Tilt mapping for zigzag-shaped concrete panel in retaining structure using terrestrial laser scanning

Traditional monitoring systems are not able to monitor the global behavior of large retaining structures, and terrestrial laser scanning was performed for monitoring a retaining structure for this paper. The three-dimensional point cloud was obtained by scanning at seven locations with seven reference targets to cover the retaining structure having 180 m length and 25 m high. To evaluate the long-term behavior of the retaining structure, point clouds obtained by performing eight laser scanning at the same locations over 4 years were compared with each other. In this paper, the tilt mapping method was applied to define the global behavior of the entire retaining structure. The P2P-TA (Plane-to-Plane-Tilt Angle) comparison method was used to calculate the tilt angle by comparing the normal vectors of the planes created by the point clouds, because simple comparison methods are not able to be applied to compare points clouds of zigzag-shaped concrete panels. A laboratory test was conducted to determine the applicability of laser scanning and P2P-TA analysis, and the error range was conservatively set to 0.15°. The results of laser scanning and P2P-TA analysis applied to 231 concrete panels are shown in the tilt mapping of the retaining structure. The differential tilt angle was significantly increased every year at the bottom of the concrete panel adjacent to the tunnel. It can be seen that the concrete panel having a large differential tilt angle affects the differential tilt angles of others, because it is linked to other concrete panels.