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

Abstract

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 exploratorily 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 mechanized mining of deep resources.

Keywords

Hard rock fragmentation / Indentation tests / Cutting pick / Rock mass conditioning / Mechanized mining scheme

CRediT authorship contribution statement

Pingkuang Luo: Writing – review & editing, Writing – original draft, Methodology, Investigation, Formal analysis. Diyuan Li: Supervision, Resources, Project administration, Funding acquisition, Data curation. Hiroyuki Noda: Supervision, Methodology, Investigation, Conceptualization. Ruiyuan Li: Supervision, Resources, Project administration, Funding acquisition, Data curation.

Data availability

Data will be made available on request.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors would like to thank the National Major Science and Technology Project for Deep Earth Exploration (No. 2025ZD1008301) and National Natural Science Foundation of China (No. 52374153) for the financial support. The author acknowledges the support of the China Scholarship Council. In addition, the authors thanks to Mr. Hao Gong, Jie Tao and Jiaming Yang for the preparation of the experimental.

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