Utilizing LiDAR Technique in Monitoring Tunnel Deformations

Monitoring tunnel deformation is a crucial task for assessing long-term safety of a tunnel. This task requires an accurate and high-resolution spatial technique to precisely retrieve the abnormal signals on a tunnel surface. Among many measurement techniques in monitoring tunnel deformations, the Light Detection and Ranging (LiDAR) technique is capable of collecting spatial data automatically and rapidly. Although raw LiDAR dataset contains useful and important information, it lacks explicit geometric interpretation. In this study, an efficient approach for establishing a tunnel model to analyze deformation signal with multi-epoch LiDAR datasets is presented. By utilizing in situ control features, tunnel profiles (2D model) and 3D tunnel model from multi-epoch LiDAR datasets can both be expressed in a common reference frame definition. Then the minimum-distance projection (MDP) algorithm is proposed to estimate the 2D and 3D deformation signals on a tunnel surface. Furthermore, a rigorous covariance propagation approach is introduced to provide explicit quality indications on the obtained solution. Based on the results of simulation tests and a real case study of Hsuehshan (Xueshan) Tunnel, it has been shown that the LiDAR technique makes possible an efficient and accurate solution for monitoring tunnel profile deformations when the proposed approach is implemented in such task.