Preliminary Assessment of Joint Roughness Coefficient of Rock Slope Using UAV–SfM Photogrammetry Technique

Joint roughness coefficient (JRC) is an important criterion to determine the shear strength of rock, for example, as one of the inputs for the Barton–Bandis model. Conventionally, the Barton comb profilometer is widely used in the field but it is labour-intensive, has limited accessibility and involves potential hazard. This study aims to evaluate the structure from motion photogrammetry technique in producing reliable JRC measurements. To achieve this, a sample from a rock slope is used to determine the JRC readings. A drone is used to take a high-quality image of the rock slope using unmanned aerial vehicle photogrammetry method. Image processing consists of four quality ratings: low, medium, high and ultra-high. Digitalisation of the JRC of the rock slope takes place to create a 3D model using photogrammetry. The JRC measurement results are compared with the manual Barton comb profilometer method to verify the photogrammetry technique. As a result, the JRC of the rock slope can be produced by using the image analysis technique. The ultrahigh quality has the most accurate measurement as actual length with 0% error compared to actual measurements using Barton comb. For low, medium and high quality, the errors were 10.26%, 7.69% and 2.56%, respectively, to the actual length of the selected lines. However, the medium quality is the most efficient way because it can produce the reliable JRC measurement within a short period and can be used in fieldwork.