Evaluation of existing criteria in estimating shear strength of natural rock discontinuities

As evident from the literature, there are a number of shear strength criteria proposed by different researchers. In spite of that, Barton's JRC-JCS model is probably the most widely used criterion in routine engineering environments. Ease of determining the input parameters and efficiency in estimating the shear strength are the two key aspects which make this criterion widespread in rock engineering activities. When the shear strength criteria existing in the literature had been analyzed by the authors, it became apparent that the difficulty levels or eases involved in determining the input parameters of eleven criteria, including Barton's criterion, are broadly comparable. However, the existing criteria do not seem to have been compared in terms of their practicality/applicability while estimating shear strength of 'real' natural rock discontinuities. In the present investigation, a total of 196 direct shear tests were performed on natural discontinuities of three distinct rock types (i.e. granite, quartzite, and sandstone) from India at normal stresses within a range of 0.22-2.01 MPa. The estimated shear strengths were compared to the determined shear strengths. The efficacies of the eleven shortlisted criteria in estimating shear strength of 'real' natural rock discontinuities were critically evaluated. The criteria emerged to be the most efficient in this regard were highlighted and plausible reasons behind all the findings of this study were also explained.