Influence of mining subsidence on soil water movement law in blown-sand area of Western China

The extraction of shallow buried coal seam often induces a series of ecological environment problems.Taking the shallow buried coal mine of blown-sand area as the study object,the influence of mining subsidence on soil water movement law was studied.The influence of coal mining subsidence on aeration zone structure was divided into three stages:prior to mining,the vadose zone thickness was thin,and the soil particles were relatively uniform;mining in progress,the water level dropped obviously,the vadose zone thickness increased sharply,and the homogeneity of soil particles became worse;end of mining,most of the ground fissures in blown-sand region were naturally healed,but the clay particles in the soil were reduced and the sand particles were increased,resulting in obvious soil coarsening phenomenon.Based on this definition,a two-dimensional simulation model of soil water transportation with different fissure widths was created.The results showed that the wetting front of soil water was downwards paralleled,and the soil moisture content of the same depth was essentially the same.However,the wetting front quickly moved down along the fracture and the dominant seepage phenomenon was obvious.With the increase of fissure width,the soil moisture tended to decrease while the impact radius of soil moisture tended to increase.The infiltration amount was basically irrelevant to the aeration zone thickness when aeration zone thickness was greater than the ultimate evaporation depth(300 cm),and the increasement of the aeration zone thickness only extended the time of groundwater recharge from precipitation.The field ecological investigation was also carried out in study area.The average aboveground biomass of Artemisia in mining subsidence had a reduction of 22.2% compared to normal area because of soil water shortage (insufficient water sources,the soil water content was less than 0.1 cm3/cm3) and root damage (fewer water channel,the dry root weight decreased 21.7%).The means of regulation and control for soil water movement in mining area were proposed:in order to reduce the loss of soil water content in subsidence area,the degree of fracture development would be reduced by adjusting the mining width and height in progress of mining;at the end of mining,a 10-30 cm thicknesses of loess liner laid under the soil layer was recommended when carrying out soil reconstruction in subsidence area,which could greatly improve the soil water content of vegetation root zone and accelerate the process of vegetation restoration.