Rockburst characteristics of gypsum-like rocks after fatigue cyclic loading

In underground engineering applications, surrounding rock is often subjected to dynamic disturbances, such as vehicle loading, earthquakes, blasting, or other vibrations. Consequently, fatigue damage, collapse, and rock burst may happen. In this study, a dynamic fatigue rock mechanics testing machine was used to study the rock burst characteristics of gypsum rocks before and after cyclic loading. With increasing fatigue frequency, the energy consumed by each loading and unloading cycle and the accumulated fatigue damage gradually increase. Hysteresis loops of the stress–strain curve gradually transition from elongated to near circular, and the area of loops gradually increases. With increasing loading time, the damage variable of the sample increases, while the growth rate decreases, which conforms to a logarithmic growth law. At a central value of fatigue loading C = 9 MPa, the uniaxial compressive strength of specimens weakened, but increased in response to high frequency fatigue loading. For C = 18 MPa, the jitter adjustment trend in the post-peak strength phase became apparent, which led to a decrease of rock burst trend. At C = 27 MPa, the rock burst tendency increased significantly. The acoustic emission characteristics correspond well with both the loading process and full stress-time curves. Several indexes (i.e., impact energy, elastic energy, and elastic modulus) follow a quadratic nonlinear relationship with loading frequency, which can be used to predict rock burst tendency.