The gas distribution network in northern Germany has been extended thanks to speedy teamwork with a Herrenknecht microtunnelling machine on the recent pipejack project below the River Elbe. Excavation work was successfully completed in December 2014.
Long-term Herrenknecht contractor A.Hak Drillcon used a 3.02m AVND2400 machine for the 1.5km long excavation, which descended up to 35m below the Elbe and passed through various, partially complex geological zones – sandy gravel with stones, boulder clay layers with rocks, and clay. Water pressures were up to 4 bar.
The major pipejacking project is part of a modernisation programme for the regional gas supply network in northern Germany. Under high pressure in terms of both time and water, the tunnel was driven from the town of Hetlingen to the target shaft on Lühesand Island.
Large boulders were encountered almost 200m into the drive but and the experienced jobsite team swiftly overcame the obstacles.
Following replacement of worn tools, the microtunnelling machine picked up speed and on the remainder of the drive achieved advance rates of up to 40m/day.
The entire length of tunnel was able to be handled by the main jacking station in the starting shaft, and there was no needed for intermediate jacking stations on the drive – one of the longest pipejacking jobs in the world. This top performance was attributable to the consistent application of AVND technology, automatic annular gap lubrication and the great teamwork.
As a result, excavation on the 1,528m long drive was completed in 112 days, and the contractor finished in early December – in time for the feast day of Saint Barbara, the patron saint of tunnel builders and miners.
"Construction of the two new gas transit pipelines enables us to guarantee gas supplies for Northern Germany and Scandinavia in the future", said Dr Philipp v. Bergmann-Korn, spokesman for the client, Gasunie Deutschland Services GmbH.
As drilling contractor, A.Hak Drillcon relied right from the start on the expertise and support offered by Herrenknecht. Even during the refurbishment of the used microtunnelling machine, and undertaking project-specific modifications, A.Hak Drillcon and Herrenknecht worked hand-in-hand. A videoscope examination of the main bearing was undertaken, and the manlock and main bearing were modified to seal against water pressures of up to 4 bar.
The collaborative success extended very positively to the jobsite. Two Herrenknecht machine operators were available to support A.Hak Drillcon during the tunnelling process, and so helped to enable efficient three-shift operations and round-the-clock working. At all times, experienced service technicians – and electrician and a mechanic – from Herrenknecht were also on hand to provide tunnelling support on site.
"On such a challenging project, continuous mutual exchanges of experience are simply advantageous. We appreciate that. Comprehensive service is as important as good technology," said Peter Dennig, manager at A.Hak Drillcon.
For the purpose of increasing safety, A.Hak Drillcon also ordered an entire range of navigation, survey and monitoring technology from Herrenknecht’s subsidiary VMT. Using IRIS.microtunnel – a web-based, data management and monitoring system – it was possible to continuously monitor support pressures and compare them with the fluctuating tides of the Elbe.
Furthermore, the comprehensive HADES communication system featuring several modules such as video surveillance, fire alarm or RFID jobsite access control was used for the first time in Germany.