Experiment of influence of fractures on coal/rock acoustic velocity: with Carboniferous seams of Qinshui basin as example

In order to study the impact of fractures on the ultrasonic velocity, multi-azimuth ultrasonic velocity of coal were tested under the pressure similar to buried stratum in Qinshui basin. The experimental results shows that:(1) Fractures will reduce ultrasonic velocity, but when the confining pressure increases to 10 MPa, most of fractures are closed together, the velocity comes table; (2) orientation of fractures makes certain impact on acoustic propagation velocity. Along the fracture direction, acoustic wave goes the fastest, acoustic wave propagates the slowest perpendicular to the fracture direction. This research provides basic data to predict fractures in seams.