WATER & SEWER TUNNELS | UTILITIES
a specific Safe System of Work (SSOW) to do so. While this situation is made slightly easier by the fact that most of the butterfly valves on the network have access hatches into the tunnel on either side of them to allow the workforce entry, these are often at great depth and difficult to reach. Perhaps the biggest and most important of our
maintenance challenges relates to the Thames Water Ring Main, the 80km-long tunnel running beneath London and supplying approximately one-sixth of the capital’s daily water requirements. The Ring Main’s critical role in London’s water supply
means that nowhere is the need for careful outage management better illustrated and we work closely with Thames Water to ensure that we maximise the opportunity each time a section of the tunnel is isolated and drained. Maintenance work here relates to both the tunnels
and the 21 shafts that drop down onto the ring main, the deepest of which is more than 65m. The Ring Main has a capacity of 405 million litres
of water – the equivalent of a large reservoir – and it is important for both distribution and storage. Outage management is critical and we collaborate closely with Thames Water to optimise resource deployment while sections of the Ring Main system are isolated and drained to allow work to be carried out. The collaborative approach has yielded some
impressive results. The works between Surbiton and Merton presented a very difficult outage of the Ring Main, initially earmarked for six weeks. Through collaboration with Thames Water, the team worked to an accelerated 24/7 programme, which reduced the programme to just 10 days. This enabled the client to restore the section to service and to meet the surge in customer demand for water during a key Bank Holiday weekend. For the first time, double sections of the Ring Main are
being isolated simultaneously. In 2021, the Barrow Hill – Park Lane/Park Lane – Battersea sections were carried out as a single outage, delivering significant efficiencies. Two outages originally programmed for 10 weeks were compressed to one, delivered in eight weeks - including two weeks of significant tunnel repairs not originally programmed. This delivered a performance efficiency saving of 33% and a carbon saving of approximately 11%.
We have recently been working to replace more
than 270,00 White Caps, the push-fit caps covering the lifting eye sockets on each tunnel plate with new, screw-fit types as part of the ongoing maintenance programme. To improve future management of the Ring Main,
Barhale has embarked on a project to capture the entirety of the asset in a digital map. In terms of scale, this will be one of the largest digital tunnel mapping exercises ever undertaken. Among other factors, it will lower health and safety risks by reducing the need to negotiate the very long underground transits and confined space working. It will allow:
● Remote management, allocation of tasks, supervision, and review of work giving a real-time progress status snapshot;
● The replacement of paper-based safety and quality records;
● Digital inventory of assets and parts, simplifying future maintenance;
● Assets and equipment can be procured without multiple inspections; and,
● Reduced intervention and reduced carbon footprint.
Above:
A new gate valve is lowered into place at Barrow Hill, one of the Thames Water Ring Main shafts
Above: Thames Water Ring Main shaft model September 2024 | 23
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