Preparations to start London supersewer excavation 10 Aug 2017

Julie Burchell, TunnelTalk

NFM and Herrenknecht are to supply two TBMs each to the Tideway supersewer tunnel project under the River Thames in London. Following the course of the River, the TBMs will excavate the 25km long tunnel from Acton in the west to Kirtling Street in the centre and on to the Abbey Mills pumping station in the east (Fig 1).

Herrenknecht EPBM for the West contract
Herrenknecht EPBM for the West contract

Work is underway on the banks of the Thames as Tideway workers excavate a 30m diameter access shaft at Kirtling Street from which the two NFM machines for the Central contract will progress. FLO, the construction JV of Ferrovial-Laing O’Rourke, procured the two 8.84m diameter NFM EPBMs to complete the 12.7km of the Central contract excavating about 5km to the west and 7.7km to the east. NFM Technologies is currently assembling the two EPBMs in its facilities in Le Creusot, France, where they are being prepared for their factory acceptance tests.

Herrenknecht is to supply an 8m diameter EPBM to the BMB Balfour Beatty-Morgan Sindall-BAM Nuttall JV to excavate the 6,950m drive for the West Contract from Acton to Carnwath Road.

The second Herrenknecht machine is an 8.8m diameter slurry TBM for the CVB Costain-Vinci-Bachy JV for the 5,530m East Contract drive from the Chambers Wharf site to the Abbey Mills pumping station.

Fig 1.  Elevation of the gravity-fed sewer, the geological profile and boundaries of the three construction contracts
Fig 1. Elevation of the gravity-fed sewer, the geological profile and boundaries of the three construction contracts

The segments for the tunnel lining of each contract are also moving into production. Segments for the 6.5m i.d. West tunnel are being produced at the Morgan Sindall precast factory at Ridham Dock in Kent. Dramix 4D8060BG steel fibre from Bekaert Maccaferri are in the concrete mix for the fibre reinforced segmental lining.

For Tideway Central, FLO has engaged Pacadar of Madrid, Spain, to cast the 7.2m i.d. lining. The casting yard facility at Thamesport Kent on the Isle of Grain is equipped with 45 moulds supplied by cbe of France to cast the seven segments plus a key in each 350mm thick x 1.8m x 8.5m o.d. x 7.8m i.d. ring of lining.

Segments for the 7.2m i.d. lining rings for the East Contract drive are being manufactured by Tarmac and Max Bögl at a precast factory at Tallington near Stamford in Lincolnshire. Mould suppliers for the East and West tunnel contracts are yet to be confirmed.

The tunnel is scheduled to take seven years to build and will run mostly under the tidal section of the Thames. Along the route the tunnel will intercept 34 combined sewer overflows, connect existing sewer lines to the new Tideway tunel via transfer adits, and will convey all flow to the Beckton Sewage Treatment Works passing through the recently completed 6.4km long x 7m i.d. Lee Tunnel between Abbey Mills and the Beckton treatment plant (Fig 2).

30m diameter shaft to start excavation on Tideway
30m diameter shaft to start excavation on Tideway
Fig 2. Thames Tideway alignment under the river bed
Fig 2. Thames Tideway alignment under the river bed

The new supersewer infrastructure is being financed and built by Bazalgette Tunnel Limited (BTL), a consortium of investors comprising Allianz, Amber Infrastructure, Dalmore Capital and DIF, which will also maintain and operate the facility once completed. BTL started the project on 3 November 2015 and is expected to bring the facility into operation in 2023.


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