Due to investigate the acoustic emission(AE) characters of coal specimens' deformation and failure process under different stress paths, the general uniaxial compression, triaxial compression and confining pressure reduction experiments were performed by RMT-150B rock mechanics test system. Test results indicate that the AE characters of coal specimens are different under different load path. In experiments of general uniaxial compression, AE events take place in different degrees on every stage, comparing with experiments of uniaxial compression in triaxial cylinder, the values of cumulative AE counts and energy are obviously larger and the values of maximal counts and energy on the peak point are approximately equal; In experiments of general triaxial compression, AE events occur less before yielding and increase obviously after yielding. At stage of post-yielding, AE counts and energy are quite active and enhance rapidly, these are signs of failure portent, AE counts and energy reach maximum at stress peak point; In experiments of confining pressure reduction, with decreasing of confining pressure and friction provided by positive stress, the samples' inner zones with low strength yield to fail and slide, AE events occur in small amount before yielding, at stage of post-yielding, AE counts and energy are quite active and enhance rapidly, these are also signs of failure portent, AE counts and energy reach maximum at stress peak point; and increase sharply just before failure point. Comparing with general triaxial compression, the maximal values of AE counts and energy are much larger and the failure intensity of coal specimens on such condition is more violent.
It is generally accepted that rock materials emit low-level seismic signals when they are stressed or deformed. In the geotechnical field, this phenomenon is generally referred to as acoustic emission (AE) activities. When rock fractures, it produces AE signals transmit through the rock as elastic waves. As a tool of reflecting the internal state change of rock, AE events can be analyzed and studied to infer internal state and inverse the mechanism and degrees of rock failure. AE law of different kind of loaded rock are studied and the research achievements are used to predict the failure process of rock engineering and precursor of earthquake.
Plenty of research achievements on AE characteristics of rock are published [1~8]. ZHANG Huihui[1] studied AE characters of big gneiss samples during failure process under triaxial cyclic loading; YU Xianbin[2] gave research on AE laws in direct drawing, shearing and uniaxial compressing tests of sandstone and lime; WU Gang[3] studied AE characteristics on loading, unloading and different unloading path of rock material; LI Yuanhui[4] used numerical software (RFPA2D-Rock Failure Process Analyses) to simulate rock sample's AE characters under three different stress paths and analyzed the influence of rock's AE Kaiser effect on different stress paths; LIU Baoxian[5] researched remodeling coal samples' AE characters and deformation damage under uniaxial compression; YANG Yongjie[6] studied the AE characters of coal under uniaxial compression; WANG Enyuan[7] studied AE's spectrum characteristics of coal samples' failure process under uniaxial compression.
