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Q-system (geotechnical engineering)

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For the linguistics formalism, see Q-systems.

The Q-system for rock mass classification is developed by Barton, Lien, and Lunde et al[1][2][3][4][5][6][7][8]. It expresses the quality of the rock mass in the so-called Q-value, on which design and support recommendations for underground excavations are based.

The Q-value is determined with

The first term RQD (Rock Quality Designation) divided by {J_n} (joint set number) is related to the size of the intact rock blocks in the rock mass. The second term Jr (joint roughness number) divided by Ja (joint alteration number) is related to the shear strength along the discontinuity planes and the third term Jw (joint water parameter) divided by SRF (stress reduction factor) is related to the stress environment for the discontinuities around the tunnel opening.

A multiplication of the three terms results in the ‘Q’ parameter, which can range between 0.00006 for an exceptionally poor rock mass to 2666 for an exceptionally good rock mass. The numerical values of the class boundaries for the different rock mass types are subdivisions of the Q range on a logarithmic scale.

Intact rock strength influences the result only when the intact rock strength is relatively low compared to the stress environment. Jr and Ja are the parameters for the discontinuity roughness and alteration of the weakest discontinuities (Barton et al., 1974) or the discontinuity most likely to allow failure to initiate (Barton, 1976a). The Q-value determines the quality of the rock mass, but the support of an underground excavation is based not only on the Q-value but is also determined by the different terms in the above equation. This leads to a very extensive list of classes for support recommendations.



The Q-system uses six different parameters to assess the rock mass quality. The parameters are:

  • Rock Quality Designation RQD
  • Joint set number Jn
  • Roughness of the most unfavorable joint or discontinuity Jr
  • Degree of alteration of filling along the weakest joint Ja
  • Water inflow Jw
  • Stress Reduction Factor SRF

The Q-factor can then be calculated as:

References

  1. ^ Barton, N.R.; Lien, R.; Lunde, J. (1974). "Engineering classification of rock masses for the design of tunnel support". Rock Mechanics and Rock Engineering. 6 (4). Springer: 189–236. doi:10.1007/BF01239496.
  2. ^ Barton, N.R. (1–5 November 1976). "Recent experiences with the Q-system of tunnel support design". In Bieniawski, Z.T. (ed.). Proc. Symposium on Exploration for Rock Engineering, Johannesburg. Vol. 1. Balkema, Cape Town. pp. 107–117. ISBN 0869610899. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help)CS1 maint: date format (link)
  3. ^ Barton, N.R.; Lien, R.; Lunde, J. (1977). "Estimation of support requirements for underground excavations & discussion". In Fairhurst, C.; Crouch, S.L. (eds.). Proc. of 16th Symp. on Design Methods in Rock Mechanics, University of Minnesota, Minneapolis, U. S. A, 1975. American Society of Civil Engineers (ASCE), New York. pp. 163–177, 234–241. OL 19853458M. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help)
  4. ^ Barton, N.R. (1988). "Rock Mass Classification and Tunnel Reinforcement Selection using the Q-system". In Kirkaldie, L. (ed.). Rock Classification Systems for Engineering Purposes: ASTM Special Technical Publication 984. Vol. 1. ASTM International. pp. 59–88. doi:10.1520/STP48464S. ISBN 978-0803109889. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help)
  5. ^ Barton, N.R.; Grimstad, E. (1994). "The Q-system following twenty years of application in NMT support selection; 43rd Geomechanic Colloquy, Salzburg". Felsbau. Verlag Glückauf GmbH, Essen, Germany: 428–436. ISSN 1866-0134.
  6. ^ Barton, N.R. (2000). TBM Tunnelling in Jointed and Faulted Rock. Taylor & Francis. p. 184. ISBN 978-9058093417.
  7. ^ Barton, N.R. (2002). "Some new Q-value correlations to assist in site characterization and tunnel design". International Journal of Rock Mechanics and Mining Sciences. 39 (2): 185–216. doi:10.1016/S1365-1609(02)00011-4.
  8. ^ Barton, N.R. (2006). Rock Quality, Seismic Velocity, Attenuation and Anisotropy. Taylor & Francis. p. 729. ISBN 978-0415394413.

Further reading

  • Bieniawski, Z.T. "Engineering Rock Mass Classifications", John Wiley and Sons, New York, 1989
  • Hack, H.R.G.K. (25–28 November 2002). "An evaluation of slope stability classification. Keynote Lecture.". In Dinis da Gama, C.; Ribeira e Sousa, L. (eds.). Proc. ISRM EUROCK’2002. Funchal, Madeira, Portugal: Sociedade Portuguesa de Geotecnia, Lisboa, Portugal. pp. 3–32. ISBN 972-98781-2-9. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help)CS1 maint: date and year (link) CS1 maint: date format (link)
  • Pantelidis, L (2009). "Rock slope stability assessment through rock mass classification systems", International Journal of Rock Mechanics and Mining Sciences, 46(2), (315–325).


See also

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