Floor and Pillar Stability Investigation of Coal MinesSouthern Illinois University
Illinois Clean Coal Institute 2014-2016 Project Description: The effects of slurry backfilling of abandoned coal mines on floor and pillar stability of mines are evaluated using both numerical modeling and empirical correlations. |
A computer simulation of a room and pillar coal mine and the results of the stability analysis
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Related Publications:
Floor and Pillar Stability Considerations for Underground Disposal of Fine Coal Waste
49th US Rock Mechanics/Geomechanics Symposium (ARMA). San Francisco, CA, 2015
Presentation: Investigation of the Effect of Different Variables on Coal Mine Roof Fall Stability Based on Multiple Regression Analysis
Location: Spring Symposium in STEM, Chicago, IL
INTRODUCTION
Based on the estimation of the Illinois State Geological Survey, about 330,000 unit houses are exposed to the dangers of surface subsidence [1]. Consequently, stability of mines has been one of the main concerns in Illinois which should be professionally and practically addressed. The stability of mines deteriorates when exposed to moisture. On the other hand, due to more stringent Environmental Protection Agency (EPA) regulations slurry backfilling of mines as one of alternatives for disposing fine coal waste, has attracted more attention. Slurry backfilling consists of pumping coal fine refuse to abandoned space. Slurry backfilling of coal waste can remove environmental, social, and health problems [2]. In light of many case studies by different researchers and committees such as Griffith and Connor [3], on different mines, hydraulic backfilling has been recommended. However, some studies show that slurry backfilling does not work well for all types of mines. For example, in the Donovan study [4] this method has been recommended only for thin-seam coal mines.
One detrimental effect of slurry backfilling is that it increases moisture content within the immediate layer and consequently, softens the floor [5, 6]. This phenomenon can result instability issues. Lands which are situated over mines may also face the risk of surface subsidence due to the failure of pillar or floor. Even though partial extraction can help to prevent subsidence, it has been observed that the pillars could not stand the overburden stress in some cases [4].
Backfilling can increase mine stability specifically pillar stability, as slurry applies confining pressure to the pillars [7]. Backfilling helped extraction ratio to be increased up to 64% in one Illinois mine case study [8]. However, in mines with weak floor, some stability problems may be of concern. Typically, in the Illinois Coal Basin, a weak claystone layer, called underclay, is located immediately below the coal seam. Morgenstern and Eigenbrod conducted an experimental study of several rock and clayey samples and demonstrated that softening can decrease strength values of the samples by 60% [9]. Swelling is another major problem as Krishna and Whittaker observed three different types of floor heave including ejection of claystone from underneath the pillar, swelling of underclay layer, and penetration of steel support into the floor [10].
Afrouz demonstrates a close connection between the water content of the floor and its mechanical behavior [11, 12]. It was determined that each one percent increase in moisture content caused 0.7 percent of total heave in a claystone layer. As slurry backfilling softens the claystone layer, it will adversely affect mine stability. Empirical and numerical stability analysis of weak floor is also considered by several investigators [13, 14, 15, 16, 17].
In this paper, pillar and floor stability for two mines in Illinois are analyzed. Empirical correlations are used to evaluate floor and pillar stability. The results are compared with some numerical analyses outcomes. The effects of slurry backfilling on pillar and floor stability is also considered based on empirical correlations.
REFERENCES
1. Illinois State Geological Survey, 2015. University of Illinois at Urbana-Champaign.
2. National Academy of Sciences. 1975. Underground Disposal of Coal Mine Wastes, National Academy of Engineering, Washington, D.C., 172.
3. Griffith, W., and E.T. Connor. 1912. Mining Conditions under the City of Scranton. Pa. USBM Bulletin 25. Washington, DC: Government Printing Office.
4. Donovan, J.G. 1999. The Effects of Backfilling on Ground Control and Recovery in Thin-Seam Coal Mining. Virginia Polytechnic Institute and State University.
5. Marino, G. G., and S.H. Choi, 1999. Softening effects on the bearing capacity of mine floors. J. Geotech. Geoenviron. Eng., 125(12), 1078–1089.
6. Marino, G. G. and A. Osouli. 2012 The Influence of Softening on the Mine Floor Bearing Capacity: A Case History. Journal of Geotechnical and Geoenvironmental Engineering.
7. Morgenstern, N.R., and K.D. Eigenbrod. 1974. ‘Classifications of Argillaceous Soils and Rocks. J. Geotech. Engrg. Div.. ASCE, 100(GT10), 1137–1156.
8. Deb, D., J. Ma, and Y.P. Chugh. 2000. A Numerical Analysis f the Effects of Weak Floor Strata on Longwall Face Ground Control. Proc., SME Annual Meeting. Society for Mining Metallurgy and Exploration, Englewood, CO.
