Super sewer: an update on Thames Tideway

Tideway, an independent licenced infrastructure provider consisting of a consortium of investors, has been making good progress with construction of London's new 25 km long 'super sewer', the £4.2 billion Thames Tideway tunnel (Stride, 2016).

Ahead of tunnelling in 2018, the main focus of work has been at the three main drive sites. These are for launching the 7.8 m diameter tunnel boring machines (TBMs) and will serve as material transport hubs and head offices for each of Tideway's three main NEC3 works contracts – west, central and east.

Drive site construction

Chambers Wharf in Bermondsey was one of the first to start, beginning with the removal of thousands of tonnes of contaminated spoil. This was the first opportunity for Tideway to use the river to transport materials, in this case from site to a location outside London for safe disposal.

At Chambers Wharf, the east team has constructed one of the largest new areas of London in over a century, with an infilled cofferdam of 744 piles creating nearly 1 ha of new foreshore. It will form the temporary construction platform for a 25 m diameter, 57 m deep launch shaft for the east TBM, which is due to start tunnelling in 2019.

At Kirtling Street near Battersea power station, Tideway's central team is building the main 33 m diameter double drive shaft, using a hydromill to create 42 shaft wall panels 86 m deep. The next task will be a new jetty to receive the two TBMs later in the year, as well as for delivery and removal of materials by river.

The third drive site is at Carnwath Road in Fulham, where the west team has undertaken significant river-wall strengthening ahead of secant wall piling to create the launch shaft. Like all Tideway's drive sites, it comprises a number of brownfield land parcel and has required significant clearance and demolition.

Drop shaft enabling works

At Blackfriars the central team has recently delivered a new £8 million river-boat pier, lift and stairs to connect river traffic and Blackfriars railway station for the first time. This has enabled removal of the existing Blackfriars pier, which in turn will allow construction of a 24 m diameter, 53 m deep drop shaft to intercept the Fleet Main combined sewer outfall (CSO) – one of 34 being picked up by the new tunnel.

At Victoria Embankment near the Houses of Parliament, the team has also moved the floating bar PS Tattershall Castle 125 m downstream to make room for a 13 m diameter shaft to intercept the Regent Street CSO.

In 2017 there will be noticeable progress on more than a dozen shaft sites across London, including delivery and assembly of TBMS at the west and central drive sites.

The project remains on schedule for completion in 2023, when it will provide a direct 7.2 m diameter link from storm tanks in Acton in the west to Beckton sewage treatment works in the east via the recently completed 6.9 km Lee tunnel.

Cutting untreated sewage flow

Together with sewage treatment works improvements, the Tideway and Lee tunnels will cut the untreated sewage which flows into the river each year from 39.5 Mt to just 2.4 Mt.

This article is based on an article published in the August 2017 issue of Civil Engineering.