Investigation on the Deformation and Failure Characteristics of Shale Samples Containing Circular Hole considering the Bedding Angle Effect under Uniaxial Compression

The drilling and blasting method (DBM) is widely used in the excavation of tunnel engineering, and it is essential to first drill circular holes. This paper experimentally explored the influence of bedding angles on crack propagation of shale containing a circular hole. Specifically, the uniaxial compression tests were carried out on shale samples with a single prefabricated hole combined with digital image correlation technology (DIC) to obtain the real-time deformation process near the macro damage. The results show that the peak strength, global shear strain field, failure mode around the circular hole and macro crack failure mode of shale with prefabricated circular hole are closely related to the bedding dip angle. The strength generally increases with the decrease of the bedding angle. Two transitions of failure mode were observed at the point of 45° and 75°: tensile shear mixed failure around the circular hole (less than 45°) first transits into no damage around the circular hole (60° and 70°), and then, tensile failure occurs around the circular hole (90°). In addition, for the cases of 60° and 75°, tensile failure away from the circular hole occurs along the weak surface of bedding, while for the other cases, the tensile failure through the circular hole mainly occurs. These findings have implied that the bedding angle is one essential parameter that needs to be considered for the stability of tunnel surrounding rock.