Landfill Leachate Diversion And Recharge Study

China’s landfill waste food waste and other high water content components accounted for a relatively high,coupled with landfill expansion and design defects,domestic landfills generally have leachate water level is too high.In this paper,the following research is carried out for the water level control problem of high water level landfill.Firstly,the non-homogeneous distribution law of each geotechnical parameter of landfill waste and its influencing factors are studied by the method of statistical analysis.After that,on the basis of considering the non-homogeneous characteristics of landfill waste,a vertical diversion well model was established,and the effects of diversion time and pumping pressure on the precipitation efficiency and slope stability were studied.For the difficult problem of leachate treatment,a vertical recharge well model was established based on the consideration of the non-homogeneous characteristics of landfill waste and the clogging degree of the bottom conductive layer,and each design parameter of the vertical well was studied,and the control method of the vertical well design parameters was given.Finally,taking an engineering example as the research object,the seepage field of its full landfill cycle was simulated considering the endogenous water yield of waste,and the existence form of each water level in the pile and its development law were analyzed.According to the research results of this paper,it can provide reference and reference for stability evaluation and drainage reinforcement and leachate treatment of high water level landfill.（1）The non-homogeneous distribution pattern of landfill waste geotechnical parameters and its influencing factors were studied by the method of statistical analysis.The initial moisture content of domestic MSW ranges from 45%to 61%,and its average initial moisture content is about 52%.The field water holding capacity of landfill waste is closely related to the age and compaction degree,which gradually decreases and finally stabilizes as the age and compaction degree increase.The saturation permeability coefficient of landfill waste in the direction of burial depth takes values in the range of10^-3～10^-8m/s,with strong inhomogeneity.The hydraulic conductivity characteristics of shallow waste are better than those of middle and deep landfill waste,and the water-holding characteristics of deep waste are better than those of middle and shallow landfill waste.The distribution of landfill waste capacity values ranges from 3.3 to 20KN/m³,and the influence of landfill waste components on the capacity weight is large.The values of landfill waste cohesion are in the range of 0-77.4KPa,the values of internal friction angle are in the range of 0°-59°,the components have a greater influence on the shear strength,and the internal friction angle is negatively correlated with the cohesion in the direction of burial depth.（2）On the basis of considering the non-homogeneous characteristics of the pile,a vertical diversion well model is established,and the influence of diversion time and pumping pressure on the precipitation efficiency and slope stability is studied,and the method of determining the optimal value of the stable value of diversion time and pumping pressure is given.And it is found that the influence depth of the pilot shaft is mainly influenced by the pumping pressure and the effective depth of the shaft,while the influence radius of the pilot shaft is mainly influenced by the pilot time and the model boundary.The slope stability safety factor Fs is mainly influenced by the leachate water level in the near slope area,followed by the water level inside the pile.（3）Based on the consideration of the non-homogeneous characteristics of landfill waste and the degree of blockage of the bottom leachate conductive layer,a vertical recharge well model was established,and the effects of injection pressure,anisotropy coefficient,backward tilting distance and well distance on the recharge efficiency and slope stability were analyzed,and the design diagrams of injection pressure and backward tilting distance and well distance were given.And it is found that the increase of injection pressure and anisotropy coefficient leads to a significant increase of volume in the recharge affected area under the case of pile blockage.The volume of the recharge affected area develops slowly in the early stage of recharge,and when a certain moment T_b is reached,the volume of the recharge affected area increases rapidly,which is defined as the moment of recharge rate increase.The development trend of the recharge influence area is that the leachate develops along the horizontal and burial depth direction from the injection section,and its rate depends on the anisotropy coefficient,while the leachate on the bottom conductive layer develops gradually,and its rate depends on the blockage degree,and develops toward the near slope area when the leachate in both directions is connected.（4）Based on the consideration of the endogenous water yield of waste and the inhomogeneous characteristics of the pile,the seepage field simulation of a high water level landfill was carried out for the whole landfill cycle,and the existence forms of each water level in the pile and its development law were summarized.The water table in the pile mainly exists in the form of main water table and stagnant water table,in which the location of the main water table is from one to six layers with a height of 41.28m,and the stagnant water table exists in the remaining layers of the pile,in which there is also the phenomenon of multiple layers of stagnant water table in a certain pile,and the most pile layer has three layers of stagnant water table,and there is also the phenomenon of penetration of stagnant water table in adjacent piles.The main water table and stagnant water table are preferentially developed on the slope surface and develop horizontally and highly with the filling time,and the overall shape of the slope surface,where the main water table is formed by the penetration of each layer of stagnant water table.In the case of piles filled with gentle base surface,the main water level and stagnant water level will be uniformly distributed on the base surface and develop in the height direction with the filling time.