膨胀土和黄土的细观结构及其演化规律研究

应用CT-三轴仪，系统地研究了河南南阳靳岗村和陶岔渠坡的膨胀土、宁夏扬黄扶贫工程11号泵站Q3黄土和陕西蒲城电厂Q2黄土在多种应力路径、湿干循环、浸水膨胀、浸水湿陷过程中的细观结构演化特性，取得了大量CT图片和数据资料。研究结果表明：膨胀土和黄土的各种宏观力学反应与它们的细观结构变化及其CT数据是密切相关的；原状膨胀土在加载和侧向卸荷过程中以及重塑膨胀土在无载湿干循环过程中裂隙萌生扩展，结构损伤；而具有初始裂隙的重塑膨胀土在加荷过程和三轴浸水过程中裂隙均趋于闭合，细观结构得到修复；原状黄土在加载过程中细观结构的变化趋向与吸力和围压水平有关；在一定应力状态下浸水，原状黄土中的空洞和裂隙逐渐减小以至消失，并可能形成新的均质结构；较高应力单独作用或低应力下浸水都不能使大孔隙破坏。依据CT数据，定义了描述膨胀土和黄土细观结构的定量指标，提出了这两种土在多种工况下的细观结构演化方程，建议了一种确定土的结构屈服应力的新方法。CT技术使土的细观结构研究达到了定量阶段，建立土的结构演化方程和结构性本构模型有了实在的试验基础。

Research on meso-structures and their evolution laws of expansive soil and loess

The characteristics of meso-structure evolution of expansive soil and loess were studied systematically with a CT-triaxial apparatus in various stress paths, wet-dry circle, soaking swelling and inundation-collapse. The expansive soil samples were taken from two sites located in the canal slope of the Middle Route Engineering of South-to-North Water Transfer Project in China. The loess simples include Q3 loess and Q2 loess, and the former was taken from the site of Pumping Station #11 in Ningxia Province, and the later was taken from the site of Pucheng Power Plant in Shaanxi Province. A number of CT images and CT data of meso-structure evolution of the samples were obtained. The research results show that the macro-behaviors of samples are closely related with their meso-structure changes and CT data. The fissures sprout and develop during loading and lateral unloading on undisturbed expansive soil and during wet-dry circles on remolded expansive soil in free state; and their meso-structure are damaged. However, the original fissure in remolded expansive soil is toward close under loading and immersion; and the meso-structure of the soil is repaired. The tendency of meso-structure change of intact loess in loading process is dependent on the stress and suction level. The holes and fissures of intact loess become gradually small even disappear during inundation; and the original structure of intact loess failure and a new homogenous structure would be formed. The macro-void of intact loess cannot be destroyed ether by high stress or by the combination action of low stress and immersion. On the basis of CT test data, the quantitative indexes describing the meso-structure of expansive soil and loess were defined; and the structure evolution equations for the soils under various test conditions were proposed; as well as a method to determine the yield stress in triaxial test was suggested. Thus, CT technology makes the research of meso-structure of soils to reach the quantitative stage; and the technique also provides a practice test foundation to establish the evolution equations of meso-structure of soils and corresponding structural constitutive model.