The recent collapse of another ‘tunnel’ in the UK (p8) could spell trouble for the British tunnelling industry. I’ve put tunnel in inverted commas because many believe it not to be a tunnel at all! The structure being built at Gerrards Cross is in-fact a 320m long concrete vault, being built to cover an existing rail line using precast concrete arches on piled foundations. This was to be covered with fill to create a level ground area required for the construction of a new supermarket above the rail line.
Recent reports have stated that the collapse was a direct result of overloading of the crown due to inadequate fill placed on the tunnel’s sides. Seems a pretty basic error, but one that could have the insurers pulling out of tunnelling at light speed. The problem here is that the contractor was not regarded in the UK as a specialist tunnelling contractor, and the structure probably isn’t a tunnel anyway. But, to the nervous insurer, who already has reservations about the UK’s track record, this really doesn’t make any difference. It is still unclear who is at fault but we must make sure that the UK’s ‘real’ tunnelling industry doesn’t end up paying the price for what looks like a rudimentary error during the construction of a basic structure.
Tris Thomas
