Preliminary assessment of joint roughness coefficient of rock slope using close-range photogrammetry technique

Abstract

Rock shear strength can be estimated using the Barton–Bandis model, which relies on the joint roughness coefficient (JRC). The Barton comb profilometer is widely used in the field. However, it requires much labor. It is also difficult to access and potentially dangerous. As far as we know, no comprehensive work is dedicated to determining the JRC of the rock block sample using the image analysis technique. The JRC measurement results are compared with the manual Barton comb profilometer results to determine the reliability of the close-range photogrammetry (CRP) technique. This photogrammetry technique is applied to measure the JRC of the rock slope in the study area. Using the CRP method, a drone (DJI Phantom 4 Pro) captures a high-resolution image of the rock slope. The JRC of the rock slope is digitized through image processing to create a three-dimensional model comprising four quality ratings: low, medium, high, and ultrahigh. The ultrahigh quality has the most accurate measurement among all the quality ratings. It has a 0% error compared with the actual measurement using the Barton comb, whereas low, medium, and high qualities have 15.54%, 9.46%, and 2.7% errors, respectively. However, the medium quality is the most efficient because it can produce a reliable JRC measurement within a short period and can be used for fieldwork.