FP McCann Precast Concrete Segmental Shaft Forms Combined Stormwater Attenuation Tank for Yorkshire Water

Project: Combined StormWater Holding Tank – Dick Lane, Bradford, West Yorkshire

Client: Yorkshire Water

Term Contractor: Peter Duffy Ltd.

Installation Contractor: HB Tunnelling Ltd.

Installation Process: Jacked Caisson Method

Product Supplied: 20.0m id Back-Bolted Precast Concrete Segmental Shaft; 20.0m diameter Precast Concrete Cover Slab

FP McCann’s back-bolted segmental shaft rings have been used to build a 20.0m id storm overflow holding tank as part of Yorkshire Water’s project to improve the water quality in Pudsey Beck. Once complete, the works at Dick Lane Bradford are forecast to reduce storm overflow discharge by up to 65%. Yorkshire Water is making planned improvements to a number of its wastewater treatment works and overflow network to tackle the number of discharges from storm surge events across its operating region.

The 3,000m³ segmental shaft attenuation tank has been installed by HB Tunnelling Ltd on behalf of Yorkshire Water term contract partner Peter Duffy Ltd. The CSO holding tank will capture excessive volumes of stormwater and then release volumes at a system-controlled level into the nearby sewage treatment works for processing. The extra storage will slow the flow of wastewater to storm overflows, reducing the number and duration of discharges during prolonged or heavy rainfall, before returning the stored water to the sewer network for treatment.

The 20.0m id shaft has been sunk 14.0 metres deep using the jacked caisson method of construction with the individual back-bolted precast concrete rings forming the shaft wall as each was jacked down into position. The design of the structure includes the use of a universal transition recessed choker ring manufactured by FP McCann which sits on top of an FP McCann concrete cutting edge; the choker incorporating recesses cast into the intrados that provide shear interaction with the concrete base to resist floatation.

Each load of precast concrete segments was delivered on specialist vehicles on a just-in-time schedule to ensure ease of access to the tight, traffic managed site. The individual 20.0m id rings were then formed on site by the skilled HB Tunnelling team. To complete the shaft build, a central column consisting of FP McCann 3600mm diameter caisson rings has been constructed to span precast beams across the shaft onto which a 20m diameter multi-section precast concrete cover slab has been laid.

The FP McCann precast concrete cover slab has been installed in 25 individual sections spanning 8 FP McCann precast radial beams.
Both the segmental rings, beams and cover slab sections were manufactured and transported from FP McCann’s Cadeby factory near Nuneaton, Warwickshire.
Central column caisson rings were also delivered from the Company’s Cadeby factory.

Commenting on behalf of HB Tunnelling Ltd, Site Engineer Declan Conlon 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 20m id precast concrete segmental caisson shaft provided the most efficient solution to deal with the limited working space available. The much smaller footprint over other tank construction options considered, reduced the volume of material to be removed. From a safety aspect, the back-bolted rings meant that our operatives didn’t need to enter the shaft until the central column was installed and the base plug cast. From the installation of the first ring and jacking collar to the bulk excavation and caisson sinking, the shaft itself was sunk in 6 weeks. Once commissioned this 3,000m3 attenuation chamber will receive excess combined stormwater from the local drainage network and will significantly improve the water quality in Pudsey Beck by doing just that”.

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