Measurement for monitoring, probing and recording evidence - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 160

Figure 4-26 Trivec device
for the measurement
of three displacement
components along a
vertical measurement line;
Solexperts AG.
The principle of a tunnel scanner is based on a “stereo-photogrammetric” image of the
tunnel surface, which means that all areas of the tunnel surface are scanned simultane-
ously from two different positions to enable 3D reconstruction. The position of the instru-
ment is fixed by surveying, for example with auto-targeting theodolites. An example of
such a system is shown in Fig. 4-27.
The scanner works with two high-resolution digital cameras (Charge Coupled Device,
CCD), which are mounted on a frame and successively record the tunnel wall (Fig. 4-27).
The recorded data can be digitally further processed into a digital model of the tunnel sup-
port layer. This system offers the following advantages in tunnelling [254]:
- Short recording times.
- Simple handling by one person without special training.
- Robust nature of the system.
- Precise results (± 1cm for 3D images).
- Simple and rapid processing.
- Direct digital further processing.
- Flexible display of results.
The DIBIT scanner (Fig. 4-27) was used in the driving of the Hellenberg Tunnel to record
the profile of the shotcrete layer. Since it demonstrated a complete over-profile, it was