摘要
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。
Damage and dilation characteristics of the granite from great depth at Beishan under triaxial cyclic loading-unloading conditions were investigated using the rock mechanical test machine MTS815 and the acoustic emission（AE） measurement system PCI-2. Complete stress-strain curves associated with the accumulative AE hits and the 3D distributions of AE events were analyzed. The mechanisms of fracture evolution of the rock samples during deformation were revealed. The variation of dilation angle with plastic shear strain was characterized and the confining stress dependent dilation behavior was discussed according to the established plastic strain locus. The 3D distributions of AE events in the process of loading-unloading indicated that the maximum gradient of crack growth occurred at the stage of strain softening. In this stage,the cyclic loading was the main factor triggering the drastic damage and the macro coalescence of fractures in the rock. At the stage of＆amp;nbsp;residual deformation,there were almost no newly generated cracks. The incremental AE events at this stage were primarily attributed to the frictional sliding of the shear plane. This explained why the volumetric strain rate approached zero near the end of loading. Compared with the loading process,the repeated unloading had smaller effects on the development of cracks. Due to the different states of crack propagation,a significant difference in AE characteristics before and after the crack damage stress（σcd ） were observed. The calculated post-peak dilation angle deceased with the increasing of the plastic shear strain and its decaying gradient decreased with the increase of the confining stresses. A model for dilation angle was established using an exponential function to reasonably describe the dilation behaviors of Beishan granite.
出处
《岩石力学与工程学报》
EI
CAS
CSCD
北大核心
2014年第9期1740-1748,共9页
Chinese Journal of Rock Mechanics and Engineering
基金
国家自然科学基金资助项目(11102061)
关键词
岩石力学
北山花岗岩
循环加
卸载
损伤
扩容
剪胀角
rock mechanics
Beishan granite
cyclic loading-unloading
damage
dilation
dilation angle
