Determination of joint roughness coefficient using a cost-effective photogrammetry technique

The presence of discontinuities in the rock mass is extremely crucial in many engineering applications of rock mechanics. The estimation of the joint roughness coefficient (JRC) utilising easily accessible camera-friendly devices and application software has recently gained prominence. The joint roughness coefficient of a jointed rough surface may be calculated using either contact methods (physically contacting the surface to get the profile) or non-contact methods (extraction of the profile without physically touching the surface using laser profilometry or 3D laser scanning and photogrammetry techniques). The 3D laser scanner is widely used for its accuracy in obtaining the surface topography of rock masses; however, the practice is often uneconomical due to the high equipment cost. In this study, the smartphone photogrammetry technology is used to extract the three-dimensional surface topography of a jointed rough surface in order to evaluate the JRC. For the comparative study, the surface profile was retrieved using a surface profilometer, 3D scanner and photogrammetry method. The JRC values for the surface profiles gathered through smartphone photogrammetry, 3D scanning and surface profilometer have been estimated using visual analysis, fractal dimension and statistical techniques. The study found that the surface profile generated using the photogrammetric approach utilising smartphone delivers more realistic profiling than the surface profilometer because of the lower least count and greater precision. The predicted JRC values for smartphone photogrammetry profiles agreed well with the JRC values obtained for 3D scanner and surface profilometer profiles.