DEFORMATION�MONITORING�WITH�TERRESTRIAL�LASER�SCANNING:�MEASUREMENT�AND�PROCESSING�OPTIMIZATION�THROUGH�EXPERIENCE

Abstract

Terrestrial laser scanning offers the possibility to collect millions of very accurate 3D points in a short time. As a result of the high measurement speed and the achievable accuracy laser scanning has become a commonly used technique for recording e. g. archaeological artifacts or cultural heritage sites. Furthermore, terrestrial laser scanning is frequently deployed in civil engineering projects. Based on the experience from two recent deformation monitoring projects in Belgium, the applicability of terrestrial laser scanning for ovalization monitoring of newly built tunnels is assessed. During these monitoring projects, different types of measuring instruments (laser scanners and robotic total stations with scanning function) were tested and compared. For all measuring instruments, an experimental standard deviation was calculated, so an accuracy assessment could be made. In order to optimize the measurements on site, further research has been performed on the optimal scanning positions, scanning resolution and placement of reference markers ('targets') during the measurements. Moreover, the workflow for processing the laser scan data and the comparison of the subsequent measurements of a specific tunnel ring has been developed and optimized during these monitoring projects. This workflow aims to process the data as efficient and as accurate as possible, with user supervision in every step of the workflow. These processing steps result in clearly interpretable results, such as easily comprehensible drawings and tables, containing all necessary information on the changes in ovalization of a specific tunnel section. By controlling and optimizing each step in the project, a thorough risk assessment of the tunnel structures is ensured. Also, the risks of performing the actual measurements on site are minimized by optimizing the measuring equipment, the instrument settings and the measuring process in order to reduce the required measuring time, without reducing the quality of the data.