Study on static and dynamic mechanical properties of fractured coal under dynamic disturbance based on PFC simulation

In practical engineering, dynamic disturbance causes irreversible damage to fractured coal. To investigate the static and dynamic mechanical properties of fractured coal under dynamic disturbance, the particle flow code (PFC) was employed to establish a discrete element numerical model of fractured coal considering dynamic disturbance. Static uniaxial compression tests and dynamic impact tests were conducted on the numerical model to analyze the influence laws of different prefabricated fracture lengths, different prefabricated fracture distribution patterns, and different impact loads on the stress-strain curve characteristics, mechanical parameters, and failure characteristics of fractured coal. The results show that: with the increase of prefabricated fracture length, the static and dynamic compressive strengths of fractured coal decrease continuously, and the decrease amplitude of dynamic compressive strength is significantly larger than that of static compressive strength when the prefabricated fracture length is long. When the prefabricated fracture inclination angle is 30°, increasing the length of the prefabricated fracture has a significant impact on the mechanical properties of the fractured coal. Under the same prefabricated fracture length, the static peak strength of fractured coal with cross fractures is lower than that of fractured coal with parallel double fractures, indicating that the fracture distribution pattern has a certain influence on the compressive strength of fractured coal. With the increase of dynamic disturbance times, the continuous increase of the initial damage degree of fractured coal will leads to earlier instability and failure. The dynamic compressive strength of fractured coal increases continuously with the increase of impact load, and fractured coal show brittle crushing failure at final destruction. The increase of impact load significantly raises the number of microcracks with medium inclination angles and causes the failure mode of fractured coal to gradually shift from tensile splitting failure to tensile-shear mixed failure.