Redundant 400kV oil filled cable removal in Ross-on-Wye, Hertfordshire.

Delivery and approach

JSM were appointed to remove the redundant Ross-On-Wye 400kV oil filled cable route section of a 1.98km circuit. This included joint bays between Walford SEC and joint bay 11/12, near the Wye River in a site of special scientific interest (SSSI) site. The total length of this twin circuit was 1.98km.

100% of the cable route chosen sections were extracted. The only open cut sections on the route were the joint bay locations and the launch and receive pits. Existing joint bays were used as launch and receive pits.

Of the total route length, only 2.6% required to be open cut on this project.

Scope Of Work:

• Attend EAW PC’s site induction to CDM area.

• Carry out daily risk assessments and task RAMS briefings.

• Set up access to and site boundaries as per CDM area plan.

• Consult current service drawings.

• Cat scan & locate all know 3rd party services at areas to be excavated.

• Earth down circuit cables to eliminate impressed voltages.

• Excavate HDD launch and receive pits, over the circuit to be removed. insert shoring or batter excavations as required.

• Cables are drained of free oils, allow to Remove any residual leeched cable oils in all three phases of the circuit.

• Receive permit to cut/spike cables from PC or the SAP.

• Spike, cut and cap cables adjacent to joint bay 11/12, copper caps x 3 on joint bay side, heat shrinks on open cable side x3 including pilot cable.

• Set up HDD rig and de-bond cables from backfill.

• Once loosened commence recovery process per phase x3.

• Backfill void using bentonite slurry additive.

• Recover any excess drilling fluids/bentonite (gully sucker)

• Cut cables and temporarily seal ends for transport to be processed/recycled.

• Backfill and compact launch and receive pits.

• Remove fencing and leave site clean and tidy as found.

Challenges

The route crossed through a rural environment with joint bays located near the Wye River in a SSSI site. Part of this rural environment was the woodland coppice which was found to house breading wild fowl. The route also encountered buried services throughout.