Sensitivity Testing of the Newly Developed Elliptical Fitting Method for the Measurement of Convergence in Tunnels and Shafts

Light Detection and Ranging (LiDAR) has become more widely used in the geotechnical community as its number of applications increases. It has been shown to be useful in tunneling for applications such as rockmass characterization and discontinuity measurement. LiDAR data can also be used to measure deformation in tunnels, but before a comprehensive methodology can be developed, the accuracy issues associated with scanning must be fully understood. Once the accuracy issues associated with LiDAR are well understood, any analysis technique that uses LiDAR data must be tested to ensure that the determined accuracy issues have minimal impact on the results of the analysis. To prove the usefulness of the newly developed elliptical fitting method for the measurement of convergence in tunnels and shafts proposed by Delaloye et al. (Eurock 2012), a comprehensive analysis of accuracy issues associated with LiDAR scanning was conducted and then a sensitivity test of the convergence measurement technique was completed. The results of the analysis show that using the statistical techniques built into the elliptical fit analysis and LiDAR profile analysis, levels of real change (convergence), within the nominal level of random and systematic noise included in the data, can be measured with confidence. Furthermore, the new analysis is robust enough to handle large amounts of occlusion or missing perimeter coverage within data sets.