| The paper took Shendong Coalfield in daliuta mining area as the research object, by using field tests in situ monitoring and laboratory analysis, explored key water holding characteristics variation in coal mining subsidence of soil, seasonal frozen soil depth, soil moisture content, distribution and moisture migration characteristics during freeze-thaw process, attempted to reveal the coal mining subsidence freeze stagnant water variability and mechanisms, thus providing technical support for arid and semi-arid sandy area in ecological restoration collapse and rational usage of water resources. The main conclusions are as follows:The composition on the whole of the particles in the study area was mainly silt and fine sand, average sand particle content was more than 85% within 0-60cm soil silt, On the vertical soil profile, with soil depth increasing, the content of fine particles had the same trend as well. After coal mining subsidence, surface microenvironment changed, subsidence coarse-grained particles became prominent,0-40 layers of soil composition only contained sand with rough soil texture, vertical variation of soil particles showed that with increases of depth, the particles became finer.Mining Subsidence made the soil subjected to external force, thus structure deformation loosed, resulting in lower soil density and soil bulk density decreased greatly with depth. Soil porosity increased with soil depth and had evident trend, 80-100 layer soil porosity increased to 41.38% from 39.02%. Surface subsidence result in disturbances, and this disturbance occurred in every slope position, the top and middle position of the hill was the most intense.Horton formula for wind sand infiltration rate had good applicability under this circumstance.Different width of the cracks had different influence on the surrounding soil strength, showing different spatial variability of soil moisture, with the crack width increased, and the spatial variability of soil water content increased. The spatial distribution of soil level trends showed cracks farther away, the more calm the moisture change, water content close to CV, at every point in the cracks had the lowest water content.For the seasonal frozen soil, set crack as the center, as the horizontal distance increased, the maximum depth of frosted soil decreased, the existence of cracks altered its spatial distribution of soil freezing within their sphere of influence not only vertically (up and down) of water, heat exchange, there was lateral (left) exchange as well, and leading to the degree of lateral exchange of frosted depth presentation level differentiation. Cracks on both sides of the soil moisture is higher than the cracks, the farther away from the crack, the higher soil moisture, during soil freezing process, the water to freeze migration fronts had a great relationship with the freezing rate, slower soil freezing, greater freeze increase the amount of water at the front face. Cracks in the surrounding neighborhood, with increasing horizontal distance, showing the maximum amount of soil water rising.Stagnant water moisture to freeze rates showed an inverted rich water in the study area,and the phenomena appeared in 10-20cm soil. The melting process of the vertical distribution of soil moisture became arc-type inverse distribution, moisture content of the overall trend showing decreased after the first increase.The soil in the freeze stagnant water in this area could be divided into fall and fall-winter freezing process, winter cooling process and winter-spring thaw process. As soil subsidence cracks acted as channel for outside water, heat exchange exacerbated freeze thawing process. Soil freezing helped maintain moisture. After thawing, the collapse exposed the cracks, water loss exacerbated, thawing was the beginning of soil water content in subsidence sandy area entered deficit situation. |
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