Experimental Study Of HYDRUS Simulation-based Soil Moisture And Solute Transport In Mining Subsidence Area

Coal mining causes changes in the stress state of the overlying rock layer,resulting in movement and deformation of the ground surface,generating cracks and surface subsidence of different degrees.The mining subsidence will produce a series of ecological and environmental problems such as the change of surface water and groundwater transport cycle and soil quality degradation in the subsidence area.In order to investigate the soil water and solute transport patterns in mining subsidence,this thesis uses indoor soil column simulation tests to investigate the soil water and solute transport patterns in different subsidence stress zones during soil evaporation and infiltration,and combines HYDRUS software to numerically simulate soil water and solute transport in different subsidence stress zones.It provides a theoretical basis for systematically revealing the influence mechanism of mining subsidence on soil water and salt transport and scientifically evaluating the environmental effects of mining subsidence.The main research results are summarized as follows.（1）In the evaporation test,under the mining subsidence disturbance,the soil capacitance in the tension stress zone on the 0-40cm depth decreases,evaporation is strong,and soil moisture reaches stability at about 40d.At 40-100 cm depth,soil moisture transported to the sinkhole area.Total soil salinity is more susceptible to sinkhole stress disturbance than moisture.0-60 cm soil salinity is strongly influenced by moisture transport and reaches stability at about 40 d.60-100 cm depth soil salinity is influenced by the sinkhole area and the direction of advancement,and salt transport decreases.At the later stage of the experiment,the soil surface layer 0-5cm accumulated salts significantly and was highly salinized.Ca²⁺,Mg²⁺,Cl^-,SO₄^2-,CO₃^2-were transported to the tensile stress zone,and Na⁺was transported to the extrusion stress zone.The accumulation depth of different types of solute ions all gradually shifted downward,and with deepening depth,different types of solute ions gradually changed from double-peak to single-peak characteristics.In the simulated soil profile,Na⁺and Mg²⁺accumulated toward 20-40 cm,CO₃^2-accumulated toward 60-80 cm,and Ca²⁺,SO₄^2-and Cl^-accumulated toward 40-60 cm.（2）In the infiltration test,the tensile stress promotes the advancing distance and infiltration rate of the wetting peak.At the same time,the water holding capacity of the soil is weakened,making the saturated water content of the soil in the tensile stress area smaller than that in the extrusion stress area.Soil salt transport rate lagged behind water transport rate,soil salts accumulated near the wetting peak,and soil salts increased significantly in the deep layer.Ca²⁺,Mg²⁺in the deep soil layer to the tension area,Na⁺and Cl^-in the shallow soil layer to the tension area.（3）In the simulation of soil water and salt transport in different stress zones of mining subsidence using HYDRUS,the numerical simulation and physical simulation results have a high degree of agreement,which can simulate the soil water distribution and solute transport law in different subsidence stress zones and reveal the soil water and solute transport law caused by subsidence stress.Overall,the mining subsidence stress increases the soil water retention at20-100 cm depth and promotes the downward migration of soil salts.In addition,the mining subsidence stress accelerates soil salt leaching during soil infiltration and makes it seep along the tension zone.