To keep the traffic flowing safely, it is vital that no water can drip though the roof of the newly built Förbifart Tunnel, Project FSE403. So our team in Sweden is using an interesting technology to create a free-standing waterproof concrete vault. How it works:
1. First of all, 180,000 mounting bolts are set into the tunnel ceiling.
2. 200,000 square metres of membrane are hung on these bolts to create a diaphragm vault.
3. Precast wall elements are mounted on both side walls of the tunnel. Each of these 9,000 elements is 3x5 metres in size and weighs almost 6 tonnes.
4.60 truck-loads of reinforcing mats are mounted on the ceiling bolts.
5. A 10 cm thickness of shotcrete is then applied to these mats to create a free-standing and waterproof concrete vault between the wall elements. An escape route is located behind the elements on one side of the tunnel.
6. A conduit for all the electrical installations and fire suppression water pipes is created under the concrete walkway.
The “Förbifart Stockholm” bypass is a new three-lane motorway that links the south (Kungens Kurva) and north (Häggvik) of the city. To minimise the environmental impact, most of the 21 kilometre road will be underground. (Picture: Implenia)