Assessing the stability of high-level pillars in deeply-buried metal mines stabilized using cemented backfill

Abstract

Obtaining a reasonable assessment of the stability of high-level pillars stabilized using cemented backfill is particularly important when designing deeply-buried metal mines. This research determined the average vertical stress in high-level pillars in deeply-buried metal mines and also their strength when subjected to the confining pressure generated by cemented backfill. An expression was thus proposed for the stability of the cemented-backfill-stabilized high-level pillars in deeply-buried metal mines. The results show that the improved formula for estimating the strength of the high-level pillar gives a better reflection of the impact of on-site size and shape effects on the strength of the high-level pillars. The strength of a high-level pillar subject to on-site size effects was obtained by considering the compressive strength of the rock-mass of the pillar under confining pressure provided by the cemented backfill body in the deeply-buried mine. The shape effect was taken into account by considering that the ratio of the effective width to the height of the high-level pillar modifies its strength. At the same time, the concept of load transfer distance was introduced to determine the average vertical stress in the high-level pillar. This method effectively improves the tributary area method which overestimates the average vertical stress in the high-level pillar. When mining the ore body inside a pillar's zone of influence, the area of the orebody excavated should not exceed 0.80 (otherwise it will cause a significant increase in the average vertical axial stress in the high-level pillars). The new method proposed in this study allows the stability of high-level pillars stabilized using cemented backfill to be assessed when an insufficient amount of large-scale in situ testing has been conducted in a deeply-buried metal mine. It also provides a fast, economical, and reliable method for assessing the stability of mined-out areas in deeply-buried metal mines.