Factors Controlling Cuttability of Pre-Fractured Hard Rock: Insights from Conical-Pick Indentation Tests

Pre-fracturing is a promising approach for improving rock-breaking efficiency, reducing cutting resistance, and mitigating mechanical wear in the mechanical excavation of hard rock. However, the cuttability of hard rock under the combined effects of pre-existing weak surfaces, in situ stress, and lithology remains poorly understood. To investigate these coupled effects, true-triaxial conical-pick indentation tests were conducted on pre-fractured rocks of different lithologies under equal and unequal lateral stress conditions. Cutting load, specific energy, acoustic-emission activity, and failure morphology were examined to characterize the fragmentation process and crack evolution. Results show that rock properties govern the cuttability, whereas the lateral stress state controls crack initiation, deflection, and coalescence. Under equal lateral stresses, increasing confinement suppresses crack opening and enhances the load-bearing capacity of the crushed–compacted zone, while its effect on cuttability is non-monotonic and depends on the stress-to-strength ratio. In contrast, lateral-stress asymmetry preferentially directs cutting-induced cracks toward the lower-stress side and generally reduces cutting load and specific energy. When the crack grows toward a pre-existing fracture or free surface, the rock bridge becomes shorter and the rock block breaks away more easily. In addition, the effect of stress redistribution is stronger in lower-strength rocks. A cutting-path optimization strategy is proposed to improve excavation efficiency by maintaining favorable lateral stress conditions during cutting. This study provides a mechanistic basis for pre-fracturing and cutting-path design, supporting more efficient mechanical extraction of hard-rock mineral resources.