Clever Planning

New HDD bore length record for Broadband

The list of Germany’s so-called households with poor access to modern data networks is still quite long, despite the German Government’s Digital Agenda, claiming that the NGA-Networks (‘Next Generation Access’) were supposed to be made available to the whole country by the end of 2018. This is not a great surprise as the time from the application being sent to the German Support Programme for Digitalisation up to the point where users can start to surf the net on home computers being stretched to the limit and is much longer than expected.

The Handewitt region, in Northern Germany near the city of Flensburg, is one of these regions with poorly supplied households. Three years ago, the ‘Glass-Fibre Extension Project’ was launched and in February 2020 the practical measures requested started to take shape. The provisions for the set-up of a FTTB/H-Network were published. The relevant extension area covered approximately 1,000 households in all 8 villages in the region – an area of 7.800 hectares.

HDD crossing under a major motorway

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MRK Media AG, with its head office in Munich, is the contracted planning office for this task. On behalf of Datacentre Flensburg-Handewitt GmbH, the company was also asked to plan and carry out the installation of 50 mm o.d. HDPE pipes and 50 mm o.d. multi-pipe bundles (24 x 5) for the redundant connection of partial networks directly to the fibre Backbone.

At first glance, this did not seem to be anything spectacular, but at second glance it turned out to be just that. The reason for this was that the plan called for an almost 470 m long bore path, running f rom the small village of Gottrupel close to the Scandinavian Park in an open terrain heading to the East. Here it crosses the four-lane A7 North-South motorway and then further on through open terrain again. Access to the motorway, in order to carry out control measurements with a directional drilling detection system, which would have been obligatory, as well as accessing the areas used for farming in open terrains, were strongly prohibited.

Clever planning and a reliable HDD rig

It was a clear case for the installation of the pipes underground using the HDD method, so there would be no disruption to the natural surroundings, no detriment to the motorway traffic, low emissions for noise, CO2 and fine dust, also it was a sensible solution both technically and economically. It was also a clear decision for the contractor, Bahnsen Tiefbau GmbH & Co. KG, which had the relevant equipment, the experience and necessary know-how to complete the work. The contract was established in little time, and the Bahnsen bore team arrived at the scene very quickly. In order to find out whether their ever-reliable and precise GRUNDODRILL 15XP could realise such a long bore in the prevailing ground conditions (soil classification 3-4), the Bahnsen owner and team leader Paul Baumann had previously carried out a bore at 1.5 to 2.0 m depth over a length of 430 m. This went extremely well, proving they could start this project right away.

For this task Bahnsen chose a special 3-finger bore head of 125 mm diameter as bore tool for the GRUNDODRILL 15XP and built a backreamer for upsizing the pilot bore. With its very compact dimensions, the midi HDD rig has low working space requirements, which in the small village of Gottrupel with its tight lanes, was a big advantage for the starting pit. After everything had been set-up and the drilling fluid mixture had been determined, it was time to start the pilot bore. The 3-finger bore head easily passed through the light to medium displaceable soil. The ground conditions allowed steering without any problems and the bore progress was continuous.

Record length HDD bore in one go

When crossing beneath the A7 motorway everybody held their breath for a while, given that the bore head was working its way horizontally at a depth of 7 m, ‘blind’ beneath the motorway. The Head of Motorway Works was not concerned and accepted the blind bore, relying totally on the experience of the bore crew.

After an unbelievable 469 m length the pilot bore reached the target pit without any problems whatsoever, creating a new bore length record for the Bahnsen bore team and also for the GRUNDODRILL 15XP! Even the blind bore underneath the motorway looked like becoming a new record with the height difference from the starting point at the A7 to the measuring point at the end of the A7 being a mere 10 mm. Respect!

Upsizing of the bore path with the backreamer and the simultaneous pulling-in of the HDPE pipes and multi-pipe bundles was carried out smoothly. The installation time was 11 hours, which equates to 42.6 m/h which is pretty fast. Maybe the bore team will have even more similar challenges during further broadband extensions in Handewitt. Who knows, maybe more records are waiting to be broken? Website: www.tracto-technik.com

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Newsdesk
Trenchless Works bringing you balanced journalism, accuracy, news and features for all involved in the business of trenchless and no-dig from around the world

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