Indian Journal of Fundamental and Applied Life Sciences ISSN: 2231– 6345 (Online) An Open Access, Online International Journal Available at www.cibtech.org/sp.ed/jls/2015/03/jls.htm 2015 Vol. 5 (S3), pp. 2427-2442/Mohebbi et al. Research Article © Copyright 2014| Centre for Info Bio Technology (CIBTech) 2427 ACCURATE ESTIMATION OF SCALE INDEPENDENT JOINT ROUGHNESS COEFFICIENT, JRC, BY OPTIMIZED BOX COUNTING ALGORITHM Javad Gholamnejad and Mohsen Mohebbi, Alireza Yarahmadi Bafghi, Mohammad Fatehi Marji * Department of Mining Engineering, Yazd University, Yazd, Iran *Author for Correspondence ABSTRACT Mechanical behavior of rock mass is effectively related to the shear movements of in situ joints. Roughness is known as a parameter which strongly affects the stability of rock mass by increasing the shear strength. There are some difficulties in obtaining a good approximation to JRC such as inappropriate precision in measuring joint surface topography, time-consuming nature of this measurements and some challenges involved in the expression of roughness, e.g. visual analogy, scale effects and unaffordability. Despite several attempts to handle such challenges, still there is the lack of a practical way to obtain such a correct approximation. This paper tries to take the advantages of combining digital image processing and scale independent Box Counting fractal method by employing the most efficient edge detection techniques to propose an ideal and practical algorithm which overcome these defects. Furthermore, the performance of the proposed approach is gained by identifying the probable factors affecting the results and doing the analysis of their sensitivity on JRC values. So, by employing a single image of joint trace, the algorithm offers an accurate scale independent joint roughness coefficient in an efficient time. Finally, as a case study the technique is successfully applied to JRC estimation in Choghart iron mine. Keywords: Joint Roughness Coefficient, Box Counting, Image Processing, Choghart Iron Mine INTRODUCTION The mechanical behavior of rock mass is complex due to the presence of discontinuities. These structures have a major influence on the deformational behavior of rock systems. Roughness, which influences the friction angle, the dilatancy and the peak shear strength, refers to the local departures from planarity at both small and large scales. The development of research into roughness dates back to the 1930s. It has long been recognized that the roughness of rock discontinuities, when clean and unfilled, can have a significant impact on both the hydraulic and shear strength characteristics of discontinuous rock mass (Bryan and Grasselli, 2010; Giovanni and Egger, 2003; Mariusz, 2010). So Several criteria have been proposed in the past to identify the strength of a rough rock joints. These criteria delineate the state of stress that separates pre-sliding and post-sliding of the joint. Despite providing more complicated rough joint models such as Ladanyi’s empirical (Hsiung, 1993), Amadei-Saeb’s analytical (Aydan et al., 1996; Jing et al., 1992) and Plesha’s theoretical (Kulatilake et al., 1995) etc., in engineering practice, the shear strength criterion proposed by Bartonis widely adopted and used (Nicholas, 1973; Yang et al., 2001). The joint roughness coefficient (JRC) presented in this model and several empirical formulas were connected the rock mass mechanical parameters e.g. the shear stiffness and joint aperture related to the JRC. This coefficient scales the joint roughness in the range from 20 (rough) to 0 (smooth) and can be determined either by tilt, push or pull tests on rock samples (Fardin et al., 2001). Nevertheless in order to simplify the process of JRC measurement, Barton et al., offered a technique in which, the JRC value for a given joint profile can be estimated visibly by comparing it with ten JRC profiles. This set of profiles has subsequently been adopted as a standard by the ISRM (Yang et al., 2001). However, in practice it may be difficult to determine the proper JRC due to the inductive nature. Shortly after this, several alternate approaches have been proposed to estimate joint roughness coefficient with the aim to put down the analogy, so that recent years have witnessed a rapid development of new