Dunmanway 110KV Grid Connection
Cable Route Design

Dunmanway, West Cork

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Project Details

Client: Suir Engineering

Value: Confidential

Services Provided: Civil Engineering Design, Bridge Engineering Design, Traffic and Transportation, Flood Risk Assessment

Category: Renewable Energy

Project Duration: July 2018 to July 2019

Project Description

PUNCH provided detailed engineering design services for a 110KV underground electricity cable connecting both Carrigarierk and Shehymore wind farms located north of Dunmanway in West Cork to an existing substation in Dunmanway town. The overall length of the 110KV undergound cable route was in excess of 10km and was entirely located along public roads including both local and regional roads.

The terrain traversed by the cable was highly variable with competent rock located close to the surface and outcropping along a considerable length of the route. There was deep peat present in other areas coupled with high ground water tables which presented a number of challenges which had to be comprohensively investigated as part of the design scope to mitigate both programme and cost risks.

A range of surveys and investigations were undertaken along the route. Initially a desk top study was undertaken to help identify all existing underground and over ground services present. Also, all existing bridges and culverts were identied. Once all relevant desk top information was colated, the full length of the route was then inspected on the ground. Detailed surveys of all bridges/culverts any other structures within close proximity of the proposed trench excavations (i.e. private boundary walls/buildings) were undertaken. All relevant dimensions relating to each bridge/culvert crossing point were recorded along with relevant images capturing the condition of each structure.

Geophysical surveys were also undertaken to access rock profile along the route. Localised trial pitting was also undertaken to verify rock depths, road build-ups, existing foundation details etc. to help fully inform the design.

Once all survey information was colated, PUNCH undertook the detailed design for the cable route. The scope of our design documents included production of 1:250 scale layouts for each section of the route capturing horizontal cable alignment and all existing services within the road carriageway which may have an impact on the works. The scope of our detailed design also included development of bespoke drawings for each bridge and culvert crossing which had to take account of the specific Eirgrid requirements with respect to cable cover, separation distance, vertical alignment transition restrictions etc. Directional drilling was adopted as the preferred solution for crossing some of the bridge structures. In other cases the cables were taken across above the crown of the bridge and the road levels were raised both on the bridge and on the approaches to satisfy minimum cover requirements while not impacted on the bridge structure. Loading assessments had to be undertaken where such design solutions were adopted to verify that the bridge had adequate load carrying capacity.

A further element of our design included undertaking flood risk assessments at each cable joint location to demonstrate that each joint was located outside of flood risk areas.

All details were reviewed and commented on by Eirgrid as part of design signoff and verification of compliance with their code of practice.

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