In San Francisco, US, we designed the steel immersed tunnel for the Cross Bay Tunnel, a part of the BART public transit system. The tunnel consisted of 57 elements totalling 5.8km, the longest of its kind in the world. Thanks to innovative seismic retrofitting, the tunnel was able to survive the 6.9 Richter scale Loma Prieta earthquake without any damage.
In Baltimore, US, we designed the notable steel immersed Fort McHenry Tunnel which was the widest immersed tunnel built at that time. It was the first immersed tunnel to have double tubes, carrying a total of eight lanes of traffic, laid immediately side-by- side in a single trench under Baltimore Harbor.
WSP also designed the bridge-tunnel crossings of Hampton Roads, Virginia, where immersed tunnels were built between two artificial islands that connected to the mainland via viaduct bridges. This approach was later adopted by other projects in the world, including the Oresund Bridge-Tunnel between Denmark and Sweden.
Concrete Immersed Tunnels
In Istanbul, we worked on the concrete/steel sandwich construction Marmaray Tunnel, the first tunnel to connect two continents. The rail and transit tunnel is 1.4km long consisting of 11 elements, each weighing up to 18,000 tons. At 60m (200ft) under the water’s surface, it is the deepest immersed tunnel in the world.
In Virginia, US, the Elizabeth River Tunnel (Second Midtown Tunnel) was delivered as part of a Public Private Partnership procurement process and was opened to traffic in 2016. The tunnel consists of 11 concrete elements fabricated in Sparrows Point, Maryland and towed down the Chesapeake Bay to the project site in Portsmouth, Virginia for immersion and placement under the Elizabeth River.
WSP is also performing the Independent Design Review of the Fehmarn Belt Fixed link between Denmark and Germany. Upon its completion, it will reduce the journey from Hamburg to Copenhagen by an hour and thirty minutes. At 17.6km long, it will be the longest immersed tunnel in the world. The precast concrete tunnel sections will have a rectangular cross-section of 42m wide by 10m high, consisting of four separate passageways, two for vehicles and two for rail.