Experimental and numerical studies of brittle rock-like specimens with unfilled cross fissures under uniaxial compression

Unfilled cross fissures are defects that widely exist in natural rock, and their existence has a significant impact on the mechanical behaviour of the rock. To investigate the effects of different fissure cross angles (α) and fissure lengths (Lh and Li) on the macroscopic mechanical behaviour, crack development law, ultimate failure mode and final crack distribution of preflawed rock-like specimens, four groups of rock-like material specimens with unfilled cross fissures are fabricated and subjected to uniaxial compression tests using digital image correlation (DIC) technology monitoring, computerized tomography (CT) scanning, and three-dimensional particle coding (PFC3D). These results reveal that the uniaxial compression strength (UCS) and elastic modulus (E) of the specimens all show a nonlinear increase–decrease-increase changing law with increasing α and are all weakened to a certain extent. However, the peak strain (εf) of the specimens shows a nonlinear decrease-increase changing law with increasing α. Based on DIC technology, the influence of α and Lh and Li on the crack development law can be observed. These three parameters mainly affect the crack initiation location of all specimens, and two kinds of ultimate failure modes (shear-tensile mode and tensile mode) can be observed. Based on CT scanning and PFC3D numerical simulation, it can be seen that the final crack system inside the specimen is a 3D system, and the analytical method used to analyse it should contain 2D (DIC technology) and 3D aspects (CT scanning and PFC3D simulation) at the same time.