基于多重分形理论的花岗岩岩爆试验声发射信号特征研究

Study on the characteristics of acoustic emission signals of granite under rockburst based on multifractal theory

运用声发射系统采集不同中主应力条件下花岗岩岩爆试验过程中的声发射信号,分析岩爆破坏过程和岩爆时刻竖向应力及声发射振铃计数水平,运用多重分形理论分析竖向应力快速加载至岩爆结束过程中声发射振铃计数在时域上的分布特征。研究结果表明:中主应力水平越高,岩爆破坏越剧烈,岩爆时刻竖向应力水平趋于稳定,竖向应力快速加载阶段的累计声发射振铃计数有所提升;竖向应力不断提升,声发射振铃计数多重分形谱形态呈现宽—窄—宽的变化趋势,多重分形谱宽总体呈先降后增,提取谱宽平滑曲线中先降后增的转折点进行岩爆预警,发现中主应力越高,岩爆预警时间越长,岩爆突发性有所下降;越接近岩爆,广义分形谱的非线性逐渐减弱,在岩爆发生阶段又有所凸显,且中主应力越高,声发射振铃计数在时域上的分布越均匀。该研究表明高中主应力和竖向应力快速增加可提高岩爆过程中裂纹连续扩展行为的活跃度。

During the rockburst experiments on the granite specimens under different intermediate principal stresses,the acoustic emission(AE)system is adopted to obtain the AE signal.The rockburst process,vertical stress when rockburst and the AE ring-down counts are investigated.And the multifractal characteristics of the AE ring-down counts in the time domain during the process of rapid increasing vertical stress until the end of rockburst is analyzed with multifractal theory.The results show that the higher the intermediate principal stress,the more intense the rockburst.When the vertical stress level at rockburst tends to stabilize,the accumulated AE ring-down counts during the rapid increasing vertical stress tends to increase.With the increase of the vertical stress,the multifractal spectrum of AE ringdown counts shows a trend of wide to narrow to wide variation.The width of the multifractal spectrum mainly present a decreasing-increasing trend where a turning point in the smooth curve of the spectrum width can be identified for rockburst warning.It is found that the higher the intermediate principal stress,the longer the rockburst warning time,and the decrease in rockburst suddenness.As approaching to rockburst,the nonlinearity of the generalized fractal spectrum gradually weakens,but becomes obvious when rockburst.The distribution uniformity of the AE ring-down counts in the time domain tends to increase with the increase of the intermediate principal stress.The research indicates that under the high principal stress and the rapid increasing vertical stress,the continuous cracking behavior during the rockburst experiment process will be enhanced.