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Back analysis proves basement savings potential

Analysis of the construction works for Crossrail’s Tottenham Court Road station box has revealed that savings could be made on future works through less conservatism.

Up to 12% could have been saved on construction costs if a less conservative design had been used, according to Arup director Duncan Nicholson who was speaking at GE Basements and Underground Structures Conference in London today.

“It is a balance of whether the client wants to invest in design costs or construction costs though,” added Nicholson.

Nicholson also said that the industry needs to focus on minimising wall defects and placement of tremied concrete in order to maximise returns on future projects. “Many wall defects are minor and easily resolved but problems on the Amsterdam Metro caused considerable ground movements and structural damage to neighbouring buildings,” he said. “Incidents like that damage the reputation of the whole sector in the eyes of the public.”

The other area that Nicholson believes needs further research is the implications for developing shaft friction from constructing longer piles over several shifts. “There is a trend for piles in London to extend into the Lambeth Beds and, with restrictions on operating hours on many sites, this means piles are being constructed over several days,” he explained. “Leaving the pile bore open can result in clay softening and filter cake forming in the sand layers. If this occurs then pile tests should be carried out over two days to reflect the construction process and the benefits of using polymers need to be considered.”

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