Site: M32, Bristol
Contractor: GRAHAM Construction
Products Supplied: Precast Concrete Weir Wall Flow Control Chambers and Cover Slabs
The £200 million North Fringe to Hengrove Metrobus scheme in Bristol is due to become operational later in 2017 and will include a new link road, bridge and junction leading onto the M32, north of the city. The new junction is for buses only and has a dedicated lane on the motorway.
GRAHAM Construction secured the bus interchange section of the project; included in the £10 million design and build package of works is a 35 metre span bridge over the M32. The 65 week contract was completed in spring this year.
The new bus-only junction on the M32 consists of the new bridge and city centre facing slip road, which have been carefully designed to minimise the impact on the adjacent Stoke Park estate and the surrounding area. Drainage for the new slip road access has been incorporated into the site plan and, working closely with the FP McCann design team in Northern Ireland, a precast concrete stormwater flow control chamber system has been adopted to manage excess surface water as part of a 330 metre off-line pipe run. Based on a sealed sump catch-pit design, six chambers have been installed approximately 50 metres apart, four DN2100’s and two DN1500 units ranging in height from 2.0 metres to 4.0 metres.
The added design feature of the chambers is that they have all been supplied with a weir wall fitted on-site into the chambers by GRAHAM Construction. Apertures for orifice plates and flow control units have been cast into the weir walls and corresponding brackets supplied. The split wall design allows for inspection at either side of the flow control device, as well as offering an additional water baffle system in the chamber.
The DN2100 chamber units have been cored to suit the DN900 and DN600 inlet and outlet pipes and the DN1500’s for DN375 pipes. FP McCann has also supplied twin access heavy duty precast concrete cover slabs to match. Integral ladders have been fitted on either side of each chamber to allow easy access to both sections.
The chamber units, weir walls and cover slabs have all been manufactured at FP McCann’s Knockloughrim precast facility in Northern Ireland.
Commenting on the installation of the flow control chambers, Conor Diamond, Site Engineer for GRAHAM Construction says, “The precast concrete flow control chambers, together with their corresponding weir wall sections, slotted together without a hitch. Each unit was simple to construct, enabling us to complete this part of the build in a speedy and efficient manner.”
FP McCann manufactures a range of split weir wall flow control chambers up to DN3000. They can be manufactured to any height requirements and pre-fitted with flow controls, penstocks, gravity pump units and orifice plates. All flow control chambers comply with BS EN 1917:2002.