Reflecting on Europe's first immersed tunnel 19 Mar 2013
Armand van Wijck, TunnelTalk Europe Correspondent
Just over 70 years ago the Maastunnel in Rotterdam, Holland, set the stage for what would become a fine tradition in Dutch civil engineering: the immersed tunnel. Of the 50 or so immersed tunnels in Europe, no less than 31 are situated in the Netherlands. TunnelTalk Europe Correspondent Armand van Wijck talked to Seen Van der Plas, retired Director of Maastunnel project owner Public Works Rotterdam, about its place in tunnel construction history.
Aerial view of the tunnel alignment. The ventilation building can be seen in the top left

Aerial view of the tunnel alignment. The ventilation building can be seen in the top left

Completed in 1942, and at 1,373m-long (1,070m underwater), the Maastunnel is the first example of what has become a fine tradition in Dutch civil engineering: the immersed tunnel.
Crossing the Maas river that flows through the heart of Rotterdam, the tunnel consists of four tubes combined within a single section: two tubes for cars, one for cyclists and one for pedestrians. Construction, which continued even after the German invasion of 1940, took nearly five years. Today 75,000 motorists use the tunnel on a daily basis.
"Looking back at the first half of the twentieth century, two tunnels served as a worldwide example for things to come: the New York Holland Tunnel (1927) and the Maastunnel (1942) in Rotterdam," reflects Van der Plas. "The bored Holland Tunnel was revolutionary because of its internal design," he adds, referring to the transverse ventilation developed for that tunnel by civil engineer Ole Knutsen Singstad. "It set an example for road tunnels everywhere. The traffic lane width became 6m, with small kerb edges and an elevated pavement for staff. This became a classic tunnel section for years to come."
Seen Van der Plas

Seen Van der Plas

At about the same time, Rotterdam was desperately in need of a cross river link; increasing traffic levels could no longer be served by the small steel bridge (Willemsbrug) and the few steamboat ferry services.
Initially the Dutch Government made plans for a gigantic suspended bridge 60m above the water surface and designed with a spiral tower on each side to allow cars to make their way up and down the bridge. But the city demanded an immersed tunnel.
Designer Jacobus Pieter van Bruggen (later to become Director of Public Works in Rotterdam) took his research seriously, touring the USA to gather information from other projects that might be useful. Among other proven models, he adopted the transverse ventilation system and classical tunnel section of the Holland Tunnel.
The Maastunnel was Europe's first immersed tunnel (at the time there were five examples in the USA) but what set it apart was its rectangular shaped profile and concrete construction. American tunnels of the same type boasted a circular profile and a steel frame construction.
Transportation and sinking of the caissons

Transportation and sinking of the caissons
(©Public Works - Rotterdam City Archive)

"A rectangular shape meant in this case that there was more room for the city's traffic plans: a tunnel with separate driving lanes for each direction, a separate section for bikes and a separate section for pedestrians," explained Van der Plas. "The Maastunnel became the first tunnel to have it all in one tube." A rectangular form also lowered construction costs and left enough space above the tunnel ceiling for heavy shipping using the channel above.
Backfilling invention
A rectangular shape, however, made backfilling the sides and bottom of the tunnel more difficult than for round special elements. "This problem meant a world first use of a special backfilling method, developed by Danish construction company Christiani and Nielsen (C&N), to lay the tunnel foundation," said Van der Plas.
An installation on top of the caissons injected a sand-water mixture in a space about 1m between the tunnel floor and the river bed, while jacks held the tunnel section temporarily on top of tiles placed on the river bed. Two suction pipes placed next to the end of the injection pipe assured a quick consolidation and a dense enough spacing of the sand underneath the tunnel. This method still forms the basis of many backfilling alternatives used today.
Finishing works on the tunnel interior

Finishing works on the tunnel interior
(©Public Works - Rotterdam City Archive)

Connecting the caissons seamlessly underwater posed another major problem. "They placed a large diving bell with overpressure around the caissons and worked from inside the bell to connect everything," explained Van der Plas. "It was a major underwater operation."
With this complication in mind, Public Works Rotterdam decided to develop an easier and safer method for connecting tunnel sections when designing the 1968 immersed tube metro tunnel crossing of the Maas. This project saw the birth of the Gina gasket, an air-filled rubber gasket surrounding the tunnel section, from which the air is pumped out, thus using hydrostatic pressure to compress the tunnel units together to form a watertight seal. "Public Works Rotterdam invented this gasket in collaboration with Vredenstein, a Dutch tyre manufacturer," recalls Van der Plas. "In my opinion it is one of the most important innovations in tunnel construction: it opened the possibilities for a true tunnel boom. Chief Engineer Hette van Dijk was one of the important men behind the Gina gasket, and he named it after the Italian actress Gina Lollobrigida, because of the curvy similarities."
Bikers take the escalator down to the bicycle commuter tube

Bikers take the escalator down to the bicycle commuter tube
(©Public Works - Rotterdam City Archive)

World War II
When the Germans invaded Holland on 10 May 1940, only three of the nine caissons had been rested on the river bed, but by 25 November the last caisson was lowered.
Despite its place in engineering history, the Maastunnel was never officially opened. The Germans wanted to throw a big party but this idea triggered protests from the local population, who did not want the occupying forces to take the credit. "The delivery of the Maastunnel caught the attention of engineers worldwide, but no one paid a visit because the Germans were there," said Van der Plas. In 1944 the Germans placed explosives that would enable them to blow up the strategically important tunnel but in the event this never happened, most likely because Dutch partisans tampered with the explosives.
Renovation plans
Last year was a busy year for the oldest road tunnel in the Netherlands. On its 70th anniversary the Maastunnel complex, which also includes the ventilation buildings, was made into to National Monument. The city has also made plans for a large-scale renovation.
The characteristic ventilation building

The characteristic ventilation building
(©Public Works - Rotterdam City Archive)

A fire-life safey upgrade is perhaps the most important aspect. The tunnel has to comply with new Dutch tunnel safety regulations which call for emergency exits every 100m for immersed tunnels. Fire research institute Efectis also performed in-situ fire resistance tests on the tunnel ceiling for the first time with their newly developed mobile furnace.
Unfortunately, concrete decay was found in the ventilation system underneath the road during restoration works. This means that renovation works are now likely to take until 2018. Inspections have also revealed the possible presence of asbestos, because eternit plates containing asbestos fibres were commonly used at the time in construction materials. These plates were removed last year.
"After all these years the tunnel still lays there, solid as a rock. And when the renovation works are complete, it will last for at least 50 more years," concludes Van der Plas. "The Maastunnel is truly the pride of Rotterdam."
Mobile furnace used for fire safety testing - TunnelCast, Augustus 2012
Building Holland's first double-deck tunnel - TunnelTalk, July 2012
Holland Tunnel construction, New York, USA - TunnelCast, November 2011

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