预制孔岩石破坏过程中的声发射时空演化特征研究

STUDIES OF AE TIME-SPACE EVOLUTION CHARACTERISTICS DURING FAILURE PROCESS OF ROCK SPECIMENS WITH PREFABRICATED HOLES

选取粗粒花岗岩和细粒砂岩,通过预制方孔和圆孔,开展单轴加载条件下岩石破坏声发射试验。采用单纯形定位算法,对岩石破裂过程中的声发射时空演化规律进行研究,并对声发射活动特征、能量释放率和空间相关长度进行分析。研究结果表明:对于预制孔间距与预制孔尺寸相同的试件,声发射事件主要在岩石中部群集,试件以中部剪切破坏为主,声发射三维定位事件直观反映裂纹初始、扩展直至贯通的动态演化过程;在整个加载过程中,颗粒较粗且大小不均的花岗岩试件声发射活动性较强,颗粒较细且均匀的砂岩试件声发射活动性在加载后期才开始增强;岩石破坏前,小尺度裂纹合并贯通形成大尺度裂纹,声发射率下降,能量释放率增强,出现声发射信号"平静"而能量释放"不平静"的现象;岩石在受载过程中,应力场通过迁移和重新分布逐步建立起长程相关性;岩石破坏前,空间相关长度显著增加,且在岩石破坏时达到最大值。

Acoustic emission（AE） technique was employed to measure the AE signals of coarse-grained granite and fine-grained sandstone with prefabricated square holes or circular holes under uniaxial compression test.AE time-space evolution characteristics during failure process were studied based on simplex locating algorithm.AE activities characteristics,AE energy release rate and spatial correlation length were also analyzed.The results show that the three-dimensional location of AE events directly reflects the process of initiation,propagation and evolution of microcracks and the stress redistribution within the specimens.For specimens that the distance of prefabricated holes is same with the prefabricated hole size,located AE event are clustered in the central of specimens;and shear failure occurs in the center area of specimens.The AE activities of granite with coarse and heterogeneous grains isn.t much stronger during the whole loading phase;while the AE activates of sandstone with thin and homogeneous grains isn.t enhanced until the later period of loading.Before the failure of rock,microcracks coalescence into large scale cracks,which result in AE activates weaken and AE energy release rate increases;during this phase,many AE signals are superimposing,which induces the AE quiet period and blank area of located AE events occurred.During rock fracture process,long-range correlations are established by redistribution of stress field,which cause the spatial correlation length obviously increasing before rock failure and reach its maximum value when rock failure.