基于pF Meter的土体冻结特征曲线研究

pF Meter-based Research on Soil Freezing Characteristic Curves

为解决冻土中土体冻结特征曲线(SFCC)长期以来只能通过经验模型间接推测获得,且土体冻结特征曲线(SFCC)与土水特征曲线(SWCC)间关系的相关研究也因技术手段制约而仅停留在理论假设阶段的问题,采用可直接用于极端负温条件下的pFMeter基质势传感器,得到青藏红黏土、兰州粉土、细砂这3种不同粒径土体的冻结特征曲线,获得三者在冻结过程中未冻水数量与能量变化之间的规律;对过去冻土学研究中利用Clapeyron方程间接转换获得土体冻结特征曲线方法的可靠性进行试验验证;此外,针对不同粒径大小土体冻结特征曲线及土水特征曲线进行比较,并对以往冻土冻胀研究中将饱和冻土中冰晶等划为非饱和融土中气体的方法进行验证。结果表明:Clapeyron方程得到的冻结特征曲线与实际测定的冻结特征曲线基本一致,Clapeyron方程可用于土体冻结特征曲线的预测;冻结特征曲线与土水特征曲线虽在形态上具有一定的相似性,但由于冻结过程与脱湿过程土中相的不同所致的各相间界面力不同,导致其在数值上存在一定差异,且差值大小与土体平均粒径成反比,进而证明了被广泛用于冻土研究中的将冻土中冰晶体视作融土中气体来简化冻结过程中冰晶-液态水-土颗粒关系的方法并不合理,并从理论上阐述了其机理;相关研究成果可为后续研究冻胀过程中水分迁移机制与水分迁移驱动力提供相应的基础理论支撑。

Restricted by the technology,the soil freezing characteristic curve（SFCC）in the freezing soil could only be obtained by empirical formula methods,and the research on the relationship between the soil freezing characteristic curve（SFCC）and the soil-water characteristic curve（SWCC）still rested on the theoretical assumption stage.In allusion to these problems,SFCCs of three kinds of saturated soil samples（namely,Qinghai-Tibetan red clay,Lanzhou silt and fine sand）with different particle sizes were obtained by dint of the pF meter matric potential sensor which could be used in an extreme negative temperature.The regularity of unfrozen water content and the energy change of three soil samples was acquired during the process of soil freezing.Meanwhile,the reliability of the method used to derive SFCC with tests was verified by the indirect convention on the basis of the Clapeyron-Equation.In addition,in order to verify the reasonability of the method in previous frozen soil research with regarding the ice crystal in saturated frozen soil as the gas in unsaturated soil,SFCCs and SWCCs aimed at soil samples with different sizes were compared.The results show that the SFCCs derived by Clapeyron-Equation are similar with the measured ones,so the Clapeyron-Equation can be used to calculate the SFCC.Both the SFCC and SWCC are similar in form but different in specific values.The reason is that the different phase in soil dehydration process and soil freezing process results in the different interfacial forces of phase.The difference is inversely proportional to the average particle size of soil.Therefore,the method with regarding the ice crystal in saturated frozen soil as the gas in unsaturated soil which is widely used in frozen soil is improper to simplify the relationship of ice crystal,liquid water and soil particle in the freezing process.The results provide the theoretical support for future research on the moisture migration mechanism and the moisture migration driven force in the process of frost heave.