Research On Penetration Characteristics Of Reticulated Red Clay In Pb(Ⅱ)Environment

With the rapid development of my country’s economy and the acceleration of urbanization,the number of urban domestic waste landfills is also increasing.It is of great practical significance to study the law of water transport in landfills.At the same time,water transport in landfills is a problem of unsaturated soil mechanics in macroporous media.The study of these problems will involve fluids(two-phase or multi-phase fluids such as water-gas or water-pollutants)in unsaturated soils.Flow problems in pores.However,the accurate description of the fluid flow in the pores of unsaturated soil is inseparable from the hydraulic properties of unsaturated soil(including soil-water characteristic curve and permeability coefficient).In this paper,the red reticulated clay widely distributed in Changsha area is taken as the research object,and the permeability characteristics of saturated-unsaturated red reticulated clay under heavy metal conditions are studied by configuring the heavy metal ion solution to simulate the composition of landfill leachate.The permeability evolution law and ion concentration variation trend of saturated red reticulated clay under Pb(Ⅱ)environment were discussed,and the soil-water characteristic curve models of unsaturated red reticulated clay under different gradients of Pb(Ⅱ)were obtained based on the pressure plate instrument.The main work and research conclusions of the paper are as follows:(1)The main clay minerals of the reticulated red clay in the Yuelu Mountain area are 49% illite,16% kaolinite and 35% illite/montmorillonite mixed-layer minerals,and the non-clay minerals are mainly quartz.The distribution of elements is dominated by O,Si,Al,K,and Fe,and Fe is the main reason for the red color of the reticulated red clay.The particle shape of reticulated red clay is mostly flake or flat,and a small amount is spherical or columnar,and the pore size is mainly concentrated around 100 nm.(2)For reticulated red clay,whether it is saturated or unsaturated seepage,the increase of dry density makes the soil more compact,and the fine particles are filled in the pores,and the permeability coefficient can be improved by at least 12%.The addition of Pb(Ⅱ)hinders this process,increases the mineral spacing,disperses the soil particles,increases the pores to 120 nm,and increases the permeability coefficient by more than 9%.When activated carbon and bentonite admixtures were added,the permeability and retardation of reticulated red clay were significantly improved.When the mass percentage of reticulated red clay was 79%,the mass percentage of activated carbon was 5%,and the amount of bentonite was 16%,the soil sample was The permeability is increased by 6 times,and the adsorption retardation is increased by 5 times.(3)Fredlund-Xing model has good fitting performance for the soilwater characteristic curve of reticulated red clay under different concentrations of Pb(Ⅱ),and the model parameters are very sensitive to Pb(Ⅱ).Pb(Ⅱ)increases the air intake value a and porosity n of the soil,changes the shape of the hysteresis loop,makes the hysteresis effect more obvious,the closed loop becomes narrower and longer,and the area also increases,that is,the dehumidification curve The difference between the moisture absorption curve and the moisture absorption curve is more prominent,and the corresponding matrix suction difference value is larger when the same moisture content is reached.