New measurement and control technology in tunnelling - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 245

6 New measurement and control technology in tunnelling

6.1 General

The development of tunnelling machinery has led to a particular degree of automatic con-
trol. This has many reasons, of which the most important are:

- Automation can accelerate working processes and improve machine utilisation.
- The precision of machine control is essential for subsequent costs, for example the lin-
ing of the tunnel. The precision requirements for water and sewer tunnels with little fall
are particularly stringent.
- The working conditions for the operation of manually controlled tunnelling machinery
often lead to worsened health risks and mistakes due to obstructed view and noise.
Automation leads to an optimisation of control and often permits remote control, par-
ticularly in small-section tunnels.
On the other hand, there are limits in all fields to the degree of automation, and these have
sometimes been reached. This is mostly due to the inadequate capability of automatic con-
trols to react to extreme conditions. Almost all systems therefore allow manual override
in order to overcome particularly difficult situations. For the surveying of an excavated
section of tunnel, devices have been developed, which can cope with the conditions bet-
ter than formerly, particularly the urgency and inaccessibility of the areas to be surveyed.

6.2 Measurement instruments

6.2.1 Gyroscopic devices
A gyroscope is a spinning rotor that maintains its axis of rotation and revolution speed as
long as no external torque is applied. Technical gyroscopes are flattened and symmetrical
bodies, which rotate about the principal axis with the largest moment of inertia; the mo-
ments of inertia for the other two principal axes are equal. The rotation speed of technical
gyroscopes is between 3,000 and 48,000 rpm.

Free gyroscope. A gyroscope that can freely rotate in two further axes in addition to its
spinning axis is called a free gyroscope. Such a gyroscope has three degrees of freedom,
which is made possible by mounting it in gimbals (Fig. 6-1 left). Since no external torque
acts on it, a free gyroscope maintains the spatial location of its axis of rotation in space. It
can therefore be used to display the direction of movement (as a directional gyro or head-
ing indicator) or vertical (as a vertical gyro). The rotation of the Earth also leads to move-