By delivering millions of very accurate 3D points, laser scanning is an alternative for classical topographical measurements with a total station or digital photogrammetry for measurements in difficult field conditions. This makes terrestrial high resolution laser scanning a technique that is increasingly being used for geodetic deformation measurements of civil technical constructions, ic newly built tunnels. This paper deals with the error values during processing of a measured tunnel section and the final determination of the deformations of this tunnel section based on 3D laser scan point clouds.

The subject of this research is the still ongoing construction of two railway tunnels under Brussels Airport (Zaventem, Belgium). There are two times six tunnel sections that have to be closely monitored. These tunnel sections have to be scanned immediately after placement of the tunnel section, once a week during the first month after placement and once a month from then on until stabilization of the construction. The concrete surface of the walls is scanned with an average lateral resolution of 5 mm. During the research until now, a workflow to determine the deformations of the tunnel sections is developed for processing the data with one laser scan software package (Trimble Realworks), followed by further analysis with a CAD software. The comparison between the successive measurements is based on the determination of the section radius every 0.1 grad. The differences that are determined between the different points in time show a stabilization of the construction after the second control measurement. The comparison of the second control measurement with the previous control measurement shows a systematic and random error of less than 1 mm. Different types of laser measurement instruments are used (pulse-based and phase-based laser scanner, robotic total station with scan function) and of each type the experimental standard deviation on the measurements is determined.