2D and 3D evaluation of joint roughness exposed by rock cores

Since rock joint surfaces are not universally exposed in engineering practice, these surfaces usually cannot be easily obtained or observed. However, it is more convenient to obtain a part of these joints by drilling rock cores through them, and the diameter of the normal rock cores (75 mm or 100 mm) is close to the length of typical profiles (100 mm) given by Barton (1973). This study investigates a part of a joint splitting a rock core and the roughness of the exposed round surface. Both two-dimensional (2D) and three-dimensional (3D) methods are used to study the anisotropy of roughness at different shear conditions as well as the predicted shear strength, and a comparison between 2D and 3D methods is explored. Results confirm that shear directions affect both the 2D and 3D roughness parameters and hence shear strength with a similar variation trend according to rose diagrams. However, the rose diagram obtained by the 2D method shows central symmetry due to the central symmetry of the roughness parameter, while the diagram given by the 3D method is not. Moreover, the shear strength predicted by the 3D method is normally higher than that by the 2D JRC method at any shear direction. In addition, the weighing factor of surface roughness in evaluating the shear strength is also discussed. According to the theoretical model analysis, the study shows a potential application of rock cores in evaluating roughness, hence the shear strength of an engineering-scale joint.