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Oresund flooding delay
00:00 12 Aug 1998
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Exclusive by Patrick Reynolds
The failure of a temporary works plinth has been blamed for the sinking last week of a 57,000t section of Europe's biggest immersed tube tunnel which is being built between Denmark and Sweden.
Last Tuesday's accident on the Oresund road-rail project may mean delays of two months or more to the 3.5km long tunnel being built by Oresund Tunnel Contractors (OTC) - an international group including John Laing Construction.
Divers were this week inspecting the sunken tunnel section while engineers studied construction records to establish why the plinth failed and led to the collapse of a bulkhead in more than 15m of water. One of five bores in the hollow tunnel section flooded and the extra weight dragged down its immersion pontoon.
No-one was injured during the accident. "Investigations are ongoing but so far no damage has been found to the permanent structure," said OTC assistant project director Niels Uldall.
Uldall said that it could take at least four to six weeks just to install a new 6m by 6m bulkhead and re-float the 8.6m high tunnel section. No other tunnel sections can be placed during recovery work because the identical 176m long tunnel sections have to be laid end-to-end against each other in a seabed trench.
He said that the tunnel section was only 1.3m above the prepared foundation in the trench when the plinth supporting the bottom of the bulkhead at a rail bore failed.
The plinths are used as temporary bulkhead supports during marine operations The tops are braced with steel brackets.
Two of the bulkhead's three parts were damaged, one of which was punched into the tunnel bore and the other is hanging open "like a door".
The Oresund project will create an east-west running fixed crossing between Denmark and Sweden to be used by road and rail traffic. Oresund Consortium, the client for the 15.3km coast-to-coast section is building the immersed tube tunnel at the Danish side, an artificial island and a 7.8km long elevated bridge at the Swedish side, which includes a 1.09km long cable-stayed span.
The 39m wide immersed tube tunnel has five bores to carry different traffic streams - two road, two rail and a small service/ emergency bore. The tunnel will be formed by laying 20 tunnel sections seabed trench eastward from Copenhagen. Last week's accident happened with the 13th tunnel section.
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The failure of a temporary works plinth has been blamed for the sinking last week of a 57,000t section of Europe's biggest immersed tube tunnel which is being built between Denmark and Sweden.
Last Tuesday's accident on the Oresund road-rail project may mean delays of two months or more to the 3.5km long tunnel being built by Oresund Tunnel Contractors (OTC) - an international group including John Laing Construction.
Divers were this week inspecting the sunken tunnel section while engineers studied construction records to establish why the plinth failed and led to the collapse of a bulkhead in more than 15m of water. One of five bores in the hollow tunnel section flooded and the extra weight dragged down its immersion pontoon.
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No-one was injured during the accident. "Investigations are ongoing but so far no damage has been found to the permanent structure," said OTC assistant project director Niels Uldall.
Uldall said that it could take at least four to six weeks just to install a new 6m by 6m bulkhead and re-float the 8.6m high tunnel section. No other tunnel sections can be placed during recovery work because the identical 176m long tunnel sections have to be laid end-to-end against each other in a seabed trench.
He said that the tunnel section was only 1.3m above the prepared foundation in the trench when the plinth supporting the bottom of the bulkhead at a rail bore failed.
The plinths are used as temporary bulkhead supports during marine operations The tops are braced with steel brackets.
Two of the bulkhead's three parts were damaged, one of which was punched into the tunnel bore and the other is hanging open "like a door".
The Oresund project will create an east-west running fixed crossing between Denmark and Sweden to be used by road and rail traffic. Oresund Consortium, the client for the 15.3km coast-to-coast section is building the immersed tube tunnel at the Danish side, an artificial island and a 7.8km long elevated bridge at the Swedish side, which includes a 1.09km long cable-stayed span.
The 39m wide immersed tube tunnel has five bores to carry different traffic streams - two road, two rail and a small service/ emergency bore. The tunnel will be formed by laying 20 tunnel sections seabed trench eastward from Copenhagen. Last week's accident happened with the 13th tunnel section.
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