Geotechnical & Geological Engineering

, Volume 11, Issue 3, pp 159–184 | Cite as

The creep of potash salt rocks from Saskatchewan

  • E. J. Scott Duncan
  • Emery Z. Lajtai
Paper

Summary

The results of creep tests on the Esterhazy-and the Patience-Lake-types of potash salt rocks from Saskatchewan, Canada are presented. The investigations involved over 6 years of time-dependent experiments in uniaxial compression using potash from the Rocanville and the Lanigan mines of the Potash Corporation of Saskatchewan. A creep test at a given load would last from 2 to 8 months, with most tests conducted over a 4-month period.

Since the yield stress of both types of potash lies between 9 and 11 MPa, there is very little creep below 11 MPa. Between 11 and 13 MPa, creep strain production increases sharply through plastic deformation. Above about 13 MPa, however, plastic creep is dominated by brittle creep caused by microcracking. As a result, the lateral and volume creep strain curves may then display the transient and the steady-state, or all three stages of creep, while the axial strain, which is not affected by microcracking, usually attenuates for the whole duration.

Two different interpretations of the results are offered. Identifying the last (the fourth) month of testing with the steady-state model, the stress dependence of the steady-state rate has been established for both rock types. A unimodal rate model for the axial strain and a bimodal model for the lateral strain are suggested. The alternate interpretation proceeds on the assumption that under 13 MPa, both the axial and the lateral strain can be modelled through the power function formulation of transient strain.

