Experimental Study on Dynamic Compressive Mechanical Properties of Shale in Western Hubei

The dynamic compression mechanical characteristics of the surrounding rock mass of the shale formation tunnel in western Hubei province need detailed exploration. A Split Hopkinson Pressure Bar(SHPB) and a high-speed camera were employed to conduct impact tests on shale samples at five different bedding angles(the angle between the direction of impact loading and the normal of the bedding planes of the specimen, including 0°, 30°, 45°, 60°, and 90°). Meanwhile, the research team also studied the influence mechanism of bedding angles, impact pressure, and strain rate on the dynamic compression mechanical characteristics and failure mode of shale with different dynamic loading strain rates under different impact pressures. The research results indicate that the dynamic compressive strength of shale has an approximately U-shaped pattern with increasing bedding angles under different impact pressures and strain rates. Among them, the shale with bedding angles of 0° and 90° has relatively higher compressive strength, while the shale with a bedding angle of 60° has the most minor compressive strength. Furthermore, the dynamic compressive strength of shale with different bedding angles increases as the impact pressure and strain rate increase. The macroscopic failure modes of shale are mainly divided into tensile failure, shear failure, and mixed failure. Significantly, the macroscopic failure modes of samples with bedding angles of 0° and 90° under different strain rates are mainly tensile failure. The primary macroscopic failure mode of the sample shows a transition process of shear failure mixed failure tensile failure' as the strain rate increases when the bedding angle is 30°. The primary macroscopic failure mode of the specimen evolves from shear failure to mixed failure as the strain rate increases when the bedding angle is 45° and 60°. The energy absorption ratio of shale samples first increases and then decreases as the bedding angle increases under the same impact pressure. Additionally, the energy absorption ratio and the degree of sample damage are simultaneously maximum as the bedding angle is 60°. The degree of fragmentation of shale samples with different bedding angles increases, and the energy absorption ratio gradually tends to be consistent as the impact pressure and strain rate increase.