UTILITIES | WATER & SEWER TUNNELS
Given some of the major infrastructure projects
underway in the UK, we are regularly presented with challenges to ensure that existing assets are either able to be integrated into newer systems or protected through the construction phase. In London, at Thames Tideway Tunnel’s Blackfriars
Top: ML2 sewer reinforcing (isometric) Above: The non-structural liner to protect the ML2 sewer from HS2’s TBMs Top right: ML2 shaft constructed as a caisson using underpinning from the collar
To carry out the works, 750m of temporary
1000mm-diameter steel overland pipes was used along with a temporary pumping station monitored continuously, to over-pump the existing sewage flow with two 5.5m-high ‘Pipe Bridges’ installed over a public right of way and Anglian Water access road to minimise disruption. To prevent any interruption to customer facilities,
the over-pumping was installed and commissioned overnight during a short shutdown of the Norwich catchment and utilised a bespoke prefabricated dual manhole. To protect the workforce working downstream, three penstocks were used to control the flow out of the sewer.
26 | September 2024
Bridge Foreshore site, we were required to install a flume inside the existing Victorian Low-Level Sewer within the Thames River Wall. The pipe was made up of 41 rings of 10 individual steel segments and it carried the flow of the sewer during construction works and later allowed breakthrough to connect the sewer to the Thames Tideway Tunnel. Central London locations like this present difficulties
beyond working inside the harsh and restrictive live environment of the existing Victorian sewer. In particular, logistics can be challenging – the restrictions of tides and night time working meant that we were limited to tight three-hour working periods. By contrast, our work at the Middle Level Two (ML2)
Sewer required us to install a 75m length of non- structural liner to protect the 2m-diameter Victorian structure from construction works associated with High Speed Rail 2 (HS2). Access to install the liner was provided by two shafts
- one existing and one new. The latter was constructed at a point where the route of HS2 was in closest proximity to the sewer to optimise monitoring. The shaft was constructed as a caisson but installed using underpinning from the collar rather than by jacking so avoiding pressure on the 19th Century, brick-constructed sewer.
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