真三轴加卸载煤样声发射长程相关性特征

为模拟井下应力条件，设计固定轴压卸围压试验，得到煤样破裂过程的声发射结果，并计算不同初始围压及不同卸载速率条件下声发射时间序列的长程相关性特征，以期对煤岩体的破裂做出预警。研究结果表明:不同初始围压及不同卸载速率下声发射实验结果类似，根据声发射累计计数可将声发射变化过程分为线性增长期、平静期以及指数增长期，可以很好地反应煤样的破裂过程；随初始围压和卸载速率的增大，声发射时间序列的Hurst指数随之增大，正相关性增强；Hurst指数与分形维数的动态变化与煤样的失稳破裂过程良好对应，且不同初始围压及卸载速率下，Hurst指数与分形维数的动态变化规律类似，说明其声发射时间序列的宏观产生机制具有内在统一性，可将接近破裂荷载时Hurst指数的增大与分形维数的减小作为煤样失稳破裂的前兆信息。

Long-range correlation characteristics of acoustic emission for coal samples subjected to true triaxial loading-unloading

In order to simulate the underground stress conditions,the experiments of fixed axial compression and unloading confining pressure were designed.The results of acoustic emission(AE)during the fracture process of coal samples were obtained,and the long-range correlation characteristics of AE time series under different initial confining pressures and unloading rates were calculated to make an early warning for the fracture of coal and rock mass.The results showed that the results of AE experiments under different initial confining pressures and unloading rates were similar.According to the accumulative AE count,the change process of AE could be divided into the linear growth period,quiet period and exponential growth period,which could well reflect the fracture process of coal samples.With the increase of initial confining pressure and unloading rate,the Hurst index of AE time series increased,and the positive correlation was enhanced.The dynamic change of Hurst index and fractal dimension corresponded to the instability fracture process of coal samples well.Meanwhile,under different initial confining pressures and unloading rates,the dynamic change rules of Hurst index and fractal dimension were similar,which indicated that the macro generation mechanism of AE time sequence had the inherent unity.The increase of Hurst index and the decrease of fractal dimension near the fracture load could be used as the precursor information for the instability fracture of coal samples.