基于数字图像的冻结缘特征和冰透镜体发育模式研究

Frost heave results from ice segregation and ice lens growth as a soil freezing. Any quantitative theory of frost heave must explain a salient feature of the phenomenon: the migration of water from lower, unfrozen regions of the soil to colder regions. This refers to the characteristics of what is called the “frozen fringe”, because the phenomena which occur in this zone seem to underlie the entire frost heaving process. Without detailed observations of the frozen fringe, it might be impossible to verify these frost heave models. This project intends to carry out a series of one-dimensional freezing experiments to investigate moisture migration and ice lens growth under open system, and propose a method to predict the frost heave finally. When the soil column is cooled by the way of one-dimensional freezing, a high-resolution digital camera is used to catch a series of photographs which reflect the dynamic processes of water transporting, the frozen front advancing and the ice lens developing during soil column freezing. Analyzing these pictures by the digital image processing technology, the data of responding the moisture, freezing front and ice lens dynamic changes during soil freezing process, will be obtained. And then, combined with the results of CT scan and SEM analysis for the tested samples, the relationship between frozen fringe characteristic and ice lens development will be constructed. It is hoped that the experimental evidence of this project will provide insight to the frost heave process from which a predictive frost heave model may evolve.

研究土冻结过程中冻结缘演变及冰透镜体发育动态，是认识冻土、揭示土的冻胀机理的关键所在，是国际冻土研究的前沿领域，也是国家在冻土区进行工程建设的重大科技需求。本项目针对土冻结过程中的水分迁移和析冰过程，开展冻结缘特征和冰透镜体动态发育过程研究。通过对不同土质类型的土柱在不同温度梯度作用下进行单向冻结试验，并利用高分辨率数码相机对土柱的冻结过程图像进行实时采集，获得土柱冻结过程中冻结锋面的移动速率、稳定位置、水分迁移量、土柱位移的变化量以及土体冻结过程中冰透镜体的发育动态及冷生构造的发展过程等重要物理参数，结合土体冻结后对试后试样CT扫描和电镜扫描分析的结果，探明冻结缘位置、厚度、温度等特征参数的变化动态及其与温度梯度、含水量的关系，构建基于冻结缘特征参数的分凝冰动态发育模式，揭示土体冻结时驱动水分迁移的物理机制，服务于未来的寒区工程设计施工，同时也为人工冻结壁冻胀抑制措施的选择提供理论依据。

研究土冻结过程中冻结缘演变及冰透镜体发育动态，是认识冻土、揭示土的冻胀机理的关键所在，是国际冻土研究的前沿领域，也是国家在冻土区进行工程建设的重大科技需求。本项目针对土冻结过程中的水分迁移和析冰过程，开展土冻结过程中冻结缘特征和冰透镜体发育过程研究。首先在前人对土冻结温度研究的基础上，基于土壤水分空间分布的非均匀性，提出孔隙水压力是导致土冻结温度衰减的实质并建立理论方程；然后通过对青藏粉土进行单向冻结试验，并对土冻结过程中液态水的迁移过程和机理进行分析，得到如下结论：试样单向冻结过程将经历快速冻结和稳定冻结两个阶段. 冻结稳定后，已冻区的冷生构造依次可分为微薄层状构造区、薄层状构造区和最暖段的厚层状构造区，其中厚层状构造区中冰透镜体的生长是试样冻胀变形的主要原因；在土冻结过程中水分迁移的形式为未冻结合水膜的迁移；水分迁移的驱动力为已冻区中负温低压冷生裂隙中的“真空抽吸力”和未冻水膜在温度梯度作用下形成的压力梯度；水分迁移的通道是构造多边形边缘的纵向裂隙；并开展了青藏粉土夹砂冻结试验，对土体冻结过程中气态水的迁移过程进行验证，最后从温度场计算、水分场计算、冷生裂隙形成准则、水分迁移速率计算、冰分凝准则、冻胀量的计算6 个方面出发，建立了饱和青藏粉土一维无压冻结冻胀概念模型。