In a few years’ time, some 10,000 road users per hour will travel through the A10 tunnel on the south side of Amsterdam every day. Should something go wrong, because of a collision, for example, it will suddenly become obvious what the tunnel actually is: an underground concrete tube barely penetrated by daylight. Either way, a lot of technology is needed, from thousands of LED lights to so-called uninterruptible power supply. We joined two experts from the Zuidasdok design team and contractor VolkerWessels to take an imaginary walk past all of these installations. Zuidasdok’s Ronald Mante starts by saying something surprising: ‘In terms of technology, it’s actually a run-of-the-mill tunnel.’
Tunnel structure
In both directions of travel, the tunnel will consist of a tube for through-traffic (four lanes) and a tube for local traffic (two lanes). Between them will be an evacuation route, with a utility corridor on top of it in which countless cables, pipelines and installations will be tucked away.
No surprises…
This is not just by chance, because the A10 tunnel is being built according to the National Tunnel Standard (Landelijke Tunnelstandaard). This is a Rijkswaterstaat (Public Works Department) document running to thousands of pages which is used as the basis for commissioning every Dutch tunnel: from material choices and dimensions for construction and protocols for dealing with incidents, through to training courses for staff on duty. Mante: ‘This standardisation makes the tunnels safer, cheaper to manage and the processes more reliable.’
…but a lot of work
But, according to colleague Peter van Velden from VolkerWessels, there is still plenty that needs doing. Their team, which now includes 40 people, still goes through the complete design cycle. ‘The reason why there as many as 50 different installations is all down to safety. We start by determining the technical structure in which the different installations will be accommodated: do we want a single system for every functionality or separate installations in the same way as we used to have a telephone, a calculator and a diary before the days of smartphones? When the overall system is clear, we set out the installations needed in the definitive design. Finally, there’s the executive design, detailing the brand and model of the different installations and the suppliers, along with instructions for assembly and how maintenance should be done in the future. Then we can start building.’
Light and air
Van Velden: ‘To provide proper lighting in the tunnel, there will be a total of around 2,250 light fittings for both tunnels, which automatically adjust the light to account for the amount of daylight. Light is very welcome indeed, but exhaust fumes are not. That’s why ventilators will be positioned at the entrance to the tunnel to blow the CO2 out of the tunnel in the direction of travel. Van Velden: ‘An adaptive system adjusts the power of the ventilators if the CO2 content becomes too high, reducing visibility.’
South-westerly wind
This is especially important for the tunnel on the north side of Amsterdam Zuid station. The prevailing south-easterly wind blows into the tunnel there – against the direction of travel and the direction of the ventilation. ‘This is why the systems continually measure the wind strength, enabling you to calculate how much air needs to be moved to maintain the visibility level. That’s also automatic.’
Fire!
As stated above, the ventilators blow in the direction of travel. If a vehicle should unexpectedly catch fire, Mante points out that the black smoke needs to be kept away from the traffic jam that builds up behind it. ‘Suffocation is the main cause of casualties in a tunnel fire.’ In the event that a fire develops in a traffic jam, there will be signs, public address announcements and green contour lighting directing people to the doors of the closest evacuation route. ‘In order to keep that free of smoke, we apply a higher air pressure in the evacuation route than in the tube where the fire is, where the ventilators switch to full power in order to disperse the smoke.’
Power supply
The tunnel tube contains around 10% of the installations, 40% are in the utility corridor and the remaining 50% in the service buildings on top of the tunnel. Mante: ‘In these, there is both a general power supply from the grid and an emergency power supply. In order to bridge the gap between one switching off and the other being connected, we also have an uninterruptible power supply to ensure that power is always available. The service building is also connected to the traffic control centre, enabling us to see everything that’s happening in the tunnel using cameras and detection systems.’
This is the sixth in a series of articles about the design of the tunnel in the A10 Zuid and about the techniques and challenges involved. The first was about preparations behind the scenes, the second looked at the lack of space for construction of the tunnel, the third article was about moving the A10 Zuid, article four focused on keeping Amsterdam Zuid station accessible during construction and article 5 explored earth-retention techniques.
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