MYSTERY CRACKING has set back a £9M relining contract on Glasgow's Clyde Tunnel by at least 12 months, the city council confirmed this week.
It has emerged that design and build relining contractor Byzak has abandoned trials of a secondary fireproof lining system developed especially for the project.
This follows the appearance of major cracks in the first 20m trial section constructed last March. The relining contract was due to be complete by October this year.
In a report to the council's roads and lighting committee on Tuesday it was revealed that Byzak had so far failed to produce an alternative proposal.
The system features a 40mm thick cementitous fire protective material from Degussa. It is wet sprayed onto a stainless steel mesh backed by stainless steel sheets mounted on the tunnel lining.
The lining has also to provide a cosmetic fi nish to the tunnel interior. It was planned to coat the Degussa material with a special paint.
Glasgow City Council decided to reline the tunnel's twin 760m long bores after the aluminium frames supporting the 42 year old original PVC sheet lining were found to have corroded badly.
'We wanted a replacement lining that could cope with the pressure fl uctuations caused by traffic in the tunnels and give us two hour fire resistance, ' said Glasgow City Council structures manager Marco Bardelli 'We had to limit peak temperatures to 300ºC to protect the lead caulking between the cast iron segments, and we wanted an impermeable layer between the lining and the fire protection to protect it against damp.' Byzak has invested heavily in the development of the system.
Its first proposed fire proofing failed fire and flexure tests carried out in Holland and at BRE, and the tests had to be repeated with the Degussa material.
Any replacement system would have to go through the same series of tests, which will take months.
A Byzak spokesman said it was about to launch a detailed long term survey of possible cyclic movements in the tunnel bores, which could have caused the unexpected cracking.
'It's too early to be able to pin down the cause of the problem, and there are still a number of unresolved issues with Glasgow City Council, ' he said.
Byzak is operating under a fi xed price contract and is liable to liquidated damages of £2,000 a day.