A GEOTECHNICAL ANALYSIS OF ROCK STRUCTURE AND FABRIC IN THE C.S.A. MINE, COBAR, NEW SOUTH WALES

Rock structure and fabric at the C.S.A. Mine, Cobar, N.S.W., is defined, and the appropriate parameters are used to provide some guidelines for material behaviour and support requirements. An analysis of some 24,000 feature traces indicates that joint and minor fault intensity decreases away from the vicinity of the stopes and is lower in the inter-stope areas above 370 m. The mean normal-to-plane line spacing and length of over 1,000 predominant joints, considered in terms of a log-normal model, are revealed as 13 cm and 39 cm respectively. The joints are approximately equi-dimensional in outline with inferred mean areas of 800 sq cm and a mean relative continuity, along the line of the features, of nearly 50%. The amplitudes and lengths of surface waves are recorded on a variety of defect surfaces. Joint roughness indices are intentatively correlated with the mechanical characteristics of the discontinuities to provide indications of general friction angles of approximately 35-45 degrees. Acceptance of a joint peak shear strength, which is sensitive both to roughness and rock wall character, provides evidence to support the view that shear is unlikely to occur along joints, within the rock mass away from the vicinity of the underground openings. Fabric data are incorporated in an empirical design model to reveal a medium to high strength rock mass. Systems of rock quality designation (RQD), rock structure rating (RSR), rock mass ratio (RMR), and support index (Q) are invoked to provide guidelines for support of the underground openings. Although the systems are highly empirical and require further development, the results are often close to actual support practice. Initial results of a finite element analysis of a type cross-section indicate that failure of intact rock is unlikely and that both stress release and shear movements are feasible at localized points along the footwalls of the ore bodies. Indicated displacements, on the discontinuities within the crown pillar areas, are well within the elastic limits of the material. /Author/

  • Corporate Authors:

    Commonwealth Scientific & Industrial Research Org

    314 Albert Street
    East Melbourne, Victoria,   Australia 
  • Authors:
    • Barton, C M
  • Publication Date: 1977

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 30 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00153353
  • Record Type: Publication
  • Report/Paper Numbers: Tech. Paper No. 24 Monog Ser
  • Files: TRIS
  • Created Date: Sep 28 1977 12:00AM