Experimental study on dynamic crack growth and propagation characteristics of central hole double fracture shales under impact loading

It is greatly significant to evaluate the stability of the shales with characteristic defects that the propagation and crack initiation behavior under the dynamic impact. For studying the influence of bedding and preset cracks on the dynamic fracture characteristics of shales, the dynamic tensile mechanical test of cracked layered shales was operated using the Split Hopkinson Pressure Bar. Using high-speed photography technology to record this whole process of crack propagation and dynamic failure. According to the results, the bedding angles and pre-existing crack angles of the specimen affected the characteristics of crack initiation points, crack initiation angles, and propagation paths. As the pre-existing crack angle increases, the crack initiation points of shale specimens gradually shift from a pre-existing crack tip to a pre-set hole edge region. When these pre-existing crack angles increased, it is important to the influence of bedding angles on crack initiation angles. The cracks of the specimen mainly propagated along or across the bedding plane to both sides of the loading end. According to the crack growth and propagation characteristics, we divided the failure modes of the shale specimen into five typical modes. The study can supply some theoretical support for the actual exploitation of deep shale gas.