Creating a building pit for a scouring pumping station

The Netherlands has substantial infrastructure to protect its low lying lands against high water. A feast of engineering is the “Afsluitdijk”, a 32 km long dyke which not only connects the two northernmost Dutch provinces, but also safeguards a large part of the Dutch population against high water. Sluices in the “Afsluitdijk” ensure that fresh water flowing through the Dutch river deltas can be scoured easily in the sea making use of the tides.

Yet there are extreme circumstances, such a as North Western storm or high tides, when the scouring sluices cannot be used. Due to the increased fresh water feed, the capacity to drain this water into the “Waddenzee” had to be increased. For this purpose a triple pump scouring pumping station is being built near Den Oever. The pumping hall, located well below water level, is brought to depth using a Damen DOP submersible dredge pump.

Project set-up

The DOP200 is owned and operated by the Dutch contractor Martens en van Oord. The project set-up, just east of the Stevin Sluices, is well considered. The building pit itself, measuring some 50 by 50 meters, is created using sheet pile. The top soil has been removed by excavators. Then a pontoon has been located in the flooded construction area. On the pontoon a wire crane with DOP submersible dredge pump were located.

The DOP dredge pump is fitted out with a sand mining head. This suction head features jet water nozzles. On this location high pressure jet water is used to break up soil cohesion, resulting in relatively fine sand. The DOP sub pump pumps out this fine sand at max -19m dredging depth through a prolonged suction pipe. The dredged mixture is transported to a reservoir some 400m away.

In this settling pond the dredged mixture gradually drains; 3 more water basins ensure that finer particles will also settle. Forming a closed system, the water from the last reservoir is pumped back into the building pit to be used as transport water again.

The DOP dredge pump is hydraulically powered using a separate power pack. The sand pump is maneuvered through the building pit by the crane operator. Great care is paid to move around the structures present below the water level. The DOP pump is moved through steel pipes using precise positioning equipment as guidance.

When the building pit is deepened to -19m, the job for the DOP dredge pump is done. Then the pumping station will be shaped using concrete floors, walls and ceiling.