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Accession Number PB2013-102221
Title Evaluation of the Strength of Slender Pillars.
Publication Date 2012
Media Count 7p
Personal Author G. S. Esterhuizen
Abstract Pillars with width to height ratios of less than 1.0 are frequently created in underground hard rock mines. The strength of slender pillars can be estimated using empirically developed equations. However, the equations can provide variable results when the width-to-height ratios approach 0.5. This paper investigates some of the issues affecting pillar strength at low width-to-height ratios in hard brittle rock. The investigation includes an evaluation of empirical pillar strength data presented in the literature and observations of pillar performance in underground limestone mines in the eastern United States, supplemented by numerical modeling in which failure processes and sensitivity of slender pillars to variations in rock mass properties are evaluated. The results showed that the strength of slender pillars is more variable than that of wider pillars. The numerical model results demonstrated the increasing role of brittle rock failure in slender pillar strength. The absence of confinement in slender pillars can result in a fully brittle failure process, while wider pillars fail in a combined brittle and shearing mode. The onset of spalling in slender pillars occurs at or near the ultimate strength, while this is not the case for wider pillars. Slender pillars are shown to be more sensitive to the presence of discontinuities than wider pillars, which can partly explain the increased variability of slender pillar strength. Two examples are presented, which illustrate failure initiation by brittle spalling and the sensitivity of slender pillars to the presence of discontinuities.
Keywords Limestone mines
Model parameters
Numerical modeling
Pillar length
Pillar strength
Pillars
Rock mines
Underground mines


 
Source Agency National Institute for Occupational Safety and Health
NTIS Subject Category 48A - Mineral Industries
46E - Structural Mechanics
Corporate Author National Inst. for Occupational Safety and Health, Pittsburgh, PA.
Document Type Technical report
Title Note N/A
NTIS Issue Number 1306
Contract Number N/A

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