冻融与荷载共同作用下孔隙砂岩损伤力学特性研究

The macroscopic mechanical response and damage failure process of rock are closely related to its micro-structure. Taking freeze-thaw pore sandstone as research object, the project uses combination methods of test, theoretical analysis and numerical simulation to study meso-structure damage effects of porous sandstone and induced damage mechanics characteristics under coupling action of freeze-thaw and loading. Carrying out the freeze-thaw cycles tests, damage propagation of meso-structure is observed by X-ray diffraction and CT scanning test. Then, conducting the CT real-time testing of meso-damage propagation of freeze-thaw pore sandstone under uniaxial loading. The high speed photography are used to observe the process of the macro crack propagation and fracture synchronously. Based on the test, image processing and simulated results, meso-structure and meso-damage are identified quantitatively, and meso-structure digital model of porous sandstone is built. According to theory of damage and fractal rock mechanics, the complex relationship between the freeze-thaw cycles effects, porosity and mechanical parameters are discussed. In the theoretical point of view, the damage evolution equation of the porous sandstone are put forward on the condition of the freeze-thaw cycles and loads. The macroscopic-microscopic damage constitutive model of porous sandstone are established under the combined action of the freeze-thaw cycles and loads considering the meso-structure damage effects. The proposed model can reveals the internal relations of meso-structure damage and macro-mechanics characteristics. It has the important theory value and the practical significance. It provides scientific basis to revealing inherent mechanism of frozen injury under freeze- thaw environment.

岩石宏观力学响应和损伤破坏过程与其细观结构密切相关。本项目针对冻融孔隙砂岩，采用室内试验、理论分析与数值计算相结合的方法，研究冻融受荷孔隙砂岩细观结构损伤效应及其诱发的损伤力学特性。开展孔隙砂岩的冻融循环试验，采用X射线衍射、CT扫描试验分析冻融循环引起的砂岩细观结构损伤演化；进行单轴压缩荷载作用下冻融孔隙砂岩细观损伤的CT实时扫描试验，同时采用高速摄影仪观测荷载作用下宏观破坏过程。基于试验、图像处理及数值模拟，进行冻融孔隙砂岩细观结构及损伤的定量识别；建立孔隙砂岩细观结构数字化模型。运用损伤力学、分形岩石力学理论，探讨冻融循环次数、孔隙率与强度参数的定量关系；提出冻融-荷载共合作用下孔隙砂岩宏-细观损伤演化方程，建立反映孔隙砂岩细观结构特征的损伤力学评价模型，研究细观结构损伤与宏观力学性能之间的相互影响规律，为揭示冻融环境工程冻害产生的内在机理提供科学依据。

冻融岩石宏观力学响应与其细观结构密切相关。项目针采用室内试验、理论分析与数值计算相结合的方法，研究冻融受荷砂岩细观结构损伤效应及其诱发的损伤力学特性。.完成了冻融砂岩在荷载作用下的X射线衍射、高速摄影、声发射、核磁共振的宏、细观实时观测，对不同粒径砂岩受冻融作用的受拉和抗压强度变化规律进行了系统研究，提出了中央劈裂和非中央劈裂的宏观破坏模式。对粒径与冻融砂岩宏观抗拉性能及破坏模式的关联影响进行了深入探讨。声发射振铃计数峰值和累计能量可以表征冻融损伤大小和损伤演化动态过程。冻融砂岩劈裂损伤在时间域有连续演进的行为特征，冻融循环5次声发射事件频率与能量值突增，损伤发育速度突变。振铃计数和累计能量同步大幅激增可以作为冻融砂岩破坏失稳时间域的前兆信息。.获得了冻融循环对砂岩饱和吸水率、T2谱、孔隙度、峰值强度等宏、细观参数影响规律，建立了AE特征参数与宏观力学特性之间的关联。冻融砂岩的孔隙特征变化存在临界点，冻融使微孔数量减小，介孔数量增大。孔隙度与单轴抗压强度强度呈现指数递减关系，与弹性模量呈现线性递减分布。单轴压缩荷载作用下冻融砂岩损伤演化过程包括孔隙扩展、裂隙发育和裂隙扩展阶段，呈现出劈裂破坏、剪切破坏和劈裂剪切混合破坏三种破坏模式。基于损伤力学理论，定义了以AE特征参数为基准量的损伤变量，建立了能够反映冻融砂岩压密阶段特点的统计损伤本构模型，揭示了砂岩在冻融循环作用下细观结构损伤与宏观力学性能之间的相互影响规律。.实现了冻融及荷载共同作用下砂岩CT实时扫描，获得了冻融及受荷砂岩损伤演化全过程图像。研究了冻融诱发的砂岩细观结构损伤演化规律。实现了CT图像的伪彩色增强、直方图及边缘检测技术，建立了冻融砂岩细观结构数字化模型，对细观损伤过程进行了定量描述，完成了细观损伤大小和空间位置的定量评价。构建了细观结构损伤演化模型，研究了冻融循环对砂岩损伤演化过程的影响机理。