Effects of Flaw Geometry on the Fracturing Behavior of Rock-Like Materials Containing Two Arch-Like Parallelogram Flaws

Abstract

To increase understanding of the strength and failure mechanism of rocks with arch-like fractures generated in the overlying strata above a gob during coal mining, a series of uniaxial compression tests on rock-like specimens containing two preexisting parallelogram flaws at inclination angles varying from 45° to 75° were made using a rock mechanics servocontrolled testing system. Based on the experimental results, the effects of the inclination angles of two flaws having the same area on the mechanical parameters and fracturing process of the specimens were analyzed in detail. By adopting photographic monitoring, the crack initiation, propagation, coalescence, and failure modes in rock-like specimens were observed and characterized. The crack initiation stress and the second initiation stress were distinctly related to the flaw inclination angles, although the crack initiation stress presented a change trend generally similar to that of the crack second initiation stress with increasing flaw angle. Four modes of ultimate macroscopic failure morphology and the crack coalescence and failure modes of three types could be summarized. The research reported here could provide some theoretical support for the arch-like fracture evolution in the overburden during the excavation in underground engineering, especially in coal mining engineering.