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BAA denies T5 subsidence reports

Heathrow airport operator BAA last week denied that cracks in floor tiles at Terminal 5 were caused by subsidence.

“There is no problem with subsidence, whatsoever,” said BAA capital projects construction director Rob Stewart.

“If there was you would see it in the hard finishings.” Stewart confirmed that some floor tiles had been damaged − during or after installation − but that this had nothing to do with the terminal structure.

A BAA spokesman added that the claims could be part of a campaign to discredit proposals for a third runway at Heathrow.

Rumours that floor tiles needed to be replaced because of subsidence began circulating last year after the opening of T5 and had been resurrected in a Daily Telegraph article earlier this month.

Extensive pile testing

But Mott MacDonald transportation director Alan Powderham said foundations were designed to accommodate ground movement.

He said extensive pile testing was carried out for a year before piles were installed and that the clay was expected to swell.

“The clay has less load on it now than it did before.”

Alan Powderham, Mott MacDonald

“The fact that we’ve excavated away 65Mm³ here means that the clay has less load on it now than it did before the clay was taken out because the building is lighter [than the clay].”

“At foundation level we created a void so that the clay could move into it [under lighter loadings].”

Movement is controlled with 1,100, 2.1m diameter reinforced piles. To create working loads up 36M.N, the team created a 6m under-ream for 40 of the piles to enhance end bearing capacity without going deep into the less stable Lambeth group.

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