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Double trouble

Construction of a new road tunnel in the congested heart of the Dutch city and port of Rotterdam is demanding some careful engineering. Bernadette Redfern reports from the Netherlands.

Rotterdam's Weenatunnel is a core part of the development of the city's central rail hub. The main station is being rebuilt to handle swelling passenger numbers coming from the completion of a high speed rail line passing through the city on its path between Amsterdam and Belgium. A new metro system will bring commuters to Rotterdam from the Hague and the neighbouring city of Zoetermeer and tram lines feed passengers across the city.

Click here for map of area

Running directly in front of this major public transport hub is a congested two lane road tunnel, a hangover from the 1950s and desperately under-capacity. With users of the central station about to soar from 140,000 to 210,000 the Weenatunnel is in desperate need of upgrade.

Work is now well underway to achieve this, in the form of a £225M contract let to BAM Civiel Projecten. BAM is in the midst of building two new 350m long cut & cover tunnel sections, each carrying two lanes of traffic – doubling the capacity of the tunnel.

The new tunnel will be just 15m longer than the old Weenatunnel and will have a modest 135m of enclosed road tunnel, with 107.5m of cutting at each portal. But despite appearances, work is extremely complex.

Click here for overview of the Weenatunnel

The tunnels have had to be built without closing the thoroughfare at any point. The second tunnel actually follows the exact route of the existing tunnel, with old foundations hampering works. In places, the site has up to 5m of made ground containing bricks, stones and rubble from the bombing of the city in 1940.

To further complicate matters a light rail system runs over the existing tunnel, and ground anchors from the tower blocks that stand alongside the tunnel extend into the route of the
new underpass. There is also a high level of groundwater in the area.

"It has been very challenging and there have been lots of problems," explains BAM site manager Ton van Gils. "We found lots of things that we weren't expecting when we began the foundations."

These problems have had a significant impact on the project programme and led to BAM accelerating the last two phases of the four phase scheme in order to meet the December 2009 deadline.

The first two phases consisted of building a new tunnel south of the existing passage – phase one being the western section and phase two the east. Once complete, traffic could be diverted into the new tunnel whilst the existing tunnel was rebuilt in phases three and four.

Because of poor ground conditions both tunnels are being supported by 500mm diameter cased piles. Each has a 320mm square precast reinforced concrete pile inside. In total 700 concrete piles are being installed down to a maximum depth of about 26m. Beneath the made ground about 4m of clay and sands overlies sands, in which the piles found.

"A steel casing is driven up to 26m below surface and the precast concrete pile is then placed in the pipe and the space between the casing and the pile filled with grout," explains project director Ramon de Bruijn.

"The casing is then pulled out of the ground with vibrating equipment and the process begins again. There are approximately 700 piles along the tunnels which have a total surface area of 4,500m2."

Click here for cross-section of tunnel

Before concrete tunnel sections can be cast, site workers install temporary steel sheet piles to hold back the walls of the excavation. Where extra load bearing capacity is needed the tunnel is lined by temporary steel combi-walls.

The 800mm concrete tunnel sections are cast in-situ. "The pouring of the floors, walls and roof sections are in a length of approximately 20m long and 9m wide. One total section is poured in one week," says de Bruijn. Dewatering had to be undertaken throughout construction and pumps are operating at approximately 250,00lt per hour.

Click here for artists impression of completed area

The first two phases were completed in June 2008 and traffic has now been redirected through this tunnel to allow the contractor to construct sections three and four.
These are now being done simultaneously to save time, using the same method as for the first tunnel.

On the eastern section the presence of ground anchors from a neighbouring tower block has forced the team to rearrange the location of the steel sheet piles. "These were every three to four metres so we had to stagger the sheet piles" says van Gils.

Despite such unexpected challenges the team still intends to complete on time. "We have had time issues, the site is also very congested, but we will meet the deadline," says van Gils.

Royal Bam

From this month BAM will become a more familiar name in the UK as Edmund Nuttall and parent company HBG take on the identity of their Dutch owner.

It is more than five years since HBG was acquired by the Netherlands' largest contractor Royal BAM. But it is only now that its UK operations are taking on the company name.

"We have had this strong parent company but we haven't used it to enhance our reputation as much as we should," Nuttall chief executive Martin Rogers tells NCE.

The move comes as an increasing number of Royal BAM subsidiaries are winning work in the UK.
BAM Rail for example was the successful contractor for the Edinburgh tramway PPP. Appointed by the Siemens/Bilfinger Berger consortium, the firm will commence construction of 38km of track in October for completion at the end of 2010.

As more subsidiary firms work in the UK market it made less and less sense that they were not all easily identifiable as one group. So from 6th October Edmund Nuttall will be known as BAM Nuttall and HBG as HBG BAM.

Having the support of a company which turned over more than Euro 4.2bn (£3.3bn) in the first half of 2008, with an average margin of 3.9% is something that Nuttall expects will stand it in good stead when bidding for major projects. And the major project it really wants is Crossrail. "We have submitted our prequalification documents and in the fullness of time we will form a joint venture for the major works," says Rogers.

Not surprisingly BAM Nuttall is looking to create a joint venture for the project consisting of BAM companies. A source in the organisation says that despite working with Kier on High
Speed 1, contract 250, it is unlikely the two will work together again. It will however be renewing its partnership with BAM's German subsidiary Wayss & Freytag Ingerierbau, which was the third partner on contract 250.

Since High Speed 1, the tunnelling industry in the UK has been relatively quiet however the firm is keen to point out that international tunnelling projects have been keeping it busy.

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