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采用MTS815岩石力学试验机和声发射监测系统,研究我国高放废物地质处置库北山预选区深部花岗岩在三轴循环加、卸载条件下的损伤和扩容特性。基于试验结果,分析岩石全应力–应变曲线与累计声发射撞击数和事件数的时空分布关系,进而揭示其破裂演化机制。通过构建岩石在循环加、卸载过程中的塑性应变轨迹,获得峰后剪胀角随塑性剪切应变的变化规律,探讨岩石扩容对塑性剪切应变和围压的依赖性。研究结果表明:(1)声发射事件增量最大值出现在应变软化阶段,在该阶段的反复加载是加剧其内部损伤和裂隙宏观贯通的主导因素,残余变形阶段的裂隙行为主要表现为宏观断裂面间的摩擦、滑移,岩石扩容率趋于恒定;(2)卸载过程对于裂隙发展的影响远小于加载过程,由于裂隙的发展状态不同,在裂隙损伤应力(σcd)之前和之后卸载导致的声发射特征具有显著的差异性;(3)峰后剪胀角随塑性剪切应变的增加而减小,并随围压增加其衰减梯度不断减小,采用指数函数建立围压和塑性剪切应变为影响因素的剪胀角模型,可合理描述北山花岗岩的扩容特性。
MTS815 rock mechanics testing machine and acoustic emission monitoring system were used to study the damage and expansion characteristics of deep granite in Beishan preselected area of China’s high-level radioactive waste disposal and disposal under triaxial cyclic loading and unloading conditions. Based on the experimental results, the relationship between the total stress-strain curve of rock and the cumulative number of acoustic emission impacts and the number of events is analyzed, and the mechanism of fracture evolution is also revealed. By building the plastic strain trajectory of the rock during cyclic loading and unloading, the variation law of post-peak dilatancy angle with plastic shear strain was obtained and the dependence of plastic expansion strain on plastic shear strain and confining pressure was discussed. The results show that: (1) The maximum value of acoustic emission event appears in the stage of strain softening. Repeated loading at this stage is the dominant factor that aggravates the internal damage and macro-fracture of the fissure. The fissure behavior in the residual deformation stage is mainly macroscopic fracture (2) The effect of unloading process on the development of fractures is far less than that of the loading process. Due to the different developmental states of the fractures, unloading occurs before and after the fracture damage stress (σcd) (3) The post-peak dilatancy angle decreases with the increase of plastic shear strain and decreases gradually with the increase of confining pressure. Exponential function is used to establish the confining pressure and plastic shear The dilatancy angle model, which should become the influencing factor, can reasonably describe the expansion characteristics of Beishan granite.