In order to investigate the characteristics of ultrasonic wave velocity and acoustic emission activity of salt rock under triaxial loading

the triaxial loading tests are conducted. Employing a device composed of acoustic wave testing system

acoustic emission testing systems

we obtain the following results: Four stages are identified in the process

including stageⅠof the elastic compression

stageⅡof initiation and stabilized growth of fractures

stage Ⅲ of accelerated growth of fractures

stage Ⅳ of sustained strength. During phaseⅠ

the velocity of ultrasonic wave of salt rock has a slight increase，and a few acoustic emission(AE) events happen in this stage. In the stageⅡ

P-wave and S-wave remain stable

AE events become active. In phase Ⅲ and Ⅳ

AE activity of salt rock performs intensely

and the velocity of P-wave remains stable while velocity of S-wave reduces significantly. The level of confining pressure significantly influence ultrasonic wave velocity and acoustic emission activity. The rate of change of velocity of ultrasonic wave is large at a low level of confining pressure while small at a high level of confining pressure. When dynamic axial strain is 10%

the total amount of AE events is 16 271 under confining pressure of 5 MPa

the number decreases to 8 764 under confining pressure of 10 MPa due to the effect of compaction

3 041 under confining pressure of 15 MPa

and 906 under confining pressure of 20 MPa

which indicates that the level of confining pressure greatly influenc the AE activity

showing “the effect of confining pressure densification”.