Barhale has secured a contract from Thames Water to reline a section of the abstraction tunnel serving Ashford Common Water Treatment Works (WTW) in Surrey, following inspections that identified defects in the tunnel’s existing lining.
The civil engineering, infrastructure and tunnelling contractor will carry out the work on the Southern Inlet tunnel, which forms part of the West London Abstraction (WLA) system supplying raw water to the treatment works. The project is intended to protect the long-term integrity of the tunnel and help safeguard a key component of London’s drinking water infrastructure.
The contract follows completion of an Early Contractor Involvement (ECI) phase, during which Barhale worked with Thames Water to refine the design and develop construction methods capable of overcoming the site’s complex underground access constraints.
Mandatory five-year inspections undertaken by Barhale’s Tunnels & Aqueducts team identified inconsistencies in the existing glass reinforced plastic (GRP) liner, creating a potential risk to the underlying wedgeblock tunnel structure.
Construction will begin with a 3m-deep excavation to expose the tunnel access chimney and riser. Sections of the riser will then be demolished to allow personnel to reach the tunnel invert, approximately 19.5m below ground level.
Scaffolding will be installed inside the tunnel to provide access for removal of the existing GRP liner. The contractor will then break out the existing grout and concrete before constructing a new reinforced concrete liner designed to restore the tunnel’s long-term structural integrity.
Florin Edu, Regional Manager at Barhale, said: “The works will ensure the resilience and reliability of this strategic asset for the long term.
“We have collaborated with Thames Water through the ECI phase to shape our approach. It will be carefully managed to ensure at least a minimum flow rate from the other WLA area reservoirs into the works is maintained to sustain the treatment process and prevent the treatment beds from deteriorating.”
The West London Abstraction system comprises 10 raised storage reservoirs supplied by abstractions from the River Thames. These are connected by a network of tunnels and large-diameter pipelines feeding four water treatment works, which in turn supply London via the Thames Water Ring Main.
Barhale has previously undertaken repairs to the Northern tunnel at Ashford Common WTW after routine inspections identified localised defects. A full relining of that section is planned as part of a future project.
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