Study on the most optimistic hole spacing for double-hole blasting under high in-situ stresses

As a typical contour blasting technique，presplitting blasting is widely used in rock engineering excavation for foundation pits，highway slopes，open-pit and underground mines. Due to the influence of in-situ stress，deep presplitting blasting requires small-diameter fully coupled charges and closely spaced holes，which affects construction timelines and significantly increases costs. This study aims to investigate the correlation between optimal hole spacing and radial decoupling coefficients under high in-situ stress through theoretical derivation and numerical analysis. A double-hole presplitting blasting model is established using linear elastic theory，incorporating the stress wave superposition effect. This model determines the optimal relationship curves for hole spacing and radial decoupling coefficients under different high in-situ stresses. Using the self-developed OpenFDEM software，simulations are conducted to assess the expansion of the blasting fragmentation zone and fracture zone under various stress conditions and radial decoupling charges. The results indicate that the stress wave superposition effect promotes crack penetration. At low stress conditions，a lower decoupling coefficient significantly enhances crack extension. However，it also increases the density and extent of fracture branching. This enlarges the damage zone and hinders the formation of pre-splitting cracks. As in-situ stress increases，the influence of the stress wave superposition effect diminishes. This further affects the pre-splitting cracks formation in double-hole blasting. This paper proposes optimal hole spacing values that fully consider the interaction between high in-situ stress and stress wave superposition effects，providing important references for enhancing pre-splitting cracks formation in double-hole blasting.