9. Southern Illinois University. 2001. Underground Placement of Coal Processing Waste and Coal Combustion By-Products Based Paste Backfill for Enhanced Mining Economics. Final technical report, Southern Illinois University, Carbondale, IL.
10. Krishna, R., and B.N. Whittaker. 1973. Floor Lift in Mine Roadways. Colliery Guardian, November, 396-402.
11. Afrouz, A. 1975a. Floor Behavior along Longwall Roadways. Int. J. of Rock Mech. and Min. Sci., Vol. 12, 229-240.
12. Afrouz, A. 1975b. Yield and Bearing Capacity of Coal Mine Floor. Int. J. of Rock Mech. and Min. Sci., Vol. 12, 241-253.
13. Heasley, K.A., and M.D.G. Salamon. 1994. The Effect of Weak Floor on Pillar Strength. Proceedings of the 5th Conference on Ground Control for Midwest U.S. Coal Mines, Collinsville, IL, 71-87.
14. Rockaway, J.D., and R.W. Stephenson. 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.
15. Chugh, Y. P., C. Bandopadhay, and R.D. Caudle. 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.
16. Chandrashekhar, K. 1990. Effects of Weak Floor Interaction on Underground Room-and-Pillar Coal Mining. Ph.d. Dissertation, Southern Illinois Univ., Carbondale, IL.
17. Bandopadhay, C. 1982. Analysis of Soft Floor Interaction on Underground Mining at a Western Kentucky Mine. M.S. Thesis, Southern Illinois Univ., Carbondale, IL.
18. Gadde, M.M. 2009. Weak Floor Stability in the Illinois Basin Underground Coal Mines. College of Engineering and Mineral Resources at West Virginia University.
19. Terzaghi, K., R. Peck, and G. Mesri. 1996. Soil Mechanics in Engineering Practice, Wiley, New York.
20. Vesic, A.S. 1975. Bearing Capacity of Shallow Foundations. Foundation Engineering Handbook, Winterkorn, H.F., and Fang, H., Eds., Van Nostrand Reinhold, Co., 121-147.
21. 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.
22. Giger, M. W., and R.J. Krizek. 1977. Estimate for Bearing Capacity of a Prismatic Pillar. Rock Mech. Rock. Eng., 9(4), 189–211.
23. Drescher, A., and Y. Zhang. 1986. An Approximate Analysis of the Bearing Capacity of Prismatic Rock Pillars. Int. J. Rock Mech., 23(5), 355–362.
24. Michalowski, R. L. 1985. Limit Analysis of Quasi-Static Pyramidal Indentation of Rock. Int. J. Rock Mech., 22(1), 31–38.
25. Itasca Consulting Group Inc. 2014. FLAC3D, Minneapolis, MN.
Floor and Pillar Stability Considerations for Underground Disposal of Fine Coal Waste
49th US Rock Mechanics/Geomechanics Symposium (ARMA). San Francisco, CA, 2015
Presentation: Investigation of the Effect of Different Variables on Coal Mine Roof Fall Stability Based on Multiple Regression Analysis
Location: Spring Symposium in STEM, Chicago, IL
INTRODUCTION
Based on the estimation of the Illinois State Geological Survey, about 330,000 unit houses are exposed to the dangers of surface subsidence [1]. Consequently, stability of mines has been one of the main concerns in Illinois which should be professionally and practically addressed. The stability of mines deteriorates when exposed to moisture. On the other hand, due to more stringent Environmental Protection Agency (EPA) regulations slurry backfilling of mines as one of alternatives for disposing fine coal waste, has attracted more attention. Slurry backfilling consists of pumping coal fine refuse to abandoned space. Slurry backfilling of coal waste can remove environmental, social, and health problems [2]. In light of many case studies by different researchers and committees such as Griffith and Connor [3], on different mines, hydraulic backfilling has been recommended. However, some studies show that slurry backfilling does not work well for all types of mines. For example, in the Donovan study [4] this method has been recommended only for thin-seam coal mines.
One detrimental effect of slurry backfilling is that it increases moisture content within the immediate layer and consequently, softens the floor [5, 6]. This phenomenon can result instability issues. Lands which are situated over mines may also face the risk of surface subsidence due to the failure of pillar or floor. Even though partial extraction can help to prevent subsidence, it has been observed that the pillars could not stand the overburden stress in some cases [4].
Backfilling can increase mine stability specifically pillar stability, as slurry applies confining pressure to the pillars [7]. Backfilling helped extraction ratio to be increased up to 64% in one Illinois mine case study [8]. However, in mines with weak floor, some stability problems may be of concern. Typically, in the Illinois Coal Basin, a weak claystone layer, called underclay, is located immediately below the coal seam. Morgenstern and Eigenbrod conducted an experimental study of several rock and clayey samples and demonstrated that softening can decrease strength values of the samples by 60% [9]. Swelling is another major problem as Krishna and Whittaker observed three different types of floor heave including ejection of claystone from underneath the pillar, swelling of underclay layer, and penetration of steel support into the floor [10].
