Failure modes and process of tunnels reinforced by rockbolts under top explosion

Based on model tests and numerical analysis, failure modes and process under top explosion are studied. According to the results of the model tests, the tunnels reinforced by rockbolts under top explosion have four kinds of failure modes, that is tensile failure, shearing failure, compressive failure, compressive and shearing failure. By analyzing the experimental profile and the propagation rules of stress waves, when the stress waves reach the surface of the tunnel, spalling failure will appear, which may make similar half elliptical rock mass peel off. Both sides of the tunnel produce cracks easily. With the increase of blast load, if the anchor reinforcement strength is weak, local collapse will appear, and once the intensity of anchorage zone is large, it will lead to collapse of the tunnel from spandrel to explosion center. Finally, in accordance with the action process of stress waves, the stress distribution and the development process of plastic zone, failure modes and process are further discussed through numerical analysis.