Back in 1948 Grand Isle stood tall and deep thanks top its firm foundations, but the search for untapped resources took oil companies into evermore hostile waters. For the 120 metre Beryl Alpha to survive the ravages of the North Sea the platform would have to be made of sterner stuff than steel.

When engineers want to build an oil rig in the Beryl field off the British coast, they must find a way to protect it from the violent North Sea. Its foul weather and killer waves are a huge problem for oil platform engineers as their traditional construction material steel has a big weakness. In shallow waters a steel platform is stout and strong enough to resist the pounding of the waves, but in the deeper waters of the North Sea where its legs must be longer it faces a problem. The steel legs are now so flexible that the power of the waves can bend the rig backwards and forwards, over time it will develop weak points and break.

To get round the problem engineers come up with a new concept, an oil platform cast in concrete. It will have a massive base that locks it in place on the seabed, and its concrete legs will be so rigid that they won’t bend in the waves. Concrete made in layers is not strong enough, so engineers find a new way of casting concrete structures in a single piece. In 1973 Norwegian engineers use this technique to build an oil rig tough enough for the North Sea.

They pour concrete into moulds to form 19 hollow chambers which make up the base of the platform. When the chambers reach a height of 15 metres the builders flood and float the whole structure out into deep water. As they keep pouring concrete into the moulds the platform sinks ever deeper until it reaches its full height. Then they float the platform deck over the legs and bolt it on. Finally they pump air into hollow chambers in the base to float the 300,000-tonne monster back up to the surface. Now the rig christened Bery Alpha is ready for its maiden voyage. In July 1975 it begins the trip out to the Beryl oil field using tugboats that have a combined pulling power of 85,000 horses. Beryl Alpha becomes the heaviest thing mankind has ever dragged across the planet. When the concrete giant reaches its destination it’s dropped to the bottom of the North Sea, where it stands to this day.

Clip from the “Big Bigger Biggest” documentary series exploring the engineering breakthroughs that have enabled us to develop some of the largest structures in existence.

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