A semi-automated method for extracting vertical clearance and cross sections in tunnels using mobile LiDAR data

The applications of laser scanning technology are rapidly expanding in the civil engineering domain. LiDAR technology is now commonly used in the surveying and monitoring of large infrastructures. In particular, tunnels have become key transport infrastructures, subjected to maintenance processes that allow quality checks for tunnel modifications or tunnel clearance and profile checks. The research described in this paper targets developing an approach to semi-automatically retrieve the tunnel vertical clearance based on ground based mobile LiDAR data. The steps of this approach include extraction of cross sections orthogonal to the vehicle trajectory and road markings based on radiometric information, and conversion of cross section to a two-dimensional profile to estimate the vertical clearance. The validation of the developed approach is done using real-life case study, a road tunnel in southern Galicia, Spain. An accuracy of 100% in detection of cross sections is achieved. Only one of the cross sections shows a relative error in vertical clearance measurement higher than 1%. The results demonstrated the effectiveness of the developed approach for computing vertical clearances and demonstrating that tunnel management activities can definitely benefit from using mobile LiDAR by minimizing survey time and increasing productivity in dangerous environments.