Mechanical properties and risk characterization of surrounding rocks containing various blocks of arch-shaped holes under biaxial compression

In most rock engineering, the rock mass was cut into different blocks by natural structural planes, and the stability of underground openings was affected by the type, number, position and mechanical properties of rock blocks. In this study, the biaxial compression tests were conducted using rock-like material specimens with prefabricated arch-shaped holes and different types of blocks, and the failure and crack propagation properties of surrounding rocks were studied. Firstly, the location and danger degree of blocks in rock mass were classified, and the rock block danger analysis (BDA) method was proposed. Secondly, the support effect on the stability of surrounding rocks with different blocks was studied. Then, the deformation, strength, crack area ratio, and debris distribution characteristics of specimens were analyzed. Finally, the reasonable support schemes were proposed for surrounding rocks with different types and sizes of blocks. The test results showed that the sigma-epsilon curve of holed rocks was similar to that of intact rocks, and the micro-cracks evolved into macro-cracks at crack destabilization expansion stage, followed by large deformation of whole specimens and spalling. Under support condition, as the block size increased, the crack area ratio decreased and the stability of holed specimens improved. Furthermore, the biaxial compressive strength of the surrounding rock and the stability of the holed specimens decreased as the block danger coefficients increased.