Influence of Opening Penetration Ratio on Mechanical Behavior and Fracture Characteristics of Sandstone Rock: Experimental and Numerical Studies

The natural non-penetrated openings in natural rock masses due to weathering and erosion and the artificial non-penetrated openings formed in deep mining and tunneling have significant effects on the stability and safety of rock engineering. Hence, the uniaxial compression test, 3D particle flow code (PFC3D) simulation, and digital image correlation (DIC) method are used to systematically investigate the influence of the opening penetration ratio (OPR) on the mechanical behaviors and fracture characteristics of rocks containing the non-penetrated opening. Further, the maximum principal strain/stress distributions around the opening on both sides of the specimen are compared to quantitatively analyze the effect of OPR on the crack initiation mechanism from the microscopic perspective. The results show that as OPR increases, the uniaxial compressive strength (UCS) and elastic modulus (E) of sandstone/numerical specimens show a linearly decrease law, and the failure mode exhibits a law of shear failure to tensile-shear mixed failure and then to shear failure. The fracture process analyses show that the two sides of specimens containing non-penetrated opening have different cracking characteristics and belong three-dimensional failure, while the specimen containing penetrated opening are two-dimensional failure. The stress/strain distribution around the opening is altered by the support effect in the non-opening part of specimens. Therefore, as the OPR increases, the crack initiation stress level decreases and the crack initiation crack type around the opening changes from the tensile-shear to tensile. Finally, implications of the study for fracture prevention in underground excavation engineering and early warning of instability in rock engineering are given. These findings enrich the study on the failure mechanism of rock masses containing defects, which is of great importance for rock engineering safety.