Determination of the strength of hard-rock mine pillars

Abstract

This paper presents the results of research that has been undertaken in order to develop an improved method of determining the strength of hard-rock mine pillars. Pillars are found in various shapes and sizes in all underground mining operations. Prudent engineering design requires that if pillars are to perform as desired, both the pillar strength and the pillar stress must be determined. A detailed pillar stability study has been combined with an extensive database of published pillar case histories (178) resulting in a new hybrid pillar strength formula, The Confinement Formula, that utilizes classic strength of rock methods combined with empirical methods. The Confinement Formula utilizes a mine pillar friction term calculated from the average minorlmajor stress ratio within the pillar core. Statistically, the new formula provides better results at predicting pillar strength for the combined database than the best empirically fit pillar methods that currently exist. The Confinement Formula allows for the determination of the strength of mine pillars with an increased level of confidence over previously applied methods.