Thames Tideway Tunnel: beneath the Thames tunnelling challenges and achievements

The Thames Tideway Tunnel represents one of the most ambitious and transformative infrastructure undertakings in London's recent history. Central to the project was the construction of the main tunnel, spanning approximately 25 km across central London and engineered to capture, store and transfer combined sewer overflows to the upgraded Beckton Sewage Treatment Works through the completed Lee Tunnel. The main tunnelling operations were executed using tunnel boring machines (TBMs). This paper examines some of the technical aspects of the TBM tunnelling works, highlighting innovative approaches and best practices implemented throughout. Key areas of focus include the construction approach, the requirement for high-pressure hyperbaric interventions (which required special dispensation from the Health and Safety Executive) and the management of tunnelling operations through areas of deoxygenated ground. The paper also addresses the management of complex contractual and construction interfaces, as well as the successful transit of numerous high-profile third-party assets, including the iconic Tower Bridge. The challenges were effectively managed through coordinated engineering solutions, effective mitigation and continuous monitoring. The successful completion of the tunnelling works underscores the meticulous planning and execution that have defined the success of the Thames Tideway Tunnel project.