The works comprised the boring of six (6) 688 m long, 505 mm diameter ducts for the installation of high voltage power cables as part of the Bacharach Erdkabelanbindung project. The installation was complicated by the fact that the routes of all six ducts was required to include a 506 m radius curve.
The E-Power Pipe® system is a small diameter microtunnelling arrangement that in this instance utilised a Herrenknecht AVNS350XB microtunneller. The challenge for the project was that, with the combination of the included curve and the long distance, guidance for the small diameter microtunneller was a challenge.
To overcome this, the contractor called on tunnel navigation specialist VMT’s expertise to design a special guidance system to provide the necessary accuracy for the bores. The system developed utilised two proven techniques which included both a Gyro MWDII and a Paratrack 2 System (magnetic probe).
VMT’s challenge was to provide a guidance system that would not only ensure accuracy of the individual bores but also handle the challenging environment which included high voltage power lines which crossed the site which, as the project proceeded, led to erroneous readings with the Paratrack 2 System.
The project was something of a pilot project in that the systems had not been used like this in combination before. However it was decided that the comparison of the sensor data from both navigation devices would provide sufficient data to show if the navigation system could be trusted. Manual measurements with a TCA showed that the vast majority of the data from the magnetic probe was very useable. Where any minor discrepancies from the magnetic probe did occur this could be adjusted for by using the data from the gyro, so at no time was there any potential for the microtunneller to operate without confidence in the steering.
The fact that the personnel involved had no experience of such a system did not deter VMT’s staff and with a lot of new enhancements to VMT’s guidance software prior to the project a system was developed that it was believed would provide the accuracy required.
Ultimately on the successful completion of the bores the VMT system utilised by the E-Power Pipe® system proved to be a very suitable guidance solution for TBMs without a line of sight available and where no conventional control measurements were possible as all drives reached their target.
According to the VMT crew onsite for the works: “We learned a lot about the system during the advance and were able to gradually reduce the service on site and transfer more automation in the process as the project was ongoing.”
At a Glance Fact Sheet: