Tunnel face videogrammetry for low-cost digitization and discontinuity set orientation measurements

Discontinuities significantly impact the stability of a rock mass and its hydraulic conductivity. Therefore, mapping rock discontinuities is essential to study rock mass behavior. This study explores the use of videogrammetry for digitizing rock mass at the tunnel face and measurements of joint orientations. Utilizing a mobile device for video capture, the method is compared against traditional laser scanning and mobile photogrammetry. Videogrammetry allows rapid data collection with smartphones or action cameras, emphasizing low-cost and accessibility. Results indicate that videogrammetry with a smartphone provides an acceptable level of 3D reconstruction, with 3 mm control distance error and 1 cm cloud-to-cloud distance compared to a reference high-resolution laser scan. Discontinuity orientations measured from the videogrammetric 3D model show reasonable errors of less than 2-6 on average compared to data measured from the reference laser scan. The study validates videogrammetry as a practical, efficient alternative for rock mass characterization in underground settings.