不同围压下岩石破坏过程的声发射频率及b值特征

ACOUSTIC EMISSION FREQUENCY AND b VALUE CHARACTERISTICS IN ROCK FAILURE PROCESS UNDER VARIOUS CONFINING PRESSURES

开展大理岩岩样常规三轴加荷破坏试验研究,分析大理岩变形破坏过程各阶段声发射及其频率、b值变化特征,探索不同围压下岩石破坏前兆信息。结合极点对称模态分解方法(ESMD方法)对声发射数据进行去噪处理后的试验结果表明:三轴压缩破坏岩样声发射水平在压密阶段和弹性阶段较小,塑性阶段逐渐活跃,扩容应力后声发射水平显著提高,在峰前塑性阶段存在声发射平静期。岩样变形破坏过程中的声发射频率与b值整体表现为上下波动态势,加载初期声发射频率与b值波动较大,并保持在较高水平,塑性变形阶段声发射频率与b值变化幅度减小。与声发射平静期相对应,塑性阶段存在声发射频率与b值变化相对稳定阶段。低围压下岩石破坏前声发射频率与b值均出现骤降特征,岩石发生脆性断裂,高围压下岩石破坏前声发射频率与b值变化相对平稳,岩石发生渐进式破坏。

The failure tests on marbles under conventional triaxial loading were carried out. The ringing count rate of acoustic emission(AE) of rock,the frequency as well as the variation of b value at the failure stage and the sign of rock failure under various confining pressures were investigated. The experimental data were processed with the extreme-point symmetric mode decomposition method. The AE in the triaxial compression test was small at the compaction and elastic stages and was larger after entering the plastic stage and was increased significantly after the stress expansion. There was an AE quiet period before the peak strength. AE frequency and b value fluctuated all the time which varied drastically at the initial loading process and stayed at a higher level. At the plastic stage,they changed less and stayed at a lower level. Corresponding to the AE quiet period,there was a period that AE frequency and b value changed relatively small in the plastic stage. Under the lower confining pressures,the AE frequency before rock failure and the value of b dropped dramatically,indicating that the brittle failure of rock occurred. Under the higher confining pressures,the variations of AE frequency before the rock failure and the value of b was relatively stable,suggesting that the progressive failure in rock occurred.