Abstract
Automatic concrete spalling detection has become an important issue for metro tunnel examinations and maintenance. This paper focuses on concrete spalling detection research with surface roughness analysis based on point clouds produced by 3D mobile laser scanning (MLS) system. In the proposed method, at first, the points on ancillary facilities attached to tunnel surface are considered as outliers and removed via circular scan-line fitting and large residual error filtering. Then, a roughness descriptor for the metro tunnel surface is designed based on the triangulated grid derived from point clouds. The roughness descriptor is generally defined as the ratio of surface area to the projected area for a unit, which works well in identifying high rough areas on the tunnel surface, such as bolt holes, segment seams, and spalling patches. Finally, rough area classification based on Hough transformation and similarity analysis is performed on the identified areas to accurately label patches belonging to segment seams and bolt holes. After removing the patches of bolt holes and segment seams, the remaining patches are considered as belonging to concrete spalling. The experiment was conducted on a real tunnel interval in Shanghai. The result of concrete spalling detection revealed the validity and feasibility of the proposed method.
Highlights
Different from on-ground infrastructure, tunnels are always under the complex environmental conditions and constant heavy traffic loads
The captured point cloud data by mobile laser scanning (MLS) system mainly contains the information of the tunnel surface where it is mixed with some outlier points originating from the subway tracks, cables, lighting equipment, and other facilities, which will inevitably have great interference on the concrete spalling
In order to identify the points belonging to spalling patches, we used the method of rough area classification described in Section 2.4 to separate bolt holes and the segment seams from rough points, so that the concrete spalling patches can be remained
Summary
Different from on-ground infrastructure, tunnels are always under the complex environmental conditions and constant heavy traffic loads. It is not uncommon to have damage on the tunnel surface due to the possibility of external forces and material deterioration [1, 2]. During the service period of a tunnel, regular inspection activities should be carried out to check its health condition and regular maintenance measures should be taken to keep its structural integrity and ensure the safety in the operation process [3]. A concrete spalling [4,5,6], as shown, is a small but nonneglected tunnel damage which refers to the happening of surface defects whose depths are deeper than normal scaling, caused by material deformation or fragile deterioration. Concrete spalling is one of the most serious problems that affects the performance and reliability of a tunnel [7]. It is urgent to replace the traditional method with a more accurate and automatic sensor-based method
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