花岗岩破裂过程中声波与声发射变化特征试验研究
Experimental research on ultrasonic velocity and acoustic emission properties of granite under failure process
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摘要: 采用声波、声发射一体化监测装置研究了单轴加载及循环荷载作用下花岗岩波速和声发射变化特征。研究结果表明:①加载初期,岩石内部微裂纹受力闭合,纵波、横波波速显著增加,而声发射事件数量极少;加载中期,岩石处于线弹性变形阶段,纵波、横波波速缓慢增加后保持稳定,声发射事件少量产生,约占声发射事件总量的9.44%;加载后期,岩石处于破裂损伤阶段,裂纹开始萌生,拓展,岩石纵波波速呈现略微下降趋势,而横波波速明显降低,声发射活动剧烈,约占声发射事件总量的50.63%。峰值应力之后,花岗岩横波波速开始急剧下降,而纵波波速缓慢降低,声发射活动依然活跃。②由于岩石的内部损伤需要积蓄一定能量才会形成,因此声发射活动呈现“相对平静、间隔突发”的规律,“相对平静期”最明显的时段位于峰值应力之前。③循环加卸载条件下,岩石的波速和声发射变化特征与应力状态表现出良好的一致性。统计分析声发射事件数量随应力的变化规律,论证了岩石的Felicity效应;比较分析加载过程中的Felicity比变化,证明了岩体的累积损伤。Abstract: The experiments on granite under uniaxial compression and cyclic stress loading are carried out, and changes in velocity and the activities of acoustic emission are recorded by the ultrasonic velocity and acoustic emission synchronous monitoring devices. The results show that: (1) In the beginning of the loading tests, the shear-wave velocity and longitudinal-wave velocity have a significant ascension due to the closure of rock micro-cracks, while the AE events are rare; the granite is in the linear elastic deformation stage in the middle of compression experiments, the ultrasonic velocity increases firstly and then keeps stable for a while, and a small amount of AE events, about 8.77% of all the AE events, will occur; because of generating and expanding of cracks in the rock samples, the granite will suffer serious damage in the later period of compression tests, the longitudinal-wave velocity decreases slightly and the shear-wave one reduces significantly, and AE has positive activities, about 50.96% of all the AE number. After the stress peak, the shear-wave velocity begins to reduce sharply and the longitudinal-wave one decreases slowly, while the AE remains active. (2) Because the rock damage needs enough energy accumulated, the AE exhibits a law of “quiet relatively and bursting at intervals”, and the most evident “ relatively quiet period” happens before the peak stress. (3) In the tests of cyclic stress loading, the ultrasonic velocity and AE activities of the rock have a good consistency with stress condition. Change of AE events at peak stress can reflect accumulated damage of the rock, and the Felicity effect can be demonstrated by comparing the AE events at the same stress stage.