Development of an elliptical fitting algorithm to improve change detection capabilities with applications for deformation monitoring in circular tunnels and shafts

• Published in: Tunnelling and underground space technology 2014-07, Vol.43, p.336-349
• Main Authors: Walton, Gabriel, Delaloye, Danielle, Diederichs, Mark S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Buildings. Public works; Change detection; Circularity; Deformation; Deformation analysis; Elliptical fitting; Exact sciences and technology; Geotechnics; Laser scanning; LiDAR; Measurements. Technique of testing; Monitoring; Scanning; Soil investigations. Testing; Surface chemistry; Tunnel monitoring; Tunnels (transportation); Tunnels, galleries
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2014.05.014

•The state of practice for deformation monitoring in tunnels is reviewed.•The capabilities and limitations of LiDAR for deformation monitoring are introduced.•Ellipse fitting algorithms for the analysis of tunnel point cloud data are presented.•A workflow for tunnel profile analysis using LiDAR data is developed.•The analysis method is shown to provide mm accuracy for detecting diametric change. Terrestrial laser scanning, also known as Light Detection and Ranging (LiDAR) is an emerging technology that has many proven uses in the geotechnical engineering community including rockmass characterization, discontinuity measurement and landslide monitoring. One of the newer applications of LiDAR scanning is deformation monitoring and change detection. In tunnels, deformation is traditionally measured using a series of five or more control points installed around the diameter of the tunnel with measurements recorded at regular time intervals. LiDAR provides the ability to obtain a more complete characterization of the tunnel surface, allowing for determination of the mechanism and magnitude of tunnel deformation, as the entire surface of the tunnel is being modeled rather than a fixed set of points. This paper discusses terrestrial LiDAR scanning for deformation mapping of a surface and for cross-sectional closure measurements within an active tunnel using an elliptical fit to data for profile analysis. The methods were found to be accurate to within a few millimeters when measuring 58mm of diametric difference over an 18.3m diameter circular profile, even when some sections of the data were removed from the analysis.