Harefield to Southall Gas Pipeline Tunnel

Tunnel Segments Reinforced Solely with EPC’s Synthetic Fibre Concrete Reinforcement

Project Details

The Harefield to Southall Gas Pipeline is a 27 bar, 18.5 km, 1.2m diameter gas pipeline in Middlesex, UK, commissioned by National Grid to meet rising gas demands in West London. Murphy Pipelines Ltd was contracted to design and construct the pipeline which became operational in 2009.

Construction was in a substantially urban environment and required over 2.3km to be constructed in four 2.5m diameter segmentally lined TBM driven tunnels, approximately 21 m below ground level.

EPC’s BarChip synthetic fibre was the sole reinforcement in 976 m of the segmental lining.

Design Details

The synthetic fibre reinforced tunnel was driven by TBM through London Blue Clay. 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 with 7kg/m3 of EPC’s BarChip synthetic fibre reinforcement.

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.

Project Benefits

The use of BarChip synthetic fibre in these segments proved very effective in meeting all the design requirements as well as ensuring that the segments sustained minimal damage from the jacking rams during installation. The segments have since performed to the specified design criteria.

The use of EPC’s BarChip fibres has lowered the overall carbon footprint of the project, negated any corrosion either of the internal steel gas pipe through cathodic protection and of the segment reinforcement itself.

Video — EPC Synthetic Fibre Reinforced Precast Concrete Tunnel Segments