Joseph Gallagher Ltd
Hinkley Point C – Fish Return
Aerial view of the Hinkley Point marine construction facility
Joseph Gallagher Ltd was appointed to deliver a technically demanding 1.8‑metre‑diameter, 620‑metre sea outfall tunnel using a pipe‑jacking methodology. The works required the controlled installation of a closed‑face TBM to be recovered above the seabed – an operation demanding high precision, detailed planning, and specialist offshore expertise.
Project Description
The company drove the tunnel from a restricted launch site along a complex alignment featuring double vertical curves and a challenging angled breakthrough. The TBM advanced through varying geological conditions before entering a 45‑metre offshore concrete structure, where breakthrough and recovery were carried out in a marine environment frequently affected by adverse weather and significant tidal variation. To maintain consistent progress, Joseph Gallagher adopted a closed‑face tunnelling method supported by a separation system designed to fully recycle process water, satisfying both the technical and environmental requirements of the project.
Challenges
The project introduced several major engineering challenges. The confined launch site required careful sequencing of all plant, equipment, and personnel. The TBM had to be launched and aligned at an angle, demanding highly accurate control throughout the drive. As face pressures increased, hyperbaric interventions of up to 2.4 bar were undertaken to ensure safe inspection and maintenance of the cutterhead. The double vertical curves required precise gyroscopic guidance, particularly as the TBM approached the offshore structure. Marine operations added further complexity, with variable weather and significant tidal fluctuations influencing offshore access windows.
JGL pipe‑jacking launch frame in position, ready for TBM installation during shaft preparation works
Expertise and Solutions
Joseph Gallagher Ltd applied its full tunnelling capability to meet these challenges. Specialist pipe‑jacking teams managed the drive using proven marine project methodologies, supported by experienced hyperbaric crews for pressurised interventions. Dedicated offshore lifting and tunnelling systems enabled safe recovery of the TBM above the seabed. Advanced gyroscopic navigation ensured alignment accuracy, while a fully integrated separation system allowed continuous recycling of process water.
NRC heavy‑lift crane operating alongside tunnelling plant in a busy urban construction site
Environmental performance was prioritised throughout. High‑quality pipe manufacturing ensured long‑term outfall durability. All process water was recycled, preventing marine discharge, and tunnel arisings were reused on site. Only biodegradable chemicals were used, and recovering the TBM in wet condition minimised seabed disturbance.
Value Added
Joseph Gallagher Ltd delivered the works on programme and within budget. Bespoke engineering solutions addressed the unique offshore breakthrough requirements, supported by the company’s strong hyperbaric experience.
Additional Capabilities
The project benefited from extensive resources across the Joseph Gallagher Group, including tunnelling systems supplied by SPA and lifting equipment from NRC, ensuring safe and efficient tunnelling and offshore operations.
Precast concrete tunnel segments stored and ready for installation
For More Information, contact us at https://www.josephgallagher.co.uk/
