基于微米CT技术的黄土水敏性微观机制研究

Loess is a typical type soil with water sensitivity, and the water sensitivity is the essence of loess mechanical properties. In loess distribution area of China, it is necessary to pay attention to the basic influence of loess water sensitivity in the study of water-induced geological control. Research on the microscopic mechanism of loess water sensitivity has been a long-standing and persistent scientific issue, in particular, micro-structure changes after the infiltration of water are main reasons leading to water sensitivity of loess, and they also can help to clarify the microscopic mechanism of loess water sensitivity. Aiming at the weak links in the study of loess water sensitivity, this project selected the sandy loess in the Northwest loess plateau as the object, and a series of Micro CT scanning tests under continuous humidification condition were proposed. The spatial distribution of micro structural elements including particles, pores and micro fractures were studied, the 3D digital core models of loess with different moisture contents were then established. On the basis of multi-fractal theory, indexes which can quantitatively describe the spatial distribution characteristics of microstructural elements in loess were proposed, and the corresponding mathematical evaluation model was established to evaluate the spatial evolution rules of microstructural elements of loess after the infiltration of water. Based on the soil-water characteristic curve of loess, the impacts of microstructural elements on water sensitivity of loess such as suction and strength were analyzed, and the microscopic mechanism of loess water sensitivity was further explained.The results will provide experimental data and quantitative physical model for the study of loess water sensitivity.

黄土是具有水敏性的特殊土，且水敏性是黄土力学特性的本质所在，在我国黄土分布区水致地质防治研究中必须重视黄土水敏性的基础影响。黄土水敏性微观机制研究一直是被广泛关注的科学问题，尤其是水进入黄土后引发的微结构变化是黄土水敏性产生的重要原因，对明确黄土水敏性产生的微观机制具有重要的协同意义。本项目针对黄土水敏性研究中的薄弱环节，选取黄土高原西北部砂质黄土开展连续增湿条件下的微米CT扫描试验，系统分析不同含水量状态下黄土中颗粒、孔隙和裂隙等微结构要素的空间分布及变化特征，进而建立三维数字岩心模型；在多重分形理论的基础上，提出可定量描述黄土各微结构要素空间分布特性的指标，揭示微结构要素随含水量演化的规律；最后，结合黄土的土-水特性，分析不同微结构要素的变化对吸力、强度等表观水敏现象产生的影响，从而阐释黄土水敏性产生的微观机制。研究成果可为黄土水敏性特殊问题的研究提供试验数据和定量物理模型。

黄土是一种具有水敏性的典型土，水敏性是黄土力学特性的本质所在，在世界黄土分布区水致地质灾害研究中，必须特别关注黄土水敏性的基础影响。黄土内部发育着大量形态和性质应迥异的空隙，构成了黄土的微观界面，微观界面分割了黄土中的颗粒体，给黄土水力特性及灾变效应的研究带来了挑战。本研究项目针对水进入黄土后引发的微结构变化，选取 了中国黄土高原北部延安地区天然沉积黄土，开展了连续增湿条件下的微米CT扫描试验，同时获取了系列扫描电子显微镜图像。借助微米CT技术与图像处理技术建立了原状黄土的孔隙网络模型，并在此基础上分别研究了含裂隙、含管状通道与不含优势通道单元体的渗流特性；研究结果表明，优先流对黄土内部的微观孔隙结构存在着一定的改造作用，同时裂隙与管状通道也能促进土体整体的渗透特性。基于本研究项目，还提出微观界面的概念，从界面角度出发研究了黄土中形态和性质应迥异的空隙结构，在多重分形理论的基础上，量化分析了黄土微观界面的发育规模和几何形态，并从微几何形态与接触关系的角度将黄土微观界面划分为三种类型：狭长形、管束状和圆形；连续的增湿受力试验结果表明，黄土体中不同类型的微观界面表现出不同的灾变力学效应，且相互之间可以转换。本项目的研究成果可为黄土水敏性特殊问题的研究提供试验数据和定量物理模型。