Determination of normal joint spacing from apparent joint spacing measurements

Abstract

Normal joint spacing is either measured directly from parallel joint members of the same set or indirectly obtained from the apparent joint spacing measurements. The latter is achieved by considering the geometrical relationship between the joint orientation and the scanline/rock core orientation. In common practice, one can compute either an individual weighting factor for each member in the joint set, or only one weighting factor for the entire joint set based on the mean joint set orientation. These methods yield the same normal joint spacing values if the joint members are perfectly parallel. However, natural joints are rarely perfectly parallel, resulting in the discrepancy (error) of normal joint spacing. In this paper, another means for determining the normal joint spacing from apparent joint spacing based on the geometrical relationship between the scanline orientation and the averaged orientation of two adjacent joint members of the same set is examined. A detailed analysis is conducted on different sizes of randomly-generated joint set data with respect to differently oriented scanlines. The absolute error of the normal joint spacing calculations obtained by proposed method, which is found to be always smaller than that by the conventional practice, is thus recommended. © 2013 Taylor & Francis Group, London.