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[photo foundation]

Parts ball-joint and foundation

The ball-joint is not a perfect sphere but consists of various segments of a sphere or "shell elements": a forward shell, rear shell and a two-part under- shell. The steel sphere rotates in ten cast-steel pedestals: a large rear- pedestal, a smaller front-pedestal and eight small under-pedestals. The shells are attached to the concrete basin in the foundation by means of steel anchors. When the gate is being driven in, the hinge rests with the bottom shell on the under-pedestals. The sphere is not pressed into the rear shell until submersion and the water-pressure differential is taken up.

The hinge-foundation is required to transmit the immense horizontal forces of the water pressure to the subgrade. The foundations consist of a concrete construction in the form of a wedge of cake, with an ultimate weight of 52,000 tonnes (520 x 10E06 N). Not a single pile was used in the construction of this colossal foundation. Radical soil improvement enabled the foundation to be built directly onto a firm, compressed sand-layer. The concrete foundation and hinge may be compared with a soft, yielding cushion. The subgrade is composed in such a way that the foundation is able to move by some 22 centimetres to a depth of 40 metres in the event of a severe storm. Once the load has eased the foundation gradually springs back. Allowance is made for the fact that part of the shift will be permanent, so that there is a chance that the barrier will end up several centimetres closer to Rotterdam after a severe storm. The amount by which the barrier shifts permanently will be greater the first time the barrier is closed for a storm than later on, when the sand beneath the foundation has been compressed even further.