基于三轴压缩声发射试验的岩石损伤特征研究

STUDY OF ROCK DAMAGE CHARACTERISTICS BASED ON ACOUSTIC EMISSION TESTS UNDER TRIAXIAL COMPRESSION

利用MTS815岩石伺服试验系统和AE21C声发射监测仪,对灰岩进行三轴压缩声发射试验,利用声发射参数,分析三轴压缩条件下岩石的损伤演化特征。试验结果表明:(1)相同试验条件下,检波器置于三轴室内时的声发射振铃计数和能量的最大值分别比置于室外时高27%和32%,表明,声发射检波器置于三轴室内能够接收到更全面、真实的声发射信号。(2)围压使岩石压密阶段声发射活动降低,同时声发射振铃计数最大值稍滞后于岩样宏观破坏时间,说明围压提高了岩石的剪切强度和峰后承载能力。(3)建立基于声发射累计振铃计数的岩石三轴压缩损伤演化模型,岩石的损伤演化过程可划分为初始损伤阶段、损伤稳定发展阶段、损伤加速发展阶段和损伤破坏阶段。初始损伤阶段,声发射参数较小;损伤稳定发展阶段,声发射活动明显活跃,振铃计数和能量逐渐增加;损伤加速发展阶段,声发射活动异常活跃,宏观破坏后不久声发射振铃计数和能量达到峰值;损伤破坏阶段,岩石仍具有相当的承载能力,在破坏过程中仍有声发射活动出现。

Acoustic emission tests under triaxial compression of limestone were carried out by MTS815 servo-controlled rock mechanical test system and AE21C acoustic emission monitor. The characteristics of limestone damage evolution under triaxial compression are analyzed through acoustic emission parameters. The results show that： （1） Under the same experimental condition, the maximum acoustic emission ringing counts and energy with the detector inside the confining chamber are more 27.0% and 32% higher than that outside the confining chamber, respectively. The more comprehensive and real acoustic emission signals can be received with the detector inside the confining chamber. （2） The confining pressure can make the acoustic emission activities decrease in the stage of compaction. The time of acoustic emission ringing counts reaching its highest value lags behind the time of the macroscopic failure of the specimen, which indicates that the confining pressure not only improves the shear strength of rock, but also its bearing capacity after the peak stress. （3） The rock damage evolution model is established with the acoustic emission ringing counts under triaxialcompression. The damage evolution process of rock can be divided into following four stages： initial damage stage, stable damage evolution and development stage, damage speeding development stage and damage failure stage. The acoustic emission activities are less in the initial damage stage. In the stable damage evolution and development stage, the acoustic emission activities begin to be active with the increase of the acoustic emission ringing counts and energy. In the damage speeding development stage, the acoustic emission activities become extremely active; and the acoustic emission ringing counts and energy reach their peak values short after the macroscopic failure. In the damage failure stage, the rock still has bearing capacity and some acoustic emission events are still active.