The Simulation Experiental Study On The Moisture Migration Of The Sanjiang Plain Wetland Soil Under The Condition Of Freezing And Thawing

China is the third of the world in frozen soil area, the seasonal frozen soil areaaccounted for more than half of the land area, while the Sanjiang plain is the biggestone with the largest area and types of wetland in our country. The Sanjiang plainwhich locate in the south of the China’s permafrost is a seasonal frozen region. Itfreezes in around November and thaws in March or April of the next year, then meltsin June or July, the process of freezing and thawing occupy the time of half an year.So, it has important theory significance and project application value to the study ofSanjiang plain wetland soil moisture during the freezing and thawing process.This paper introduces a new type of freezing and thawing test device and itsapplication. The test device is used to simulate natural freezing and thawing processof Sanjiang plain area. There are two typical wetland specimens treat of the capillarywater with the same temperature. We analyze the moisture migration and itsinfluencing factors under different initial water content in order to further investigatethe relationship between the effect of freezing and thawing and wetland soil moisture.It analyzed the temperature and moisture field changes of three kinds of soil. Themain conclusions in this study are as follows:（1）It experienced four processes: rapid cooling stage, the slow cooling stage,continuous cooling stage and slow freezing temperature stage in the freezing andthawing process. The soil freezing temperature is low and need a long time withhigher initial water content, however, the soil freezing temperature is high and need ashort time with lower initial water content.（2）By analyzing the moisture variation trend of different soil layers in thefreezing and thawing process it concluded that: the upper soil moisture contentincreased but lower reduced for frozen soils; the upper soil moisture content reducedand the lower layer increased for thawed soils. The soil moisture content increasingrange Calamagrostis angustifolia Marsh was larger than that of Deyeuxia angustifoliaMarsh.（3）Through the analysis of influence factors to the moisture migration infreezing and thawing soil it concluded that the following two factors are mainlyaccount for it. Firstly, soil characteristics. Soil particle size which is a indicator ofcapillary function intensity affect the water transfer speed. Bulk density has influenceon soil compactness and soil permeability. The soil porosity reflect the soil water permeability, gas permeability and water retention capacity. Secondly, the initial watercontent, the freezing speed is slow with long the freezing time and large quantity ofmoisture migration under the condition of higher initial moisture content; conversely,vice versa.