An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

Abstract

Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures. In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures (a horizontal fissure and an inclined fissure) were created by inserting steel during molding the model specimen. Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servo-controlled testing system. The peak strength and Young’s modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from $$0^{\circ }$$ to $$75^{\circ }$$ . In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process. Moreover, acoustic emission (AE) monitoring technique was also used to obtain the AE evolution characteristic of pre-fissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up: when a new crack was initiated or a crack coalescence occurred, the corresponding axial stress dropped in the axial stress–time curve and a big AE event could be observed simultaneously. Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures. In the present study, two unparallel fissures (a horizontal fissure and an inclined fissure) were created by inserting steel during molding of the model specimens, which were fabricated by cement, sand, and water. All specimens were tested under uniaxial compression. Photographic monitoring was adopted to capture images during the entire deformation to investigate the crack initiation, propagation, and coalescence process. Moreover, the acoustic emission (AE) monitoring technique was also used to obtain the AE evolution characteristics. Finally, the mechanism of crack propagation under microscopic observation was discussed. Fig: AE counts and crack evolution process of rock-like material specimen containing two unparallel fissures for $$\alpha = 30^{\circ }$$