Barhale to help protect London water supply: tunnel relining lessons for engineers
Reviewed by Joe Ashwell
First reported on The Construction Index
30 Second Briefing
Barhale has secured a Thames Water contract to reline the Southern Inlet abstraction tunnel at Ashford Common Water Treatment Works in Surrey, after five‑year inspections found inconsistencies in the existing glass reinforced plastic liner that threatened the underlying wedgeblock tunnel. Construction will involve a 3 m deep excavation to expose the chimney and riser, demolition of riser segments for safe descent to the 19.5 m invert, scaffold installation, GRP removal, grout and concrete breakout, and installation of a new reinforced concrete liner. The scheme follows an Early Contractor Involvement phase to resolve access constraints in congested, layered tunnel infrastructure and builds on Barhale’s earlier local repair in the Northern tunnel.
Technical Brief
- Mandatory five-year tunnel inspections by Barhale’s Tunnels & Aqueducts team triggered the relining scope.
- Inconsistencies were detected specifically in the Southern Inlet tunnel’s existing GRP liner during these statutory inspections.
- Identified defects were assessed as posing a risk of structural damage to the underlying wedgeblock tunnel.
- Early Contractor Involvement with Thames Water focused on resolving access within congested, layered tunnel infrastructure.
- Safe access strategy uses chimney and riser exposure before controlled demolition of riser segments.
- Scaffold installation from the 19.5 m invert provides working platforms for liner removal and reconstruction.
- Previous Northern tunnel defects were picked up through routine proactive inspections, leading only to localised repair.
- The staged approach at Ashford Common illustrates how periodic inspection regimes directly inform major safety interventions.
Our Take
Barhale’s work at Ashford Common WTW and the West London Abstraction area sits alongside its recent Thames Water Ring Main inspection contract, signalling that Thames Water is consolidating complex deep-asset inspection and maintenance with a contractor already proven on large-diameter tunnels.
The 19.5 m tunnel invert level depth at Ashford Common is comparable to the 16 m deep shaft Barhale is delivering for Severn Trent Water in Silverdale, suggesting the contractor is building a niche in deep-shaft and tunnel access works that water utilities can leverage across multiple regions.
Within our 880 Infrastructure stories, Barhale appears repeatedly with Thames Water, Severn Trent Water and Yorkshire Water, indicating that for UK water operators in London, the Midlands and Yorkshire, it is becoming a go-to for resilience and safety-critical projects rather than one-off civils packages.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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