FP McCann caisson shaft segments form large stormwater tank on Southampton Housing Development

For Inland Homes PLC

10th October 2019
FP McCann’s precast caisson shaft segment rings are being used to build a 25m internal diameter underground stormwater holding tank on a new housing development at Chapel Riverside, Southampton. Once complete, Southern Water will adopt the tank which will be integral to 300m of flood protection work on-going along the River Itchin.
  • Status In Progress
  • Location Chapel Riverside, Southampton
  • Division Tunnels & Shafts
  • Main Contractor B&W Tunnelling Ltd
  • Market Sector Housing, Water

The tank is being installed as part of the third phase development of the project where brownfield regeneration specialist, Inland Homes PLC are constructing 450 new homes on a former waste reception and recycling site managed by Southampton City Council. During significant rainfall, excess water will be channelled into the tank and gradually released back into the main drainage network. Flooding will be minimised, protecting the local river environment from excess overflow.

The contract to build the stormwater tank and other associated ground engineering works have been awarded to Bridgend based specialist contractor B&W Tunnelling Ltd.

The 25m internal diameter precast concrete segmental shaft is being sunk from ground level using the caisson method of construction. Sinking is aided by 12 hydraulic jacks with FP McCann’s standard precast concrete rings forming each complete section of the shaft wall. The steel cutter choker ring was initially installed and subsequent rings are being placed on top. This allowed the shaft to sink under its own weight helped with the jacks and some partial mechanical undermining of the harder layers beneath the cutter shoe. Once the shaft build is complete, a mass concrete pour into the base will form a 3m deep plug.

The stormwater tank is made up of 15 segmental rings including the choker ring. A bespoke corbel has been designed to take a part landing slab with manhole access. On completion of the main shaft build, a smaller 6m internal diameter shaft will form the central supporting column to take precast beams that will support a 25m diameter precast concrete cover slab. All products are being supplied from FP McCann’s Cadeby precast concrete factory in Warwickshire.

Commenting on the shaft build, Tony Regola Project Manager for B&W Tunnelling says, “The precast concrete segmental shaft caisson build offers the most efficient and structurally sound solution to construct a stormwater tank of this size. This method of construction is simple and allows for ease of ground excavation. From the installation of the first ring and jacking collar to the bulk excavation and on-going caisson sinking, the shaft build has continued uninterrupted”.

FP McCann’s precast concrete shaft segments are all factory fitted with EPDM rubber gaskets which provide an immediate watertight seal upon construction. Key features and benefits of FP McCann’s front and back bolted smoothbore shafts are:

  • Smooth internal faces
  • Simple locking process
  • Speedy installation
  • Increased site productivity
  • Safe build features
  • Technical advice and support