土体冻融特征研究现状与展望

Study of the freezing and thawing features of soil:current situation and outlook

冻土中水分迁移是导致土体冻胀的关键因素,而研究水分迁移及其驱动力的核心问题是要充分理解未冻水含量与温度、基质吸力等变量之间的关系,这些关系可充分体现土体在冻融过程中土水变化特征.长期以来,对土体冻融特征的研究采取的是与非饱和土力学中的土水特征类比的方法进行,结果也证明了二者存在一定的相似性.但是冻土中因冰-水相界面作用产生基质吸力与融土中水-气相界面作用产生基质吸力的机理并不完全相同,而由于相变等其他作用产生的冻融滞后效应与融土中孔隙"墨水瓶效应"等引起的滞后效应机理也有区别.针对这些机理性的不同,还需要做大量的研究工作才能真正揭示土体的冻融特征.通过对目前土体冻融特征方面研究进展和存在问题的归纳总结,笔者认为今后在这方面还需深入开展如下研究:建立适合各类土壤冻融特征的一般预测模型,使得在缺少数据条件下能快速获取所需土样的冻融特征;研究土体在冻融和干湿变化过程中存在的类似性及区别,对冻融过程中存在的滞后效应机理给出合理的解释;提升冻融特征变量的测试技术水平,研发高精度的相关仪器设备.

Water migration is the key contributor for frost heave during soil freezing, and the driving force of water migration depends on soil temperature, unfrozen water content, matric suction and the relationship between them. The relationship is known as the soil-water characteristics in frozen soils. Generally speaking, the soil- water characteristics and the hysteresis effects have similar change laws between drying-wetting and freezing- thawing processes. It seems that the soil-water characteristics in frozen soils can also be explained based on the existing theories on soil-water characteristics in unfrozen soils. However, there are several special factors cannot be ignored, such as negative temperature, phase change and so on during freezing and thawing process. There- fore, it is believed that although the soil-water characteristics and the hysteresis effects are similar, their mecha- nisms may be quite different. Therefore, a great deal of work need to be done to develop the soil-water charac- teristics during soil freezing and thawing. Detailed analysis and summary are provided about the present situation and the existing problems of the water characteristics during soil freezing and thawing, as well as references for the aftertime study are put forward： a） establishing a typical model to the soil below freezing point to predict soil-water characteristics effectively with limited data; b） investigating the similarity and difference of the soil- water characteristics effect between unfrozen and frozen soil, and demonstrating the mechanism of the hysteresis effect during freezing and thawing ; c） promoting the research of measurement techniques of the soil-water char- acteristics in frozen soil.