Giant Seals Help Protect Tunnel under Saint Petersburg Flood Barrier
Saint Petersburg is situated at the point where the Neva River flows into the Gulf of Finland, so when strong winds in the gulf blow eastwards, they act as a barrier against the Neva flowing westwards. As a result, the waters can rise in only a few hours, threatening Saint Petersburg’s 4.6 million people and its priceless historical sites, such as the world-renowned Hermitage Museum.
Last January, Russia’s cultural capital was flooded for the 302nd time in its 303-year history. The water level rose more than two metres above normal, flooding some of the streets bordering the waterfront.
In 1979, the Soviets began the construction of a storm flood barrier across the Gulf of Finland, but the project had to be abandoned a few years later for financial reasons as the demise of the Soviet Union began. However in 2003, Russian President Vladimir Putin, a native of Saint Petersburg, ordered the project to restart and it is now supported by the European Bank for Reconstruction and Development (EBRD).
The storm flood barrier consists of a 25 km dam, six discharge sluices and two navigation channels. The main channel is 200 metres wide and will be sealed using two 130 m curved doors. These amazing structures will normally rest in curved dry docks on either side of the channel. When needed, the docks will be flooded and the doors will be floated to closure.
As the barrier will be part of the ring road around the city, a 1.2 km-long 2 x 3-lane tunnel, 17 metres under the flood gates, has been designed to pass under the main channel. In the 1980s, all fifteen tunnel sections were constructed without being connected. Halcrow is designer and Royal Haskoning of the Netherlands is the project manager. Click ru/24. Visit www.halcrow.com and www.royalhaskoning.com
Omega seals
Trelleborg designed a sealing system that connects the tunnel sections. The company is more or less supplying the missing links. The seals are sufficiently resistant that they will protect the tunnel from water gushing in under high pressure. At the same time, they are flexible enough to allow movement by the tunnel sections.
It was essential that the 40 m-wide, 7 m-high seals were made to the highest standards of quality. They are called Omega because they have the shape of the Greek letter. Once the seals are laid, it is impossible to go in and repair them. These seals are made to provide resistance for the next hundred years.
The seals were manufactured in the Netherlands, at Trelleborg Bakker’s factory in Ridderkerk, outside Rotterdam. Construction of the Saint Petersburg dam is scheduled to finish in 2008. So January’s flood may hopefully turn out to be the last in the city’s history.
This is the first time that Omega seals have been used in a tunnel of the type being constructed in Saint Petersburg, which is a cut-and-cover tunnel, whereby a hole is dug in the dry at the site of the main navigation channel, each reinforced concrete box is constructed bit by bit, and then covered with sand. The channel will then be flooded once the tunnel is finished.
What is also unique is that the tunnel will be provided with a double sealing system, an outer Omega seal and an inner one, as a back-up. Omega seals can withstand high water pressure in combination with relatively large displacements in all three directions. They can also withstand temperatures ranging from minus 30°C to plus 70°C. Visit www.trelleborg.com 41/07.
