Multi-scale analysis of stress-corrosion failure and anti-corrosion strategies for anchor bolts in Tashan coal mine.

Frequent failures of roadway anchor bolts in the roof-dripping zones of the Tashan coal mine endanger roadway stability and safety. To clarify the stress-corrosion cracking (SCC) mechanism and identify mitigation strategies, we combined water-chemistry analysis, multi-scale fractography, slow strain-rate tensile (SSRT) testing, and on-site anti-corrosion trials. Mine water showed weak alkalinity (pH 7.06-7.82), high mineralization (970-1980 mg L- 1), and elevated Cl⁻/SO42- suggesting strong pitting tendencies. Failed field bolts displayed limited necking, step-like fracture sections, and dendritic crack networks initiated at pits. SSRT tests in simulated solution revealed marked reductions in plasticity and strength compared to air; the SCC susceptibility index (ISCC), based on elongation, rose from 15.76% at 10- 3 s- 1 to 59.23% at 10- 7 s- 1, demonstrating greater SCC sensitivity at lower strain rates. SEM confirmed reduced dimples, deep pits, and reticulated cracking. A four-stage mechanism was proposed: pit initiation, crack nucleation via anodic dissolution under stress, occluded-cell-assisted propagation, and unstable fracture, often intergranular. Field trials with hot-dip-galvanized bolts showed intact surfaces and stable axial-force responses for over 30 days in dripping zones, confirming both barrier and sacrificial-anode protection. These results provide mechanistic insights and may offer practical guidance for improving corrosion-resistant anchor bolt design in aggressive underground environments, while recognizing that long-term monitoring and broader protective strategies remain necessary.