On the applicability of self-affinity concept in scale of three-dimensional rock joints

► Joint failure causes large instabilities in rock structures. The failure is highly dominated by surface topography of joints.
► Since measuring the entire surface is not possible, examining a portion of it and its attribution to the entire surface is used in the literature.
► Self-affinity is a common way for such approach. The best methods for measuring the surface topography are first introduced.
► Using such methods, the applicability of self-affinity concept in scale of joints is then examined and it is demonstrated as deficient.
► In this way, there is no relationship between the roughness of a portion of the joint surface and that of the entire surface.