高压力作用下深部黏土冷却过程及其特征研究

深部黏土的埋深决定着深部黏土在进行人工冻结期间所承受的地压力的大小,而较大的地压力将会影响冻结壁形成时冻结温度的大小以及冻结壁的冷生构造,从而影响冻结壁的强度与稳定性。本研究通过对高压力作用下的深部黏土在不同含水率状态下进行冷却过程试验,分析了压力大小对不同饱和状态的深部黏土冷却曲线形式及初始结晶温度、冻结温度及过冷度的影响。结果表明:深部土的冻结温度、初始结晶温度以及过冷度都与土体所承受的压力密切相关。不论是非饱和状态、饱和状态还是过饱和状态下的深部黏土,其冻结温度都随土体所承受压力的增大而减小,而初始结晶温度则随压力的增大呈起伏状变化。利用物质结晶理论,进一步分析后认为冻结过程主要是自由孔隙水的相变过程;而压力作用会通过改变土体中土颗粒对孔隙水分子的吸附作用,改变土体中自由水的含量,进而改变土体冻结过程中潜热释放量的大小,最终影响土体冷生构造。

Effects of high pressure on cooling process of clays in deep alluvium

Considering that large earth pressure will influence the strength and the stability of frozen wall by means of changing soil frozen temperature and its cryo-structure, a series of cooling process tests on clays from the deep stratum with different water contents and applied pressures prior to freezing are performed to study their cooling process characteristics. The aim of the tested samples subjected to a certain pressure is to simulate the earth pressure of the freezing ground. In order to reduce the error of the testing system, the initial temperatures of the tested samples prior to being frozen are 5°C, and the ultimate temperatures after being frozen are -10℃. The results show that the frozen temperature, initial frozen temperature and super-cooling degree closely relate to the suffered applied pressure of the tested soils. No matter the soils are saturated the frozen temperature decreases with the increase of the applied pressure, while the initial frozen temperature shows a fluctuation with the change of the applied pressure. Applying the crystallization theory of materials, it is concluded that the freezing process of soils mainly relates to the phase-change process of void free water. The applied pressure will change the adsorption capacity of soil particles to water molecules to influence the amount of free water in soils, and further change their latent heat releasing during crystallization. As a result, the applied pressure in freezing process of soils influences their cryo-structure.