不同应力路径大理岩声发射破坏前兆的试验研究

应力路径不同,岩石变形和破坏过程中伴随的声发射特征也不同,通过不同路径大理岩加、卸荷试验,结合分形维数原理,探讨声发射破坏前兆随应力路径的变化规律。试验结果表明:1岩样破坏处的声发射计数率和破坏前的累计计数率增长率由大变小的应力路径为加轴压卸围压、恒轴压卸围压、单轴、常规三轴路径。2常规三轴路径下岩样临近破坏时,声发射事件计数率存在明显的"低声发射期",围压越大,声发射前兆"低声发射期"越明显;同时累计振铃计数率增长速率降低的拐点出现后很短时间,岩样也会发生破坏。3低围压下恒轴压、卸围压路径岩样破坏时累计振铃计数率的增长速率近似为切线。加轴压、卸围压岩样破坏前一段相近计数率后存在声发射计数率的"平静期",围压增加,"平静期"持续时间增加,岩样破坏产生的计数率越高。4在低围压应力环境下应力比0.8、高围压应力环境下时间比0.4时声发射分维数降低的特征可以作为岩样的破坏前兆分析。

Experimental study on acoustic emission failure precursors of marble under different stress paths

There are diverse acoustic emissions during the process of rock deformation and breakage in various stress paths. To explore the relationship between emission failure precursors and stress paths, loading and unloading tests on marble under different stress paths are carried out. The results show that: (1) According to the growth rate of accumulated ring count rate before failure and the emission count rate at failure point, the sequence of stress paths from the largest to the smallest is loading axial stress and unloading confining pressure, constant axial stress and unloading confining pressure, uniaxial compression, and conventional triaxial compression. (2) Before failure under conventional triaxial compression, there exists an obvious low emission period of acoustic emission count rate. The larger the confining pressure, the more obvious the low emission period as the failure precursor. Rock samples fail within a very short time after the inflection point of growth rate of accumulated count rate appears. (3) The growth rate of accumulated count rate of constant axial stress and unloading confining pressure tests at failure point is approximately tangent with the low confining pressure. There is a quiet period of acoustic emission count rate after close count rate before failure of loading axial stress and unloading confining pressure samples. The duration of the quiet period increases with the confining pressure, and rock failure leads to a higher count rate. (4) When the stress ratio is more than 0.8 under low confining pressure or the time ratio is more than 0.4 under high confining pressure, the decreasing characteristics of fractal dimension of acoustic emission can be regarded as the failure precursor of rock.