To deliver the Crossrail branch to Abbey Wood, a major proportion of the construction work involves reusing disused rail infrastructure including the Connaught Tunnel on the former North London Line branch to North Woolwich and disused National Rail tracks to Custom House - which both closed to passenger traffic in December 2006.
The history of the Connaught Tunnel dates back to 1878. It allowed the railway to be diverted under the Connaught Passage, a water link which connected the Victoria and Albert Docks.
The Connaught Tunnel is around 550 metres long and runs between Royal Victoria Dock and Royal Albert Dock close to London City Airport. We will be enlarging the existing tunnel so that it can accommodate Crossrail trains and overhead line equipment.
Reconstruction and refurbishment
Sections of the existing tunnel are in a poor structural condition. The central section of the Connaught Tunnel became weaker after the Royal Victoria Dock was deepened in 1935 to allow larger ships to enter the dock. This resulted in the roof of the Connaught Tunnel below the dock becoming exposed. As part of work to deepen the Royal Victoria Dock, the central section of the Connaught Tunnel was narrowed with brickwork removed and cast iron tunnel segments installed.
Crossrail originally planned to strengthen the central section of the tunnel by removing the existing steel linings and back filling the entire section with concrete foam. These tunnels would then have been enlarged by boring through the concrete to create tunnels that are large enough for Crossrail trains to pass.
Crossrail will now place cofferdams in the Connaught Passage between the Victoria and Royal Albert Docks, pump out the water and create a dry construction site allowing workers to dig down to the tunnel to undertake the enlargement work through a ‘cut and cover’ approach.
During World War II, more than 40,000 explosive devices were dropped on London with the docks and rail lines particularly targeted due to their crucial role in delivering supplies to the British war effort.
Connaught Tunnel was hit by a bomb in 1940. Crossrail will be undertaking further repair work to the damaged section of the tunnel.
Ahead of major works on the Connaught Tunnel commencing next year, Crossrail is undertaking an extensive search of the wider construction area to identify any remaining undiscovered devices that failed to detonate on landing during World War II. The geology of the Royal Docks area meant that some devices that didn’t explode on landing sunk into the first few metres of soil.
A team of highly trained specialists are currently using armoured vehicles with magnetic equipment to investigate the ground around Connaught Tunnel. Their work involves sending probes into the ground in three metre intervals and analysing the results.
Crossrail already has a detailed understanding from existing London-wide maps and ground surveys about where potential devices could exist.
The dock floor above and around the Connaught Tunnel has already been searched by divers and was given the all clear. The specialists will shortly begin surveying under Connaught Bridge directly above the Connaught Tunnel.
Any potential devices identified in the ground through the survey will be reported to the authorities for further investigation. Similar ground surveys will be undertaken at other Crossrail sites in east London.
After surveys for unexploded ordnance are completed, Crossrail archaeologists will open excavation trenches in an attempt to locate evidence of human settlement and farming in the area dating back nearly 6,000 years. Working with the Museum of London Archaeology, Crossrail also aims to map the effect of the River Thames on the area during historic and prehistoric times.
Sitting above the Connaught Tunnel near Connaught Bridge is the tunnel pump house. This attractive Victorian building is too small to accommodate the larger modern pumping equipment that will be installed as part of the tunnel’s major refurbishment. Subject to structural surveys, Crossrail proposes donating the structure to the SS Robin Trust.
The SS Robin is one of the world’s oldest steamships and was built in east London. The ship’s trust is seeking a permanent berth in the Royal Docks and the pump house structure would form the quayside ticket office.
The cofferdam works which will commence in 2013 have been planned in conjunction with the Royal Docks Management Authority and timed to start after the London Boat Show.