Spatial variation characteristics of temperature and moisture in shallow loess layer under freezing-thawing condition

The variation of temperature and moisture inside the soil body is obvious when loess slope is freezing and melting in the loess plateau, which is located in the typical seasonal cryolithozone of Northwest China. As a result, there is a corresponding variation of water content and groundwater table inside the soil body, which tends to induce a series of geological environment problems such as landslide and collapse. In this paper, in-situ monitoring of loess temperature and water content was conducted during freezing and melting in Heifangtai loess slope of Yongjin County, Gansu Province. The authors studied variation characteristics and interrelation between temperature and water content of the freezing layer on loess slope under the freezing-thawing condition. It is found that the depth of freezing loess is around 52cm at the monitoring site, and the temperature of loess profile can be divided into three characteristic zones, namely, steady transfer zone, fluctuation zone and significant alternation of temperature. Water content was controlled by temperature during freezing-thawing of loess slope, and hence this changing process can be divided into three phases. First of all, the water content is nonlinearly increased with temperature when it is less than 2℃. Then, water content declines randomly when it is between 2℃ and 6℃. When it is greater than 6℃, water content increases slightly until stableness, and the temperature effect weight decreases. With the fully dissolving of frozen soil body, the freezing moisture melts rapidly and migrates downwards, leading to the sharp increase of water content. It is thus held that, from freezing to thawing, sharp increase of water content is the dominant factor for the slide and collapse of shallow loess.