Traditional tunnelling contractors are shying away from the £2.2 billion Thames Tideway tunnel in favour of Crossrail.
French construction firm Vinci is set to bid for the first phase of the job in a joint venture with Morgan Est and Amec, while Murphy said it would make a decision once the design is unveiled.
Foreign firms, including Hochtief and Nishimatsu, are also expected to bid.
But Nuttall and Skanska are looking to Crossrail for their next big tunnelling work.
One firm said: “Contractors will be selective with what work they do and there is much more of an attitude to taking lower-risk contracts, especially with tunnelling. And this project is just too risky.”
The first phase of the ambitious project to capture sewer overflow involves the £800 million construction of a 6.8 km spur tunnel in east London called the Lea Tunnel.
The contract notice for the Thames Tideway was due to go in the Official Journal this week, but has been delayed.
Thames Water has said its procurement strategy will feature significant early contractor involvement, including the lining design, shaft site set up, muck shifting and tunnel boring machine consultation. The project is due to be awarded in March 2009, with construction beginning immediately and finishing in 2014.
The Lea Tunnel, with a diameter of 7.2 m, will pass under the original northern outfall sewer and also below the recently constructed lower Lea Valley cable tunnels.
It will lie within the upper chalk layers at depths of 60 to 75 m, connecting with the Thames in places. Planning permission will be sought next May.
Thames Water says the tunnel is needed to comply with the urban waste water treatment directive and that it will eliminate almost all overflow spills, improving river quality.
Outfalls to use pumps and gravity
The route of the Tideway Tunnel follows the River Thames as it snakes its way to the sea.
From its start in Hammersmith, west London, the tunnel will link up with 36 sewage outfalls.
These will provide one of the project’s biggest technical challenges for contractors as they reach up to 80 m in depth.
Some of the outfalls will use pump technology to deliver the water to the main tunnel, while others will rely on gravity.
Analysis: A challenging but manageable project
By Steve Walker
The Thames Tideway tunnel will intercept more than 35 combined sewer overflows and prevent their discharge into the Thames.
The £2.2 billion project has two main elements. The first is the 6.8 km Lea Tunnel which will connect Abbey Mills pumping station in east London to Beckton sewage treatment works in Newham. Building is expected to start in 2009 and run to 2014.
We’ll also have the more complex 32.2 km Thames Tunnel from Hammersmith to Beckton, at depths between 30 and 70 m. Construction will start in 2012 and run to 2020.
The main challenges, particularly at the eastern end of the scheme, are the high water pressures, managing the wear on the machines due to the presence of flints, treatment and reuse of the chalk material and the construction of the walls of the shafts.
There are also many different land owners we will need to consult.
But though the scale of the activities sets this project apart, the construction methods proposed are well proven and within the range of experience of tunnelling specialists.
Steve Walker is Thames Water major projects director