Dynamic response mechanism of rock-like materials with different shape holes

To reveal the cross-sectional shape effect of a deeply buried roadway under dynamic load, cement mortar rock-like material samples with five different hole shapes (rectangular, R, circular, C, straight wall arch, S, vertical, E-parallel to, and horizontal ellipse, E-perpendicular to) were prepared, and the dynamic response characteristics of the samples were studied by using the drop weight impact test system. The influence of hole shape was discussed from three aspects: strain time history curve, crack propagation process around the hole, and failure mode. The dynamic compressive strength and meso-cracking mechanism were analyzed by PFC2D. The results showed that the ultimate strain of the specimen with E-parallel to was the largest under the same impact load. The crack initiation position of the hole roof's macroscopic crack was in the middle. The cracks at the bottom of specimens with the R and S were more likely to extend downward from the corner point, while the other specimens extended downward from the middle of the bottom. The roof of R, S, and E-perpendicular to specimens was dominated by tensile-shear composite failure. In contrast, the tensile failure of the roof of C and E-parallel to specimens was more significant. The dynamic compressive strength of E-parallel to, S, C, R, and E-perpendicular to specimens decreased sequentially, therefore, the E-parallel to specimen had the best impact resistance. During the initial dynamic loading stage, the tensile stress was mainly concentrated at the roof of the hole, and the concentrated area was proportional to the transverse span of the upper boundary of the hole. When the stress was close to peak, the tensile stress gradually diffused to both sides of the specimen. In the post-peak stage, the rebound modulus of the E-parallel to and C samples was close to the elastic modulus, the plastic deformation was small, while the other samples showed a higher residual strain.