考虑双孔隙结构的红黏土胀缩变形的多尺度响应机制与损伤模型研究

In soil mechanics the topic of mechanism of swell-shrinking deformation of red clay is a very difficult issue. The study on swell-shrinking mechanism in meso-scale is the most essential approach, on account of red clay belongs to structural soil and has typical double structure characteristics. This proposal is based on the double structure, focuses on swell-shrinking deformation induced by the effects of wetting-drying and coupling with stress, studied on multi-scale response mechanism of meso-scale structure damage and macro-scale swell-shrinking deformation, built a quantitative evaluation index of meso-scale structure damage, and established a damage model of swell-shrinking deformation of red clay. Firstly, in the macro-scale, the swell-shrinking deformation tests by the coupling effects were conducted by employed the tri-axial tests. Secondly, in the meso-scale, the pore distribution and structure damage were monitored by used of MIP, SEM and CT before and after the tri-axial tests of red clay. And then the damage variable and damage model were determined by combining with the macro-scale and meco-scale parameters, and the quantitative evaluation index reasonable was proposed and presented. Finally, based on the damage theory and double structure model, developed the damage finite element model of red clay for swell-shrinking deformation. These researches could help to solve the long-term scientific problem of restricting the application of red clay, and provides a basis for durability design and stability control of red clay subgrade engineering. And it lays the foundation for the development of basic theory of soil mechanics, and has important scientific significance and application value.

红黏土在干湿循环下的胀缩机制是土力学研究中的难点。红黏土属于结构性土，具有典型的双孔隙结构特征，从细观层面研究胀缩变形机理是最接近本质的途径。本项目在考虑双孔隙结构的基础上，聚焦干湿-应力耦合作用对胀缩变形的影响效应，研究细观结构损伤和宏观胀缩变形的多尺度响应机制，构建细观结构损伤的定量化评价指标，建立红黏土胀缩变形的损伤模型。首先，在宏观尺度上，基于三轴试验研究干湿-应力耦合时红黏土的胀缩变形规律。其次，在细观尺度上，采用MIP、SEM和CT测试红黏土胀缩前后的孔隙分布和结构损伤。进而，结合宏细观参数选择损伤变量和损伤模型，构建结构损伤的定量化评价指标。最后，基于损伤理论和双孔隙结构模型，建立红黏土胀缩变形的损伤有限元模型。本项目的研究，解决了长期制约红黏土应用的科学难题，为红黏土路基工程的耐久性设计和稳定性控制提供了依据，为土力学基本理论的发展奠定了基础，具有重要的科学意义和应用价值。

本项目在考虑结构性红黏土的双孔隙结构特征的基础上，聚焦干湿-应力耦合作用对累积变形的影响效应，研究细观结构损伤和宏观累积变形的多尺度响应机制，构建损伤发展的定量化评价指标，建立红黏土累积变形的损伤预估模型。本项目以浙江庆元县的高液限红黏土为研究对象，首先，通过动三轴试验分析动应力比、围压、压实度、干湿循环等参数对饱和红黏土累积变形发展规律的影响。结果表明：提高压实度和降低动应力比可以显著减小红黏土的累积变形。红黏土累积变形曲线随循环振次的变化呈稳定型、临界型、破坏型三种类型。进一步分析发现：饱和红黏土在循环荷载作用下存在临界动应力比。当循环荷载的动应力比小于临界动应力比时，红黏土累积变形的发展处于稳定状态，土体的累积变形较小，试件不会发生破坏。基于临界动应力比的定义，分别以围压和压实度为基准构建了的临界动应力比预估模型，可用于判断不同工况下饱和红黏土在循环荷载下的累积变形发展类型，预估土体的稳定性。针对红黏土的稳定型累积变形发展过程，引入相对动应力比的概念，构建基于循环振次和临界动应力比的饱和红黏土累积变形预估模型和动弹模量预估模型。上述模型规避了既有模型需要代入动力试验结果的弊端，实现任意循环振次下红黏土累积变形的预测，推动了红黏土累积变形发展的研究。针对循环加载前后的红黏土开展压汞试验，明确了红黏土的孔隙率随围压和压实度的递增均表现为负指数幂衰减趋势，而孔隙率随动应力比的增长呈线性递增；增大动应力比显著地改变中、大孔隙结构，孔径分布曲线由双峰孔隙逐步转变为三峰孔隙；红黏土的宏观变形主要源于大、中孔隙结构的坍塌和重组。上述结论为红黏土路基工程的耐久性设计和稳定性控制提供了依据，为土力学基本理论的发展奠定了基础，具有重要的科学意义和应用价值。.基于以上成果，完成硕士论文3篇，培养硕士研究生3人，副教授1人；申请专利3项，授权1项；出版专著1本；已投稿论文5篇，其中SCI检索期刊4篇，EI检索期刊1篇；正在撰写中的论文1篇。