Study On Experimental And Numerical Simulation Of Saline/Fresh Water Infiltration Considering Gas Phase Influence

The study of the law of soil infiltration is the basis of solving practical problems such as rainfall infiltration.The study of freshwater infiltration takes this as the starting point.At present,the influence of infiltration mechanism and soil characteristics on infiltration process has been systematically studied at home and abroad.The research on salt water infiltration law is based on irrigation.With the contradiction between the high demand for grain production and the shortage of fresh water resources,more and more attention has been paid to the use of brackish water for crop irrigation.Therefore,the law of infiltration of salt water has been carried out at home and abroad,mainly for the infiltration of brackish water.According to the actual situation,the soil is often unsaturated when infiltration occurs.The existence of vapor phase in soil hinders water infiltration.Therefore,it is of great practical significance to study the influence of vapor phase in infiltration process.At present,there are two main methods to study the law of soil infiltration: experiment and numerical simulation.It is found that in the process of soil infiltration experiment,the experimental conditions have a greater impact on soil infiltration,which is often neglected in previous studies.So the main contents and achievements are as follows:(1)The infiltration tests of saline and fresh water with different boundary conditions and initial volume water content of soil columns under 12 conditions were designed and carried out respectively,and their influences on the soil infiltration process were analyzed respectively.(2)Air boundary,closed boundary and liquid boundary are used for the lower boundary of soil column.The infiltration time under air boundary is the shortest,the liquid boundary is the second,and the closed boundary is the longest.The air boundary soil reaches saturation from top to bottom,and the closed boundary infiltration process is saturated from top to bottom and from bottom to top.The water migration at the liquid boundary is similar to the former.The air pressure in the soil column with air boundary rises respectively and reaches stability at the same time of saturation.At the initial stage of infiltration,the gas pressure rises synchronously and,after saturation,the pressure from bottom to top increases and stabilizes.The change of boundary pressure of zero pressure liquid surface is similar to that of the latter in the early stage of infiltration and to that of the latter in the late stage of infiltration.(3)The initial moisture content of the sand increases,and different effects are produced under different boundary conditions.Under the air boundary,the increase of the initial moisture content of the sand will prolong the time when the soil moisture reaches a stable state,and the air pressure will appear negative after stabilization.Under the other two boundaries,the increase of initial moisture content of sand will weaken the influence of boundary conditions on the infiltration process.The experimental data after stabilization under the two boundaries is closer than that in dry sand.The values of stable infiltration rate under three kinds of boundary conditions are lower than those of dry sand.(4)TOUGH2 was used to establish soil column infiltration model,assisted experimental data,explained experimental phenomena,and analyzed the variation trend of soil parameters after the test from the perspective of time.