Solutions

Due to the extremely poor ground conditions with depth of peat in excess of 5m at locations the key element considered when evaluating a ducted solution was how to minimise the requirement for personnel to enter the trench. HDPE was a front runner as it can be provided in 100m lengths which could be welded together to form long strings on the windfarm access roads prior to being lifted into the cable trench.

The laying of duct in a trefoil and pulling cables at a later date as opposed to the traditional open cut with cable direct lay with sand & geotextile surround provided some obvious pros:

• Safety: Excavations open for much less period of time. Much less of requirement for operatives to enter the trench in very soft ground. Much less manual handling of cables in trench.

• Environmental: Much less requirement for dewatering, silt management, management of sand washout.

• Cost: duct replaced the need for sand and geotextile surround, quicker civils operation, much less maintenance / rework of trenches to facilitate safe access

• Operational: civils works could be completed in advance of electrical cable work reducing interface with different trades, facilitated more time for cable procurement, cables could be installed into ducts just in time minimising potential for damage to cables

• Technical: duct provides a much better mechanical protection to the cable throughout the lifetime of the windfarm, zero cable faults were recorded upon testing installed cables, any future maintenance/changeout of the cables can be completed with very minimal excavation works.

Project Results

Radius supplied 35,000m of ducting installed in trefoil over a 8 week period. Much improved safety and environmental implications when compared to traditional cable lay. Importantly ZERO cable faults after cable installation.