Measurement for monitoring, probing and recording evidence - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 157

Drilling and the installation of the measuring equipment should be completed before driving
the tunnel in order to be able to record the first deformation of the rock mass (Fig. 4-21).
Figure 4-22 Simple deflectometer from
Interfels GmbH (see legend in text).
Settlement measurement. Another use of the deflectometer, apart from installation in a
borehole to measure transverse displacements, is to set them horizontal at ground level to
measure settlement. This procedure was used, for example, on contract A2 of the Stadt-
bahn Bochum [98]. In addition to a dense grid of levelled points on the surface, an open
chain of deflectometers was installed at right angles to the direction of advance, which
recorded the vertical displacements at short intervals with automatic registration and thus
the settlement rates (Fig. 4-23).
Figure 4-23 Use of an
open deflector measur-
ing chain on contract
A 2 of the Stadtbahn
Bochum [98].