New measurement and control technology in tunnelling - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 268

The steering possibilities are limited, due to both the ground around the shield and the
segments inside the shield tail. In order to avoid damage to the segments and unnecessary
constraint forces, the steering should always avoid contact between the segments and the
shield tail.
The shield has the following movements, which have to be recorded for control purposes:
- Pitch and roll angles are deviations from the vertical and are best determined with
inclinometers.
- The horizontal deviation from the design axis is called the yaw angle. It can be de-
termined optically using two targets in combination with a laser beam. Gyroscopic
devices can also be used to determine it, normally meridian compasses, although these
only deliver measurements when the machine is stopped between strokes. They are
particularly suitable when the tunnel alignment is a great depth and the correct direction
is difficult to transfer to the machine.
- The parallel divergence, that is the distance of the machine from the design axis in
vertical and horizontal directions, can be determined as follows:
1. A target on the machine is sighted with a theodolite.
2. The entire parallel divergence can be determined using a laser beam in the design
axis in combination with passive or active targets.
3. The horizontal deviation can be determined with a meridian compass by taking bea-
rings. A gyroscopic device in the shield indeed only delivers the yaw angle but can,
when no sideways jumps of the shield movement are to be expected (correction
steering in inhomogeneous ground), be used to calculate the horizontal locational
divergence from the yaw angle and the travelled distance. When a gyroscopic device
is used, the vertical divergence still remains to be determined. This can be measured
with a laser level or a water level.
Figure 6-26 Control of full-face machines
and shield machines. Steering, which only
reacts to current divergence (top) and
steering with anticipation (bottom) [197].