Determination of joint roughness coefficient (JRC) for slope stability analysis: a case study from the Gold Coast area, Australia

Surface roughness of rock discontinuities is an important factor that determines the strength characteristics of rock mass. Joint roughness coefficient (JRC), which is typically measured by means of Barton's combs in the field, is widely used to describe the joint roughness. However, this traditional method of measurement can be rather subjective, labor-intensive and time consuming. In contrast, photogrammetry can provide an alternative method to obtain relatively simple and fast measurements of JRC based on high resolution 3D models. However, the reliability of such measurements still remains an issue as the results from photogrammetry can be affected by the quality of images. This study seeks to clarify whether photogrammetry can produce accurate measurements of JRC that can be used to assess the stability of slopes. A rock slope with a recent wedge failure in the Gold Coast area, Australia was selected for this purpose, and three different methods such as manual measurements, photogrammetry, and tilt tests were employed to determine the JRC. The obtained results showed some discrepancy in the values of JRC obtained from these three different measurements. In particular, the JRC obtained using the Barton's comb had slightly higher values compared to those determined through the photogrammetry method while the tilt test results tended to yield overestimated values of JRC. Computer analysis using Universal Distinct Element Code was also performed to study the effect of JRC variation on the slope stability. It was found that an increase in the JRC led to an increase in the safety factor of the slope.