WATER & SEWER TUNNELS | UTILITIES
HOW IS THE DETERIORATION ASSESSED AND PLANS FOR ACTION DEVELOPED? Corrosion in large diameter cast iron water mains is difficult to detect but can lead to major bursts. A thorough inspection of an asset will typically require its isolation. Considerable work is currently being done to explore new technologies that will allow investigation of conditions “’n-pipe’ without any risk or supply interruption to customers. Under the Reservoirs Act 1975, all raw water tunnels
over a certain size and flow need to be inspected for structural stability at regular intervals. To make this possible, the tunnels need to be removed
from service, isolated, drained and then cleaned of all debris to expose the internal linings of the tunnel for inspection. This is always the largest and most high risk part of the work. Once cleaned and, depending on the requirements
of the inspection, the team will use a combination of survey methods including: ● Visual inspection; ● Tap survey; ● Line and level surveys; ● Laser scan 3D surveys; ● ROV surveys; and, ● Internal GPR surveys.
At this stage, the reservoir engineer will produce a report which will evaluate the risk to the network presented by the condition of the asset and make recommendations on necessary works.
MEETING THE CHALLENGES Barhale has recently been appointed to a package of schemes under Thames Water’s Raw Water Tunnel Inspection & Refurbishment Programme, which provide a good example of the sort of remediation and maintenance work necessary to keep the water flowing. Under this contract, we are inspecting 35km of raw
water tunnels across West and North London. We are removing debris, silt and invasive species. Zebra Mussels have formed substantial concentrations
across the network and it is anticipated that, in the most affected tunnels, as much as 140m3
of mussels will be
removed. Once cleared, the tunnels will be inspected and any
structural repairs will then be carried out. Although several methods are used for removing the
silts and mussels, Barhale’s preferred method is by high suction vacuum. As the waste is essentially a saturated particulate,
when moved it easily turns into an unmanageable slurry. By using high suction vacuum, the waste is removed and contained in pipework, until it reaches the surface, and deposited directly into a storage tank. When filled, it is discharged directly to a waste tanker through pipework. This method means that the waste is fully
contained from the extraction point right through to the final discharge location and so eliminates the risk of cross contamination or pollution of the local areas.
September 2024 | 21
Above left:
Manually removing Zebra Mussels
Above right: Shaft excavation, QEII Reservoir
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