As part of a Wellington Water capital scheme to cater for growth in the city's main residential and business area, FP McCann's back-bolted caisson shaft segment rings have been used to build a 6.5m diameter deep waste water pumping station in the heart of Wellington's Central Business District (CBD).

The new sewer infrastructure project will also relieve pressure on the existing pumping stations, thereby reducing the possibility of overflow into the harbour.

The contract to build the shaft and other associated pipeline upgrade engineering works was awarded to Brian Perry Civil (PBC), part of the NZX/ASX listed Fletcher Building group.

The 6.50m internal diameter shaft was sunk from ground level using the caisson method. Sinking was partially aided by four hydraulic jacks with FP McCann’s back-bolted standard precast concrete rings forming each complete section of the shaft wall.

Commenting on the shaft build, Daniel Doyle, Project Engineer of BPC says, “The precast segmental caisson provided the most efficient solution to deal with the limited working space available and to handle the water table that sat at 4.5 metres below ground level. The much smaller footprint over other options considered, reduced the volume of material to be removed and also allowed us to retain existing street light poles and a protected tree, that otherwise would have had to be removed. From a safety aspect, workers didn’t need to enter the shaft until the base plug had been poured.”.