Little Horsted Substation

Civil and Structural Works Design and Engineering Specialist Plant and Equipment Environmental and Sustainability Services Ground Improvement and Enabling Works
Sector:
Environmental and Renewables
Client:
Balfour Beatty / National Grid
Main Contractor:
Balfour Beatty
Location:
Little Horsted, East Sussex

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Project background

National Grid is constructing a new 400kV substation and associated infrastructure at Little Horsted, East Sussex, to reinforce the electricity network, improve security of supply, and connect new energy projects across the South East.

The £42 million project, contracted to Balfour Beatty PLC, commenced in early 2024 and is scheduled for completion in autumn 2025. The scheme includes the delivery and installation of two 178-tonne supergrid transformers.

The project has been developed to address constraints on the only existing 400kV circuit serving the south coast, supporting increased electricity demand and enabling greater integration of renewable energy. The substation is located on land off Palehouse Common and Sand Hill Lane, Framfield, acquired through a Compulsory Purchase Order (CPO) confirmed in May 2023.

Environmental and community considerations form a key part of the scheme, with commitments including the planting of over 20,000 plants and trees.

The development also forms part of a wider strategy to boost grid capacity in the region, with a proposed 300MW Battery Energy Storage System (BESS) set to connect to the new substation.

Project Overview

As part of the early works package, Joseph Gallagher Ltd was appointed to deliver civil engineering works for the new substation. To support programme requirements, Joseph Gallagher Ltd engaged Penfold Verrall to undertake the earthworks package.

In March 2024, Penfold Verrall mobilised its team within just seven days of appointment, ensuring the project remained aligned with National Grid’s programme despite challenging winter ground conditions.

This project highlights Joseph Gallagher Ltd’s ability to successfully deliver complex infrastructure schemes through effective supply chain collaboration, strong programme management, and high environmental and safety standards.

Little Horsted Substation
Joseph Gallagher works at Little Horsted Substation
JGL Little Horsted Sky View
JGL Little Horsted Substation Works

Scope of the works

  • Earthworks – Excavation and Surface Preparation 50,000m3
  • Retaining wall – 49m
  • Site SW and Foul Drainage and outfall– 940m
  • Temporary site access Roads – 1.1km of kerbs
  • Concrete and stone footpaths, site wide
  • 700t Super Transformer Bunds Bunds 2 no
  • 287no AIS Foundations for supporting structures
  • Type 3 over the whole site 65,000m2
  • Granite Chippings over the whole site 65,000m2
  • Ducting and trenching – 2.6km;
  • Earthing mat excavation – 7km
  • Precast Trough installation - 474m
  • 5000m2 tarmac 1.1km kerbs for the access road and parking area
  • Additional 3000m lighting and fibre ducting, 70 chambers and 79 bases.
  • Site Ancillary works, water supply and tank.

Key Challenges

Rapid Mobilisation

With programme timescales tight, Penfold Verrall mobilised all resources and equipment within seven days, allowing Joseph Gallagher Ltd to maintain momentum from the outset.

Wet Winter Conditions

Works commenced following an especially wet winter, with saturated ground complicating the initial large-scale topsoil strip. Priority areas were stripped to expose subsoil and promote drying, enabling early progress to formation.

High-Volume Logistics

The scale of the muck away operation required careful coordination both on site and at receiving facilities. Daily movements regularly exceeded 100 loads, allowing the operation to be completed ahead of programme.

Transformers - JGL at Little Horsted

Project Progression

Initial works focused on topsoil stripping to expose subsoil in priority zones. Once prepared, areas were excavated to formation level, enabling Joseph Gallagher Ltd to commence construction of two large concrete bunds for the supergrid transformers. Following bund completion, earthworks progressed methodically across the site. Excavated material was transported using 30-tonne ADTs to a designated stockpiling area before removal via eight-wheeled tippers.

Once formation was achieved, surfaces were compacted, separation fabric installed, and aggregate import commenced at a rate of approximately 1,000 tonnes per day. Completed areas were trimmed, proof rolled, and handed over to Joseph Gallagher Ltd for follow-on works.

Aggregate Import & Formation Build-Up

A total of 42,000 tonnes of Type 3 aggregate was imported to create a stable and durable formation for the substation platform. The material was:

  • Laid in 300mm layers as an attenuation layer
  • Compacted in 150mm layers as works progressed

This methodology delivered a robust foundation suitable for drainage, ducting, and concrete structures installed by Joseph Gallagher Ltd during the winter months.

Successful Completion

Joseph Gallagher Ltd successfully delivered the civil engineering works for the Little Horsted 400kV substation, maintaining programme certainty despite adverse ground conditions and logistical challenges. The project demonstrates Joseph Gallagher Ltd’s capability to manage large-scale, complex infrastructure projects through effective collaboration, robust planning, and high operational standards. The successful partnership with Penfold Verrall and Balfour Beatty PLC reinforces Joseph Gallagher Ltd’s reputation as a trusted delivery partner within the UK civil engineering and energy sectors.

Execution, Environment & Compliance

Despite challenging weather conditions and a demanding programme, works were executed efficiently and safely.

Joseph Gallagher Ltd ensured that all soil movements complied with the Materials Management Plan, with full traceability and disposal at licensed facilities.

This approach demonstrated a strong commitment to sustainability, regulatory compliance, and responsible construction practices, while ensuring uninterrupted progress on site.

Joseph Gallagher works in Little Horsted Substation

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