An aerial view projects a bridge suddenly disappearing in the middle of the sea. The mapping view projects a bridge high above the sea and gradually fading into the deep blue waters. Connecting one of the busiest cities in the world, Copenhagen, and one of the quieter regions, Malmo. The Oresund bridge comprises of one of the most sophisticated designs of a bridge, an underwater tunnel to connect two countries. What better way to link two nations with two different engineering wonders combined as one – The Oresund Bridge
Why the Oresund Bridge?
Oresund is the largest motorway and railroad bridge in the whole of Europe, connecting Denmark and Sweden in a span of 16 Km long bridge and tunnel combined. The idea first propped up in 1936 to build a national motorway of Denmark. Copenhagen one of the busiest business hubs in Europe had high influx of expats but little in terms of housing. About 4 miles west, was the Swedish town of Malmo which offered affordable housing. Having a link in Sweden with the housing and driving down to Copenhagen for work seemed an altogether solution for both the countries.
But there was a catch. On the Denmark shore, was a bustling airport and the on the Swedish side a quiet town. Building a high bridge all the way would have caused an obstruction for the planes, building a lower level one would have caused mayhem for the cargo ships in the oresund strait. The solution- build a bridge high above the seas on the Swedish side and an underwater tunnel on the Denmark side.
Engineering the marvel:
The idea having been coined first in 1936 could not see daylight till 1991 due to legal and industrial negotiation hurdles. The actual construction started in 1995 after a consortium of companies from both the countries agreed to take up the project.
First hurdle: Design
Geographically connecting two shore points seemed to be not such a tedious task, but when commercial interests come up, the scale tends to differ. Massively!. On the Denmark side there was a busy airport, which could not prospect the idea of a high level bridge. But a low level bridge would cripple the crucial ship movements along the strait. The solution- a bridge high enough for ships to pass and an underwater tunnel for a no obstruction air movement. Interestingly a competition was held for the best design for the bridge.!
With the finalized design, the engineers required a land mass for the bridge to continue into the undersea tunnel. The base soil of the Peberholm, the artificial island in the middle of the strait, consists soil from the natural island of salthom in Sweden. The completed artificial island increased the land mass of Denmark by 1.3 million sq meters.
In total, the Oresund bridge is segregated into 4 kilometers of tunnel, 4 kilometers of island and 8 kilometers of bridge.
Builiding the tunnel bridge: Wonder!
To build a bridge supporting the rail and road traffic while keeping the 1090 meters of concrete and steel are suspended mid-air, mid-sea 60 meters above the water, the engineers decided on a cable stayed bridge. A cable stayed bridge is the one where the support cables are directly attached to the support towers instead of a hanging wire which saves tonnes of steel making the option viable and economical. The support towers of the Oresund form one of the tallest concrete structures in Sweden with an enviable height of a 60 story building. The foundation base of the bridge was built on a dry dock and transported to the sea using two barges acting like catamaran. To inspect the bridge, a gantry was built to span the whole bridge , even bypassing the towers by changing it’s direction.
Building the artificial island was a mammoth task with the deadline being 14 months. Work began on the 17th August 1995 when the billions of stone and rock were dumped in the sea. A perimeter of 12 kilometers was first placed with the stone brought from Sweden. Next step- Dig and fill up the perimeter. How? – Dredge! To stay on schedule, millions of cubic meters had to be dredged each day. The ‘Chicago’, one of the most powerful dredging machine was brought in which dredged out 22 cubic meters of the sea bed with one scoop.
The trench for the tunnel is 11 meters deep and 46 meters wide to support two lane parallel rail and road and one emergency lane. Dredging the Copenhagen limestone, an ultra hard rock proved to be an uphill task even for the ‘Chicago’. One of the most powerful cutter suction dredgers, The Castor, with enormous cutting teeth weighing 20 kilograms each was brought in to complete the task. Altogether roughly around 52000 teeth were replaced in the island building process.
The Drogden tunnel is a five lane corridor with two rails, two roads and one for emergency purpose. Due to its complexity the tunnel was built in parts and assembled in the sea. One part of the tunnel built every month for 20 months. This feat was an appreciable one in itself. 150 trillion liters of concrete, 1100 million kilograms – this is the magnitude of the Drogden tunnel. The tunnel segments were placed on the rafts which enabled them to float and were transported to the open seas using the Lock system( flood the gates and submerge the tunnels). The margin of error when assembling the segments underwater was less than 0.25 centimeters.
Value of the Oresund bridge: Immense!
On the 14th of August 1999, The Crown prince of Denmark and the Crown princess of Sweden met midway to officially open this wonder construction. The traffic increased rapidly and from 2005 onwards, scores of Danish citizens took advantage of the affordable housing in Sweden and scores of Swedes took advantage of the commercial and industrial boom in Denmark. The combined gain of the Oresund bridge is estimated to be roughly 8 billion euros annually with the traffic seeing a positive increment every year.
With the gigantic scale of this marvelous wonder, the Oresund bridge engineered a diversification across high seas which sees growth and heights till date right from commercial to cultural ideologies.
tinhad.wordpress.com 