冻融条件下浅层黄土中温度与水分的空间变化相关性

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

黄土高原是西北典型的季节性冻土区,在黄土斜坡冻结和融解过程中土体内的温度、水分变化显著,导致土体中含水量及地下水位发生相应的变化,诱发一系列的滑坡、崩塌等地质环境问题。选择甘肃永靖县黑方台黄土斜坡为研究区,原位监测冻结至融解过程中黄土的温度和含水量,研究冻融条件下黄土斜（边）坡冻结层温度和水分及变化特征及其关系。结果表明,本次监测点黄土冻结深度为52cm,黄土剖面温度表现为3个特征带：温度稳定传递带、温度变动带、温度交替显著带。温度在黄土斜（边）坡冻融过程中对水分具有控制性作用,含水量随温度变化划分为3个阶段：1小于2℃,含水量随温度呈现非线性递增趋势;22~6℃,含水量随温度呈现波动性下降;3大于6℃,水分由小幅增加直至稳定,温度影响权重减小。随着冻结土层完全融解,被冻结水分融解后向下运移,最终导致剖面含水量急剧增加,因此,冻结至融解过程中含水量发生急剧增加,是导致浅层黄土滑塌的重要因素。

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 interrelationbetween 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 52 cm 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.