Ever since the manufacturers of electronic total systems introduced instruments onto the market with coaxial distance measurements and accuracies satisfying the demands of the geotechnical engineers, the optical 3D displacement measurement displaced the thus far conventional convergence measurements, using a precision measuring tape together with levelling.

3D-displacement measurements with free stationing  during  excavation

This provided the geotechnical engineer with a new set of instruments which, for the first time, enabled the evaluation of absolute displacements in three-dimensional space. Numerous new ways of displaying the results graphically support the geotechnical interpretation of the deformation behaviour of the tunnel surface. Because the measurements are fast, inexpensive and generally do not interfere with the construction activities, it is possible to significantly increase the information density as a function of the geological and geotechnical conditions.