Effect of the Number of Free Faces on Excavated Volume, Advance, and Specific Charge in Model-Scale Single-Hole Blasting: Experiments and Numerical Simulations

Abstract A free face is an exposed, unconfined rock surface that allows blasted rock to move or expand freely upon detonation. The number of free faces fundamentally governs blasting performance in both surface and underground excavation, yet its effects have not been sufficiently quantified under controlled experimental and boundary conditions. This study quantified its influence on excavated volume, advance, and specific charge in single-hole blasting using scaled physical model tests and three-dimensional numerical simulations. Model-scale single-hole blasting tests were conducted on concrete specimens under two-free-face (2FF), three-free-face (3FF), and four-free-face (4FF) conditions, and the results were used to validate a three-dimensional numerical model, which was then used to examine the effects of burden, lateral burdens, and charge weight. The experimental results showed that the excavated volume increased by 9.7% and 25.1% under the 3FF and 4FF conditions relative to the 2FF baseline, with corresponding advance increases of 8.2% and 12.8%. For blast-pattern design, the numerical analyses identified an optimum spacing-to-burden ratio (S/B) of approximately 1.27 when advance was prioritized and approximately 2.2–2.3 when excavated volume was prioritized. The specific charge correction factors obtained from the simulations were 0.68 and 0.51 for the 3FF and 4FF conditions, in close agreement with previously proposed empirical values. Charge weight reduction analyses demonstrated that the charge weight can be reduced under both the 3FF and 4FF conditions while maintaining advance and breakout angle at or above the 2FF baseline.