A refurbished 3m diameter Lovat EPB TBM was launched last month on a 3.3km long sewer tunnel in High Wycombe, UK. It marks a return to major tunnelling for UK-based contractor Amec, who was awarded the contract by client, Thames Water, based on the group’s previous tunnelling experience through chalk in the UK.
“Amec undertook a similar project in Ipswich, and in that we get a lot of confidence,” project manager for Thames Water, John Griffiths, said.
The 3m diameter tunnel will house two separate pipes: a 1m diameter pipe to convey sewerage to the improved waste water treatment works in neighbouring Little Marlow (under construction); and a 0.6m diameter pipe, which will return clean effluent to High Wycombe to maintain levels in the River Wye. The larger pipe will operate with gravity, while the pumping equipment for the smaller pipe will be housed in Little Marlow.
A 1.5km long open-cut section will be constructed concurrently at the southern end of the alignment. A 3.5m deep trench will house two pipelines of 600mm and 800mm.
The then named Miller Tunnelling and Brown & Root (now Morgan Est Tunnelling Division and KBR respectively) undertook an eight-month development study in 2000, which involved the drilling of 20 boreholes. The tunnel will pass through new pit chalk, chalk rock and Lewes chalk, which may contain bands of flint.
The TBM will erect concrete rings as it goes, each 1m thick, consisting of six segments with 12 bolts. Amec hope to achieve average daily rates of 25 rings in each 24-hour shift, with top rates of 40 rings per day.
Estimator on the project, David Brett, told T&TI that the bid price allowed for two complete tool changes on the cutterhead – to take into account the foreseen presence of flint on the alignment. Brett also said that the project was awarded on a target cost basis, and that any profit will be shared between Thames Water and Amec.
Tunnel construction is scheduled to be completed by November 2003. The existing Wycombe Marsh Sewage Treatment Works will be redeveloped to include residential units, retail warehousing, a restaurant, and a fitness centre.
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High Wycombe Sewer
