Crossrail’s tunnelling projects are set to catalyse a major development in tunnel technology in the UK, one leading tunneller said last week.
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Mott MacDonald tunnel engineer Brian Lyons said that wider use of composite tunnel linings which allow load to be shared between primary and secondary linings would emerge as a result of their use on Crossrail.
Lyons has worked on designs for Crossrail’s sprayed concrete lined station platform tunnels and was speaking at NCE’s Tunnelling 2010 conference last week.
Exploiting this composite action would lead to quicker and cheaper project delivery, he said. This is because a composite lining could use thinner layers of concrete, reduce excavation volumes and speed up work.
He said that the use of this method for the secondary lining on the tunnelling for the Highways Agency’s A3 Hindhead improvement project, where concrete was sprayed on top of a sprayed waterproofing membrane, had shown the applicability of the technology.
“Where we are headed is a composite lining which includes a spray applied [waterproofing]membrane. You can see that the money spent on material, and in programme time, can be saved,” he said.
He said there was an improvement in the quality of materials and workmanship which had made this possible. The key, he said, was to get shear transfer across the waterproof membrane.This may require a change in design standards, he added.
“We believe that the water will act on the back face of the primary lining, so the linings will take all of the ground and all of the water pressure together. I think it will be successful in the coming years - where we’re going to be in four or five years time post-Crossrail.”