Ultrasonic and CT scanning analysis of coal-rock mass under the primary bedding structure

In order to study the influence of the primary bedding structure on wave velocity and mechanical properties of coal-rock mass, multilayer and multi-directional ultrasonic and CT scanning tests were carried out in laboratory. It also aims to improve the accuracy, rapidity and convenience of obtaining the wave velocity and mechanical parameters of coal-rock mass in laboratory. Based on the ultrasonic test, the characteristics of wave velocity and wave velocity ratio at different layers of coal-rock mass under the primary bedding dip angle were obtained. Combined with CT scanning and 3D reconstruction technology, the calculation method of CT gray mean value in different layers was proposed by using the data of the gray frequency of coal and rock. And the variation law of gray value and coal and rock content of coal-rock mass in different layers under different primary bedding dip angle was obtained. Meanwhile, the relationships between CT gray mean value and wave velocity, mechanical parameters of coal-rock mass were established. Considering the effect of bedding dip angle and the content of coal and rock, the calculation model of longitudinal wave velocity of coal-rock mass was constructed. Then the correctness of the model is verified by comparing the test data. The results show that: ① the wave velocity and wave velocity ratio of coal-rock mass with primary bedding are linearly related to bedding dip angle; with the increase of bedding dip angle, the longitudinal wave velocity of coal-rock mass decreases linearly, while the distribution range of wave velocity ratio expands; ② the mean wave velocity of CT is linearly correlated under different bedding dip angles, and the wave velocity of coal-rock mass increases linearly with the increases of CT gray mean value; ③ the density of coal-rock mass increases linearly with the increase of CT gray mean value, the dynamic elastic modulus and shear modulus of coal-rock mass have third order polynomial relationships with the mean value of CT gray level, and they tend to increase with the increase of the mean value of CT gray level; ④ compared with the bedding dip angle, the wave velocity of coal-rock mass is more sensitive to the coal and rock content, and the wave velocity changes largest during the content of coal and rock similar.