Works at Connaught Tunnel pick up pace

Crossrail has begun drilling wells at Connaught Tunnel to draw down the water table ahead of works to deepen and widen the 130 year old tunnel in east London.

Once the wells are completed, drawing down of the water table will begin next month which is required ahead of works to widen and deepen the central section of the Connaught Tunnel so it can accommodate Crossrail’s larger trains. The water table is also being lowered to allow for the pump house shaft to be deepened by another seven metres to 25 metres in order for it to accommodate modern pumping equipment that will work to keep the tunnel dry.

During the coming weeks the 130 year old pump house will be removed brick by brick and will be donated to Newham Council. 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. Demolition of the former North London Line station at Silvertown is commencing.

Works in Connaught Tunnel are well underway with the ballast – loose stone ground cover – and rail tracks already removed. Major piling works are also underway at the western approach to the tunnel in order to strengthen the ground. Survey work for to identify potential unexploded ordnance from World War II has been completed in the tunnel’s western approach with the all clear given. Crossrail’s archaeologists have opened their fourth and final trench for the site, searching for possible evidence of human activity dating back 6,000 years.

Connaught Tunnel Project Manager Linda Miller said: “Works are progressing extremely well and we are on track for turning this Victorian railway tunnel into modern infrastructure that will service London well into the next century. Major works will begin early next year after the London Boat Show, which will include placing coffer dams in the passage between Royal Victoria and Royal Albert docks, pumping out the water and performing engineering open heart surgery to widen and deepen the central section of the tunnel.”

Connaught Tunnel in the Royal Docks was built in 1878 and was part of the North London Line until 2006. The tunnel will be extensively refurbished as part of works to construct Crossrail’s new Abbey Wood branch.

Sections of the existing tunnel are in a poor structural condition. In 1935, larger ships began scraping the bottom of the Royal Victoria Dock which sits above Connaught Tunnel. As part of work to deepen the dock, the central section of the tunnel was narrowed with brickwork removed and steel 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 large enough for Crossrail trains to pass. However, concerns about the structural integrity of the tunnel as a result of work in the 1930s to narrow the tunnel have led to a new approach which will involve workers digging down to the tunnel to undertake the enlargement work. This will be the first time the tunnel has been exposed from above ground since its construction in the 1870s.