Investigation on Damage and Failure Mechanisms of Roadway Surrounding Rock Triggered by Dynamic–Static Combined Loads

The stress state of roadway surrounding rock is often quasi-dynamic, which is usually subjected to static–dynamic loads. The aim of this study was to investigate the damage process and mechanisms of roadway surrounding rock under combined static–dynamic loads. Uniaxial compression tests were conducted on natural cyan sandstone cube specimens (100 mm × 100 mm × 100 mm) with pre-fabricated circular cavities using a self-developed physical simulation test system for static–dynamic loads of coal–rock masses. The quasi-dynamic loads were set as sinusoidal waves while the compression tests were performed for various frequencies and amplitudes. The results indicated that the damage process of the sandstone specimens in a pre-fabricated circular cavity under combined static–dynamic loads was characterized by temporal synergy. Additionally, the damage process can be divided into three phases: fragments ejection, spall deformation, and destruction. Furthermore, as the dynamic frequency increased, the deterioration degree and average dynamic elastic modulus increased while the dissipated energy decreased. The damage severity of the rocks was also reduced. Conversely, as the dynamic amplitude increased, the average dynamic Poisson’s ratio and the dissipated energy increased while the average dynamic elastic modulus decreased. Consequently, the fracture development and specimen damage were severe.