Challenges and Solutions
An intrusive asbestos survey carried out at the start of the upgrade works to review the project risks revealed the works would be far more complex than expected. This was due to the joints between the tunnel’s precast soffits having been originally sealed with a caulking material which contained some asbestos. Due to years of water ingress and contamination, the caulking material had begun to decay.
To combat this, the team utilised an asbestos encapsulation system designed by asbestos and environmental services specialist Forest Environmental. A curing membrane from structural repair specialist Flexcrete was applied to seal the substrate and consolidate any loose material. Then a water-based, non-hazardous cementitious coating was then applied in two coats to lock in any remaining asbestos fibres and provide a permanent, waterproof seal over the surface of the joints.
A lighting condition survey confirmed the installed lighting in the tunnel was below acceptable standards. A temporary lighting solution and speed restrictions were implemented for road user safety in November 2014 while a detailed lighting design featuring new LED lighting was developed.
LED luminaires are usually fixed directly into the tunnel soffits. However, in this case drilling into the soffit to install the luminaires would undermine the integrity of the encapsulation system. To solve this, the CONWAY AECOM team designed a bespoke stainless-steel bracket system which the luminaires and supporting cabling infrastructure could be mounted onto and fixed to the wall.
The works were delivered to a 16-week programme, with all traffic management being paced and removed on a nightly basis. All plant and materials had to be cleared from and returned to the site within each shift.
Tom Chipperfield, Contracts Manager at FM Conway, explains the challenges the team faced:
“Our overriding objective throughout the project was to minimise disruption for tunnel users by making the best use of the time we had on site. Working closely with TfL and their LTRA Cs Contractors (CUBIC), we enabled other planned works to be undertaken at the same time as the lighting upgrade, including the renewal of the PA, radio and CCTV systems. The lighting upgrade project was completed safely in just 16 weeks.”