Study On The Interaction Mechanism Of Water And Heat In Freezing Thawing Soil And Its Environmental Response

Snow cover is a black soil area of Songnen Plain is most common and the most common freezing thawing soil form of boundary conditions, the soil freezing and melting process will will cause dynamic changes of soil liquid water content and heat transfer. On the basis of consulting the domestic and foreign literatures, the temperature and moisture content of the soil during freezing and thawing period were measured by the method of continuous dynamic observation and fixed point quantitative measurement. Analysis and research the Songnen Plain hinterland areas in the bare land treatment, natural snow, compacted snow and snow thickened cover treatment under the condition of soil freezing process, soil moisture and heat coupling, soil water and heat migration in response to the environmental factors and soil water heat response function. The main contents and conclusions are as follows:(1) The freezing and thawing period, soil showed the Unidirectional Freezing and two-way melting phenomena, in the freezing and thawing process according to the size of freezing rate will be divided into three stages, namely fast freezing period, stability during freezing and thawing period. The soil freezing process and the maximum freezing are affected by the boundary conditions of the soil. With the increase of the thickness of the snow cover and the increase of the density, the maximum freezing depth of the soil is gradually decreased. At the same time, the snow covered soil system affects the absorption heat and release status, the different mulching plots of each soil layer soil freezing to date difference, with the increase of the amount of snow cover, the delay phenomenon of soil freezing date is more and more obvious, in the depth of 10 cm, natural snow, snow and snow covered with thick compaction under the condition of soil freezing to date were compared with bare land 2, 3, 8D processing delay, at the same time, the soil melting period of soil thawing time were also compared to bare land treatment delay phenomenon, show that the snow cover for water and heat transfer between soil and environment have certain negative effects and energy exchange.(2) In seasonal frozen soil area, the freezing period, the soil temperature and liquid water content rate from will reduce the phenomenon, and melting period, with the increase of environmental temperature, soil solid ice will phase transformation, temperature and liquid water content will appear the phenomenon of the increase in. At the same time, soil temperature and liquid water content rate in soil spatial distribution also exist similarities and differences, withfrozen layer formation and development, soil temperature and liquid water content rate in soil space will appear the phenomenon of the redistribution of specific performance for surface soil temperature variation amplitude large on the lower level, with the depth increasing amplitude becomes smaller gradually. In addition, with snow covering the increased thickness and density increase, at the same soil layer soil temperature and liquid water content of the changes in the amplitude of the relatively lower.(3) In the process of soil water and heat transfer of internal, the variation of soil temperature lead to temperature gradient, in the role of the driving force, the soil liquid water content rate of migration of a certain phenomenon will occur, at the same time, the change of soil temperature will cause soil moisture transformation. In addition, soil moisture changes will also affect the soil heat flux distribution in a certain extent. Therefore, in the seasonal frozen soil region, the temperature and the moisture content of the soil in the soil have mutual influence and mutual restriction.During the freezing period, the bare land treatment under the condition of surface soil temperature and liquid water content rate of the coupling relationship between good, model is of high precision,also with the snow cover depth is early more and the increase of the density, soil water and thermal migration of by the external environment affect the lower, in natural snow, compacted snow and snow thickened coverage Soil Hydrothermal Coupling between conditions gradually increased.With the increase of soil depth, the coupling relationship between the two gradually enhanced, but at 60 cm depth, due to the distance of the level of soil freezing front is close, the coupling effect of the soil have certain effect. The melting period, snowmelt infiltration affects the coupling effect of soil temperature and liquid water content, so in each soil layer, with snow covering the increased thickness and density increases, the coupling effect between the two gradually weakened.(4) The water heat transfer process of freezing and thawing soil is influenced by many environmental factors, and the coupling relationship between these factors and the liquid water content and temperature of the soil is the subconscious. Through the grey relational degree analysis showed that in environmental factors, environmental temperature, atmospheric net radiation and soil temperature correlation is strong, and the environment humidity and the dew point humidity and liquid soil water rate between correlation larger. Also in the analysis of environmental temperature and soil temperature correlation shows that, with the increase of soil depth, the correlation between the two gradually decreased, at the same time, with the increase of the quantity of snow cover, two correlation has also been a certain impact. In the same way, the relationship between soil moisture content and environmental humidity is similar to that of soil temperature and environment temperature. In addition, through the screening of soil temperature and humidity higher correlation with environmental factors and soil water heat build multivariate regression function, the significant analysis shows that more than 60 cm soil layers of soil temperature and liquid water content and meteorological factors between the multiple regression model are higher, and below 60 cm soil layers of soil temperature and water content andenvironmental factors is established between a multiple regression model was not significant correlations in the lower.