软岩遇水易软化，力学性质劣化迅速，是诱发软岩边坡、巷道围岩等工程软岩地质体失稳破坏的重要原因。针对水岩作用下软岩宏-细观软化机制不明确，尤其是细观尺度软化损伤难以定量化表征的问题，本文从室内试验、理论模型和数值计算三个方面重点开展了软岩浸水软化过程中微细观结构损伤特性与宏观时效性力学特性关联关系的研究。论文的主要研究内容和成果如下：(1) 通过XRF和XRD试验，确定了软岩的主要矿物元素成分；通过ICP-OES测试，得到了软岩浸泡液中主要元素浓度随时间的变化规律；通过偏光显微薄片试验，分析了软岩细观结构的演化特征；提出了“界面胶结连接”结构模型，为软岩软化过程的精细结构描述提供了理论依据；基于分子扩散理论，推导了描述软岩界面胶结连接结构时间损伤效应的解析解，理论方程与试验结果拟合较好，定量揭示了软岩软化的非线性动力学特性；推导并提出了软岩细观软化损伤因子，为数值仿真研究软化问题提供了理论依据。(2) 开展了不同浸水时间软岩的单轴压缩试验、巴西劈裂试验和三轴压缩试验，得到了单轴压缩强度、弹性模量、抗拉强度、内聚力、内摩擦角等基本力学参数以及声发射信号强度随浸水时间的变化规律；分析了基本力学参数衰减规律与细观软化损伤因子的关系。(3) 研发了水-力耦合作用下软岩损伤破坏过程实时监测可视化试验平台，提出了基于数字化X线摄影系统和卷积神经网络技术的软岩破裂实时定量分析方法，分析了裂隙流体的流态变化、应力-声发射耦合特性以及裂隙演化的分形特征，揭示了水力诱导二次损伤裂隙的作用机理。(4) 采用Voronoi多边形单元及其间的接触单元分别表征不同物质组分和界面胶结连接结构，编写了二维和三维随机矿物细观非均质数值计算模型的构建算法，给出了考虑材料和接触类型双重非均质性数值模型细观参数的标定方法。(5) 引入细观软化损伤因子，考虑了不同物质组分交界面以及胶结物本身在水作用下的弱化过程，建立了考虑软化时间损伤效应的细观离散元模型；对比分析了二维和三维均质模型和非均质模型不同浸水时间和不同围压条件下的模拟精度和损伤破坏特性，补充验证了细观软化损伤因子在数值模型中的合理性和可用性。
Soft rock is easy to soften when it meets water, and its mechanical properties deteriorate rapidly, which is an important reason to induce the instability and failure of soft rock geological body such as soft rock slope and roadway surrounding rocks. In view of the unclear macro-mesoscopic softening mechanism of soft rock under water-rock interaction, especially the meso-scale softening damage quantitative characterization, this paper focuses on the study of the correlation between the damage characteristics of meso structures and the time-dependent mechanical properties during the process of water-rock interaction based on laboratory tests, theoretical model and numerical simulation. The main research contents and findings of this paper include:(1) The main mineral elements of soft rock are determined by XRF and XRD tests. The variation of element concentration with time is obtained based on ICP-OES experiments. The evolution characteristics of meso-structure of soft rock are analyzed by polarizing microsection test. The structural model of Interfacial Cemented Bonding (ICB) is proposed, which provides a theoretical basis for describing the fine structure of softening process of soft rock. Based on the molecular diffusion theory, the analytical solution to describe the time-dependent damage effect of ICB is derived. The theoretical equation fits well with the experimental results, and the nonlinear dynamic characteristics of soft rock softening are revealed quantitatively. A meso-softening damage factor are deduced and put forward, which provides a theoretical basis for numerical simulation to study the softening problem.(2) The uniaxial compression tests, Brazilian splitting tests and triaxial compression tests of soft rock with different soaking time are carried out, and the basic mechanical parameters such as uniaxial compression strength, elastic modulus, tensile strength, cohesion and internal friction angle as well as the acoustic emission signal intensity with soaking time are obtained. The relationship between attenuation law of basic mechanical parameters and mesoscopic softening damage factor is analyzed.(3) A visual experimental platform for real-time monitoring of soft rock damage and failure process under water-rock hydro-mechanical coupling is developed, and a real-time quantitative analysis method for crack extraction is also proposed based on Digital Radiography (DR) system and convolutional neural network. The change law of fluid regime, stress-acoustic emission coupling characteristics and fractal characteristics of fracture evolution are analyzed. Besides, the mechanism of hydraulic induced secondary fracture damage is revealed.(4) The Voronoi polygon elements and contact elements are used to characterize different material components and ICB structure, respectively. Then, the algorithms of establishing two dimensional (2D) and three dimensional (3D) stochastic mineral mesoscopic heterogeneous numerical models are proposed. A mesoscopic parameter calibration method considering the double heterogeneity of materials and contact types is presented.(5) The mesoscopic softening damage factor is introduced into the numerical model in order to consider the weakening process of the interfaces of different material components and the cement itself under water action. A mesoscopic discrete element model considering the softening damage effect is then established. The simulation accuracy and damage characteristics of 2D and 3D homogeneous models and heterogeneous models under different immersion time and confining pressure are compared and analyzed. Finally, the rationality and availability of mesoscopic softening damage factor in numerical models are verified.
