Client / awarding authority
National Grid Electricity Transmission (NGET), UK
Winning contractor(s)
Ferrovial Construction (Spain) – BEMO Tunnelling (Switzerland) Joint Venture
Project scope
National Grid Electricity Transmission has awarded a design and build contract for the Grain–Tilbury electricity infrastructure upgrade, including construction of a replacement Thames Cable Tunnel beneath the River Thames between Tilbury (Essex) and Gravesend (Kent), UK.
The works involve the design and construction of a new underground cable tunnel to replace the existing Thames Cable Tunnel commissioned in 1970 and approaching the end of its operational life. The tunnel will accommodate 400 kV electricity transmission cables forming part of the UK high-voltage grid network.
Scope of the contract includes:
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Construction of a 2.2 km long cable tunnel beneath the River Thames
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Excavation and lining of two deep access shafts approximately 35 m deep, with diameters of 15 m and 12 m
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Construction of two surface headhouses providing operational and maintenance access
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Installation of Cable Sealing End (CSE) compounds connecting underground cables to the overhead transmission system
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Associated electrical and mechanical infrastructure
The scheme forms part of National Grid’s wider Grain–Tilbury transmission reinforcement project within the UK electricity transmission network.
Tunnel characteristics
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Tunnel type: cable tunnel for high-voltage transmission infrastructure
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Length: approximately 2.2 km
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Alignment: beneath the River Thames between Tilbury and Gravesend
Excavation of the main tunnel drive will be carried out using a slurry or mixshield tunnel boring machine (TBM) suitable for:
The two access shafts will be constructed using a Vertical Shaft Sinking Machine (VSM), enabling simultaneous excavation and lining installation from surface level in water-bearing ground.
Contract value
Approximately £230 million
Duration
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Contract award: December 2024
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Construction start: early 2025
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Tunnelling phase: 2025–2026
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Project completion: Q1 2029
Location
Tilbury, Essex – Gravesend, Kent, United Kingdom.
