Anisotropic characteristics of ultrasonic transmission velocities and stress inversion during uniaxial compression process

Abstract In order to study change characteristics of ultrasonic transmission velocities (UTV) during the uniaxial compression process of the coal and rock material, advanced UTV measurement device and loading device are used to establish experiment system for measuring UTV in different direction. The experimental results show that there exist obvious differences between UTV in axial and radial directions. Based on Effective Medium Theory, it is found that anisotropic property of UTV is consistent with the change in strain of microcrack structure, revealing that the change in microcrack structure is one of the critical factors leading to UTV discrepancy. According to acoustic formation factor concept and fractal theory, a coupling model that can be capable of describing quantitative relationship between UTV and the external stress is built. Furthermore, a stress inversion method based on UTV in multiple directions is proposed and verified, which is capable of describing the entire sample buckling failure process well. This research can provide useful reference for understanding anisotropic characteristics of UTV in coal and rock samples during uniaxial compression process, and it has very important meaning for evaluating the stability of coal and rock mass using UTV.