Comparative Experimental Study of Fracture Mechanisms and Characteristics of Coal-like Materials under Quasi-Static and High-Pressure Air Blasting Fracturing

High-pressure air blasting is a burgeoning techniquefor anhydrousfracturing. A crucial prerequisite for the application of air blastingis to comprehend the distinctions between air blasting and quasi-staticfracturing, as well as the change in fracture control factors withvariations in blasting pressure. This research undertook experimentson coal-like material specimens with quasi-static fracturing and blastingfracturing with blast pressures ranging from 5 to 10 MPa, by utilizinga self-designed air fracturing experimental system. The fracturingmechanism and characteristics of specimens subjected to differentloading conditions were analyzed using a pressure sensor, high-speedcamera, and fractal theory. The following primary findings were obtained:The average fracture pressure under quasi-static loading was 3.269MPa, exhibiting similar absolute deviations. The pressure-timecurve of blast fracturing was found to undergo four distinct stages:pressure surge, pressure fallback, pressure maintenance, and pressureplummet. The duration of the pressure maintenance stage exhibiteda negative correlation with the blast pressure, ceasing to exist atpressures above 9 MPa. This suggests that the dynamic impact effectgradually supplants the dominant role of the air wedge effect. Quasi-staticfracturing formed single fractures, whereas blast fracturing tendedto generate complex fracture networks. The increase in blast pressurecould significantly enhance the complexity of the fracture networkin a logarithmic fashion. The fractal dimension of quasi-static fracturingwas slightly higher than that of 6 MPa blast fracturing, indicatingthe prevalence of quasi-static action under low blast pressure. Thesmash district increased exponentially as the blast pressure increased,and the average particle size decreased gradually. These investigationsprovide valuable insights for designing high-pressure air blastingfracturing procedures.