Tideway is delivering the biggest infrastructure project ever undertaken by the UK water industry, which will see 25 km of tunnels constructed beneath London. It will make London’s sewerage network fit for the 22nd century and will help prevent millions of tonnes of sewage pollution that currently discharges into the tidal River Thames every year.
The East section package includes the construction of two tunnels – a 5.5-km section of the main 25-km tunnel and a 4.6-km connecting tunnel for combined rainwater and wastewater – both of which will serve the east of London. Located between 45 and 65 m (150 to 215 ft) 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 7.2 m (23.6 ft), while the diameter of the connecting tunnel will be 5 m (16.5 ft). The East section also includes the construction of five large shafts using diaphragm walls to a depth of 72 m (235 ft) and with diameters of between 17 and 25 m (55 and 80 ft), 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 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 optimization phase, which includes design and methods, is almost completed and the design team is delivering the first conceptual designs using state-of-the-art building information modeling models and processes. The works are scheduled for delivery in 2023.