Much of Britain’s vital transport infrastructure has had a long life; some has been in place for more than a century, with occasional improvements to upgrade it. Among the sites on these "to-do" lists is the 113 year old Blackwall Tunnel in London, which is currently undergoing a renovation to improve its safety systems.
Despite the difficulties of working in such an old structure, the project has been progressing ahead of schedule since starting in February and will now be complete six months early. This success follows an innovative style of night time possessions and weekend closures that has allowed accelerated work while keeping London moving.
The improvements to the tunnel follow the 1999 Mont Blanc tunnel fire that led to the adaptation of a European directive on tunnel safety. This includes the creation of 26 emergency niches, so called safe havens, which will allow broken down cars to get out of the running lane of traffic to seek help.
Ventilation is also being upgraded with the installation of four new bespoke fans within the tunnel's four shafts. These will drive smoke out of the tunnel in the event of a fire.
Improved CCTV, public address systems and radio rebroadcast, which cut safety broadcasts into car radios will also be installed, along with new lighting and detectors for smoke, stopped vehicles, pedestrians, debris and over-height vehicles.
Because of the new regulations following the Mont Blanc fire, similar work to this has been carried out in tunnels across the UK, including in the southbound Blackwall tunnel, which was built in the 1960s.
Director of roads at Transport for London Dana Skelley saysthe work on the systems in the parallel tunnel helped make decisions on what to do. The team looked at work in other UK tunnel upgrades but added: "I can't say there's anything like the Blackwall tunnel, it's unique".
"Scoping a project like this takes some consideration, as does getting the industry
interested in doing a project like this because it was high risk, working on an unknown, very old structure," she said.
As a result there was "open engagement" with the potential contractors in £70M programme “about what they’ve got to let themselves in for, and what we expect from them”. Skelley adds there was a need for more than one open event and industry day, before BAM Nuttall was selected as the contractor.
Part of the uniqueness of the project is that most of the work is taking place overnight in possessions from 9pm to 5am, Sunday to Friday since February this year. Each day the tunnel is reopened to traffic and "we have to appear like we weren't there, every single day, like an invisible operation", Skelley says.
The tunnel is constructed in a bore with large cast iron rings providing the structural support. These are then filled in with concrete, to which brackets are attached for protective cladding. A height restriction of 2.8m is in place in the tunnel, but even so around 2000 over-height vehicles try to use it each year causing delays which sometimes lead to tunnel closures if cladding from the tunnel is damaged when they go through.
As part of the refurbishment the concrete in the tunnel structure is being milled down to the rings and replaced with a thinner amount, before new cladding is then applied. The tunnel will then have "an extra few inches" of clearance, particularly at certain pinch points, Pidcock says.
"Every time someone hits the cladding it causes damage and we may need to have a
maintenance closure. The high risk areas are predominantly near the four tunnel shafts," he adds.
The refuge points are being created by using space where the original fire hydrants for the tunnel were placed behind a dwarf wall in front of the tunnel walls. Moving cabling, which was also located there, further up the walls creates the space for the safe havens, and emergency points.
The four tunnel shafts are being completely revamped, and reinforced for the arrival of the new fans. Work is ongoing on shafts two and three and will begin on shafts one and four during a weekend closure in October.
The shafts have had new floors constructed to support the fans, and will also be able to act as access and evacuation routes in an emergency. "We're certainly on target for that new completion date,” says Skelley.
Pidcock adds that other parts of the project, including the new lighting system are making "tremendous progress", meaning that even this new completion date could be beaten.
"We're challenging all the systems at the moment to see if we should bring them online one at a time, looking at what benefits we can bring, how quickly can we commission, and see if we can shorten the project further," he says.
Article courtesy of New Civil Engineer- september 2010
Peter Bishop - Head of Public Relations & Corporate Communication
BAM Nuttall Limited
St James House, Knoll Road, Camberley,
Surrey GU15 3XW
Tel: 01276 63484