Client: Network Rail Duration: 7 weeks Value: £260,000

Requirement: To control the 4m/s fast flow of water through the culvert structure below the railway line and highway, so that a structural survey and any remedial works could be carried out safely.Cobb Valley, North Wales.

Cobb Valley Culvert in Anglesey, North Wales, runs directly under the A5 highway, A55 mainland Rail track between Valley and Holyhead adjacent to the Cymyron Strait. With water flowing through the structure at speeds of approximately 4m/s, the high flows and poor conditions prevent any safe means of access to carry out inspections and repair works.

Kaymac were commissioned by Network Rail to control the flow of water through the structure, so that a structural survey and any remedial works could be carried out safely. However, this was no easy challenge, with the Irish Sea to the North and the inland tidal lagoon to the South of the structure, there is constant flow, making this a dangerous operation if not controlled correctly. Working against the clock during a Saturday night possession, steel guides were installed and a sluice gate lifted into position ready for installation at slack water using a 25Tonne Crane positioned within the road closure on the A5 highway. Slack water was at approximately 2am and there was a 10-15 minute window to lower the gate into place, which was successfully achieved.

A stop log system was then installed at the seaward side of the structure at relevant states of the tide throughout the week using a 10Tonne mobile crane working within the temporary traffic management set up on the A5. Following installation of the stop logs and the final sealing, the sluice gate was removed using two 6Tonne air hoists during another Saturday night possession; a road closure was in place and 25Tonne Crane on site as a precautionary measure.  The whole structure became totally accessible and was inspected safely by divers with repairs carried out accordingly.

On completion of the repair works the sluice gate was re-fitted allowing safe removal of stop logs, the sluice gate was then removed at slack water allowing free tidal flow through the structure. 

Cob Valley Raising of the Sluice Gate


Cob Valley Raising of the Sluice Gate



Stop logs


Cob Valley Raising of the Sluice Gate

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