WATER & SEWER TUNNELS | UTILITIES
ELAN VALLEY AQUEDUCT
The Elan Valley Aqueduct (EVA) is a Victorian culvert which, for the past 100 years, has supplied water from mid-Wales to Birmingham. Deterioration of the original structure meant that replacement of the conduit was required in three locations – Bleddfa, Nantmel and Ffrydd Wood (Knighton). The techniques used in the original Victorian construction
of the EVA include mined tunnels, open-cut conduits and inverted syphon pipework. It is a 2.4m x 2.8m inverted U-shape, advanced primarily with timber heading and lined with concrete, filled behind permanent brick formwork. The replacements consisted of 3.05m-internal diameter segmentally lined tunnels, located adjacent to the existing aqueduct. Installed offline, each section is more than 1km in length.
Above: : The 45m x 25m secant piled pit Innovation delivered valuable savings in the shape if
rationalising the TBM launch connection structures into a single secant piled cofferdam capable of accommodating both requirements – an approach that was echoed at our recent sewer diversion work at The Greenway in Ruislip. The approach saved programme time and reduced the required working area and earthworks. A critical phase of the project was connecting the new tunnels and turning flows at the connection points. The hydraulic design required minimal frictional losses through the change in the cross section to the new circular tunnel from the rectangular aqueduct. The transition sections therefore required a gradually varying cross section from one shape to another. This was achieved through a modular precast concrete system for the base and walls. ‘Special’ sections were then lowered into the aqueduct to turn flows into the new tunnel. The channels were finished with precast concrete roof sections bolted into the top of the precast walls. A key benefit was that the civils works for the connections
Top: Elan Valley Aqueduct breakthrough Above: Elan Valley Aqueduct tunnel
As the original Victorian aqueduct was constructed from unreinforced concrete, a key success factor was eliminating the risk of structural failure. So instead of exposing and unloading the structure through excavation, the aqueduct was exposed in short hit and miss sections and encapsulated in mass concrete. The TBM launch arrangements were also designed to eliminate the risk of loading the EVA.
could be achieved within a three day outage – eliminating the possibility of a drinking water shortage in Birmingham. Clever modular construction meant the elements were manufactured off site and dropped into the channel when required during the outage. Our success at the EVA will ensure that Birmingham and the surrounding areas has a resilient water supply for years to come. It has been calculated that the UK’s active water infrastructure extends to more than 300,000 km of buried pipes, some of which date to Georgian times. As the population grows and climate change presents greater impacts, the requirements for its effective maintenance and remediation will only grow.
September 2024
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