Client-contractor collaboration helped ensure early completion of refurbishment work for the northbound Blackwall Tunnel in east London. Jo Stimpson reports.
Motorists visiting shops in central London or attending events at the O2 arena this Christmas will unknowingly reap the benefits of an NEC3 contract between Transport for London (TfL) and Bam Nuttall.
Close collaboration between client and contractor enabled an impressive 13 months to be shaved off the timescale for safety upgrades to the northbound Blackwall Tunnel, meaning it can remain open overnight during the Christmas shopping period.
The project has brought the 114 year old, 1.4km long tunnel under the River Thames in east London in line with European standards, thanks to new shaft ventilation fans; improved incident detection, lighting, CCTV and communication systems; 26 new safety inlets for drivers suffering breakdowns; and a new system to prevent over-height heavy goods vehicles (HGVs) trying to squeeze through the tunnel.
Last year, incidents involving over-height vehicles caused the northbound Blackwall Tunnel to be closed 1,448 times, causing 56 hours of avoidable closures. A closure of just five minutes at peak time can cause 30 minutes of congestion, says TfL development and delivery manager Shaun Pidcock.
Now, an infra-red detection system identifies when a vehicle in the HGV lane is too tall and automatically activates red lights and a barrier, diverting the vehicle away from the tunnel entrance. TfL hopes that over time, the system will deter over-height vehicle drivers from trying their luck at all.
The new ventilation system is no less sophisticated. Designed to operate in a fire situation, and to mitigate air pollution when traffic in the tunnel is slow moving, the newly installed system detects when extra ventilation is needed and automatically activates 16 new heavy duty fans, weighing 6t each, in the tunnel’s four vertical ventilation shafts. New roof hatches complement the fans and can be remotely opened when needed, to maximise ventilation.
“The project has brought the 114 year old, 1.4km long tunnel into line with European standards”
Work on the ventilation system was a complex project in itself, and involved the use of a 1t Brokk robotic demolition tool, referred to by the project team as “the nibbler”. This gradually removed the existing concrete domed shaft roofs, taking a week to complete each one.
“We had to make sure that was done in a controlled way,” says Bam Nuttall project manager Jay Moorhouse. The new roof hatches were constructed from steel and plywood to resemble the original domes.
Despite - or perhaps because of - its complexity, the new ventilation system installation programme was where many of the project’s time savings were found. This work was originally planned to be done over 10 weekend closures during the three year refurbishment programme. Major events at the O2 and Jubilee Line engineering works overlapped with the schedule and led to “long debates about when we could actually go to work”, says Bam Nuttall major projects manager Jim Morgan.
However, TfL and Bam realised that constructing temporary platforms within the shafts would allow work to continue above moving traffic on days when the tunnel was open. However, the need to keep ventilation channels open meant no more than two shafts could be worked on at one time.
The work was also helped by the use of a noise reduction membrane in the shafts. This
reduced the amount of noise that could be heard by local residents and allowed construction to carry on through the night.
In the end, only six of the planned 10 weekend closures were required. Work began in February 2010, and the tunnel will be fully re-opened to traffic tomorrow.