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Project Overview

• Project: Civil and Structural Design for Gonerby Moor Substation [GNBY] Electrical Substation and Energy Storage Facility
• Location: Gonerby Moor, Grantham
• Scope: Civil and structural substructure design for foundations, oil retaining bunds, and compound access

Overview

The Gonerby Moor project required the design of robust foundations for a new electrical substation and energy storage facility. The site presented distinct geotechnical and environmental challenges that informed the structural approach:

• Variable Ground Conditions: The site contained areas of soft clay with high deformability and low bearing capacity, unsuitable for standard shallow footings without improvement. Deeper excavations for transformer bunds encountered firm clay but revealed aggressive ground chemistry.
• Environmental Protection: The presence of oil-filled transformers required alignment with DEFRA and Environment Agency guidelines to mitigate the risk of environmental contamination.
• Soil Chemistry: Site investigations identified a severe Design Sulphate Classification and Aggressive Chemical Environment for Concrete (ACEC) class in accordance with BS 8500, posing a significant risk of chemical attack to the reinforced concrete structures.

Our Approach

Our engineering team developed a split foundation strategy tailored to the specific equipment loads and soil strata. We utilised a range of design standards, including National Grid specifications, BS EN 1992-3 (Liquid Retaining Structures), and CIRIA C736, to support operational safety and environmental compliance.

Key Design Solutions

1. Oil Retaining Bunds (Environmental Containment) To contain potential oil escape, we designed the Grid and Auxiliary Transformer bunds as monolithic reinforced concrete structures sized to retain a volume exceeding the oil capacity.

• Leak Mitigation: The design incorporated continuous reinforcement across construction joints and water bars to target a rigorous Tightness Class as defined in BS EN 1992-3, designed to strictly limit liquid migration.
• Fire Suppression: We integrated a passive fire suppression system by filling the bunds with graded gravel, maintaining adequate freeboard between the maximum oil level and the stone surface.
• Chemical Defence: To mitigate aggressive soil conditions, we specified specialised protective measures, ensuring the concrete mix and barrier systems met the requirements of BS 8500 for high sulphate resistance.

2. Shallow Foundations (Ground Improvement) For lighter equipment such as Cable Sealing Ends, Surge Arrestors, and Disconnectors, we utilised mass concrete pad foundations.

• Soil Replacement: Due to the soft clay in the upper ground units, we mandated soil replacement to a sufficient depth below the foundations.
• Bearing Capacity: By replacing the poor soil with clean granular material, we achieved an improved allowable bearing capacity suitable for the equipment, minimising settlement risks.

3. Site Infrastructure & Access

• Heavy Access: We designed the compound access road and transformer bund access to withstand heavy plant loading, accommodating mobile cranes required during maintenance.
• Safety Features: Foundations with large plan areas were designed with upstand plinths and chamfered corners to improve safety for personnel walking through the site.

The Outcome

This comprehensive design package successfully validated the civil and structural elements for the Gonerby Moor facility. By addressing the aggressive ground chemistry and implementing rigorous containment strategies, we delivered a solution designed to remain structurally sound, environmentally secure, and capable of supporting operations throughout its intended design life.