The paper describes an empirical law of friction for rock joints which can be used both for extrapolating and predicting shear strength data. The equation is based on three index parameters; the joint roughness coefficient JRC, the joint wall compressive strength JCS, and the residual friction angle. All these index values can be measured in the laboratory. They can also be measured in the field. Index tests and subsequent shear box tests on more than 10 joint samples have demonstrated that the residual friction angle can be estimated to within plus or minus 1 degrees for any one of the eight rock types investigated. The mean value of the peak shear strength angle for the same 100 joints was estimated to within 1/2 degrees. The exceptionally close prediction of peak strength is made possible by performing self-weight (low stress) sliding tests on blocks with throughgoing joints. The total friction angle at which sliding occurs provides an estimate of the joint roughness coefficient JRC. The latter is constant over a range of effective normal stress of at least four orders of magnitude. However, it is found that both JRC and JCS reduce with increasing joint length. Increasing the length of joint therefore reduces not only the peak shear strength, but also the peak dilation angle and the peak shear stiffness. These important scale effects can be predicted at a fraction of the cost of performing large scale in situ direct shear tests. /Author/

  • Corporate Authors:

    Norwegian Geotechnical Institute

    P.O. Box 40 Tasen
    Oslo 8,   Norway 
  • Authors:
    • Barton, N
    • Choubey, V
  • Publication Date: 1978

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 54 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00183663
  • Record Type: Publication
  • Report/Paper Numbers: Publication No 119 Proceeding
  • Files: TRIS
  • Created Date: Dec 3 1978 12:00AM