The influence of impacting orientations and tunnel filled on the fracture characteristic of crack.

• Crack parameter test meter was applied in crack propagation speed calculation. • A large specimen with tunnel was used to calculate rock dynamic fracture toughness. • The crack growth behavior outside the roadway under different impact loading directions was studied. • Stress wave and fracture mechanics theories were used to explain the interaction mechanism between cracks and tunnel. The backfilling of the tunnel is crucial for the stability of the goaf. To investigate the differences in crack propagation behavior before and after tunnel backfilling under different impact directions, a large rectangular plate LSCSC model was conducted. A crack parameter test meter was used to monitor the crack expansion behavior of pre-cracks under dynamic load in real time. Subsequently, the AUTODYN and ABAQUS software were used to simulate the crack propagation path and dynamic fracture toughness, and the following conclusions were obtained. The presence or absence of tunnel backfilling does not affect the crack propagation path, and the primary critical areas of the surrounding rock remain essentially the same. But have significant influences on crack propagation speed and fracture toughness. After backfilling, the crack propagation speed decreases significantly, and there is a noticeable crack-stopping phenomenon during the interconnection process. In addition, the influence of different wave impedance materials on the fracture behavior of cracks varies. In the selected filling material used in this paper, the initiation fracture toughness of the cracks increases by 45 %, and the average propagation toughness increases by 50 %. [ABSTRACT FROM AUTHOR]