You always meet twice In life” goes an old German adage. This also held true when Frank Schwarzer’s phone at Tunnel24 started ringing a few months ago. Simon Millard from Joseph Gallagher International was on the other end of the line. Around 20 years ago, the two had worked together on a number of projects.
Millard describes the situation he was facing as follows: the construction of the Deep Gravity Line project in Abu Dhabi, in which he was currently involved, was being carried out by Joseph Gallagher International – represented by Colm Dickey as project manager and Millard in his capacity as tunnelling and technical manager.
The project comprised a total length of 25km of microtunnelling with nominal diameters ranging between DN400 and DN2000. The project started in December 2018 with a scheduled construction time of 20 months. Five Iseki and three Herrenknecht machines were in use on the project.
The geology of the region consisted of mixed sands and calcites. The section described in this article refers to a DN1800/ DA 2220 drive of 520m length excavated with the help of 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, 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.
Since the mid-nineties, Schwarzer has focused on the development of gyrocompass-based navigation systems for pipejacking and microtunneling purposes.
As more and more customers have requested gyro-based surveying systems over the course of the previous years, Tunnel24 two years ago took the decision to develop a new system on the basis of the sound knowledge it had gathered in the past. These efforts have culminated in the release of the Nav24 system.
The core components of the system are the MWDR gyrocompass, which performs non-stop measuring operations, combined with a high-accuracy electronic hose levelling unit that allows for precise measurement to the nearest millimetre regardless 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 Poltinger Precision Systems (PPS) company.
For decades, Munich-based PPS has been a well-established entity in the field of guidance systems – mainly in connection with large tunnel projects.
The company’s hardware and software are developed inhouse and continuously refined, with the firm’s own engineers operating the devices at construction sites worldwide.
At the end of the phone call between Schwarzer and Millard, the two agreed that the new NAV24 was to undergo its ‘baptism of fire’ during the driving operation that was already in progress.
The system was called up and prepared for shipping while the necessary export permit was obtained from the appropriate authority.
Once the system had arrived in Abu Dhabi, it was immediately installed and integrated into the ongoing driving operation on site.
Since drive site temperatures were extremely high as described above, this installation required a high level of commitment and endurance on the part of everybody involved. After one day, the bulk of the work had been successfully completed, whereupon the calibration and setup of the system began.
The on-site installation of the system was performed by PPS with the support of Tunnel24. PPS 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 20 September 2019, with the exact target location being hit after a section of 520m had been driven.
NAV24 is offered as a stand-alone device or may be integrated into the systems architecture of any standard machine manufacturer.
