Effects of schistosity on rock fragmentation and associated energy dissipation under blasting

Drilling and blasting in foliated rock masses widely occur in tunnel engineering and mining operations. However, the effects of schistosity on rock fragmentation and energy dissipation behavior remain insufficiently understood. This study first conducts schist blast testing to investigate the influences of schistosity characteristics on rock fragmentation pattern and fragment size distribution, utilizing image processing to analyze the variations in fragment shape and fracture energy dissipation. Finite element models of schist blasting are then developed to simulate the successive process of detonation-induced stress propagation, crack network evolution and rock fragmentation. Blast testing and following image analysis reveal that schist fragments exhibit pronounced foliated features, with many fragments displaying platy shapes, and the average aspect ratio of rock fragments is primarily concentrated in the range of 0.5–0.7. When the schistosity is perpendicular to borehole and the proportion of harder rock matrix increases, the mean fragment size increases, the uniformity of fragment size distribution reduces, and thus the rock fragmentation performs worse. The mean aspect ratio of fragments increases with rounder rock fragments. Compared to blasting with schistosity perpendicular to borehole, blasting with schistosity parallel to borehole consumes more explosive energy, with an average increase of 27.28% in blast testing. Numerical simulations demonstrate that during the propagation of stress waves in schist, cyclic reflections occur at schistosity planes, mainly resulting in fracture and breakage in the weaker rock matrix. This leads to blast-induced cracks growing parallel to schistosity planes at intervals, forming flattened rock fragments with relatively small aspect ratios. The current findings suggest that schistosity perpendicular and parallel to borehole is unfavorable and favorable for rock fragmentation, respectively. Thus, in blasting engineering practice with simple layered structures, aligning the borehole with the dominant schistosity direction is an effective strategy for optimizing rock fragmentation performance, particularly when the harder rock matrix constitutes a large proportion.