The shear strength of a discontinuity in a soil or rock mass may have a strong impact on the mechanical behavior of a soil or rock mass.[1][2][3][4][5][6] The shear strength of a discontinuity is often considerably lower than the shear strength of the blocks of intact material in between the discontinuities, and therefore influences, for example, tunnel, foundation, or slope engineering, but also the stability of natural slopes. Many slopes, natural and man-made, fail due to a low shear strength of discontinuities in the soil or rock mass in the slope. The deformation characteristics of a soil or rock mass are also influenced by the shear strength of the discontinuities. For example, the modulus of deformation is reduced, and the deformation becomes plastic (i.e. non-reversible deformation on reduction of stress) rather than elastic (i.e. reversible deformation). This may cause, for example, larger settlement of foundations, which is also permanent even if the load is only temporary. Furthermore the shear strength of discontinuities influences the stress distribution in a soil or rock mass.[7]

Shear strength

The shear strength along a discontinuity in a soil or rock mass in geotechnical engineering is governed by the persistence of the discontinuity, roughness of discontinuity surfaces,[8][9][10][11][12] infill material in the discontinuity,[13] presence and pressure of gasses and fluids (e.g. water, oil), and possible solution (e.g. karst) and cementation along the discontinuity. Further the shear strength is dependent on whether the discontinuity has moved before in the geological history (i.e. are the asperities on opposing walls of the discontinuity fitting or non-fitting, or have the asperities been sheared off).

Determination shear strength

Only for simple models of discontinuities the shear strength can be analytically calculated.[8] For real discontinuities no analytical calculation method exists. Testing on various scales in the laboratory or in the field, or empirical calculations based on characterizing the discontinuity[12][14] are used to establish the shear strength.

Discontinuity shear strength tests

Empirical calculations based on characterization

See also

Discontinuity (Geotechnical engineering)
Direct shear test


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  7. Gaziev, E.; Erlikhman (4–6 October 1971). "Stresses and strains in anisotropic foundations". Rock fracture: proceedings of the International Symposium on Rock Mechanics ISRM. Nancy, France: École Nationale Supérieure de Géologie Appliquée et de Prospection Minière : École Nationale Supérieure de la Métallurgie et de l'Industrie des Mines, Rubrecht, Nancy. p. 11-1.
  8. 8.0 8.1 Patton, F.D. (25 Sept-1 Oct 1966). "Multiple Modes of Shear Failure in Rock". In Rocha, M.. Proc. 1st Congress of International Society for Rock Mechanics (ISRM). 1. Lisbon, Portugal: Laboratório Nacional de Engenharia Civil, Lisboa, Portugal. pp. 509–513. Error: Bad OL specified!.
  9. Rengers, N. (1970). "Influence of surface roughness on the friction properties of rock planes". Proceedings 2nd International Congress on Rock Mechanics, ISRM, Belgrade. 1. ISRM. pp. 229-234.
  10. Fecker, E.; Rengers, N. (1971). "Measurement of large scale roughness of rock planes by means of profilograph and geological compass". Proceedings symposium on rock fracture, Nancy, France. pp. 1–18.
  11. 11.0 11.1 Script error
  12. 12.0 12.1 12.2 Barton, N.R.; Bandis. "Review of predictive capabilities of JRC-JCS model in engineering practice". In Barton, N.; Stephansson, O.. Rock Joints. Regional Conference of the International Society for Rock Mechanics ISRM. Loen, Norway: Balkema, Rotterdam, Taylor & Francis. pp. 603–610. ISBN 9789061911098.
  13. Phien-wej, N.; Shrestha, U.B.; Rantucci, G. (1990). "Effect of infill thickness on shear behaviour of rock joints". In Barton, N.R.; Stephansson, O.. Rock Joints. Balkema (Taylor & Francis), Rotterdam. pp. 289-294. ISBN 978-9061911098.
  14. 14.0 14.1 Hack, H.R.G.K.; Price, D.G. (September 25–29, 1995). "Determination of discontinuity friction by rock mass classification". In Fujii, T.. Proceedings 8th International Society for Rock Mechanics (ISRM) congress. 3. Tokyo, Japan: Balkema, Rotterdam, Taylor & Francis. pp. 23-27. ISBN 9789054105763.