Structural Characteristics And Deformation Law Of Underlying Stratum In Landfill

The environmental disasters and safety problems have become one of the most prominent problems now and in the future,which caused by a large number of irregular domestic refuse dumps and substandard domestic refuse treatment facilities(collectively referred to as stock dumps).The liner anti-seepage system was penetrated under the influence of long-term landfill leachate corrosion,which leads to leachate leakage.These processes eliminate the protective functions of anti-seepage system,and change the engineering characteristics of the underlying stratum in landfill,and reduce the bearing capacity of the underlying stratum in landfill.The consolidated-undrained triaxial shear test(CU),X-ray diffraction,scanning electron microscopy,laser particle size,and nuclear magnetic resonance tests was carried out to evaluate the strength characteristics,mineral composition,surface morphology,particle size distribution and pore structure characteristics of undisturbed and disturbed soil under different leachate pollution conditions in this paper.The structural parameters(?,?)that reflecting the structural characteristics of soil polluted by landfill leachate were calculated.(1)The maximum deviator stress,cohesion,internal friction angle,and structural strength of undisturbed and disturbed soil decreased continuously with an increase in the leachate pollution days or leachate concentration.The strength indexes of undisturbed soils were always greater than those of disturbed soils.When the leachate was eroded for 365days,the strength exertion under confining pressure of 50,100 and 150 kPa was 8.93%,8.79%and 6.64%,respectively.At the initial stage of leachate erosion(<15d)or after leachate erosion with lower concentration,the deformation of soil samples exhibited a shear failure surface and the stress-strain curve was strain softening.With the increase of erosion time or concentration,the deformation of soil sample demonstrated"bulging",and its stress-strain curve gradually transforms to strain hardening.(2)The content of clay minerals(illite,montmorillonite)gradually decreased with the increase of leachate erosion days or concentration.After 365 days of leachate erosion,illite and montmorillonite in undisturbed soil decreased by 29.09%and 35.63%,respectively.When the leachate concentration was 100%,illite and montmorillonite in undisturbed soil decreased by 26.02%and 23.93%,respectively.The change of mineral composition in disturbed soil was more complex than that in undisturbed soil.(3)With the increase of leachate erosion days or concentration,the overhead voids on the surface increased,and there were mostly unstable flocculent and honeycomb structure.Many cracks appeared in the soil.The particle size distribution curve were unimodal.The volume curve of coarse grains tent to be smooth gradually.The average particle size decreased,the specific surface area increased,the value of D_v(50)decreased at first,then stabilized.The soil particles gradually become small,uniform,and porous.(4)Pores in undisturbed and disturbed soils polluted by leachate were mainly inter-particle pore,intra-aggregate pore and inter-aggregate pore,among which inter-particle pore account for the largest proportion.The pore sizes of soils after leachate contamination for different time were mainly concentrated in the range of 0.02~1 and 2~50?m.The percentage of pore volume,maximum and optimal pore size increased with the increase of leachate contamination days or leachate concentration.(5)The cohesion and internal friction angle of soil were positively correlated with average particle size and negatively correlated with specific surface area.The structural parameters(?,?)that reflecting the structural characteristics of soil polluted by landfill leachate were calculated.The mathematical expressions between structural quantitative parameters and different days,concentrations was further obtained.