Construction of Deep Gravity Line project in Abu Dhabi

NAV24 – Navigation with Gyrocompass

ProjectConstruction of Deep Gravity Line in Abu Dhabi
CustomerJoseph Gallagher International Ltd.
Project ManagerColm Dickey
Technical ManagerSimon Millard
Scope of works25 km of Microtunneling with nominal diameters from DN400 to DN2000
Construction timeDecember 2018 + 20 month
GeologyMixed sands and calcites
TBM’s used5 ISEKI and 3 Herrenknecht machines
Drive with NAV24DN1800 / DA 2220 drive of 520 m length by using an ISEKI TBM


Owing to the difficult climate conditions – the temperatures measured in the initial excavation pit were at approximately 40°C, those in the TBM went up to as much as 58°C – and due to the high level of humidity inside the pipe, the VL70 drifting laser manufactured by the GEO company had soon reached its limit despite its good quality.

After a distance of just under 400m had been covered, the diameter of the laser spot was approximately 80mm wide with the spot position being highly unstable. Even during the day, the position and the altitude shown on the laser display varied to such a degree that it was very difficult and sometimes practically impossible to exactly control the driving operation.

For this reason, Simon Millard urgently needed a solution enabling him to drive the remaining 120m of the tunnel.

Since he had recently learned that Tunnel24 had launched its new NAV24 navigation system, and given the fact that the two men had efficiently worked together some years ago, it was only natural that he got in touch with Tunnel24 under these particular circumstances.

The core components of the system comprise the MWDR gyrocompass, performing non-stop measuring operations, combined with a high-accuracy electronic hose levelling unit that allows for precise measurement to the nearest millimetre irrespective of drive length.

The system components are connected via a CAN bus system, with the computer being well shielded and protected in the WS box. Operating the system is a rugged tablet PC, a so-called “toughbook”, which runs Windows 10. This toughbook is connected to the WS box via a wireless LAN. This solution affords the machine operator maximum flexibility. Should the toughbook ever fail to properly perform its duties, it may be replaced by any device supporting Windows 10.

Drive lengths, pressure levels of intermediate jacking stations and main station can be integrated into the system as an extra.

The system used in Abu Dhabi was permanently connected to the Internet to ensure that the system could be monitored and supported from Germany at any given time.

The NAV24 system installation and support are ensured by means of a cooperation agreement concluded with the PPS company.

The on-site installation of the system was performed by PPS with the support of Tunnel24.

PSS also familiarised the local surveyor with the system setup and calibration. All in all, everything went off without a hitch so that regular driving operations could be resumed after two days.

The breakthrough into the target pit took place on Friday, 20 September 2019, with the exact target location being hit after a section of 520 metres had been driven.

The NAV24 system as well as the cooperation between Tunnel24 and PPS have proven to be effective under extremely adverse conditions.