SPI Piling Ltd have installed a single circular cofferdam in an existing wastewater treatment works.

The sheet piled cofferdam has been installed to facilitate the construction of an additional wastewater treatment basin which includes above and below ground structures.

This cofferdam comprised of 52nr ‘U’ profile sheet piles at 10m long and has been designed and installed in order to facilitate the extraction of all temporary works sheet piles for future use.

The wastewater treatment works in Tarvin serves the greater Tarvin area near Chester.

The site comprises an operational wastewater treatment works, which needed to remain fully operational during the piling works. The main offices to the site are located in the southeast at the entrance, with the main wastewater treatment facilities to the north.

The sheet piles were initially installed using the ABI TM14/17 leader rig which needed to work from within the cofferdam due to restricted access. Since the cofferdam consists of just 52 piles, the leader rig was only just able to fit within the cofferdams footprint to perform this function.

Circular cofferdams can be notoriously difficult to ‘close’, however the excellent work by the operatives meant that they were able to close the cofferdam without the requirement for a special welded connection.

SPI Piling Ltd subsequently returned to site to extract the sheet piles to be reused an subsequent projects and due to the restricted access this was performed using a crane and vibratory hammer.