Lithology-dependent energy partitioning and multi-hole fragmentation control in blasting of hard and soft rocks

Lithology-dependent blasting fragmentation remains a critical challenge in rock engineering, with representative hard- and soft-rock cases exhibiting contrasting damage and fragmentation responses. This study conceptualizes these responses as a lithology-controlled energy partitioning problem linking single-hole energy transmission and damage evolution to multi-hole fracture coalescence and fragmentation control. A fluid-structure interaction model was established in ANSYS/LS-DYNA and validated against blasting tests and dynamic-response characteristics. The effects of charge radius, borehole radius, and borehole medium were examined to clarify how lithology controls energy partitioning between near-borehole crushing and crack extension. The results indicate that soft rock is more sensitive to energy input, with a crushing-ratio growth coefficient 1.52 times that of hard rock, whereas hard rock is more sensitive to radial-decoupling-induced weakening of borehole-wall loading. High-transmission borehole media promote crack extension in hard rock but intensify near-borehole crushing in soft rock. These differences persist in multi-hole blasting: hard rock develops more concentrated inter-hole stress-wave interactions and straighter presplit fractures, whereas soft rock shows stronger near-borehole dissipation and more diffuse non-target damage, with fractal dimension used as an auxiliary evaluation tool for fracture complexity. In production blasting, diagonal delayed initiation facilitates crack coalescence and reduces oversized fragments, with the three-parameter generalized extreme value (GEV) distribution used to characterize fragmentation. A multi-index evaluation criterion and a staggered borehole pattern with distributed low-charge multi-hole loading were proposed to coordinate damage control, fragment size, and fragmentation uniformity in soft rock.