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With the scheme progressing well, summer 2016 saw the completion of piling, and a move onto ground works and the preparation of foundations for bringing in large, pre-cast concrete units.

Due to numerous physical and time constraints at Woolston wastewater treatment works, the 4Delivery team challenged in situ construction practices to build the majority of the redevelopment’s large concrete tanks and structures using pre-cast concrete sections.

Off-site manufacture of those sections allows work to be undertaken in controlled settings whilst on-site preparation is underway. The units can be fabricated with openings and dimensions specific to the requirements of the structure, as can be seen in the image below.

More importantly, using pre-cast methods can improve the level of safety on site through reduced risks of working at height; reduced temporary works requirements and fewer lifting operations and plant & vehicle movements.


The first pre-cast units arrived in late summer 2016 to begin the construction of the Combined Sewer Overflow (CSO); other structures using pre-cast concrete sections include the lamella, the Activated Sludge Plant Membrane Bio Reactor (ASP MBR) tanks and the inlet works.

The sections are stitched together using reinforcement steel, formwork shutters erected and concrete placed, forming a watertight seal.

The number of units required to build these structures totals an impressive 745 units, the largest being 8.35m tall and weighing in at 22.823 tons which forms the corner of the lamella structure.

Deliveries of the pre-cast units will be ongoing until early 2017.

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