| With the increase of underground coal mining, the scale of surface subsidence area is extending. The landform is damaged, and soil quality is declining in subsidence area. Meanwhile, environment problem, such as soil and water loss, is constantly emerging. However, the soil crack preferential flow in mining subsidence areas does not cause much concern. In this paper, classification study of soil crack preferential flow was conducted. And the formation and evolutionary process of soil crack preferential flow was simulate. What is more, the application of high density resistivity method in the representadion of soil crack preferential flow path is explored. So the characteristics of soil crack preferential flow were recognized, and the impacts of soil crack preferential flow on soil and water loss in mining subsidence areas were studied.1. The genesis of soil crack preferential flow was analyzed, and the driving factors were summarized as well. So the classification study was carried on. The genesis should not only include the role of natural environment, but also include the human engenerring impacts. The specific genesis factors, distribution, crack size, distribution characteristics, formation and evolution cycle of soil crack preferential flow of both genesises were summarized. With the classification study, the particular characteristics of soil crack preferential flow under human engenerring impacts were found. Crack distribution could be predicted to a certain degree. The main distribution forms are nearly parallel strips or concentric rings with characteristics of dynamic evolution, directivity and non-planar distribution under some given conditions.2. The application results of high density resistivity method in the representadion of soil crack preferential flow path are as following. The mining subsidence deformation and soil crack formation process of preferential flow path were simulated well on the designed physical model. Under the experiment condition, the area where the soil resistivity is about 50Ω·m～180Ω·m or the soil resistivity ratio is about 1.2～2.0 is the soil crack location. And the depths of these areas are the quantized depths of cracks. The soil resistivity or soil resistivity ratio variation could reflect the crack width variation. The results of high density resistivity method in characterization of soil crack preferential flow are affected by electrode spacing, electrode distribution shape of crack location and formation. The reducing of the electrode density could improve the efficiency of high density resistivity method.3. The simulation results of soil and water loss on mining subsidence slopes under the condition of soil crack preferential flow with rainfall and leaching are as following. Surface soil slope changes obviously in coal mining subsidence areas with a final gradient of 2.08°. And soil crevices take place in sloping fields, with a maximum depth of 0.55m, which changes the seepage characteristics of the soil. The migration of nutrient in the soil is affected obviously. In the later stage, the average soil ammonia nitrogen content along the L (with crevices) district sampling line is 1.0 mg/Kg lower than that of Z (without crevices) district sampling line, which indicates that the soil ability to maintain nutrients decreases with the contribution of soil crevice preferential flow. The slope changing of the sloping fields enhances the surface soil particle transport of rainfall. With the eroding of rainfall, the clay particle percentage on the top slope is as much as 13.9%, while the sand particle percentage on the bottom slope is as much as 21.7%. Soil crevice preferential flow provides a preferential path for water to transport soil particles from the surface layer to the deep layer. And crevices with soil particles filled will become long-term preferential flow paths. To sum up, soil crevice preferential flow is a significant driving factor for soil erosion in coal mining subsidence areas. |
