Direct-pipe in Limburg

A.Hak performed a direct-pipe drilling for Gasunie when crossing the Meuse River in Limburg. ‘Using this drilling method, we managed to deliver the project safely, on time, and within budget, despite the difficult-to-drill soil layers,’ says project manager Raymond Bos from A.Hak Drillcon.

Since 2008, Gasunie has invested heavily in expanding the gas transport network in the Netherlands. The ambition is to make our country Europe’s gas hub. Therefore, many kilometers of additional natural gas pipelines have been laid throughout the Netherlands as part of the North-South Route. Two new compressor stations have also been built.

On October 1, 2010, the first phase of the North-South Route was completed with the delivery of 275 kilometers of gas transport pipeline and the Scheemda compressor station. A year later, another 100 kilometers of pipeline was delivered along with the Wijngaarden compressor station. The Limburg route Odiliapeel-Melick belongs to the third phase of the North-South Route.

‘In spring 2012, various A.Hak divisions started work on the route,’ says Raymond Bos. ‘But first, we conducted additional soil research because we needed more information about the ground conditions under the Meuse. The Limburg subsoil is characterized by the presence of large amounts of gravel, for which conventional drilling techniques are not suitable. That’s why we advised Gasunie to use the direct-pipe drilling technique.’

Collaboration
Through smooth cooperation between A.Hak Drillcon, A.Hak Leidingbouw, and dewatering company Tjaden, the new gas pipeline now lies under the Meuse. ‘Currently, A.Hak Leidingbouw is busy returning the soil to the excavated route,’ says Bos. ‘The work is expected to be completed in June this year, allowing Gasunie to put the pipeline into operation in October.’

Besides the direct-pipe drilling method, A.Hak Drillcon also used other drilling techniques on this route. ‘Gasunie’s engineering department had asked us to apply the H.D.D. method because they didn’t want to cut down forest on part of the route. We also performed seven closed-front drillings in total, including one under a railway line and one under a highway.’ This drilling was necessary because ProRail has strict requirements for pipelines running under the tracks. ‘That’s why we first created a concrete sleeve. Then the gas pipeline was installed. This reduces the chance of fractures and other problems. This also requires considerable technical insight and expertise. ProRail therefore sets high standards for contractors, but we have held all relevant certificates for quite some time,’ says Bos.

Taking Action
There was some pressure on the work because Rijkswaterstaat’s permit took some time to arrive. Rijkswaterstaat had stipulated that the entire pipeline in the flow section of the Meuse should be in place by the end of December 2012. After all, the river’s floodplains play an important role in capturing excess water during high water levels. ‘We met the deadline well ahead of schedule despite a few minor technical problems with the drilling machine,’ says Raymond Bos. ‘Due to a defective pump, water had entered the pipe, which could potentially cause disruption. Fortunately, that didn’t happen, and we were able to remove the water in time.’

How does direct-pipe work?
In the direct-pipe drilling method, a special tunnel boring machine (TBM) is attached to the front of the production pipe. This machine is approximately 20 meters long and has a cutting blade adapted to the local soil structure, multiple measuring systems, steering cylinders, and bentonite injection points. In direct-pipe drilling, like in horizontal directional drilling, the first step is drilling downward at an angle, followed by making a vertical curve. Once at depth, the tunnel boring machine is steered again to continue drilling horizontally. As the drilling progresses, the TBM is steered once more to make a vertical curve upward. This is how we crossed the Meuse in Limburg.

Bronze-green oak woods preserved
The Meuse is not the only stream crossed in South Limburg. Further south along the route, the pipeline also goes under the small river Swalm. In Swalmen, a village that is now part of the municipality of Roermond, Gasunie decided to drill with a wide margin under the Swalm so that peace would not be disturbed in an adjacent forest. The new 330-ton HDD drilling rig was used for these drillings.