Lee tunnel project – the first step toward a cleaner River Thames

Completed in 2016, the Lee tunnel is the largest-diameter and deepest tunnel ever built in London. The 6·9 km long, 7·2 m dia., 80 m deep storage tunnel for combined stormwater and sewage was also Thames Water’s largest ever infrastructure project. The tunnel has already cut combined sewage and stormwater overflows from London into the Thames by over 40%. In 2023 it will carry nearly all of the capital’s overflows when the £4·2 billion Thames Tideway tunnel connects into it. This paper describes the design and construction of the award-winning project. Innovations included steel-fibre-reinforced concrete slip-formed shaft linings, launching a tunnel-boring machine from a shaft without a back-shunt, full-round shuttered secondary tunnel linings and water-cooled pump motors.