457mm/18” diameter Quinton Oaklands - Longbridge gas pipeline. The pipeline is contained with a 24” sleeve that protects the pipeline as it passes over the watercourse. Inspections have revealed that the blockwork walls that previously supported the sleeve have collapsed, causing the sleeve to drop and rest on top of the gas pipeline contained within.
It was not known whether the gas pipeline had suffered any damage.
It was proposed that a temporary working platform is installed beneath the pipeline in order to facilitate the removal of the sleeve and the inspection of the pipeline. Carried out by National Grid.
The platform will be supported off screw-pile foundations that will be installed in the banks of the watercourse.
The screw-pile foundations shall be adapted to support the pipeline as part of the permanent works, if required.
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View of pipe sleeve dropped & resting on top of pipe
The temporary works comprised of the following:
Install silt curtain downstream of works;
Remove the failed supports from the watercourse;
Install screw pile foundations and working platform, as per approved design, ensuring that the flow in the watercourse is not abated;
Hand site over to National Grid for removal of sleeve, pipe inspection & coating;
Remove working platform & screw piles.
The permanent works comprised of the following:
Excavate the banks of the watercourse to achieve a straight flow through the worksite, ensuring that the flow is not restricted at any time;
Install rip-rap/rock armour to the bottom of the banks to prevent future erosion of the banks;
Extend/divert the existing land drains;
Remediate the banks above the rip-rap/rock armour to prevent future erosion.
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View of site prior to any brush & tree clearance.
Because of the proximity of the live gas pipeline, National Grid’s permit system was thoroughly adhered-to and a Competent Person was on-site throughout the works. The site was on private farm land with no public access.
Prior to the start of works extensive ecological surveys have been conducted, identifying wildlife & environmental issues.
The works have been planned so as to impose minimal impact on the surroundings, silt curtains will be used within the water course & the works are being conducted during a time that inflicts minimal impact on wildlife. Once the works are completed & the river banks have established growth it will promote & encourage new habitats for wildlife.
Any waste materials were taken off-site and disposed-of in accordance with the Site Waste Management Plan.
The public and Local Authorities will be updated throughout the project and all interested parties kept informed of progress at all times.
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View of collapsed pipe supports.
200mm gas pipeline, NL0014 Reading Branch, crosses a watercourse, The Cut, just north of the M4 near Maidenhead.
Inspections had revealed that, because of scour partly caused by upstream vegetation and debris, a section of the riverbank had eroded to the point where the pipe’s swan-neck, previously within the bank, had become exposed, putting the pipeline at risk of damage.
Northern Divers were employed through an existing National Framework Contract to undertake the survey, design and repair of the eroded bank in order to maintain protection to the pipeline.
