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Influence of fissure–hole offset on the temporal evolution of cracking and failure mechanisms in red sandstone under compression–shear loading: Experimental and numerical study
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DOI：10.1016/j.tafmec.2026.105861.png)
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Abstract
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To reveal the controlling effect of the relative offset distance between fissures and a hole on the spatiotemporal evolution of cracks and the failure mechanism of brittle rock under compression–shear loading, natural red sandstone specimens containing a single circular hole and two prefabricated fissures were prepared, with fissure–hole offset distances of 0, 10, 20, and 30 mm, and subjected to 45° compression–shear loading tests. Acoustic emission (AE), digital image correlation (DIC), and the discrete element method (DEM) were comprehensively employed to analyze crack initiation, propagation, coalescence, and instability in the specimens at three scales: macroscopic mechanical response, surface strain localization, and mesoscopic bond failure. The results showed that, as the fissure–hole offset distance increased from 0 to 30 mm, the peak load of the specimens increased from 74.08 to 108.08 kN, representing an increase of 45.90%, while the peak displacement and pre-peak energy-storage capacity generally increased. Crack evolution gradually changed from rapid local coalescence along the short rock bridge between the hole and fissures at small offset distances to multiple-site initiation, deflection, branching, and large-scale coalescence. AE activity was mainly concentrated in the unstable crack-propagation stage and the post-peak instability stage, while the b-value exhibited an overall decreasing trend during loading and showed low-value fluctuations before instability. The RA–AF and DIC analyses showed that local shear slip first occurred near the hole wall and fissure tips during the initial loading stage, followed by a continuous increase in tensile deformation, with tensile cracks gradually controlling crack propagation and macroscopic coalescence, ultimately forming a mixed tensile–shear failure mode dominated by tensile failure and jointly involving local shear slip and fracture-surface friction. The DEM results further showed that the fissure–hole offset distance regulated the degree of superposition between the stress fields of the hole and fissures, the crack coalescence path, and the mode of energy release by changing the spatial relationship between the circular hole and the inclined principal-stress transfer band. The findings can provide a theoretical reference for instability-risk identification, monitoring and early warning, and support-design optimization in zones containing coupled fissure–hole defects within the surrounding rock of underground caverns and tunnels.
Keywords:
compression–shear loading
coupled fissure–hole defects
relative offset distance
acoustic emission
digital image correlation
particle flow method
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