Abstract
Global inspection of large-scale tunnels is a fundamental yet challenging task to ensure the structural stability of tunnels and driving safety. Advanced LiDAR scanners, which sample tunnels into 3D point clouds, are making their debut in the Tunnel Deformation Inspection (TDI). However, the acquired raw point clouds inevitably possess noticeable occlusions, missing areas, and noise/outliers. Considering the tunnel as a geometrical sweeping feature, we propose an effective tunnel deformation inspection algorithm by extracting the global spatial axis from the poor-quality raw point cloud. Essentially, we convert tunnel axis extraction into an iterative fitting optimization problem. Specifically, given the scanned raw point cloud of a tunnel, the initial design axis is sampled to generate a series of normal planes within the corresponding Frenet frame, followed by intersecting those planes with the tunnel point cloud to yield a sequence of cross sections. By fitting cross sections with circles, the fitted circle centers are approximated with a B-Spline curve, which is considered as an updated axis. The procedure of “circle fitting and B-SPline approximation” repeats iteratively until convergency, that is, the distance of each fitted circle center to the current axis is smaller than a given threshold. By this means, the spatial axis of the tunnel can be accurately obtained. Subsequently, according to the practical mechanism of tunnel deformation, we design a segmentation approach to partition cross sections into meaningful pieces, based on which various inspection parameters can be automatically computed regarding to tunnel deformation. A variety of practical experiments have demonstrated the feasibility and effectiveness of our inspection method.
Highlights
With the recent advances of 3D scanning sensors, digitalizing large-scale tunnel structures with 3D point clouds is becoming increasingly convenient, which could benefit a variety of applications such as tunnel deformation analysis and 3D modelling
Through fitting the cross sections into circles, the centers of fitted circles are approximated with a B-Spline curve, which is considered as an updated axis
According to the practical mechanism of tunnel deformation, we design a segmentation approach to partition the tunnel ring lines of cross sections into meaningful pieces, based on which various inspection parameters can be automatically computed regarding to tunnel deformation
Summary
With the recent advances of 3D scanning sensors, digitalizing large-scale tunnel structures with 3D point clouds is becoming increasingly convenient, which could benefit a variety of applications such as tunnel deformation analysis and 3D modelling. Due to various factors, such as tunnel construction, unexpected earth pressure, and geological conditions, the state of health of the shield structure could be strongly influenced. The most metro tunnel are constructed by shield tunneling machine and the design cross section of the tunnel is circle. The frequent routine inspection of tunnels is a crucial task to determine structural stability [1]. Accurate deformation analysis to meet the requirements of tunnel gauge and driving safety still remains a challenge in nowadays.
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