New high-voltage connection under the Haringvliet

New high-voltage connection under the Haringvliet

Engineering film Joulz constructed a new high-voltage connection between Middelharnis and Geervliet, commissioned by Stedin. The 18-kilometre-long connection is part of improvement works to the electricity grid on Goeree-Overflakkee.

The connection runs under the Haringvliet, which is around 5 kilometres wide. Visser & Smit Hanab installed two series of casing tubes with a length of 2.5 kilometres, which were connected at the halfway point. The sections were joined together on opposite sides of the Haringvliet at Middelharnis and Zuidland. 126 sections of 20 metres - an impressive length.

The work island

In order to cross the water, V&SH placed a work island in the middle of the Haringvliet: a sheet-pilling trench filled with sand from this former estuary. The drilling rig, on a pontoon built in Dordrecht, was moored to this. There was a second drilling rig on the shore at Middelharnis. This was used to the implement the meet-in-the-middle technique. V&SH drilled 1,500 metres on one side and 1,000 metres on the other. Once the intercept shaft had been created, the pilot hole could be vacated. V&SH then drew the first casing tube through. The drilling was completed. This meant that the connection on the Middelharnis side was ready. In the second drilling phase, V&SH  connected the island to the Zuidland side.

Patent pending

The pontoon  then returned to Dordrecht to collect the winches required to draw the cables through the tube: three reels weighing 68 tonnes, which were delivered from Germany by ship. During the reconstruction, the work island was excavated and V&SH placed small pontoons supporting the connecting frame here. This were used at a later date to connect and sink the two halves of the crossing. So V&SH worked with pioneering methods in all areas of this project. This applies to the lengths involved as well as the innovative technique devised to draw the cables through. There is even a patent pending on this. The intensive cooperation between the different departments on the technical design, drilling and cabling work is remarkable. It's a great example of the cooperation within our company.