Fragmentation characteristics and mechanical response of hard rock indented by cutting picks: Effects of confinement, spacing, and pre-grooving

• Unidirectional stress concentration exhibits a dual effect on rock fragmentation, initially enhancing then reducing indentation force and energy as horizontal stress increases. • Optimal pick spacing promotes radial crack coalescence, while too small spacing causes re-fragmentation and too large spacing leaves unbroken ridges. • Pre-cut grooves significantly reduce indentation force and specific energy, improving fragmentation efficiency, with diminishing returns beyond 10 mm depth. • A novel "stress-structure dual control" mechanism and "pre-drilling unloading-alternate stopping" mining scheme are proposed for deep resource extraction.