ABSTRACT

Ground stability continues to be a significant concern in underground stone mines. The National Institute for Occupational Safety and Health (NIOSH) is currently conducting a research project to investigate the stability of pillars and interburden in multiple-level stone mines. In multilevel mining, a stable interburden is required because it is the foundation for the top-level pillars and forms the roof for the bottom level mine. In this study, the effect of overburden depth, extraction ratio, interburden tensile strength, in-situ stress conditions, and the degree of columnization between mining levels on interburden stability were examined. The critical interburden thickness required to form a stable beam under different conditions and the interburden thickness required to mostly eliminate interaction between levels are both explored. The model results showed that there is an interaction between numerous factors that control the stability of the interburden. A combination of these factors may lead to various degrees of multiple-seam mining interaction. In low horizontal stress field models, interburden stability generally decreases with decreasing the pillar overlap, decreasing interburden thickness, increasing depth, and increasing extracting ratio. These patterns do not necessarily remain true for high horizontal stress cases.

1. INTRODUCTION

The stability of underground stone mine workings in challenging conditions is the focus of a current research project at the National Institute for Occupational Safety and Health (NIOSH). Multiple-level mining is commonly practiced in the underground stone mining industry, and previous NIOSH pillar design guidelines do not apply to these mining conditions. Seams being mined below or above a previously mined seam are subject to disturbances due to mining-induced strata movement (Zhou and Haycocks, 1990). An interaction between levels in underground stone mines is typically unfavorable. Attempting to vertically align pillars across levels is commonly referred to as columnizing, or stacking (Slaker et al., 2020). Columnization of the pillars is considered the standard design practice when thin interburden interactions are a concern. Columnization minimizes the shear stress in the interburden and also provides a more uniform stress on the pillars, minimizing the risk of pillar failure (Mark, 2007).

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