1 Executive Summary

Sweco has been instructed by SSE to carry out an assessment of delivery routes for abnormal transformer loads for three substation locations and HGV access to two trenched section access points.

The aim of the assessment is to identify any potential obstructions and areas of over‑run and over-hang for the safe delivery of abnormal indivisible loads along the existing roads and provide proposals for the permanent access roads to the given locations. For the purpose of this report the routes have been termed as below:

• Substation Location 3
• Substation Location 8 and 9
• HGV - Cable Road Crossing 1
• HGV - Cable Road Crossing 2

A swept path analysis using Auto Track has been undertaken for each delivery route. A walkover survey has been undertaken to identify additional obstructions and record any measurements where applicable. Results from the swept path analysis and walkover survey have been recorded on drawings and summarised within this report. In addition, the walkover survey was recorded using dashcam equipment and issued to SSE separately.  

No topographical data was available during the assessment. This should be obtained and used to ensure there is no risk of grounding for the preferred delivery route. Note, the walkover survey did not highlight any obvious locations where grounding would be a concern.

It is recommended the following structural assessments are undertaken to fully evaluate each route.

Substation Location 3

Structural assessment of road bridge crossing railway before proposed permanent access road. Railway bridge west parapet also to be dismantled. Initial approvals from Network Rail and Transport Scotland will be required.

Substation Location 8 and 9

Structural assessment of culvert crossing below road approaching substation location. Note that no information was determined on the details of the culvert due to overgrown bushes and limited access.

HGV - Cable Road Crossing 1

Structural assessment of road bridge crossing railway before trenched cable road crossing location.

HGV - Cable Road Crossing 2

Structural assessment of road bridge crossing watercourse before trenched cable road crossing location. Note that limited details and dimensions of the bridge were obtained due to restricted access.

The capacity of manholes along each route should be confirmed. Additionally, any bridge or culvert crossing along the A1 should also be confirmed (out with the boundary limits of this report). Note Sweco have been advised not to consult with local roads authority, network rail etc. at this stage.

For undersized or unclassified manhole covers, a temporary steel plate rated to D400 loading in accordance with BS EN 124 should be designed as a minimum during the temporary work stage.

A cost estimate (+25%/-15%) for the new access road construction and improvements to current infrastructure has been assessed using values calculated from Spon’s Civil Engineering and Highways Work Price Book, the Estimator’s Pocket Book and information provided to Sweco by contractors.

A summary of the cost estimate for each substation route is presented below.

Substation Access Road Construction Cost Estimate

It is advised to obtain a more detailed cost estimate from several contractors once topographical data and ground investigation information are made available. Note prices will vary between contractors and are subject to market conditions.

2 Introduction

Seagreen Charlie Wind Energy Limited and Seagreen Delta Wind Energy Limited are developing the Seagreen 2 and Seagreen 3 Offshore Windfarms respectively, in the Firth of Forth.

It has been identified the export cable from Seagreen 2 will make landfall south of Dunbar and connect to the grid at Branxton.

A previous study into the preferred location for the substation was undertaken which identified sites primarily on the basis of topography to minimise ground works requirements.

Since the initial study, the footprint of the substation has increased and locations 8 & 9 are currently the preferred options when utilising Landfall 3 considering topography, access, impact on local residents and other constrains such as historic monuments.

When considering the cable route from Landfall 5, the preferred substation is at Location 3. Given the restrictions with topography at location 3, the required construction lay-down area will need to be situated approximately 500m away, a new access road would be required.

The three proposed substation locations and abnormal delivery routes are shown in Figure 2‑1. The proposed delivery route for substation 8 and 9 is similar. As such it be considered as one within the context of this report.

Figure 2‑1 Substation Location and Access Routes

2.1 Scope of Document

Sweco has been instructed to carry out an assessment of the delivery route for the three proposed substation locations and two trenched section access points on behalf of SSE. The purpose of this report is to evaluate substation delivery routes for abnormal and HGV access from the A1.

The routes consider the existing roads and include proposals for the permanent access roads to the substation location for delivery of the transformer.

In addition, access to trenched sections of the cable route from Substation 8 and 9 via HGV (44 tonnes) is included. The locations of the trenched cable crossings are presented in Figure 2‑2.

Figure 2‑2 Trenched Cable Road Crossing Locations

2.2 Methodology

The study used Auto Track to provide a swept path analysis of all potential access routes along existing and proposed roads. Identified areas of concern were then investigated by two Sweco engineers during a route walkover survey to obtain further information and measurements where required.

The swept path analysis identifies the road edges and areas of over-run and over‑hang for the given vehicle dimensions outlined in Section 2.4.

The walkover survey identified additional obstacles including locations of overhead lines, trees, bridge parapets, manholes, potholes and steep embankment batter. Vehicle clearance checks were also performed on structures such as bridges.

Photographs taken during the walk over survey are presented in Appendix C. Where appropriate clearances have been recorded and highlighted on the swept path analysis drawings. Locations where alterations are required have also been identified. A tabulated summary of each route and the required improvements is presented in Section 3.

At the time of the swept path analysis, topographical data was not provided, and therefore a vertical clearance check has not been carried out. However, the walkover survey did not indicate any obvious locations where grounding would be a concern. It is still advised that a check is performed to ensure there is no risk of grounding for the preferred delivery route at a later stage.

A video survey of each proposed route was recorded during the walkover survey and has been issued to SSE separately.

2.3 Delivery Routes and boundary limits

The boundary limits of this report are described in Table 1 and illustrated in Figure 2‑3 to Figure 2‑5.

It has been assumed that all sections of the A1 are suitable for abnormal loads including transformer components. However, it should be confirmed that any bridge or culvert crossing is suitable for the given delivery loads.

Table 1 – Delivery Route Boundary Limits

Figure 2‑3 Substation 3 Delivery Route

Figure 2‑4 Substation 8 & 9 Delivery Route

Figure 2‑5 HGV - Cable Road Crossing 1 and 2 Delivery Route

2.4 Delivery Vehicles

2.4.1              Transformer Delivery Vehicle

Specific details for the transformer delivery vehicle have been provided by SSE. This includes vehicle dimensions and axel loadings. The specific details have been used as input to the swept path analysis in Auto Track. Details of the vehicle provided by SSE are presented in Appendix A.

2.4.2              HGV (44 tonnes)

Details for a 44 tonnes HGV have been extracted from the Auto Track library. This has been used as input to the swept path analysis along the HGV delivery routes. Details of the proposed HGV are presented in Figure 2‑6.

Figure 2‑6 HGV (44 Tonnes) Details

3 Swept Path Analysis Results

The swept path analysis highlighted physical obstructions and areas of over-run and over‑hang for each delivery route. These areas have been dimensioned on drawings in Appendix B.

A summary of drawing included in Appendix B are listed in Table 2.

Table 2 - Drawing List

The physical obstructions and constraints along each route including indicative details of measures required to mitigate against each are presented in Table 3 to Table 6.

For clarity, photographs taken during the walkover survey of each obstruction or constraint are referenced and included in Appendix C.

3.1 Substation Location 3

Table 3 - Substation Location 3 Delivery Route Summary