Design of retaining wall

The conditions under which the retaining wall must remain stable (i.e. rough weather and the force differential caused by the differing water levels) make exacting demands on the design. In testing the wall it was discovered that it began oscillating uncontrollably under certain conditions. The wall was for example sucked downwards by the high velocity of current below the wall (i.e. a Venturi effect).

This problem was resolved by modifying the shape of the wall by tapering the underside on the seaward side and by introducing skirts (i.e. stabilising strips at the outer bottomside of the retaining wall).

The sections forming the retaining wall are hollow. This is why the walls float and can be moved and be sunk down by letting them fill with water. The lower buoyancy chambers have computer-operated valves. The upper chambers have perforations and automatically fill with water and empty again.

The perforations and computer- operated pumps also help guarantee the stability of the wall.

There are leaks in the barrier. These are not however a cause for concern: the barrier need not keep out all the water but is a reductor. It proved simpler to leave a gap of one and a half metres between the walls to prevent them from "banging" against one another in the closed position. The opening means that water can pass through the barrier, although this is made more difficult as a labyrinth of two steel plates has been constructed. Water can also pass beneath the wall, while in a heavy storm water will also spill over the top. Water also leaks through the parking dock. In total these leaks have a surface area of some 125 m2, or 2.5 percent of the total retaining surface.