Investigating the effects of non-persistent cracks' parameters on the rock fragmentation mechanism underneath the U shape cutters using experimental tests and numerical simulations with PFC2D

This paper aims to study the fracture mechanism of rocks under the 'u' shape cutters considering the effects of crack (pre-existing crack) distances, crack spacing and crack inclination angles. The effects of loading rates on the rock fragmentation underneath these cutters have been also studied. For this purpose, nine experimental samples with dimensions of 5 cmx10 cmx10 cm consisting of the non-persistent cracks were prepared. The first three specimens' sets had one non-persistent crack (pre-existing crack) with a length of 2 cm and angularity of 0 degrees, 45 degrees, and 90 degrees. The spacing between the crack and the "u" shape cutter was 2 cm. The second three specimens" set had one non-persistent crack with a length of 2 cm and angularity of 0 degrees, 45 degrees, and 90 degrees but the spacing between pre-existing crack and the "u" shape cutter was 4 cm. The third three specimens' set has two non-persistent cracks with lengths of 2 cm and angularity of 0 degrees, 45 degrees and 90 degrees. The spacing between the upper crack and the "u" shape cutter was 2 cm and the spacing between the lower crack and the upper crack was 2 cm. The samples were tested under a loading rate of 0.005 mm/s. concurrent with the experimental investigation. The numerical simulations were performed on the modeled samples with non-persistent cracks using PFC2D. These models were tested under three different loading rates of 0.005 mm/s, 0.01 mm/sec and 0.02 mm/sec. These results show that the crack number, crack spacing, crack angularity, and loading rate has important effects on the crack growth mechanism in the rocks underneath the "u" shape cutters. In addition, the failure modes and the fracture patterns in the experimental tests and numerical simulations are similar to one another showing the validity and accuracy of the current study.