(1. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China；2. School of Mechanical Engineering，Nanjing University of Science and Technolog，Nanjing，Jiangsu 210094，China)
Abstract：The acoustic emission(AE) and wave propagation in granite under uniaxial compression were measured with the ultrasonic wave and AE synchronous monitoring devices. The stress thresholds were determined with the macro-micro methods firstly. Then evolution of AE and wave propagation during different phases were studied. The result shows that the evolution of micro cracks is related to the macroscopic deformation closely. As the cracks propagate mainly along axial direction under uniaxial compression，the axial stiffness is less sensitive than the nonlinear lateral deformation to the crack initiation and coalescence. The slope variation point of the instantaneous Poisson's ratio coincides with the stress thresholds. Crack initiation stress determined by AE monitoring is smaller than that by the macro strain methods. However，the initiation of micro crack is accurately reflected by AE. The temporal and spatial hypocenter distribution of AE events was refined based on the measured variation of velocity，which depicts the localization of the cracks or their propagation well. Because the amplitude and energy of AE signals emitted at different stages differ greatly，the variations of the characteristic parameters related to the crack propagation are different，especially after the crack damage stress. The outburst increase of AE energy before rock failure can be a precursor to catastrophic damage. At the initial compaction stage，the ultrasonic velocity and amplitude increase with the axial stress. However，the increasing rate decreases gradually. The lateral velocity reaches the peak near crack closure stress and remains constant in a certain later stage. Meanwhile，velocities along the other directions keep increasing. With the increase of the angle to the radial direction，the increment and the stress corresponding to the decreasing point of acoustic velocity increase gradually. The influence of damage development on ultrasonic velocity lags behind that on the AE events.
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2017, Vol. 36 
