant amount of landfill leachate was produced during the operation and use stage of the landfill.This leachate could erode and reconstruct the soil structure,significantly affecting the soil’s engineering performance and negatively affecting the long-term safe operation of the landfill’s anti-seepage liner system.Loess was used as the natural base for landfills in loess areas,but because of its high permeability and collapsibility and because of the erosion of garbage leachate,it was not suitable for direct anti-seepage treatment.Compacted clay layer was typically used as the material of anti-seepage liner system.A liner construction should have high mechanical qualities in addition to effective anti-seepage performance.Enhancing loess to satisfy the needs of the liner construction was extremely important.Lignin was used to strengthen and improve soil as a low-cost,new environmentally acceptable substance.It could not only reduce soil contamination but also find a solution to the issue of recycling waste materials.Based on these findings,this article carried out geotechnical tests for permeability,unconfined compressive strength,direct shear,and compression,examined the effects of calcium lignosulfonate on the permeability and mechanical properties of loess invaded by landfill leachate,and examined the impact of landfill leachate on the permeability and mechanical properties of loess,and based on the results of the indoor tests,conducted seepage analysis and slope stabilities.The following were the key research conclusions:（1）Testing for permeability was done on soil samples with various landfill leachate concentrations and dry densities,accounting for elements like the quantity of calcium lignosulfonate and curing age.Analysis of the impact of landfill leachate on permeability coefficient and discussion of the mechanism of action of calcium lignosulfonate were both done.The findings indicated that landfill leachate degraded soil,and that soil samples’permeability coefficients rose as leachate concentrations rose.The permeability coefficient increased from 10^-8cm/s to 10^-7cm/s when the dry density was 1.7g/cm³,and it steadily declined as the calcium lignosulfonate content increased in the soil sample.The permeability coefficient reduced from 10^-8cm/s to 10^-9cm/s at1.7g/cm³dry density;With an increase in curing age,calcium lignosulfonate fully combines with the soil,further reducing its permeability coefficient.（2）The unconfined compressive strength,direct shear and consolidation tests of loess with different landfill leachate concentration and different calcium lignosulfonate content were carried out,and the influence of curing age on the compressive strength was considered.The test results showed that with the increase of landfill leachate concentration,the compressive strength and shear strength of soil decreased,and the compressibility increased;The compressive strength and shear strength showed a trend of first increasing and then decreasing with the increase of calcium lignosulfonate content.When the leachate concentration was 0 and the calcium lignosulfonate content was 1%,the maximum compressive strength measured was 272.11k Pa,the peak cohesion was 59.56k Pa,and the peak internal friction angle was 24.67°.As the curing age increased,the compressive strength gradually increased;The compressibility first decreased and then increased with the increase of calcium lignosulfonate content.Therefore,the content of calcium lignosulfonate should be optimized in combination with the change of permeability coefficient.（3）Numerical analysis was done on the seepage and slope stability of the landfill unit based on the outcomes of indoor trials.The findings demonstrated that loess treated with calcium lignosulfonate can successfully prevent leachate infiltration when used as a liner material.When loess was used as a liner,the pore water pressure inside the layer increased from-58.84k Pa to-28.92k Pa,and it increased to 58.86k Pa when it was contaminated.Landfill leachate permeated the impermeable layer and seeped into the foundation.The safety coefficient declined as landfill leachate concentration grew,and it initially increased before decreasing when calcium lignosulfonate content increased.The safety coefficient peaked at 1.554 at 1%calcium lignosulfonate content and then gradually fell as landfill height increased.