Thames Water has awarded two separate tunnel contracts to help expand its Ring Main grid network in London but both contractors plan to use refurbished 3.21m diameter Lovat EBPMs to drive the bores, T&TI has learned.
In early February, Morgan Est won a US$74M contract to design, build and commission a 4.9km tunnel to run across south London from Brixton to Honor Oak reservoir, Forest Hill.
Work is scheduled to start on site in March for completion in three years. The mixed face TBM is due on site at Honor Oak in December to commence tunnelling in February next year, with excavation and lining due to be over by August 2008.
Morgan Est will drive the TBM through mostly chalk at depths of 32m-51m from the 11m diameter, 57m deep launch shaft to the 51m deep reception shaft of the same width. Dewatering will be employed at both shafts. The tunnel will be lined with pre-cast, bolted segmental rings of 2.85m id, and a secondary, insitu reinforced concrete lining is also proposed.
The tunnelling works will be undertaken on a target cost “pain/gain” basis under Option C of the Engineering and Construction Contract, 2nd edition. The contract also includes the provision of a pumping facility at Honor Oak with associated mechanical, electrical and control equipment.
Separately, Amec was awarded a US$54M contract at the end of January to build a 4.5km long tunnel in north London. The tunnel, running from Stoke Newington reservoir to a pumping station at New River Head, will have 2.85m id pre-cast segmental rings, again with in-situ RC pressure lining.
Geology along the route includes London Clay and Thanet Sands, and the alignment takes the tunnel under six London Underground tube lines, five rail tunnels, a canal tunnel and two major sewers.
Work on site is scheduled to start in July for completion in early 2010. The contract also involves the provision of M&E and control equipment at the pumping station.
