| Pollutants discharged or leaked by human production and living activities will enter the porous media such as underground soil,sand and rocks through the surface and continue to diffuse and infiltrate,eventually reaching the groundwater system to pollute the groundwater body.In nature,soil particles of different particle sizes are often arranged in layers.In addition,the migration of pollutant solutes in porous media is often accompanied by the transfer of heat,and temperature will also affect the hydraulic characteristics of the porous media,thereby affecting the law of solute transport in the porous media.As the last barrier for pollutants to enter the groundwater,the capillary fringe affects the infiltration path of pollutants.Therefore,this paper uses the HYDRUS 2D model to simulate and study the coupled transport laws of water,solute and heat in layered porous media,which play a certain guiding and reference significance for the prevention and control of groundwater pollution and the restoration of the ecological soil environment.The main research contents and results of this paper are as follows:(1)Explore the law of solute transport in different layered porous media,choose medium sand and coarse sand two types of porous media for layered arrangement.Change the thickness of the middle sand layer to form four layered porous media: single-layer type,double-layer type,three-layer type 1 and three-layer type 2,in which the total thickness of the middle sand layer is 10 cm,and the non-sand layer type porous The medium served as a control.The results show that: compared with the type without sand layer,the pollutants can migrate to a longer distance in the layered area,thereby effectively delaying the vertical infiltration of pollutants below the phreatic surface;the layered area in the three-layer type 2 is blocked The effect of vertical infiltration of pollutants is the best.(2)Select a single-layer type of porous media to explore the law of solute migration in the porous porous under different solution injection speeds and different lower water levels and water potential differences.The results show that when the water injection rate is high,the pollutants will migrate to the left upstream boundary.Expanded the scope of pollution;when the water injection rate is small,the pollutants will stay in the capillary water zone and move laterally;when the groundwater potential difference is large,the groundwater flow velocity increases,and the flow velocity in the capillary fringe will increase accordingly.The capillary fringe has an enhanced ability to vertically infiltrate pollutants.(3)Exploring the law of heat transfer in different layered porous media.The results show that: compared with the type without sand layer,the middle sand layer can effectively reduce the vertical convective heat transfer in the porous medium,so the heat diffusion in the vertical direction is better slow.However,the horizontal direction mainly relies on heat conduction,so the difference in the transfer speed of heat in the horizontal direction in different types of porous media is small.(4)Select single-layer porous media to explore the law of solute migration in porous media at different water injection temperatures and different groundwater flow temperatures.The results show that the higher the water injection temperature,the faster the solute migration in the porous media,but the layered area’s the ability to block pollutants is correspondingly weakened;the higher the temperature of the groundwater flow,the faster the speed of the groundwater flow,and the stronger the ability of the capillary fringe to block the vertical infiltration of solutes. |
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