A new method estimating the 2D Joint Roughness Coefficient for discontinuity surfaces in rock masses

Joint Roughness Coefficient (JRC) is one of the principal parameters used to calculate the shear strength and conducting aperture of discontinuities. Originally, 10 standard discontinuity profiles were commonly associated with JRC values. However, as the original profiles provided a rough estimation of joint roughness, many researchers attempted to investigate different methods of analysis to determine JRCs accurately. In the current study, we are proposing a new method for accurate JRC estimation. Firstly, we introduced a new roughness index (λ) using a Root Mean Square method, which considers inclination angle, amplitude of asperities and their directions. Secondly, the logistics function between λ and JRC was derived after locating the mean line, which is the line between maximum and minimum points of asperities. Finally, three formulae were developed to calculate upper-bound, suggested and lower-bound values of JRCs in relation to the variation of λ for two-dimensional discontinuity profiles. Comparison of our experimental test results with data available in the literature showed that the proposed roughness index, λ, can be used to determine JRC values accurately resulting in better estimation of discontinuity shear strength and conducting apertures. In addition, the sensitivity of JRC, shear strength and the ratio of mechanical aperture to conducting aperture (E/e) with respect to λ were also investigated. The results revealed that trends of JRC, shear strength and E/e ratios are similar. These parameters are found to be most sensitive when λ is in the range of 0.05-0.20.