Calibration of rock joint roughness and shear strength with the use of 3D laser scanning technique

Abstract

In this paper, the adequacy of adopting 3D laser scanning technique to study the characteristics of sheeting joints roughness is investigated and a methodology in determining the shearing resistance of a rock joint under different scales is proposed. Two types of 3D laser scanners were used to digitise the granite joint planes from the sizes of 60 mm to 8,000 mm in length. They generated an extensive amount of coordinate points that simulate a realistic 3D image and contour plot of the surface. Through trials of different sampling lengths in 2D analysis, the roughness angles are measured from scanned coordinates and calibrated against the peak frictional angles and the joint roughness coefficients (JRC) that have been measured in standard laboratory test. The results demonstrate that although shearing resistance of rock joint is highly scale-dependent, the proposed framework is able to quantify the shearing resistance of rock joints due to the relative contribution of large-scale undulation, and laboratory-scale asperities angle using a consistent measurement method offered by 3D laser scanner. This framework is illustrated with the help of a worked example of scanning and measuring different sizes of typical sheeting joints that are commonly found in Hong Kong.