Damen DOP350 Pump
Tackles unexploded ordnance in the North Sea
Project Leader Engineering
Martens en Van Oord
A Damen DOP dredge pump played a key role in a project involving the removal of unexploded ordnance (UXO) in the North Sea, which originated from the Second World War.
Dutch civil engineering contractor Martens en Van Oord was tasked with the creation
of two dams to protect the coastline off Cadzand, in the south west of the Netherlands, following which a new luxury yachting marina would be developed between the two dams.
Jos Schoenmakers, Martens en Van Oord Project Leader Engineering, explains why the Damen DOP350, alongside a dry-installed, electrically-driven Damen BP3530MD pump, proved the right combination for the job.
“This was an unusual project in that the dams of 315 metres and 510 metres were being created in open sea in the North Sea itself, and then the new harbour had to be developed between them, with 125 berths for yachts. On top of this, the area had an anti-invasion line with UXO from the Second World War, so stringent safety precautions were vital.”
Initially, Martens en Van Oord worked with REASeuro, a specialist company dealing with explosives removal, on the larger UXO of 4.2 inches and above, and then the company was free to dredge at the site. However, this still left the problem of UXO smaller than 4.2 inches.
The powerful Damen DOP350 was chosen for the UXO job and attached to one of Martens en Van Oord’s pontoon-based excavators, the Mantsinen 160R, and placed on the multipurpose pontoon the Scheldeoord. The DOP350 pumped the bottom material, which included sand, gravel and UXO, and then the material was taken to a special, reinforced screening installation. The oversized material was then transported to a barge. During transport the gravel and UXO travelled along a magnetised conveyor belt, which removed the UXO.
Jos says: “The submerged DOP pump was very advantageous for this project because the DOP350 ensures a continuous process (in UXO areas), as opposed to using mechanical dredging.”
Meanwhile, the dry-installed, electrically-driven Damen BP3530MD booster pump was used to pump the screened sand a further 400-600 metres to replenish nearby beaches.
Special Mining head
For sand winning, a customised sand mining head with plenty of jet water was fitted. This DOP head was designed for mining a maximum concentration using pressurised water to fluidise the bottom material. “The suction head, which was entirely developed in-house, enabled a better clearance of dirt, rubbish etc. and is much easier to clean.”
And it all had to take place in a risky UXO environment. Jos explains that UXO protection steel plates and blankets were used on the pontoon to protect workers and during production everyone had to be off the deck of the pontoon in a ‘cabin office’, which had extra thick windows to protect from projectiles in the case of an explosion. The cabin of the excavator also had extra protection and reinforced glass.
After eight weeks of preparation the project was completed in five months and finally around 250,000 m3 of material was dredged.
The Damen 350 DOP had also been used in an earlier project involving UXOs, Jos says. Here, Martens en Van Oord deployed the pontoon Roeroord with an excavator to widen and deepen the River Maas in Limburg in the Netherlands.
The UXOs were sieved by deploying a magnet roll, taken out and stored in underwater containers. “Again the DOP pump facilitated a continuous operation. The DOP is easy to use, with the excavator boom and very flexible.
“Ultimately we want to have as much production as possible. We worked closely with Damen to get really high pump power, to maximise the flow of mixture, and this was coupled with the lowest use of energy. The transport of the sand also has to be as efficient as possible. This ‘two pump’ method led to the best solution.”
Martens en Van Oord, which was established in 1986, and Damen have worked together for almost 20 years and the Dutch contractor has some 15 Damen pumps in its fleet.