不同应力路径下煤样变形破坏过程声发射特征的试验研究

 利用RMT–150B岩石力学试验机对义马耿村具有冲击倾向性煤样进行常规单轴、三轴和三轴卸围压试验，研究在不同应力路径下煤样变形破坏过程中的声发射特征。试验结果表明，煤样在不同应力路径下加载变形破坏过程中产生的声发射特征有所差异。常规单轴压缩过程中各个阶段均有不同程度的声发射事件，与三轴筒内单轴压缩相比，声发射累计计数和能量明显偏大，破坏瞬时的声发射计数和能量大致相当；常规三轴压缩试验时，在围压作用下煤样屈服前声发射事件较少，进入屈服阶段声发射事件逐渐趋于活跃，计数和能量大幅度增大，标志煤样破坏前兆，破坏瞬时声发射计数和能量达到最大值；三轴卸围压试验时，在卸围压前煤样处于弹性阶段声发射事件较少，随围压逐渐降低，由正应力提供的摩擦力不断减小，煤样内部材料强度相对较低逐步屈服破坏形成微裂纹。屈服前期产生少量声发射事件，屈服后期声发射事件逐渐趋于活跃，计数和能量大幅度增大，标志煤样卸围压破坏前兆，破坏瞬间计数和能量同时达到最大值，与常规三轴压缩相比，声发射计数更大，能量则更高，表明三轴卸围压煤样破坏时更加强烈；常规单轴压缩煤样破坏产生的声发射累计计数和累计能量明显偏大，三轴筒内单轴、常规三轴压缩以及三轴卸围压试验时，声发射累计计数和能量大致相同，没有明显差异。

EXPERIMENTAL STUDY ON ACOUSTIC EMISSION CHARACTERISTICS DURING DEFORMATION AND FAILURE PROCESSES OF COAL SAMPLES UNDER DIFFERENT STRESS PATHS

Based on investigation of acoustic emission(AE) characteristics during deformation and failure process of coal specimens under different stress paths，the general uniaxial compression，triaxial compression and confining pressure reduction experiments were performed by RMT–150B rock mechanics test system，in which coal specimens were from Gengcun Mine，Yima Mining Group with outburst proneness. Test results indicate that the AE characteristics of coal specimens were different in deformation and failure process under different stress paths. In experiments of general uniaxial compression，AE events of different degrees took place on every stage. Compared with experiments of uniaxial compression in triaxial cylinder，the values of AE counts and energy were obviously larger and the momentary values of maximum AE counts and energy at failure were approximately equal. In experiments of general triaxial compression，AE events were fewer before yielding and increased obviously then. At stage of post-yielding，AE events were quite active and enhanced rapidly，which was a sign of failure portent，and the value of AE counts and energy reached maximum at failure instantly. In experiments of confining pressure reduction，AE events were fewer，because the specimens were in elastic stage before confining pressure was relieved. With decreasing confining pressure and friction provided by positive stress，the inner zones of samples with low strength yielded to fail gradually and formed microcracks. AE events occurred in small amount in previous yielding stage，while AE counts and energy were quite active and enhanced rapidly in late yielding stage，which was also a sign of failure portent，and AE counts and energy reached maximum value and failed instantly. Compared with general triaxial compression，the maximum values of AE counts and energy were much larger；and the results indicate that the failure of coal samples in experiments of confining pressure reduction were more violent. In experiments of uniaxial compression in triaxial cylinder，general triaxial compression and confining pressure reduction，AE totalized counts and energy were approximately identical.