Mott MacDonald is designing the eastern section of the Thames Tideway Tunnel on behalf of a joint venture of Costain Ltd, VINCI Construction Grands Projets and Bachy Soletanche.

Tideway is delivering the biggest infrastructure project ever undertaken by the UK water industry, which will see 25km of tunnels constructed beneath London. The East section package includes the construction of two tunnels – a 5.5km section of the main 25km tunnel and a 4.6km connecting tunnel for combined rainwater and wastewater – both of which will serve the east of London.

Located between 45m and 65m below ground, the two tunnels will be excavated by tunnel boring machines (TBMs) using slurry pressure balance technology. The main tunnel will have an interior diameter of 7.2m, while the diameter of the connecting tunnel will be 5m. The East section also includes the construction of five large shafts using diaphragm walls to a depth of 72m and with diameters of between 17m and 25m, maritime works on the Thames, associated structures connecting with the existing wastewater collection system and electromechanical works packages.

Michael Francis, Mott MacDonald’s project director, said:

“It is fantastic to be involved in the creation of one of London’s most significant infrastructure projects. The East works package is the deepest section of the project, with tunnels driven by slurry TBMs deep in the chalk up to 70m below the water table. The deep shafts will be constructed using diaphragm walls and the complex hydraulic structures to divert flows require soil mixing ground treatment, secant piles and high-quality concrete meeting the 120 year design life.”

An optimisation phase, which includes design and methods, is almost completed and the design team are delivering the first conceptual designs using state-of-the-art building information modelling models and processes. The works are scheduled for delivery in 2023.