Summary
Based on triaxial compression studies on eight coals, the well known empirical relation
has been suggested as the best fit. The parametersa, b and internal friction μ are shown to be interrelated. Values for μ given in Bieniawski's classification tables are used to obtaina andb for a given Rock Mass Rating (RMR), according to these interrelations. This procedure thus gives a simple failure criterion for rock masses. This non-linear failure criterion has been used in developing two independent pillar strength approaches, the first based on a Wilson type method (1972) and the second by estimating the total confining stress at the pillar centre. The performance of these new equations has been compared with some of the more popular strength formulae as tested against 16 failed and 27 stable pillar case studies. A nomogram is presented for pillar design based on the second approach developed.
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Abbreviations
- w :
-
pillar width
- h :
-
pillar height
- B :
-
roadway width
- L :
-
centre-to-centre pillar size
- H :
-
depth of cover
- S :
-
pillar strength
- P :
-
pillar load
- F :
-
safety factor
- σ 1,σ 3 :
-
major and minor principal stresses
- σ x,σ y :
-
normal stresses alongx, y
- σ c :
-
unconfined compressive strength
- k :
-
in situ strength of 0.3 m cubes of coal
- φ :
-
angle of internal friction
- μ :
-
coefficient of internal friction
- τ c :
-
shear strength
- γ :
-
unit rock pressure
- E :
-
elastic modulus
- ν :
-
Poisson's ratio
References
Agapito, J.F.T. and Hardy, M.P. (1982) Induced horizontal stress method for pillar design in oil shale, inProceedings of the 15th Oil Shale Symposium, Denver, Colorado, USA.
Bandopadhyay, C. (1984) Personal communication.
Bieniawski, Z.T. (1968) The effect of specimen size on compressive strength of coal,International Journal of Rock Mechanics and Mining Sciences 5, 325–35.
Bieniawski, Z.T. (1976) Rock mass classification in rock engineering, inProceedings of the Symposium on Exploration for Rock Engineering, Johannesburg, Vol. 1 (edited by Z.T. Bieniawski), Balkema, Rotterdam, pp. 97–106.
Bieniawski, Z.T. (1982) Improved design of room and pillar coal mines for US conditions, inProceedings of the First International Conference on Stability in Underground Mining, Vancouver (edited by C.O. Brawner), AIME, New York, pp. 19–51.
Borecki, M. (1960) National Report: Poland, inProceedings of the 3rd International Strata Control Conference, Paris, Revue de l'Industrie Minerale, Paris, pp. 699–707.
Greenwald, H.P., Howarth, H.C. and Hartman, I. (1941) Experiments on strength of small pillars of coal in the Pittsburgh bed,US Bureau of Mines Report of Investigations 3575.
Hobbs, D.W. (1964) The strength and stress-strain characteristics of coal in triaxial compression,Journal of Geology 72, 214–31.
Hoek, E. and Brown, E.T. (1980)Underground Excavations in Rock, Institute of Mining and Metallurgy, London, pp. 137–77.
Holland, C.T. (1962) Design of pillars for overburden support — Part 1,Mining Congress Journal 48, 24–28 and Part 2,48, 66–71.
Khodt, V.V. and Feit, G.N. (1973) Use of hydraulic gauges to investigate the stressed state of the immediate face area of coal seams,Soviet Mining Science 9, 113–16.
Logie, C.V. and Matheson, G.M. (1982) A critical review of the current state-of-the-art design of mine pillars, inProceedings of the First International Conference of Stability of Underground Mining, Vancouver (edited by C.O. Brawner), AIME, New York, pp. 359–82.
Mogi, M. (1966) Pressure dependence of rock strength and transition from brittle fracture to ductile flow,Bulletin of the Earthquake Research Institute of Japan 44, 215–32.
Murrel, S.A.F. (1965) The effect of triaxial stress systems on the strength of rock at atmospheric temperature,International Journal of Rock Mechanics and Mining Sciences 3, 11–43.
Obert, L. and Duvall, W.I. (1967)Rock Mechanics and the Design of Structures in Rock, John Wiley, New York, pp. 542–5.
Salamon, M.D.G. and Munro, A.H. (1967) A study of the strength of coal pillars,Journal of the South African Institute of Mining and Metallurgy 68, 55–67.
Sheorey, P.R.,et al. (1982a) A numerical procedure for rock pressure problems in level seams, inProceedings of the Symposium on Strata Mechanics, Newcastle upon Tyne (edited by I.W. Farmer), Elsevier, Amsterdam, pp. 254–9.
Sheorey, P.R., Raju, N.M., Singh, B., Ghose, A.K. and Singh, R.D. (1982b) Analysis of strata control practices in board and pillar workings in India, inProceedings of the 7th International Strata Control Conference, Liège, Belgium.
Sheorey, P.R., Das, M.N. and Singh, B. (1984) Schmidt hammer rebound data for estimation of large scalein situ coal strength,International Journal of Rock Mechanics and Mining Sciences 21, 39–42.
Shepherd, R. and Kellet, W.H. (1969) Ribside destressing,Colliery Guardian 217, 166–72.
Shepherd, R. (1973) The forward abutment in longwall mining,Colliery Guardian 221, 177–84.
Steart, F.A. (1954) Strength and stability of pillars in coal mines,Journal of the Chemical, Metallurgical and Mining Society of South Africa 54, 309–25.
Wagner, H. (1974) Determination of the complete load-deformation characteristics of coal pillars, inProceedings of the 3rd ISRM Congress, Denver, Vol. 2, National Academy of Sciences, Washington, pp. 1076–82.
Wilson, A.H. (1972) Research into the determination of pillar size,Mining Engineer 131, 409–17.
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Sheorey, P.R., Das, M.N., Bordia, S.K. et al. Pillar strength approaches based on a new failure criterion for coal seams. International Journal of Mining and Geological Engineering 4, 273–290 (1986). https://doi.org/10.1007/BF01552957
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DOI: https://doi.org/10.1007/BF01552957