Mining Project: Underground Stone Mine Pillar Design in Challenging Conditions
To build the framework for expanding pillar design criteria in challenging multiple-level, deep, and dipping mining environments by undertaking thorough pillar response investigations in representative conditions at case study mine sites, and by developing design criteria for these scenarios.
Since 2005, fatalities related to ground control in underground stone mines have accounted for 50% of the total fatalities. The injury rate has increased significantly over the past two years. Likewise, the fatality rate in the underground stone sector has increased overall during the past decade. The risks driving these trends are likely to increase as operations mine under deeper cover with steeper dips and more adverse geological conditions.
NIOSH developed and made public the first pillar design software program (S-Pillar) for underground stone mining in 2011, which has been widely accepted and used regularly by mining operations and the Mine Safety and Health Administration (MSHA). The empirically based S-Pillar software was designed to meet the pillar design needs of the majority of the underground stone mine industry, but did not address several uniquely challenging environments. Stakeholder discussions have indicated to NIOSH researchers that these environments will likely be encountered more often at future mining operations. Analyzing case histories for the conditions outside the scope of the previous research is necessary to provide a detailed analysis of the hazards associated with these insufficiently studied environments.
This project involves five research aims, summarized as follows.
Research Aim 1. Develop an empirical database of existing limestone operations in multiple levels, deep cover, and dipping seams, and document fundamental pillar design parameters and qualitative performance assessments.
Research Aim 2. Identify study mines and conduct exploratory investigations to determine rock mass characterization, material properties, stress conditions, geologic features, and measured pillar responses at target locations that support a parametric assessment of pillar stability.
Research Aim 3. Identify pillar instability mechanisms occurring in challenging environments, such as multiple levels, deep cover, and dipping seams, and identify differences compared to instability mechanisms in less challenging environments that form the basis of current pillar design guidelines.
Research Aim 4. Develop and calibrate numerical models that replicate pillar responses and failure mechanisms and validate against case study mine observations and measured responses in challenging mine environments.
Research Aim 5. Assess global stability issues and develop pillar design criteria based on case study results that will form the basis for establishing universal design guidelines for stone mining in challenging environments, such as multiple levels, deep cover, and dipping seams.
Research is currently ongoing at underground stone mines in Pennsylvania, Ohio, and Tennessee, with seismic, stress, and laser scan data being collected and analyzed to help better design underground mines in challenging environments. During the execution of the project, a number of technical papers will be published as specific milestones. Results will be presented the Annual Underground Stone Seminar, the International Conference on Ground Control in Mining, and the US Rock Mechanics/Geomechanics Symposium throughout the life of the project, as well as other outlets as opportunities arise, ultimately culminating in a NIOSH Information Circular on pillar design criteria in these challenging environments.
Challenging mining conditions
- Esterhuizen, G., Tyrna, P., Murphy, M. (2019). A case study of the collapse of slender pillars affected by through-going discontinuities at a limestone mine in Pennsylvania.
- Iannacchione, A., Esterhuizen, G., Slaker, B., Murphy, M., Miller, T., Cope, N., Thayer, S. (2019). Evaluation of stress control layout at the Subtropolis Mine, Petersburg, Ohio.
- Slaker, B., Murphy, M., Miller, T. (2019). Analysis of extensometer, photogrammetry and laser scanning monitoring techniques for measuring floor heave in an underground limestone mine.
- Slaker, B., Murphy, M., Winfield, J. (2019). Tracking convergence, spalling, and cutter roof formation at the Pleasant Gap limestone mine using LiDAR.
- Sears, M., Slaker, B., Rashed, G., Winfield, J. (2019). Numerical model validation and analysis of a dipping limestone pillar using FLAC3D.
- Gangrade, V., Slaker, B., Collins, D., Braganza, S., Winfield, J. (2019). Investigating seismicity surrounding an excavation boundary in a highly stressed dipping underground limestone mine.
- Sears, M., Slaker, B., Rashed, G., Winfield, J. (2018). Numerical model simulation of a development pillar at a steeply dipping underground limestone mine.
- Slaker, B., Gangrade, V., Murphy, M., Winfield, J. (2018). Seismic data interpretation of a development pillar at a steeply dipping underground limestone mine.
- Murphy, M., Slaker, B., Iannacchione, A., Rashed, G., Van Dyke, M., Buchan, G., Minoski, T., McElhinney, D., Winfield, J. (2018). Development of a comprehensive pillar and roof monitoring system at a steeply dipping underground limestone mine.
Other Relevant Publications
- Pillar strength in underground stone mines in the United States
- Effect of discontinuity dip direction on hard rock pillar strength
- Overview of current US longwall gateroad support practices: an update
- Analysis of Pillar Design Practices and Techniques for U.S. Limestone Mines
- Assessment of Stable and Failed Pillars in Underground Limestone Mines
- Effects of Weak Bands on Pillar Stability in Stone Mines: Field Observations and Numerical Model Assessment
- Field Observations and Numerical Studies of Horizontal Stress Effects on Roof Stability in U.S. Limestone Mines
- Pillar Design Issues for Underground Stone Mines
- Pillar Stability Issues Based on a Survey of Pillar Performance in Underground Limestone Mines
- Pillar Strength and Design Methodology for Stone Mines
- Pillar Strength in Underground Stone Mines in the United States
- Roof Span Design for Underground Stone Mines
- The Unpredictable Life Cycle of a Coal Pillar