基于结晶动力学的硫酸钠盐渍土水、盐结晶过程及其变形影响机理研究

The saline soil area in China is about 0.2 million square kilometers, which accounts for about 2.1% of China’s total land area. Salt and frost heaving have been leading to a series of ground problems on infrastructure constructions such as highway and railway in cold regions. Water and salt crystallization is thought to be the reason for salt and frost heaving damage. Therefore, it is very urgent and important to reveal the process of water-salt crystallization and deformation mechanism of the saline soil. In this project, focused on the saline soil with sodium sulfate in cold regions, a comprehensive approach combing macroscopic and microscopic, experimental and theoretical methods is utilized. Based on freezing test in a constant cooling rate, freezing-thawing cycle test and mercury intrusion porosimetry (MIP) test, firstly, the dynamic processes of water and salt crystallization will be analyzed, and the formation mechanism of crystal growth will be illuminated. And then, the model for crystal nucleation and growth will also be carried out, and the relationship between the crystallization pressure and crystal size and pore size distribution of soil will also be deduced. Finally, according to the microscopic characteristics, a comprehensive model considering the mutual action of hydraulic pressure, crystallization pressure and cryosuction pressure will be established. The model will be used to calculate the macro deformation of the saline soil, and the frost heave and salt expansion mechanisms will be clarified. The aim of this project is to provide theoretical guidance to design construction and anti-saline measures in cold saline regions, and serve the need of national infrastructure construction in saline soil area along the "One Belt And One Road" regions.

我国盐渍土面积约20万平方公里，占国土面积的2.1%。受温度和湿度影响，寒区盐渍土发生的冻胀盐胀给公路、铁路等基础设施带来了一系列病害问题。盐渍土冻胀盐胀破坏的本质是水、盐结晶，揭示盐渍土在冻结时的水、盐结晶过程及其变形影响机理成为亟待解决的问题。本项目拟以寒区硫酸钠盐渍土为研究对象，采用细微观与宏观，试验与理论相结合的方法，通过等速率冻结试验、冻融循环试验和压汞试验等，分析盐渍土孔隙水、盐结晶过程，阐明冰（盐）晶体成核机制，提出冰（盐）晶体动态生长模型，建立冰（盐）结晶压力与晶体生长尺寸、土体孔径分布等的定量关系，构建硫酸钠盐渍土变形与动态水压力、冰（盐）结晶压力和冰（盐）结晶吸力的关系模型，并以此模型计算土体的宏观变形，揭示盐渍土水、盐结晶过程对其变形影响机理，以期为寒区盐渍土地区设施的设计和冻胀盐胀防治措施的研发提供理论依据，服务于“一带一路”经济带中盐渍土地区基础设施建设需求。

我国盐渍土面积约20万平方公里，占国土面积的2.1%。寒区盐渍土发生的冻胀、盐胀给基础设施带来一系列病害问题。冻胀、盐胀破坏的本质是水、盐结晶，揭示冰、盐晶体成核机制和生长规律，建立盐渍土变形与各影响因素之间的关系是本项目的关键科学问题。本项目以硫酸钠盐渍土为研究对象，采用细微观与宏观，试验与理论相结合的方法，通过等速率降温试验、冻融循环试验和压汞试验等，开展了盐渍土孔隙内冰（盐）晶体成核机制与动态结晶模型研究、盐渍土冰（盐）结晶压力模型与土体宏观力学特征研究和盐渍土冰（盐）结晶过程对变形影响机理及计算方法研究。研究结果表明：（1）冰晶体和盐晶体成核的驱动力分别是过冷度和过饱和比，成核临界半径随温度的降低而减小，建立的冰、盐晶体动态结晶模型能够计算冻结过程中的水、盐结晶量。硫酸钠含量为0%、0.5%、1.0%、1.5%和2.0%的盐渍土，非均匀成核接触角分别为50.5°、48.8°、46.5°和44.1°；硫酸钠含量为2.0%的盐渍土，初始结晶过饱和比为1.75，结晶速率常数Kr=1.8×10-3/s。（2）随着晶体的生长，盐渍土孔隙内晶-液界面产生结晶压力。冰压力与盐分、融化活化能和液体压力有关，盐结晶压力与晶体尺寸、盐分浓度和离子活度有关，作用在孔隙壁上的晶-液附加应力是盐渍土产生破坏的因素，通过盐渍土孔隙内结晶压力的微观分布可以确定其宏观应力。（3）硫酸钠盐渍土的变形是孔隙水压力、结晶压力、结晶吸力和热胀冷缩等综合作用的结果。降温作用下硫酸钠盐渍土产生水、盐结晶压力，引起孔隙水压力增加，而孔隙水压力又会对晶体产生压缩作用。晶-液界面结晶吸力驱动水分迁移，温度改变土体热膨胀系数都会影响最终变形量。降温过程中，硫酸钠盐渍土同时出现收缩与膨胀。研究结果可为寒区盐渍土地区设施的设计和冻、盐胀防治措施的研发提供理论依据。通过本项目的研究，发表论文9篇，其中SCI论文8篇，授权实用新型专利2项，培养博士、硕士研究生各1名，获批2023年度广东省自然科学基金面上项目1项。