岩石单轴压缩下损伤表征及演化规律对比研究

采用声波、声发射一体化装置同步测试单轴压缩下花岗岩应力应变、超声波及声发射(AE)特征演化规律,分析岩石特征应力对应的宏–细观表征,通过裂纹体积应变、声发射及声波特征等共同量化岩石损伤演化过程。结果表明:裂纹体积应变和波速对应的损伤起始应力吻合较好,AE事件、幅值分布、b值对应的应力特征值基本一致,但AE事件表征的损伤累积开始早于宏观变形和声波;初始加载阶段波速及各项异性系数K均逐渐增加,之后变化趋缓,起裂应力后侧向波速开始减小,而K逐渐增大;峰值应力前裂纹的快速聚结引起AE信号幅值大幅增加,伴随的是b值的快速下降和AE累积能量的陡增;基于起裂应力后损伤才开始累积的假定,量化并对比了裂纹体应变、AE事件等多参量表征的损伤演化规律,发现花岗岩损伤累积绝大部分发生在损伤应力之后。裂纹体应变表征的损伤具有明确物理意义,但裂纹体应变计算中泊松比选取存在一定主观性,裂纹体应变、AE能量、模量等参数表征的损伤在接近峰值应力前均出现大幅增加,与b值的快速下降对应。综合对比分析,AE能量表征的损伤具有更好的可靠性,反映了岩石损伤破裂的本质特征。

Comparative study on damage characterization and damage evolution of rock under uniaxial compression

The evolution of stress-strain data, acoustic emission (AE) and ultrasonic characteristics of granite under uniaxial compression are synchronously tested by using the ultrasonic wave and AE synchronous monitoring devices. The macro- and meso-characteristics of the stress thresholds are analyzed. Also, the quantitative damage evolution of granite is inferred by the crack volumetric strain, AE parameters and ultrasonic characteristics. The results show that the crack initiation stress inferred by the crack volumetric strain and ultrasonic velocity coincides well, and the stress thresholds inferred by the AE events, AE amplitude distribution and b-value are basically identical, but the damage accumulation inferred by the AE events initially begins earlier than that by the macroscopic deformation and ultrasonic testing. At the initial loading stage, the ultrasonic velocity and velocity anisotropy coefficient K increase, and the increase rate slows down gradually. After the crack initiation stress, the lateral velocity begins to decrease, while K gradually increases. With the rapid coalescence of cracks, the amplitudes of AE signals increase significantly prior to the rock failure, accompanied by the rapid decline of b-value and dramatic increase of AE energy. Assuming that the damage accumulation begins only after the crack initiation stress, the damage evolution of granite is characterized by various parameters, such as the crack volumetric strain and AE event. It’s revealed that the majority of damage occurs after the damage stress. The damage characterized by the crack volumetric strain has a clear physical meaning, but the selection of Poisson's ratio for calculating the crack volumetric strain is somewhat subjective. The damages haracterized by the crack volumetric strain, AE energy and modulus all increase significantly prior to the peak stress, which coincides with the rapid decline of b-value. It’s suggested that the damage estimation using the AE energy method should be preferred from the perspective of the reliability of the obtained damage values.