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Specialist for Tunnel Guidance Systems
In order to achieve optimal construction quality of the tunnel in a planned time, it is necessary to have precise and up-to-date information about the position and direction of the TBM relative to the Designed Tunnel Alignment (DTA). With this information the TBM operator is able to keep the TBM within a small tolerance circle to the DTA. The operator needs to perform control actions early and wants to get immediate feedback during the course of an advance. If the guidance system gives immediate feedback the advance speed can be maximized and is determined by the capabilities of the TBM. TBM steering must be done smoothly so that rings can be built without distortion. If deviation of the TBM position exceeds a certain limit the guidance system must calculate a correction curve which returns the TBM smoothly back to the DTA. This allows the operator to steer the TBM in a way so that the TBM capabilities and ring geometry are considered. Waiting time for delivery of the next ring is minimized if the guidance system precalculates the sequence of rings to be delivered to the TBM.

tacs gmbh supplies the acs guidance system, which is designed to provide all this information and more. acs

  • automatically determines the position and direction of the TBM
  • calculates the deviation and the correction curve
  • measures the position and direction of the built ring
  • shows data in clear and easy-to-read graphs
  • selects the ring to be built next
  • calculates a ring sequence
  • and produces a comprehensive, but clear data protocol for each advance.

tacs gmbh supplies and develops acs guidance system since 1993 for guidance and ring selection for segmentally lined tunnels. The tacs Video Target has been developed for use in tacs guidance systems, and has since been miniaturized. An explosion-proof (Class I, Division 2) variant of the acs guidance system is available for use in hazardous environments. tacs gmbh works closely with PSP consulting engineers, who have extensive civil engineering experience.

  acs Guidance System
The main reference point of the acs is defined by a theodolite mounted on the wall of the tunnel and emitting a visible laser beam. The useable laser-to-target distance depends on atmospheric conditions in the tunnel, the size of the target unit and the curvature of the tunnel. The lasertheodolite periodically will be relocated to a new mounting point. acs supports relocation of the lasertheodolite by an automatic, dialog guided procedure and measures the new laser position.

acs guidance system overview - Click to enlarge image

acs guidance system overview
Click to enlarge

tacs Video Targets
tacs Video Targets
With the laser beam striking at the target, distance to the lasertheodolite and roll of the TBM are measured and the position of the TBM is calculated. acs mainly uses the tacs Video Target, but also supports conventional or electronic targets. The Video Targets are available in different sizes to gain the widest possible distance for a certain DTA and TBM.

The actual TBM position and its horizontal and vertical deviation relative to the DTA are determined. The TBM position is shown in a clear and concise manner, allowing the driver to steer the machine close to the DTA.

Display of TBM Position - Click to enlarge image
Display of TBM Position
Click to enlarge


Optimal Steering The TBM
The range for steering actions however is restricted in some ways: they must respect the geometrical conditions of the ring to avoid damage to the ring or the TBM. If a TBM has articulation and/or tail jacks, other steering actions are possible. If the deviation of TBM position or direction relative to the DTA exceeds a given amount, acs determines a correction curve, which takes into account for these restrictions as well as for a given ring sequence and will lead the TBM back to the DTA.

At the end of the advance acs determines the optimal ring to build. The calculation of a ring sequence by acs allows to minimize transportation delays.

Motorized laser theodolite
Motorized laser theodolite

Different Levels Of Automation For Different Needs
The modular structure of the acs guidance system makes different levels of functionality easy to implement. This ranges from simple solutions with tunnel laser and conventional target boards, up to a fully automatic level, which gathers all measurement values electronically, and controls a motorized laser theodolite to follow the target unit in a curve.

  Data Exchange
Data can be transmitted via existing telephone lines to the site office on the surface, to monitor the current TBM position, perform automatic data backup or for remote maintenance, optionally even from tacs office in munich. Data can be exported to be processed with third-party standard software, e.g. spreadsheet software.

Industrial PC with touchscreen
Industrial PC with touchscreen

The acs guidance system has been successfully employed on projects with diameters ranging from 14.2 m (Elbe road tunnel, Hamburg) to 3.04m (water supply, Munich). Long-distance projects include 15.3 km Aguas Argentinas water supply, Buenos Aires; 10.3 km Mangfallstollen water supply, Munich. tacs guidance systems have been fitted to all makes and types of TBM and approved efficiently on many tunnel projects worldwide.

For more information on the acs guidance system please contact
tacs gmbh, Baierbrunner Str. 15, D-81379 München, Germany, tel +49 897857675 - 0, fax +49 897857675 - 20, e-mail or visit

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