Mining Project: Design Methodology for Rib Control in Coal Mines
To reduce the number of rib fall accidents in Eastern U.S. underground coal mines by developing an engineering-based design methodology that defines the appropriate level of rib support.
Currently, rib support systems in U.S. coal mines are primarily designed using a trial-and-error approach. 30 CFR and related legislation have not established any minimum design requirements for rib control systems. Because of this lack of a minimum rib control requirement in underground coal mines, the coal mining industry continues to suffer from rib-related injuries and fatalities. During the ten-year period of 2006 through 2015, 11 fatalities and 668 non-fatal days lost (NFDL) injuries caused by rib falls were documented by the Mine Safety and Health Administration (MSHA). According to MSHA statistics, between 2010 and 2015, 86% of the rib fatalities in U.S. underground coal mines occurred in the Eastern coal basins (Appalachian and Illinois coal basins). About 88% of the NFDL injuries occurred in the Eastern U.S. coal basins. Based on these injury statistics, more emphasis should be devoted to reduce rib fall incidents in coal mines operating in the Eastern coal basins. This can be done by developing an engineering-based design methodology that defines the appropriate level of rib support.
To address the above issue, this project has four research aims, as follows:
(1) develop a logical procedure for a Coal Pillar Rib Rating (CPRR);
(2) improve the understanding of coal rib deformation and rib-support interaction;
(3) identify critical parameters affecting rib stability; and
(4) develop and test the design methodology for rib control.
In the first year of this project, researchers created a CPRR rating system that was used to assess the inherent structural competency of coal ribs. The research developed data collection protocols for visited mine sites and a systematic procedure for computing the CPRR. Compressive strength testing was conducted for rib units (coal and rock). By the end of the project, this rating system will then be used to define the required support to be installed to prevent accidents that caused rib falls. These support designs will be based on engineering stress models that have been evaluated and verified at several underground mines through monitoring.
In the second and third years of this project, NIOSH researchers monitored coal rib and support response at study sites, conducted compressive strength testing for rib units, calibrated the rib model using the field monitoring studies, verified the calibrated rib model using published rib monitoring case studies, and presented papers about the project findings at international conferences.
In the fourth and final year of the project, researchers will conduct parametric studies of factors affecting rib stability, establish statistical relationships between the critical parameters and rib stability factors, develop a tool to design and analyze rib stability, and publish the project findings in a peer-reviewed journal.
Coal Pillar Rib Rating and Factor of Safety Calculations for Solid Coal Ribs
Through in-mine observations as part of this project research, three types of rib performance have been identified: solid coal rib, coal rib with in-seam thick rock parting, and coal rib with brow roof rock. Solid coal ribs are mainly composed of coal units of the same or different strengths, and these units could contain rock partings of less than two inches. By applying the CPRR technique to in-mine observations, NIOSH researchers identified the geotechnical factors that influence the structural competency of coal pillar ribs and mechanisms of rib spalling. A user-friendly application is under development to calculate the CPRR and rib factor of safety for unsupported coal ribs.
The ultimate goal of this project research is to reverse the current trend of rib fall incidents in Eastern coal basins. The achieved minimum rib support standards could be adopted by enforcement agencies that approve rib control plans.
1. Mohamed, K., Murphy, M., Lawson, H., and Klemetti, T, 2015a. Analysis of the current rib support practices and techniques in U.S. coal mines. International Journal of Mining Science and Technology, Volume 26, Issue 1, January 2016, Pages 77-87.
2. Mohamed, K.M., Tulu, I.B., and Klemetti, T., 2015b. Numerical Simulation of Deformation and Failure Process of Coal-Mass. Proceedings of the 49th US Rock Mechanics/Geomechanics Symposium, Alexandria, VA, American Rock Mechanics Association.
3. Mohamed, K., Tulu, B., Murphy, M., 2016. Numerical model calibration for simulating coal ribs. Proceedings of the 35th International Conference on Ground Control in Mining, Morgantown, WV, University of West Virginia, pp. 289–298.
4. Sears, M.M, Rusnak, J., Van Dyke, M., Rashed G., Mohamed, K., and Sloan, M., 2017. Coal Rib Response during Bench Mining: A Case Study. Proceedings of the 36th International Conference on Ground Control in Mining, Morgantown, WV, University of West Virginia, pp. 67–75.
5. Zhang, P., Mohamed, K.M., Tulu, I.B., and Trackemas, J., 2017. Coal Rib Failure and Support in Longwall Gate Entries. Proceedings of the 51th US Rock Mechanics/Geomechanics Symposium, Alexandria, VA: American Rock Mechanics Association.
6. Mohamed, K., Rashed G., Sears, M., Rusnak, J., and Van Dyke, M., 2018. Calibration of a coal-mass model using an in situ coal pillar strength study. SME Annual Meeting, Feb. 25 - 28, 2018, Minneapolis, MN.
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- Rock Falls
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