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<p>In rock engineering, stress redistribution under external loads drives the growth of critical microcracks, often triggering catastrophic failure. Understanding the cross-scale relationship between micro-damage evolution and macro-fracture is essential for rock failure analysis. This study established a series of grain-based discrete element models (DEMs) for various hard rocks by integrating mineral composition analysis and surface image processing, in which the grain size, shape and distribution were explicitly considered. A systematic investigation was conducted on how pre-existing microcracks affect tensile-to-shear crack ratios, transgranular/intergranular crack propagation patterns, and peak strength characteristics under compression and tension. Results show that failure patterns are primarily governed by intrinsic mineral composition, while pre-existing cracks serve as initial defects affecting crack initiation location and density. Under compression, shear cracks dominate the rock (accounting for 76–84% of the total cracks), while tensile cracks prevail (constituting 57–68%) within the fracture zone under tension. The presence of pre-existing micro-cracks does not change the dominance of the tensile or shear cracks in hard rocks. The height of the tensile zone of Brazilian discs decreases with increasing mineralogical complexity, and the specimens exhibit larger tensile zones if pre-existing cracks are considered. Intergranular cracks dominate under compression (60–73%), whereas transgranular cracks prevail in indirect tension (52–63%). Although pre-existing microcracks elevate crack density, they preserve rather than alter these failure modes. Both compressive and tensile strengths are reduced by pre-existing microcracks, with the extent of reduction depending on the lithology and microcrack density.</p>

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Effects of Pre-existing Microcracks on the Cracking Process and Damage Mechanism of Hard Rocks via Image-Based DEM Modeling

  • 期刊论文

  • 发表日期：

    2026年2月6日

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  • Qihao Zhang,
  • Zhenghu Zhang,
  • Na Wu,
  • Jie Feng,
  • Lei Zhu

摘要

In rock engineering, stress redistribution under external loads drives the growth of critical microcracks, often triggering catastrophic failure. Understanding the cross-scale relationship between micro-damage evolution and macro-fracture is essential for rock failure analysis. This study established a series of grain-based discrete element models (DEMs) for various hard rocks by integrating mineral composition analysis and surface image processing, in which the grain size, shape and distribution were explicitly considered. A systematic investigation was conducted on how pre-existing microcracks affect tensile-to-shear crack ratios, transgranular/intergranular crack propagation patterns, and peak strength characteristics under compression and tension. Results show that failure patterns are primarily governed by intrinsic mineral composition, while pre-existing cracks serve as initial defects affecting crack initiation location and density. Under compression, shear cracks dominate the rock (accounting for 76–84% of the total cracks), while tensile cracks prevail (constituting 57–68%) within the fracture zone under tension. The presence of pre-existing micro-cracks does not change the dominance of the tensile or shear cracks in hard rocks. The height of the tensile zone of Brazilian discs decreases with increasing mineralogical complexity, and the specimens exhibit larger tensile zones if pre-existing cracks are considered. Intergranular cracks dominate under compression (60–73%), whereas transgranular cracks prevail in indirect tension (52–63%). Although pre-existing microcracks elevate crack density, they preserve rather than alter these failure modes. Both compressive and tensile strengths are reduced by pre-existing microcracks, with the extent of reduction depending on the lithology and microcrack density.