A REVIEW OF THE SHEAR STRENGTH OF FILLED DISCONTINUITIES IN ROCK

Rock discontinuities that are filled with plastic materials represent one of the greatest problems in rock engineering. The wide range of properties and variety of occurrences make it extremely difficult to estimate the shear strength in anything but crude terms-for instance "low" (phi sub r=12 deg-20 deg), or "very low" (phi sub r = 6 deg-12 deg). Even the ability to classify in this manner may be extremely valuable when designing the optimum anchoring or bolting required to stabilize surface cuttings or the walls of large underground openings. The most complicated and critical filled discontinuities may need to be tested in situ, if the cost of failure is sufficiently high. If direct shear tests are to be performed it is extremely important that the test conditions are as relevant as possible to field conditions. The soil mechanics principles relevant to shearing and unloading problems are briefly reviewed. It would seem that slow drained teste will be the most relevant test method for all cases involving unloading above the critical filled discontinuities. An increasing degree of complexity is introduced into the problem when the clay fillings are less thick than the roughness amplitude of the wall rock. A limited shear displacement will then result in a marked stiffening when opposed rock asperities make contact. Both idealized laboratory models and engineering examples of rock wall interaction are reviewed, in an attempt to clarify the relative importance of filling behaviour and rock contact. Shear test results reported in the literature for filled discontinuities are tabulated in an appendix. /Author/

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    Norwegian Geotechnical Institute

    P.O. Box 40 Tasen
    Oslo 8,   Norway 
  • Authors:
    • Barton, N
  • Publication Date: 1974

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  • Accession Number: 00095911
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jul 2 1975 12:00AM