Keywords

Potash salt rock creep strain rate yield microcracking 

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References

  1. AndradeC.N.Cab. (1910) Viscous flow in metals, Proceedings, Royal Society of London, A. 84, 1–12.Google Scholar
  2. AubertinM., GillD. and LadanyiB. (1991) A unified viscoplastic model for the inelastic flow of alkali halides, Mechanics of Materials, 11, 63–82.Google Scholar
  3. BarrC.A. (1977) Applied Salt Rock Mechanics, Elsevier Scientific Publishing Co., Amsterdam.Google Scholar
  4. CarterN.L., AndersonD.A., HansenF.D. and KranzR.L. (1981) Creep and Creep Rupture of Granitic Rocks, Geophysical Monograph, 24, American Geophysical Union, Washington, DC, pp. 61–82.Google Scholar
  5. CarterN. and HansenF. (1983) Creep of rock salt, Tectonophysics, 94, 275–333.Google Scholar
  6. CarterN.L. and KirbyS.H. (1978) Transient creep and semibrittle behaviour of crystalline rocks, Pure and Applied Geophysics, 116, 807–39.Google Scholar
  7. CadekJ. (1987) The back stress concept in power law creep of metals: a review, Material Science and Engineering, 94, 79–82.Google Scholar
  8. CharlesR.J. (1959) Static fatigue of glass, Journal of Applied Physics, 29, 1549–60.Google Scholar
  9. Duncan, E.J.S. (1990) Deformation and strength of Saskatchewan potash rock. Unpublished PhD thesis, Department of Civil Engineering, University of Manitoba.Google Scholar
  10. Fairhurst, C. and Cook, N.G.W. (1966) The phenomenon of rock splitting parallel to free surfaces under compressive stress. Proceedings 1st Congress, International Society of Rock Mechanics, Laboratorio nacional de engenharia civil Lisbon, pp. 687–92.Google Scholar
  11. GhandiC. and AshbyM.F. (1979) Fracture-mechanism maps for materials which cleave: FCC, BCC and HCP metals and ceramics, Acta Metallurgica, 27, 1565–602.Google Scholar
  12. GrovesG. and KellyA. (1963) Independent slip systems in crystals, Phil. Mag. 8, 877–87.Google Scholar
  13. HansenP. (1985) Dislocations and the plasticity of ionic crystals, In Dislocations and Properties of Real Materials, Institute of Metals, London, pp. 312–32.Google Scholar
  14. Handin, J.W. and Carter, N.L. (1980) Rheology of rocks at high temperature, Proceedings of the 4th International Congress on Rock Mechanics, Montreux, Balkema, Rotterdam, pp. 97–106.Google Scholar
  15. HardyH.R. (1958) Time-dependent deformation and failure of geologic materials, Colorado School of Mines Quarterly, 54, 135–43.Google Scholar
  16. HorsemanS. (1988) Moisture content — a major uncertainty in storage cavity closure prediction, Proceedings 2nd Conference, Mechanical Behaviour of Salt, Hanover, Germany, Trans Tech Publications, pp. 53–68.Google Scholar
  17. HorsemanS. and PassarisE. (1984) Creep tests for storage cavity closure prediction, Proceedings of the 1st Conference on The Mechanical Behaviour of Salt, Pennsylvania State University, Pennsylvania, Trans Tech Publications, pp. 119–57.Google Scholar
  18. Jones, P.R. and Prugger, P.F. (1982) Underground mining in Saskatchewan potash, Mining Engineering, December, 1667–83.Google Scholar
  19. LajtaiE.Z. and BielusL.P. (1986) Stress corrosion cracking of Lac du Bonnet granite in tension and compression, Rock Mechanics and Rock Engineering, 19, 71–87.Google Scholar
  20. LajtaiE.Z. and DuncanE.J.S. (1988) The mechanism of deformation and fracture in potash rock, Canadian Geotechnical Journal 25, 262–78.Google Scholar
  21. LajtaiE.Z., DuncanE.J.S. and CarterB.J. (1991) The effect of strain rate on rock strength, Rock Mechanics and Rock Engineering, 24, 99–109.Google Scholar
  22. SensenyP.E. (1984) Specimen size and stress history effects on creep of salt, Proceedings of the 1st Conference on The Mechanical Behaviour of Salt, Pennsylvania State University, Pennsylvania, Trans Tech Publications, pp. 369–79.Google Scholar
  23. SkrotzkiW. (1984). An estimate of the brittle to ductile transition in salt, Proceedings of the 1st Conference on The Mechanical Behaviour of Salt, Pennsylvania State University, Pennsylvania, Trans Tech Publications, pp. 381–8.Google Scholar
  24. SkrotzkiW. and HaasenP. (1988a) The role of cross slip in the steady state creep of rock salt, Proceedings 2nd Conference, Mechanical Behaviour of Salt, Hanover, Germany, Trans Tech Publications, pp. 69–81.Google Scholar
  25. SkrotzkiW. and HaasenP. (1988b) The influence of texture on the creep of salt Proceedings 2nd Conference, Mechanical Behaviour of Salt, Hanover, Germany, Trans Tech Publications, pp. 83–8.Google Scholar
  26. StokesR. (1966) Mechanical properties of polycrystalline sodium chloride, Proceedings British Ceramics Society, 6, 187–207.Google Scholar
  27. SureshS. and BrockenbroughJ.R. (1990) A theory for creep by interfacial flaw growth in ceramics and ceramic composites. Acta Metallurgica, 38, 55–68.Google Scholar
  28. VonMisesR. (1928) Mechanik der plastischen Formanderung von Kristallen. Z. fuer Angew, Math. und Mech., 8, 161–85.Google Scholar
  29. WaversikW. and FairhurstC. (1970) A study of brittle rock fracture in laboratory compression experiments, International Journal of Rock Mechanics and Mining Science, 7, 561–75.Google Scholar
  30. WawersikW. and HannumD. (1980) Mechanical behaviour of New Mexico rock salt in triaxial compression up to 200°C, Journal of Geophysical Research, 85, (B2), 891–900.Google Scholar
  31. WawersikW.R. and ZeuchD.H. (1986). Modelling and mechanistic interpretation of creep of rock salt below 200°C, Tectonophysics, 121, 125–52.Google Scholar
  32. WorselyN. and FuzesyA. (1979) The potash-bearing members of the Devonian Prairie Evaporite of southeastern Saskatchewan, south of the mining area, Economic Geology, 74, 377–88.Google Scholar

Copyright information

© Chapman & Hall 1993

Authors and Affiliations

  • E. J. Scott Duncan
    • 1
  • Emery Z. Lajtai
    • 1
  1. 1.Department of Civil and Geological EngineeringThe University of ManitobaWinnipegCanada

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