Dynamic Mechanical Properties and Failure Characteristics of Layered Composite Rock Containing a Tunnel-Shaped Hole

To investigate the dynamic mechanical properties and failure characteristics of the surrounding rock mass in layered strata, composite specimens with a circular hole and a horseshoe-shaped hole were prepared using rock-like materials. Then, the split Hopkinson pressure bar (SHPB) test system and digital image correlation (DIC) technology were employed to conduct relevant experiments and analyses. The experimental results indicate that the influence of cross-sectional shape differences on the dynamic mechanical properties of composite specimens cannot be ignored. Compared to composite specimens with a circular hole, the composite specimens with a horseshoe-shaped hole have a more significant hindrance to wave propagation, and their dynamic compressive strength (DCS) and elastic deformation ability are also lower. In addition, the bedding inclination θ also has a significant impact on the dynamic mechanical properties. With increasing bedding inclination θ, the DCS of composite specimens shows a trend of increasing–decreasing-increasing. Moreover, the energy proportion was analyzed according to the experimental results. This study also investigated the failure characteristics of tunnels surrounding rock in layered strata. For composite specimens with a circular hole, four types of cracking and their distribution related to the dip angle of bedding planes were summarized. For composite specimens with a horseshoe-shaped hole, six types of cracking and their distribution versus the bedding inclination were summarized.