Specialist Drainage Systems Helps Preserve
A Victorian Aqueduct - continued
Reinforced insitu concrete was considered during the early stages of design but it quickly became clear that the handling and installation of the formwork would have been far too complicated for installation on site explains Richard Holloway.
In the confined space of the 15 m-deep excavation, it was easier to crane in precast components and install them one at a time than to construct a complex formwork and erect reinforcement, he explains.
The bespoke precast units, weighing up to 27 tonnes each, were all manufactured at Kijlstra’s factory in Somerset, and delivered direct to site on low-loaders.
Another major advantage of using precast concrete was that the units could be manufactured to close tolerances and a high standard of quality off-site while on-site operations continued.
Actual installation of the upstream and downstream diversions took little more than a month.
All the products were bespoke, although the U-channels were cast from our flat tables with special formwork produced by our in-house carpenter.
First we cast the walls and then stood them up and cast the base in between them. These were 3.9 m high x 2.3 m long x 4.3 m wide with 400 mm thick sections. The benching blocks moulds needed to be highly elaborate to enable us to manufacture a transitional shape from square to rounded over a length of 20 m.
Then when the new Bleddfa tunnel, complete with diversions, was ready, BNM Alliance removed the downstream stop-logs, allowing water to flow in from the existing EVA.
This allowed the new tunnel to fill steadily with water and the pressure between the old conduit and the new one to equalise.
When the pressure had equalised, we lifted the upstream stop-logs and sealed off the old tunnel so that water now flowed uninterrupted through the new tunnel
First Phase Completed
Severn Trent has completed the first of three huge multi-million pound bypass tunnels being built to reinforce water supplies for Birmingham.
Severn Trent is currently working on the basis of a three-year construction and commissioning programme and hopes to have the Birmingham Resilience Project completed by the middle of 2019.
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