Influence of free surface width on blasting damage in open stope mining in narrow vein orebodies

Abstract

Underground narrow veins, typically less than 2–3 m thick but rich in precious metals, hold significant economic value. However, the confined free surface in the open stope poses substantial challenges for long-hole blasting, often leading to overbreak and underbreak, emphasising the need for optimising blasting parameters. To address this, understanding the influence of free surface width on blasting performance becomes critical. Therefore, a modified method based on the Scaled Heelan solution was employed to comprehensively investigate this influence, particularly its relationship with burden, velocity of detonation (VOD), and initiation positions. The indicators considered include blasting damage and fragment size distribution. The analysis allows the following conclusions: (1) both the damage volume and the fragment size are positively correlated with the width of the free surface within a certain range; (2) for a fixed free surface width, damage volume and fragment size increase with burden within an appropriate range, but an excessive burden prevents a blasting crater formation; (3) higher VOD does not always result in better fragmentation near the blasthole, and an optimal VOD lies approximately between the velocity of P- and S-wave; (4) the axial damage distribution depends on the initiation position but with minimal impact on radial damage. These findings provide a theoretical basis for burden and spacing design in narrow-vein open stoping and thereby contribute to improved blasting fragmentation efficiency.