Hydro-thermal Coupling Characteristics of Soil in Loess-Aeolian Sand Coal Mining Subsidence Area During Freezing and Thawing Period

Runoff is a valuable water resource during seasonal freezing and thawing period in arid and semi-arid areas, and is of great significance to ecological restoration in coal mining subsidence areas. Through automatic in-situ monitoring of the dynamic changes of soil moisture and temperature inside and outside the coal mining subsidence area of different site types, the spatio-temporal heterogeneity of soil moisture and temperature during freezing and thawing period was analyzed, so that to explore the characteristics of soil moisture and temperature changes in the loess-aeolian mining subsidence area during the seasonal freeze-thaw process in the area connected Shanxi and Inner Mongolia. The results show that: (1) The study area belongs to seasonal frozen soil, and the freezing time is generally from December to March of the following year, and there is a certain hysteresis of soil freezing and thawing to atmospheric temperature. The influence of temperature on soil temperature is mainly concentrated in 0 ~ 40cm topsoil, and such effect intensity is negatively correlated with soil depth. (2) Different types of coal mining subsidence areas have different characteristics in soil Hydro-thermal coupling. The thawing time of the four sites from early to late: outside the loess subsidence area > within the loess subsidence area > outside the aeolian sand subsidence area > within the aeolian sand subsidence area. Among them, soil thawing in the sand and loess coal mining subsidence area lags behind the outside area. 2d. (3) The variation coefficient of soil moisture in the aeolian sand subsidence area during freezing and thawing period ranges from 0.1568 to 0.6271, which is larger than that in the loess subsidence area. Except for the 20-30cm soil layer in the loess coal mining subsidence area, the water content of other soil layers is higher than the outside; while the 0-20cm, surface layer, in the wind-sand coal mining subsidence area has higher soil water content than the 20-60cm layer outside the subsidence area. The water content is lower than outside the subsidence zone. (4) During the freeze-thaw process, the soil temperature and moisture at different depths showed a polynomial function relationship, and the correlation in the surface layer was stronger than that in the deep one. The research results can provide an important reference for understanding the relationship between soil freezing-thawing and hydrological processes in coal mining subsidence areas.