A feasibility study on confinement effect on blasting performance in narrow vein mining through numerical modelling

Due to the limited free face in narrow-vein stoping, blasting is usually subjected to excessive confinement effect that often result in difficulties in ore loss and dilution. The aim of this study is to analyze the blasting confinement mechanism in narrow-vein mining, and to quantitatively define the confinement effect The PFC and LS-DYNA numerical modelling programs are combined to investigate the effect of blasting-induced stress waves and detonation gas effects. A confinement coefficient in narrow-vein mining is introduced and defined as the ratio of the blasting crater volume or area formed in an infinite free face to that in a confined face. The blasting confinement coefficient is used to rate the confinement severity. On this basis, the effects of minable width and burden on the confinement coefficient are analyzed. The numerical simulation results indicate that the confinement coefficient decreases with increasing minable width for a given burden. The relationship between the minable width and the confinement coefficient can be described by a first-order exponential decay function. For a given minable width, the confinement coefficient increases with increasing burden. The relationship between the burden and the confinement coefficient can be expressed by a first-order exponential growth function. Based on the numerical modelling results, a design chart for the blasting confinement effect in narrow-vein mining is introduced as a guide for preliminary design of narrow vein blasting to optimize production by reducing overbreak (dilution) and underbreak (ore loss).