Record 1700mm HDD drilling! (2008)

Stellendam - Denys Engineers & Contractors has installed a 1706 metre long water pipeline in South Holland. “A Dutch long-distance record using HDD technology,” according to commercial director Martin van der Waal.

The water pipeline will provide adequate drinking water to the residents of Goeree-Overflakkee in the future. In the future the Haringvliet will be permanently connected to the North Sea as the sluices will be kept opened. “This means there is a risk, especially in dry periods, that the water in the current intake station from EVIDES, the water company, will become too salty,” explains Van der Waal. The new transport pipe from the water pipeline company Evides is 5300 metres long in total. A large part of the pipeline could be laid in an open excavation. This was not possible for the 1700 metres - where a lock, a canal and a traffic roundabout have to be crossed. Evides chose to drill for 1700 metres, 43 metres below ground level. A courageous decision, according to Van der Waal. They were pushing the limits. In the Netherlands, this distance has never been done with HDD (horizontal directional drilling) technology.” In Germany, the director knows, a 2600 metre pipeline has already been drilled.

“A pipeline should be built as straight as possible across the land. In the Netherlands there are hardly any straight stretches of motorway over that distance.” It must be laid straight in order to avoid cracking in the corrosion-resistant cement cover on the inside of the pipeline.

Cavities

The long distance also meant extra attention of the driller. During the drilling with 9.5 metre long drill rods and bentonite, he was especially wary of blow-outs. “Bentonite can break out to the surface through cracks and holes. You can never be sure whether there are any. Therefore, the driller kept the bentonite pressure as low as possible. But not too low, as the bentonite with sand has to remain flowing.” Returning bentonite was purified with a desanding machine.” Taking salt water into consideration, a risk for the stability of bentonite, Denys drilled about 200 metre per 12 hour shift. Although the pipe has a diameter of 600 millimetres, the eventually drilled hole was 20 centimetres larger. “In order to reduce friction.” After the drilling operation and a check-run (inspection), the installation of the pipeline began on Queen's Day. It could not be delayed, since this would jeopardise the stability of the borehole.

Physical tractive force

The pipeline went into the ground at half past nine in the evening at an angle of 8 degrees. Eighteen hours later the pipeline, filled with water - weighing 850 tonnes, was coming out at the other end near Delta Expo (Haringvlietplein). “Only 85 tonnes of physical tractive force was required to get the pipeline on the rollers.” Van der Waal looks back with pride on an exciting project. "The borehole could have collapsed.” Emergency phone calls were not necessary. The champagne could be opened. “And we lit a big cigar. Everyone was happy when the pipeline surfaced again.”

(Source: Thomas van Belzen, COBOUW no. 55, 09/05/2008)