三轴多级荷载下盐岩声波声发射特征与损伤演化规律研究

Damage evolution and characteristics of ultrasonic velocity and acoustic emission for salt rock under triaxial multilevel loading test

采用岩石声波、声发射一体化监测装置,系统地研究三轴多级循环荷载作用下盐岩超声波波速与声发射变化特征。结果表明:(1)岩石的超声波波速和声发射活动与应力状态呈现出良好的一致性。加载阶段,超声波波速上升,声发射活跃,卸载阶段,超声波波速下降,声发射平静,应力级数越高,这一特征越显著。(2)盐岩的声波、声发射特征与试验围压应力密切相关。围压水平越低,应力循环试验中岩石波速变化率越大,声发射事件数量越多;围压水平越高,岩石超声波波速变化率越小,声发射事件数量越少。五级应力荷载试验中,围压条件为5,10,15,20 MPa时盐岩的声发射事件数量分别为1 026,703,361和206个,显示了"围压致密效应"。(3)分别应用卸载模量、裂隙密度和Felicity比表征盐岩的损伤演化。结论认为:盐岩的裂隙密度和Felicity比变化与岩体承载破坏特征较为一致,可以较好地反映盐岩的损伤破裂过程,而利用卸载模量表征盐岩损伤误差较大,这是由于盐岩特殊的黏塑性变形特征造成的。

In order to investigate the characteristics of ultrasonic wave velocity and acoustic emission activity of salt rock under triaxial loading,the multi-level cycle loading tests were conducted using a device composed with the acoustic wave and acoustic emission testing systems. The variations of ultrasonic wave velocity and AE number of salt rock were consistent with the loading stress. In the loading process,the ultrasonic wave velocity increased and AE activity was intense. However,there were opposite characteristics when the stress was unloading. The higher level the loading stress was,the more significant the feature was. The loading level of the confining pressure had great influence on the ultrasonic wave velocity and acoustic emission activity. The rate of change of the ultrasonic wave velocity was greater and the AE events were more under the lower confining pressure than when the confining pressure were in a higher loading level. This can be explained by the principles of confining pressure densification. In the paper,the unloading modulus,the fracture density and the ratio of Felicity were used respectively to express the damage evolution for salt rock. Results showed that the features of fracture density and the ratio of Felicity had a good consistency with the salt rock damage,which reflected the process of damage fracture well. Because of the plastic deformation,the unloading modulus was not suitable for describing the damage.