Barhale has been appointed by Thames Water to reline a section of the abstraction tunnel at Ashford Common Water Treatment Works (WTW) in Surrey, UK.
The contract forms part of efforts to maintain the structural integrity of the water network supplying London.
The Ashford Common WTW is supplied by reservoirs in the West London Abstraction area (WLA), which are linked by a network of tunnels and mains feeding several water treatment sites.
During required five-year inspections, Barhale’s Tunnels & Aqueducts team identified that a section of the Southern Inlet tunnel showed inconsistencies in its existing glass-reinforced plastic (GRP) liner. Results from the inspections indicated that these irregularities could lead to damage to the underlying wedgeblock tunnel.
Work under the new contract will involve replacing only the affected section of the tunnel’s lining. According to Barhale, the company initially collaborated with Thames Water in an Early Contractor Involvement (ECI) phase to develop a workable plan that accounts for restricted access within the underground, multi-level tunnel network at Ashford Common.
The relining process is scheduled to begin with excavations to a depth of 3m to uncover the chimney and riser. Selected portions of the riser will then be demolished to allow safe access down to the tunnel’s invert, located 19.5m below ground.
Scaffolding will be installed to provide secure access along the tunnel, and the existing GRP liner in the designated section will be removed. Grout and concrete will subsequently be broken out, after which a new reinforced concrete liner will be constructed to strengthen the structure.
Barhale regional manager Florin Edu 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.”
Ashford Common WTW is one of four water treatment plants supplied by the WLA reservoirs and serves London via the Thames Water Ring Main (TWRM) network. Barhale had previously completed a repair in the Northern tunnel at Ashford Common, also identified during routine inspections; comprehensive relining of that section is planned for a future project.
In addition, Thames Water last month awarded Barhale a £12.5m contract for statutory tunnel inspection and maintenance across several assets under the AMP8 Tunnels and Aqueducts programme. This includes the Thames Water Ring Main, North London Abstraction and New River Zone raw water assets, and the production tunnels in other Thames Water treatment works.
Nearly 48km of tunnels are due to be inspected as part of that programme.
