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采用极点对称模态分解方法对大理岩卸围压破坏的声发射数据进行去噪处理,分析大理岩卸围压变形破坏全过程的声发射变化特征。加载初期声发射振铃较小且增长缓慢,扩容点后声发射振铃计数率迅速增加。声发射时频变化呈现波动特征,峰值强度前频率出现突增,临近峰值强度时频率明显降低。利用关联维数方法计算大理岩卸围压破坏过程的声发射分形维数,声发射分形维数呈现阶段性变化,先增大后减小,在应力达到峰值强度的80%附近出现陡增,破坏时分形维数又出现大幅降低。频率变化特征与分形维的变化规律具有对应关系,声发射信号频率突然上升且分形维数陡增可认为是岩石破坏前兆。
The pole-symmetric modal decomposition method is used to denoise the acoustic emission data of the unloading confining pressure of marble and analyze the characteristics of acoustic emission during the whole process of the deformation and failure of marble unloading confining pressure. The initial acoustic emission ringing at the initial stage of loading is small and slowly increasing. The counting rate of acoustic emission ringing at the expansion point rapidly increases. The time-frequency changes of acoustic emission show the characteristics of fluctuation. The frequency before the peak intensity suddenly increases and the frequency near the peak intensity decreases obviously. The fractal dimension of acoustic emission of marble during the process of unloading confining pressure was calculated by using the correlation dimension method. The fractal dimension of acoustic emission showed a periodical change, increasing first and then decreasing, and sharply increasing around 80% of the peak intensity. The fractal dimension appears to be greatly reduced when destroyed. The variation of frequency has a corresponding relationship with the variation of fractal dimension. The sudden increase of acoustic emission signal frequency and the steep increase of fractal dimension can be considered as precursors of rock failure.