Project Name:   Harefield to Southall Gas Pipeline

Location: Middlesex, UK

Application: Precast Segmental Tunnel Lining

The Harefield to Southall Gas Pipeline is a 27 bar, 18.5 km gas pipeline in Middlesex, UK, commissioned by National Grid to meet rising gas demands in West London. This included a 900m long TBM driven tunnel through London Blue Clay, approximately 21 m below ground level with a precast fibre reinforced segmental lining.

The lining was a wedge block lining made up of seven (7) segments and one (1) key. The ring had an ID of 2.59 m and each segment was 180 mm in thickness by 1.0 m width. The concrete was specified at 45MPa.
The lining was comprehensively designed and checked using the Finite Element Analysis modelling program ATENA.

Segments were produced at a local precast factory where synthetic fibre was mixed into the concrete then poured into vertical moulds. The initial segments were preassembled at the plant to form a trial ring to ensure that the correct tolerances were achieved. The segments were then horizontally stacked and trucked to site.

Outcomes:

• Corrosion concerns in the lining were eliminated
• Production speeds at the off-site production facility were increased
• The use of fibres ensured minimal damage from jacking rams
• Reduced labour and material costs during segment production
• Harefield to Southall Gas Pipeline is referenced in ITA’s ITAtech Guidance for Precast Fiber Reinforced Concrete Segments Vol 1 Design Aspects

Author:  Geoff Sedgman: gsedgman@barchip.com