Influence of Softening on Mine Floor-Bearing Capacity: Case History
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 138, Issue 10
Abstract
This paper introduces a new approach that considers the effect of softening to more accurately calculate floor-bearing capacities where difficult mine conditions are present. Because of softening and changes in confining pressures, the geotechnical properties of immediate fine-grained rock vary in the mine floor. Therefore, when floor softening is present, the conventional equations used to determine the floor-bearing capacity are not very accurate. In this study, a methodology is presented that considers the floor softening and existence of a durable layer in the mine floor. The proposed method is based on analysis of a case study located in central Illinois utilizing finite-element method (FEM) and rock mechanics laboratory data. For this case study, extensive geological mapping and laboratory tests, including rock classification, rock swell properties, and triaxial compression tests, were conducted on samples of fine-grained rocks that predominantly consisted of mudstone. The results of laboratory tests are presented and discussed in detail. Aerial and cross-sectional analyses of the floor lithology and stratigraphy were performed to evaluate the important bearing conditions across the project site. From the analyses, the immediate floor thickness and type of the nondurable and the underlying durable rock across the site were determined. DuroIndex is presented and used to determine and rate the durability of mine floor material. Considering certain pillar-to-room width ratios, two-dimensional FEM analyses were performed to evaluate mine floor capacity with both softened and unsoftened floor conditions. Consequently, the softening correction factor, or the correction for the softening effect, was determined. Finally, a procedure that takes into account the effect of softening and the existence of a durable layer was developed to determine allowable floor-bearing capacity.
Get full access to this article
View all available purchase options and get full access to this article.
References
Bandopadhay, C. (1982). “Analysis of soft floor interaction on underground mining at a western Kentucky mine.” M.S. thesis, Southern Illinois Univ., Carbondale, IL.
Bhattacharyya, A. K., and Seneviratne, S. P. (1992). “A study of floor heave in the mines of the southern coalfield of New South Wales by two dimensional finite element modelling.” Proc., 11th Int. Conf. on Ground Control in Mining, Australian Institute of Mining and Metallurgy, Carlton South, Australia, 297–301.
Bieniawski, Z. T. (1987). Strata control in mineral engineering, Balkema, Rotterdam, Netherlands.
Bieniawski, Z. T. (1992), “A method revisited: Coal pillar strength formula based on field investigations.” Proc., Workshop on Coal Pillar Mechanics and Design, Paper IC 9315, National Institute for Occupational Safety and Health, Pittsburgh, 158–165.
Botts, M. E. (1986). “The effects of slaking on the engineering behavior of clay shales.” Ph.D. thesis, Univ. of Colorado, Boulder, CO.
Brady, B. H. G., and Brown, E. T. (1993). Rock mechanics for underground mining, Kluwer Academic, Boston.
Chandrashekhar, K. (1990). “Effects of weak floor interaction on underground room-and-pillar coal mining.” Ph.D. dissertation, Southern Illinois Univ., Carbondale, IL.
Chugh, Y. P., Bandopadhay, C., and Caudle, R. D. (1984). “Effect of soft floor interaction on retreat mining at an Illinois Basin coal mine.” Chapter 4, Stability in underground mining II, Society for Mining Metallurgy and Exploration, Englewood, CO, 56–71.
Deb, D., Ma, J., and Chugh, Y. P. (2000). “A numerical analysis of the effects of weak floor strata on longwall face ground control.” Proc., SME Annual Meeting, Society for Mining Metallurgy and Exploration, Englewood, CO.
Drescher, A., and Zhang, Y. (1986). “An approximate analysis of the bearing capacity of prismatic rock pillars.” Int. J. Rock Mech., 23(5), 355–362.
Gadde, M. (2009). “Weak floor stability in the Illinois Basin underground coal mines.” Ph.D. thesis, West Virginia Univ., Morgantown, WV.
Ganow, H. C. (1975). “A geotechnical study of the squeeze problem associated with the underground mining of coal.” Ph.D. thesis, Univ. of Illinois at Urbana-Champaign, Champaign, IL.
Giger, M. W., and Krizek, R. J. (1977). “Estimate for bearing capacity of a prismatic pillar.” Rock Mech. Rock.Eng., 9(4), 189–211.
Hoek, E., and Brown, E. T. (1980). Underground excavations in rock, Institution of Mining and Metallurgy, London.
