MYSTERIOUS CRACKING has set back a £9M relining contract on Glasgow's Clyde Tunnel by at least 12 months, the city council confirmed last month.
Design and build contractor Byzak abandoned trials of a specially developed secondary fireproof lining system with two hours fire resistance and a replacement system will now be developed over the coming months.
Major cracks appeared in the first 20m trial section built last March forcing the postponement of the relining contract that was due to finish by October 2005.
A report to the council's roads and lighting committee revealed that Byzak had so far failed to produce an alternative proposal.
The system features a 40mm thick cementitious fire protective material from Degussa. It is wet sprayed on to a stainless steel mesh backed by stainless steel sheets mounted on the tunnel lining.
A Byzak spokesman said it was about to launch a detailed 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.
Glasgow City Council's contracts manager Marco Bardelli told GE: 'We are still waiting on the contractor coming back to us with revised proposals. We are assuming this will be by the end of February. In the meantime it is continuing to put in a stainless steel support framework for the tunnel lining which will be complete by the end of February.' 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.