RQD AND FRACTURAL SPACING

Rock Quality Designation (RQD) values are commonly used for estimating rock-foundation performance in engineering practice. However numerical analysis can be performed more easily with a knowledge of average fracture spacing and load deformation behavior of intact rock and fracture, e.g. Kulhawy demonstrated a procedure for estimating the settlement of loaded areas on fractured rock by a model that replaces the rock with an orthotropic continuum. For use on sites where RQD has been logged and to compare his results with empirical data, he developed a relationship between RQD and fracture spacing based on a simple geometric model. Although the two qualities are not identical, it is reasonable to assume that a relationship exists, and both depend upon the number of rock pieces in a core run of a given length. This study shows that there is a preferred relationship between RQD and random fracture spacing. Kulhawy's line, generated using a simple geometric model falls almost within the limits of values found in this study. A relationship proposed by Priest and Hudson based on a statistical relationship of joint spacing also falls within the bounds. Use of this relationship is appropriate in core lengths, where random location of joints is likely. This may not be the case in a core run that contained a change in lithology. Missing core would also introduce an error. Complete confidence in this relationship will only be available after correction and correlation of a significant amount of field data.

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Filing Info

  • Accession Number: 00310717
  • Record Type: Publication
  • Report/Paper Numbers: ASCE 15220
  • Files: TRIS
  • Created Date: Oct 8 1980 12:00AM