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| Identification research on characteristic stress in front of peak based on acoustic emission and wave velocity variation of sandstone under triaxial loading |
| ZHANG Xulong1，ZHANG Sheng1，2，WANG Longfei1，RONG Tenglong1，2，ZHOU Rui1 |
(1. College of Energy Science and Engineering，Henan Polytechnic University，Jiaozuo，Henan 454001，China；
2. Collaborative Innovation Center of Coal Work Safety and Clean High Efficiency Utilization，Jiaozuo，Henan 454001，China) |
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Abstract In order to accurately identify the pre-peak characteristic stress in the process of rock loading under different confining pressures，the pseudo triaxial tests with confining pressures of 0，10，30，50 and 70 MPa were carried out on the GCTS RTX-3000 testing machine using sandstone standard samples. The ultrasonic testing system and acoustic emission acquisition system were used to monitor at the same time，and the variation law of ultrasonic wave velocity and the distribution characteristics of acoustic emission location events during sandstone loading were obtained. A method that can shield ultrasonic interference signals from acoustic emission dates was proposed. The results show that the compression and shear wave velocities of the sample show a quadratic function relationship with the increase of confining pressure. With the increase of axial pressure，the compression and shear wave velocities of the sample show a law of growth，stability and decline. The shear wave velocities always show a downward trend before the compression wave velocities，and the shear wave is more sensitive to damage than the compression wave. The pre-peak characteristic stress can be accurately determined by comparing the change rules of volume strain，acoustic emission，ultrasonic and dynamic elastic parameters. The closure stress corresponds to the end of the rise of the shear wave velocity，the initiation stress corresponds to the beginning of the fall of the shear wave velocity and the inflection point of the dynamic elastic modulus，and the damage stress can be determined jointly by the beginning of the decline of the compression wave velocity，the rapid rise of the acoustic emission signal and the inflection point of the volumetric strain. Acoustic emission positioning can directly reflect the failure mode of the sample. Under low confining pressure，the sample will undergo split shear mixed failure，while under high confining pressure，the sample will undergo shear failure. This study is helpful to accurately identify the pre-peak characteristic stress of rock under load，and deeply understand the damage characteristics of rock under different stress conditions，which is of great theoretical significance to the stability evaluation of rock mass in deep underground engineering.
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