FP McCann Precast Concrete Segmental Shafts Form Humus Tanks For Southern Water.
Project: Humus Settlement Tanks, Tangmere WWTW Chichester West Sussex
Client: Southern Water
Supporting Contractor: GTb
Installation Contractor: Joseph Gallagher Ltd
Installation Process: Jacked Caisson Method
FP McCann Product Supplied: 12.5.m id Back-Bolted Precast Concrete Segmental Shafts; 4000mm id Caisson Rings
FP McCann’s universal segmental shaft rings have recently been specified in the build of two 12.5m id humus tanks as part of Southern Water’s on-going capital programme of work to upgrade its network of water treatment sites. The Tangmere Wastewater Treatment works near Chichester in West Sussex has just seen the completion of £7m worth of
work including a new storm tank and the two new humus settlement tanks. The work is designed to improve water quality in the Aldingbourne Rife watercourse, a vitally important wildlife corridor.
Humus tanks are a crucial part of wastewater treatment, specifically designed to remove remaining solids from the effluent after the biological filtration stage. The settled material known as ‘sludge’ is then removed for further treatment. The two 12.5m id segmental shaft humus tanks have been installed by Joseph Gallagher Ltd on behalf of Southern Water and partnering contractor GTb who are supporting Southern Water on a number of other key water treatment projects across their operating region.
The two precast concrete segmental shafts have been sunk 8 metres deep using the jacked caisson method of construction with the individual backbolted precast concrete rings forming the shaft wall as each segmental ring was jacked down into position. The design of one of the tanks included the use of a FP McCann universal recessed choker ring. The choker incorporates recesses cast into the intrados that provide shear interaction with the concrete base to resist floatation.
Delivery of the individual segments was from FP McCann’s Cadeby precast factory near Nuneaton, Warwickshire and each of the 12.5m id rings were formed on site by the skilled Joseph Gallagher team. Included in build of the humus tanks were two small central columns consisting of 2 FP McCann 4000mm id caisson rings set on top of the reinforced tremie concrete base plugs. Sloped reinforced benching was then constructed around the caisson rings including the installation of ductile pipework for efficient water flow. A capping beam has been installed on each humus tank to provide structural support, safety and as a connection point for the bridge scraper mechanisms.
Commenting on behalf of Joseph Gallager Ltd, Site Agent Ionel Croitoriu says, “The concrete segments supplied by FP McCann were simply connected on site and each ring descended with hydraulic jacking assistance under its own weight as the ground was excavated beneath. The 12.5m id precast concrete segmental caisson shaft provided the most efficient solution to deal with the limited working space available. From a safety aspect, the universal rings which were back-bolted, meant that our operatives didn’t need to enter the shaft until the central caisson rings, concrete benching and ductile pipework were installed. From the installation of the first ring and jacking collar to the bulk excavation and caisson sinking, the shafts themselves were sunk in 10 days. The two humus settlement tanks will help to significantly improve the water quality in the local watercourse”.
FP McCann’s shaft segments are all factory fitted with EPDM rubber gaskets which provide an immediate water-tight seal upon construction. 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 gasket.
Key Features and benefits of FP McCann’s back and front bolted smoothbore shafts are:-
• Smooth internal faces
• Simple locking process
• Speedy installation
• Increased site productivity
• Safe build features
• Technical advice and support
For sales and technical enquiries, contact CADEBY 01455 290780 | sales@fpmccann.co.uk
