Dynamic Mechanical Characteristics of Limestone Under Cyclic Impact of Various Confining Pressure

Studying the damage and disturbance of surrounding rocks in underground mine roadways under different confining pressures during cyclic blasting is crucial for ensuring sustainable mining practices. Representative samples of limestone from a mine roadway were drilled for conducting three-dimensional static–dynamic combined cyclic impact tests. The resulting fragments were scanned using electron microscopy to analyze their damage mechanisms and energy dissipation laws. The findings suggest that increasing the confining pressure can enhance the impact resistance of limestone. However, excessive confining pressure can deteriorate the internal damage of limestone, thereby reducing its impact resistance. Microscopic analysis of limestone fragment fracture morphology revealed two main fracture modes: brittle fracture and ductile fracture. During brittle fracture, regions rich in MgO₂ primarily exhibit transgranular fracture, while those rich in CaCO₃ mainly display intergranular fracture. Excessive confining pressure can induce a single fracture mode predominantly characterized by brittle fracture within the limestone interior, exacerbating its degree of fragmentation. The energy absorption rate and number of impacts during cyclic impact testing of limestone follow a quadratic function. The absorbed impact energy initially decreases and then increases with the increase in confining pressure. Properly increasing the confining pressure can decrease the absorption capacity of limestone, whereas excessive confining pressure will significantly increase the absorption capacity of limestone specimens.