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

Efficient hard-rock fragmentation remains a critical challenge in mechanized mining. This study designed an adjustable-spacing mold and conducted double cutting pick indentation tests on granite. Mechanical responses and fragmentation characteristics under varying horizontal stresses, pick spacings, and groove depths were systematically analyzed. Unidirectional stress concentration altered the rock fragmentation modes, exhibiting a dual effect on the fragmentation process. The maximum indentation force ( F max ), indentation hardness index ( IHI ), indentation modulus ( IM ), and indentation energy ( W ) initially increased and then decreased with rising horizontal stress. Appropriate spacing promoted radial crack coalescence, whereas too small a spacing (20 mm) caused repetitive re-fragmentation of rock chips, and too large a spacing (50 mm) resulted in unbroken ridges. Pre-cut grooves weakened the rock, reducing F max and specific energy ( SE ), thus improving fragmentation efficiency, although the improvement slowed beyond a 10-mm groove depth. Based on the results and rock-mass conditioning assisted fragmentation mechanism, a “stress-structure dual control” assisted fragmentation mechanism was proposed, and a “pre-drilling unloading − alternate stopping” mining scheme was exploratory designed. This approach creates favorable conditions for rock fragmentation by reducing stress levels and rock mass integrity in target zones, providing theoretical support and an engineering paradigm for mecheanized mining of deep resources.