The partition serves to protect the existing Coentunnel
In mid 2011, the second Coentunnel will be immersed in a dredged trench alongside the first Coentunnel. Because the second Coentunnel will be not more than twelve metres from the first tunnel, it is necessary to build a protective wall between the tunnel and the trench to be dredged. The wall consists of a drilled combination wall of steel pipes with a diameter of five feet, separated by a double sheet pile board. To ensure that the construction of this so-called partition does not affect the current location of the first Coentunnel, it was decided to use a low-vibration method. Coentunnel Construction hired the firm Fundex for this work. Poles of about 20 metres long will be driven into the ground to prevent that vibration from pile driving or compacting disturbs the subsoil of the existing tunnel.
Measuring is knowing
To exclude all risk, Coentunnel Construction has set up an extensive monitoring system, in addition to the low-vibration method. This monitoring system automatically reports absolute and relative movements of the current tunnel and vibrations and water tensions in the subsoil. Each of the four aspects has intervention values: yellow, orange or red alert.
Least possible interference with shipping traffic
Another important aspect of the work is that nearly of all it is done from two large pontoons in the North Sea Canal. To restrict the nuisance to shipping traffic, agreements have been made with the Port of Amsterdam. If, for example, the pontoons are in the fairway, ships will be receive a permanent guide. The recently started work is promising and the first piles are already at depth. The first part of the partition is now finished, which should make it possible to start dredging the trench in the autumn. The immersing of the new second Coentunnel will not take long from then!
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