岩石破裂过程中的声发射b值及分形特征研究

应用声发射及其定位技术，通过单轴受压岩石破坏声发射试验，对岩石破裂过程中的声发射b值和空间分布分形维值随不同应力水平的变化趋势进行了研究。研究结果表明：声发射分形维值D和b值反映了岩石破坏过程中微裂纹的初始和扩展；在小尺度微裂纹所占比例较高的加载初期，分形维值和b值在较高的水平波动变化，部分岩石试件分形维值和b值呈现升高现象；随着载荷的增加，岩石内部微裂纹的空间分布由无序向有序转变，大尺度裂纹所占比例增加，声发射定位事件出现群集现象，分形维值和b值开始较快速下降并在岩石失稳破坏时达到最低值。在岩石破坏过程中，声发射分形维值和b值的变化趋势相近。由于实际应用时，分形维值和b值的最小值（临界点）难以确定，故可将2个参数相结合，以分形维值D和b值较快速下降作为前兆特征，以提高现场岩体稳定性监测的准确性。

Study on b-value and fractal dimension of acoustic emission during rock failure process

Acoustic emission (AE) experiments of rock failure are carried out under uniaxial compression loading with AE location technique. Relationships between different stress levels with spatial distribution fractal dimension and b-value of AE events are studied. The results show that fractal dimension D and b-value of AE events can directly reflect the evolutionary process of microcracks initiation and propagation. In the initial stage of loading, on account of high proportion of small scale microcracks, the value of fractal dimension and b-value are higher and appear fluctuating, and in some rock samples they are increasing. With the increase of load, the distribution of microcrack turns from random to order, large scale microcrack are increasing, acoustic emission location events begin to cluster, fractal dimension and b-value begin to drop much quickly. The fractal dimension and b-value reach to the minimum value at the critical point of rock failure. During rock failure process, variable tendencies of fractal dimension and b-value are similar. Although it is difficult to confirm the minimum value of fractal dimension and b-value in practical application, continually declining of the two parameters can be seen as precursors of rock failure. Consequently, fractal dimension and b-value can be combined used to improve the accuracy of rock mass monitoring and forecasting in-situ.