Afrouz demonstrates a close connection between the water content of the floor and its mechanical behavior [11, 12]. It was determined that each one percent increase in moisture content caused 0.7 percent of total heave in a claystone layer. As slurry backfilling softens the claystone layer, it will adversely affect mine stability. Empirical and numerical stability analysis of weak floor is also considered by several investigators [13, 14, 15, 16, 17].
In this paper, pillar and floor stability for two mines in Illinois are analyzed. Empirical correlations are used to evaluate floor and pillar stability. The results are compared with some numerical analyses outcomes. The effects of slurry backfilling on pillar and floor stability is also considered based on empirical correlations.
REFERENCES
1. Illinois State Geological Survey, 2015. University of Illinois at Urbana-Champaign.
2. National Academy of Sciences. 1975. Underground Disposal of Coal Mine Wastes, National Academy of Engineering, Washington, D.C., 172.
3. Griffith, W., and E.T. Connor. 1912. Mining Conditions under the City of Scranton. Pa. USBM Bulletin 25. Washington, DC: Government Printing Office.
4. Donovan, J.G. 1999. The Effects of Backfilling on Ground Control and Recovery in Thin-Seam Coal Mining. Virginia Polytechnic Institute and State University.
5. Marino, G. G., and S.H. Choi, 1999. Softening effects on the bearing capacity of mine floors. J. Geotech. Geoenviron. Eng., 125(12), 1078–1089.
6. Marino, G. G. and A. Osouli. 2012 The Influence of Softening on the Mine Floor Bearing Capacity: A Case History. Journal of Geotechnical and Geoenvironmental Engineering.
7. Morgenstern, N.R., and K.D. Eigenbrod. 1974. ‘Classifications of Argillaceous Soils and Rocks. J. Geotech. Engrg. Div.. ASCE, 100(GT10), 1137–1156.
8. Deb, D., J. Ma, and Y.P. Chugh. 2000. A Numerical Analysis f the Effects of Weak Floor Strata on Longwall Face Ground Control. Proc., SME Annual Meeting. Society for Mining Metallurgy and Exploration, Englewood, CO.
9. Southern Illinois University. 2001. Underground Placement of Coal Processing Waste and Coal Combustion By-Products Based Paste Backfill for Enhanced Mining Economics. Final technical report, Southern Illinois University, Carbondale, IL.
10. Krishna, R., and B.N. Whittaker. 1973. Floor Lift in Mine Roadways. Colliery Guardian, November, 396-402.
11. Afrouz, A. 1975a. Floor Behavior along Longwall Roadways. Int. J. of Rock Mech. and Min. Sci., Vol. 12, 229-240.
12. Afrouz, A. 1975b. Yield and Bearing Capacity of Coal Mine Floor. Int. J. of Rock Mech. and Min. Sci., Vol. 12, 241-253.
13. Heasley, K.A., and M.D.G. Salamon. 1994. The Effect of Weak Floor on Pillar Strength. Proceedings of the 5th Conference on Ground Control for Midwest U.S. Coal Mines, Collinsville, IL, 71-87.
14. Rockaway, J.D., and R.W. Stephenson. 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.
15. Chugh, Y. P., C. Bandopadhay, and R.D. Caudle. 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.
16. Chandrashekhar, K. 1990. Effects of Weak Floor Interaction on Underground Room-and-Pillar Coal Mining. Ph.d. Dissertation, Southern Illinois Univ., Carbondale, IL.
17. Bandopadhay, C. 1982. Analysis of Soft Floor Interaction on Underground Mining at a Western Kentucky Mine. M.S. Thesis, Southern Illinois Univ., Carbondale, IL.
18. Gadde, M.M. 2009. Weak Floor Stability in the Illinois Basin Underground Coal Mines. College of Engineering and Mineral Resources at West Virginia University.
19. Terzaghi, K., R. Peck, and G. Mesri. 1996. Soil Mechanics in Engineering Practice, Wiley, New York.
20. Vesic, A.S. 1975. Bearing Capacity of Shallow Foundations. Foundation Engineering Handbook, Winterkorn, H.F., and Fang, H., Eds., Van Nostrand Reinhold, Co., 121-147.
21. 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.
22. Giger, M. W., and R.J. Krizek. 1977. Estimate for Bearing Capacity of a Prismatic Pillar. Rock Mech. Rock. Eng., 9(4), 189–211.
23. Drescher, A., and Y. Zhang. 1986. An Approximate Analysis of the Bearing Capacity of Prismatic Rock Pillars. Int. J. Rock Mech., 23(5), 355–362.
24. Michalowski, R. L. 1985. Limit Analysis of Quasi-Static Pyramidal Indentation of Rock. Int. J. Rock Mech., 22(1), 31–38.
25. Itasca Consulting Group Inc. 2014. FLAC3D, Minneapolis, MN.
