Spiral Sampling Method for Quantitative Estimates of Joint Roughness Coefficient of Rock Fractures

Representative sampling of surface roughness is essential for reliable and consistent estimates of joint roughness coefficients (JRCs) by quantitative formulations. The most commonly used sampling method is the straight-line profiling along a predetermined shear direction. Because of anisotropy and nonuniform distribution of roughness features on natural joint surfaces, this method may work well only when the potential shear direction is known or can be predicted. However, there are no guidelines for the density of parallel straight-line profiles and how these can be synthesized into a representative profile. This article presents a spiral sampling method that addresses the shortcomings of the straight-line method. The roughness parameters derived from the spiral scanlines are closely correlated with the JRC values back-calculated from direct shear tests.