Hoek, E., Carranza-Torres, C., and Corkum, B. (2002). “Hoek-Brown failure criterion.” Proc., 5th North American Rock Mechanics Symp. and 17th Tunnelling Association of Canada Conf., University of Toronto Press, Toronto, 267–271.
Hoek, E., Kaiser, P. K., and Bawden, W. F. (1993). Design of support for underground hard rock mines, Balkema, Rotterdam, Netherlands.
Hoek, E., and Karzulovic, A. (2001). “Rock mass properties for surface mines, Chapter 6, Slope stability in surface mining,” W. A. Hustrulid, M. K. McCarter, and D. J. A. Van Zyl, eds., Society for Mining, Metallurgy, and Exploration, Littleton, CO.
Mandel, J., and Salençon, J. (1969). “Force portante d’un sol sur une assise rigide.” Proc., 7th Int. Conf. on Soil Mechanics and Foundation Engineering, Vol. 2, Sociedad Mexicana de Mecanica, Mexico City, 157–164.
Marino, G. G., and Choi, S. H. (1999). “Softening effects on the bearing capacity of mine floors.” J. Geotech. Geoenviron. Eng., 125(12), 1078–1089.
Marino, G. G., and Bauer, R. A. (1989). “Behavior of abandoned room and pillar mines in Illinois.” Int. J. Min. Geol. Eng., 7(4), 271–281.
Mark, C. (1999). “Empirical Methods for Coal Pillar Design.” Proc., 2nd International Workshop on Coal Pillar Mechanics and Design, National Institute for Occupational Safety and Health, Pittsburgh, 145–154.
Michalowski, R. L. (1985). “Limit analysis of quasi-static pyramidal indentation of rock.” Int. J. Rock Mech., 22(1), 31–38.
Molinda, G. M., and Mark, C. (1994). The coal mine roof rating (CMRR)—A practical rock mass classification for coal mines, U.S. Bureau of Mines, Dept. of the Interior, Washington, DC.
Molinda, G. M., Mark, C., and Dolinar, D. R. (2000). “Assessing coal mine roof stability through roof fall analysis.” Proc., New Technology for Coal Mine Roof Support, NIOSH Open Industry Briefing, National Institute for Occupational Safety and Health, Pittsburgh, 53–72.
Pula, O., Chugh, Y. P., and Pytel, W. M. (1990). “Estimation of weak floor strata properties and related safety factors for design of coal mine layouts” Proc., 31st U.S. Symp. on Rock Mechanics, W. A. Hustrulid and G. A. Johnson, eds., Taylor and Francis, New York, 93–100.
Rockaway, J. D., and Stephenson, R. W. (1979). “Investigation of the effects of weak floor conditions on the stability of coal pillars.” Rep. No. BUMINES-OFR-12-81, U.S. Bureau of Mines, Washington, DC.
Skempton, A. W. (1977). “Slope stability of cuttings in brown London clay.” Proc., 9th Int. Conf. on Soil Mechanics and Foundation Engineering, Vol. 3, Springer, New York, 261–270.
Speck, R. (1979). “A comparative evaluation of geologic factors influencing floor stability in two Illinois coal mines.” Ph.D. thesis, Univ. of Missouri, Rolla, MO.
Terzaghi, K., Peck, R., and Mesri, G. (1996). Soil mechanics in engineering practice, Wiley, New York.
Vasundhara, V. (2001). “Geomechanical behaviour of soft floor strata in underground coal mines.” Ph.D. thesis, Univ. of New South Wales, Sydney, Australia.
Vesic, A. S. (1975). “Bearing capacity of shallow foundations.” Foundation engineering handbook, H. F. Winterkorn and H. Fang, eds., Van Nostrand Reinhold, New York, 121–147.
Yavuz, M., Iphar, M., Aksoy, M., and Once, G. (2003). “Evaluation of floor heaving in galleries by numerical analysis.” Proc., Application of Computers and Operations Research in the Minerals Industries, South African Institute of Mining and Metallurgy, Johannesburg, South Africa, 185–190.
Information & Authors
Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 138 • Issue 10 • October 2012
Pages: 1284 - 1297
Copyright
© 2012 American Society of Civil Engineers.
History
Received: Apr 2, 2011
Accepted: Jan 9, 2012
Published online: Jan 11, 2012
Published in print: Oct 1, 2012
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.