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 technique for anhydrous fracturing. A crucial prerequisite for the application of air blasting is to comprehend the distinctions between air blasting and quasi-static fracturing, as well as the change in fracture control factors with variations in blasting pressure. This research undertook experiments on coal-like material specimens with quasi-static fracturing and blasting fracturing with blast pressures ranging from 5 to 10 MPa, by utilizing a self-designed air fracturing experimental system. The fracturing mechanism and characteristics of specimens subjected to different loading conditions were analyzed using a pressure sensor, high-speed camera, and fractal theory. The following primary findings were obtained: The average fracture pressure under quasi-static loading was 3.269 MPa, exhibiting similar absolute deviations. The pressure–time curve of blast fracturing was found to undergo four distinct stages: pressure surge, pressure fallback, pressure maintenance, and pressure plummet. The duration of the pressure maintenance stage exhibited a negative correlation with the blast pressure, ceasing to exist at pressures above 9 MPa. This suggests that the dynamic impact effect gradually supplants the dominant role of the air wedge effect. Quasi-static fracturing formed single fractures, whereas blast fracturing tended to generate complex fracture networks. The increase in blast pressure could significantly enhance the complexity of the fracture network in a logarithmic fashion. The fractal dimension of quasi-static fracturing was slightly higher than that of 6 MPa blast fracturing, indicating the prevalence of quasi-static action under low blast pressure. The smash district increased exponentially as the blast pressure increased, and the average particle size decreased gradually. These investigations provide valuable insights for designing high-pressure air blasting fracturing procedures.