Application of laser scanning for deformation measurements: a comparison between different types of scanning instruments

Abstract

SUMMARY High resolution terrestrial laser scanning is more and more being applied for measuring and monitoring geometric deformations of civil technica l constructions. At Ghent University (Department of Geography), research is being perfor med on the deformation measurements of newly built concrete tunnels, by terrestrial laser scanning. In the most recent project (‘Liefkenshoek Railway Connection’, Antwerp, Belgium) two side-by-side tunnels with a length of approximately six kilometers are being mo nitored. For each tunnel, the deformations of fourteen sections in are measured by means of te rrestrial laser scanning during the first three months after ring erection. To meet the project’s requirements for the measurem ent accuracy, a phase-based laser scanner, Leica HDS6100, is being used for these measurements. Furthermore, this type of laser scanner allows performing the measurements in a limited time frame. Based on previous experiments, an experimental standard deviation of 0.4 mm is reached with this type of laser scanner under these tunnel measurement conditions (short distances < 6 m). The choice for one specific type of scanning instrument does not o nly depend on the project's requirements but also on the technical developments and possibil ities at the beginning of the project. Because of the fast and high-level developments in scanning technology, a constant comparison and testing of different types of instru ments is advisable to choose the most suited instrument. Based on earlier research, an accuracy assessment o f the results with a phase-based laser scanner Leica HDS6100, a pulse-based Leica ScanStation2 and a Trimble robotic total station S6 (2” DR300+) with scanning function was possible. Recently, a series of tunnel measurements were carried out with the pulse-based Leica C10 laser scanner and the Trimble VX robotic total station. Both sets of test measure ments are based on the same experimental set-up and processing workflow which makes a completion of and a comparison with the earlier results possible and justified. This accura cy assessment, together with other parameters such as scanning speed, performance of the user int erface and the possibility to collect nongeometric data (color and intensity) allow for comp arison of the different scanner types not only for tunnel deformation measurements but also f or other civil engineering applications with similar requirements and field conditions.