非饱和冻土气态水迁移与相变机理研究

It is reported that vapor transfer and phase change can lead to damage to infrastructures in cold and arid regions. But its mechanism has been less understood, which is regarded as an interdisciplinary research between unsaturated soil mechanics and frozen soil mechanics. In this program, pore structure of unsaturated soils during freezing will be investigated at the beginning, in order to clarify its hydraulic properties by setting up the relations among soil freezing characteristic curve, vapor (liquid water) permeability and pore structure. The governing variable and influential factors for vapor transfer then will be studied on basis of a series of laboratory tests. A model for describing vapor-ice desublimation process will be proposed, aiming to reveal the driving effect of vapor-ice desublimation on vapor transfer. Finally, a new theory for liquid water-vapor-heat coupling movement in unsaturated freezing soils will be established, which can take the full process of phase changes of water into account. The theory is going to demonstrate the causes and development of the reported infrastructures damage in cold regions. The outcome of this research would benefit some disciplines in handling with vapor transfer, meanwhile, it can provide valuable references to the construction and the safety operation of projects in cold regions.

气态水在非饱和冻土内的迁移与相变是寒旱区许多工程构筑物灾变的重要诱因，其机理涉及冻土力学与非饱和土力学的交叉研究，相关研究较少。本项目首先从微细观尺度入手，探究非饱和土的孔隙结构随冻结过程的变化，并以此建立孔隙特征与冻结特征曲线和透气（透水）的关系，阐明非饱和冻土这一特定材料的渗透特性；其次，基于微细观测试技术，阐释气态水在非饱和冻土内迁移的主控变量和影响因素，探究气-冰凝华相变的微观机制，建立相变数学模型，并揭示凝华相变对气态水迁移的驱动作用；最后，建立考虑全相变过程的非饱和冻土水热气耦合迁移理论，实现数值解析，并应用于揭示寒旱区工程灾变的产生条件和发生发展规律，提出防灾减灾的策略。研究成果可为寒旱区工程建设提供理论依据，促进各学科在水热耦合领域的交叉与融合，具有重要的理论价值和实际意义。

气态水在非饱和冻土内的迁移与相变是寒旱区许多工程构筑物灾变的重要诱因，其机理涉及冻士力学与非饱和土力学的交叉研究，相关研究较少。本项目首先从微细观尺度入手，基于核磁共振岩土微结构测试试验，对非饱和冻土孔隙结构与透水、透气特性进行研究，阐明了冻结过程非饱和土孔隙结构的变化规律，揭示了非饱和冻土水-冰相变机理，并以此为基础提出一个新的饱和冻土SFCC模型和渗透系数模型；其次，基于自主研发的非饱和冻土水气迁移试验，对非饱和冻土气态水迁移与相变规律进行研究，建立相变数学模型，揭示非饱和冻土气-冰相变机制及其对气态水迁移的驱动作用，并得出粗粒土体中气态水诱导冰透镜萌生的新判据；最后基于水膜理论提出了冻土未冻水膜压力作为冰透镜体生成的判据，并重新对水分迁移驱动作用进行描述，建立了以温度、土体孔隙比为变量的全耦合模型，通过考虑已冻区冰基质的影响，推导了涵盖原位冻胀与冰分凝两部分的冻胀量计算公式，完成了全相变过程的非饱和冻土水-热-气耦合迁移模型及数值实现。研究成果可为寒旱区工程建设提供理论依据，促进各学科在水热耦合领域的交叉与融合，具有重要的理论价值和实际意义。