Overview “O-pitblast Crack” refers to a specific failure mode affecting shotcrete, concrete linings, or rock-support interfaces where a ring- or O-shaped (annular) crack forms around an excavation, tunnel invert, or lining element. The crack commonly appears as a circumferential separation (an “O” or horseshoe) and can propagate due to a combination of stress redistribution, material shrinkage, thermal effects, water pressure, poor bond between support and substrate, or repeated dynamic loading (blasting, vibration). It’s most often reported in underground mining, tunneling, and steep-cut slope shotcrete applications where pit geometry, sequencing, and support timing produce concentrated tensile stresses.