The 25km tunnel once complete in 2023 along with associated infrastructure will be able to capture around 39 million tonnes of sewage a year. Divided into three construction packages East, Central and West, the construction in the central region is being delivered by a joint venture of Ferrovial Agroman UK Ltd and Laing O’Rourke Construction (FLO). This contract is known as Tideway Central, with work taking place from Fulham to Blackfriars.
In line with the main Tideway Tunnel project, significant capacity expansion is being undertaken on a number of existing sewage treatment works owned by Thames Water. Located in the heart of central London, work is currently ongoing at Heathwall Pumping Station where the two FP McCann precast segmental shaft structures have been sunk on the very tight site. The smaller of the shafts at 11.4m ID is the interception shaft and will transport intercepted sewage from the pumping station to a depth 28 metres below ground. The second shaft at 54m deep, is a new Combined Sewer Overflow (CSO) and is linked to the base of the small shaft by a 2.4m ID 42 metres long culvert tunnel.
The larger shaft is 17.5m ID and was sunk using the jacked caisson method to a depth 16m followed by the underpinning method of construction to a depth of 33m and Spray Concrete Lined (SCL) to a finished level 54m BGL. The smaller shaft was constructed using the same methodology.
Coventry based micro tunnelling and auger boring specialist Active Tunnelling were awarded the £5 million shaft sinking package at Heathwall Pumping Station by FLO in 2019. Over a period of 18 months the company has had to work not only within the constraints of the close proximity to the River Thames and local residents, but also to a carefully managed delivery programme. The FP McCann shaft segments were transported on a ‘just-in-time’ basis from the Company’s Cadeby manufacturing plant in Nuneaton, Leicestershire.
When fully operational, the interception shaft will capture the raw sewage before it discharges into the Thames and transfer it via the culvert tunnel into the new CSO prior to then discharging through a 4.0m ID, 43 metres long connection tunnel that will empty directly into the main ‘super sewer’ below the River. It is anticipated that the upgrade of Heathwall Pumping Station will reduce the outfall of untreated sewage by up to 90%.
Commenting on the shaft sinking processes, Richard Wilson, Project Manager for Active Tunnelling says, “The use of such universal precast concrete segmental shafts allows for an extremely efficient and structurally sound build process enabling two options, caisson and underpinning. Construction is simple and allows for ease of ground excavation. The smaller site footprint taken compared to other shaft construction options, helps to reduce the volume of material to be removed thereby minimising the environmental impact. From the installation of the first rings, both shaft builds continued uninterrupted”.
FP McCann’s smoothbore tunnel and shaft segments are all factory fitted with EPDM gaskets. Cross segment connections are made by passing a spear bolt through a pocket in one segment and screwing it into a threaded plastic socket in the adjacent segment. Circle joint connections are made using a ‘T’ bolt passing through a hole in one segment into a ‘T’ box in the adjacent segment. Bolts are designed to fully compress the gaskets.
For sales and technical enquiries, contact
Cadeby on 01455 290780 or email firstname.lastname@example.org