Cracking behavior and mechanism of sandstone containing a pre-cut hole under combined static and dynamic loading

• A new system for rock under combined static and impact loading was developed.
• The initiation and propagation of cracks under coupled loads were observed.
• The impact failure area of rock under coupled loads was quantified.
• The influence mechanism of lateral static load on impact crater was revealed.

This paper experimentally investigates the fracture process of sandstone specimen containing a pre-cut hole under coupled static and dynamic loads. A new experimental system was developed, consisting of a newly designed static loading device, an improved split Hopkinson pressure bar and a high speed video camera. Tests on sandstone specimens under combined loading indicate that static loading significantly affects the initiation of surface cracks, as well as the shape and size of the failure zone. Only under dynamic loading, the locations of surface crack initiation are randomly distributed, and specimens eventually form craters with circular openings. After the application of additional lateral static loads, surface cracks parallel to the static load start to appear in the specimen centers. These crater openings are elliptical in shape with a long ellipse axis that coincides with the direction of static loading. In addition, the crater volume increases under greater static and dynamic loads, and both static and dynamic loads promote rock failure, which is relevant for understanding deep underground engineering efforts. Finally, the mechanism by which static loads influence the impact damage of a rock under the experimental conditions is discussed. The results show that the combined effects of stress concentration around the pre-cut hole and far-field strain generated by static loading promote rock impact damage, which helps to explain the experimentally observed phenomena.