Measurement for monitoring, probing and recording evidence - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 166

Figure 4-34 Check-
ing anchor forces with
a vibrating wire sensor;
Maihak AG.
Hydraulic valve sensor. Fig. 4-35 shows a section through a hydraulic anchor force
measuring system (Glötzl-Solexperts). The equipment permits the removal of the force
sensor without unloading the anchor and can therefore be used any number of anchors.
The anchor force itself is transferred through an external anchor nut and a spreader plate
to the load cell.
Figure 4-35 Checking an-
chor forces with a hydraulic
valve sensor [243].
Example. The following example shows the evaluation and development of anchor forces
during a tunnel drive.
In order to measure anchor forces during the excavation of an investigation heading for
the Engelberg Base Tunnel on the Heilbronn - Stuttgart autobahn in Germany, a 4 m long
unbonded anchor was used as shown in Fig. 4-36. Anchor I was set after the completion of
the first partial excavation and - just like anchors II and III set in the subsequent phases of