Study On Soil Water Infiltration Law In Shen-fu Mining Area Based On Hydrus-1D

The transport of soil water in the gas zone is related to the interconversion between surface water,groundwater and atmospheric water,and is an important link in the process of surface water circulation,as well as an important carrier for transferring the required materials for the organisms in the soil.Shenmu is located in the middle of the Loess Plateau in northern Shaanxi Province and is an important energy industry base in China.The formation collapse caused by coal mining and the appearance of ground fractures have seriously affected the hydrological cycle process in the mining area.Therefore,it is of great practical and scientific significance to study the influence of water transport in the fracture zone of coal mining on the package gas zone for the construction of green mines and the understanding of the water cycle.In this paper,the fracture zones of Hongliulin mining area and Yanghuopan mining area with simple geological structure and stable coal seams are selected for in-situ infiltration test,common infiltration model fitting and field sampling to obtain actual soil characteristic parameters.The soil numerical models of the two mining areas are established based on HYDRUS-1D software,and the infiltration under ponding conditions is simulated to analyze the law of water movement;The established model is used to analyze the rainfall infiltration in the mining area to explore the supplementary effect of rainfall on the water in the vadose zone.The main conclusions are as follows:（1）The results of the infiltration test showed that the initial infiltration rate in the fissure zone of Hongliulin mine was fissure zone>ecological restoration zone>unmined zone.The infiltration rates at the time of reaching steady infiltration were 0.53cm·min^-1 in the fissure zone,0.43cm·min^-1 in the ecological restoration zone,and 0.48cm·min^-1 in the unmined zone.The infiltration rate of the soil in the fissure zone of the Yanghuopan mine was always higher than that of the control group,and reached steady infiltration at 20 mins(0.33cm·min^-1 in the fissure zone and 0.23cm·min^-1 in the unmined zone).The test results were fitted by two infiltration equations,Kostiakov and Fang Zhengsan,with good determination coefficients between 0.817 and 0.978,indicating the reasonableness of the infiltration test results.The percentage of priority flow in the whole infiltration process was quantitatively revealed by experimental methods in five different areas of the test site,which ranged from 0.25 to 0.41in the early infiltration stage and 0.16 to 0.44 in the middle infiltration stage.The infiltration rates of priority flows in the ecological restoration and rift zones in the five regions studied were much higher than those in the undisturbed areas under natural conditions.（2）Numerical models of water transport in two mining areas were established and simulated under experimental conditions to verify the accuracy of the model in terms of infiltration rate,cumulative infiltration and wetting front transport distance,and to verify the reasonableness of the model results by evaluation indexes such as Nash efficiency coefficient,root mean square error and relative error.The overall accuracy of the model simulation was found to be high in five regions.Among them,the infiltration rate of the Hongliulin rift zone increased by 50%compared with that of the unmined area,and the infiltration volume of the Yanghuopan rift zone increased by 29.5%compared with that of the unmined area;the total infiltration volume of the Hongliulin coal mining rift zone was more than double that of the unmined area,and the cumulative infiltration volume of the Yanghuopan rift zone was 48.2%larger than that of the unmined area;for the migration of wetting fronts,the water in the Hongliulin mining rift zone increased by 80%compared with that of the unmined area.For the migration of wetting fronts,the downward movement of water in the rift zone of Hongliulin mine increased by 80.4%compared with the unmined zone,while the depth of water transport in the Yanghuopan mine increased by 25.6%compared with the unmined zone.（3）The Hydrus-1D model was used to simulate the infiltration of rainfall under different soil conditions in the Shenmu area for two consecutive rainfall events that occurred from August 9-11,2020:The coal mining results in the acceleration of soil infiltration,the intensification of evaporation and the weakening of water holding capacity.Before the rainfall,the water content of the fissure zone was lower than that of the unmined zone,and the maximum soil water content only reached 10%.after the rainfall on August 9,the coal mining fissure zone directly infiltrated to the deep 150 cm of the gas envelope.The restoration area and the unmined area can only infiltrate to 150cm after two rainfalls,and the maximum soil moisture content can reach 50%.In the fracture zone,two consecutive rainfall events recharge the soil water content in the deep gas pocket,but the total soil water content is still small.Finally,the single rainfall infiltration under drought conditions is derived from the model to establish a single rainfall prediction scheme,and it can be analyzed that:under the drought conditions within the mine area,continuous rainfall is more helpful to recharge the deep pack gas zone as well as the underground aquifer.For the single rainfall,the rainfall intensity of less than 50-60mm is ineffective rainfall,which cannot effectively recharge the deep envelope moisture in the mine area.Finally,combined with all the simulation results,suggestions are put forward for ecological restoration of the mining area.