The works involved the design and installation of two circular and two rectangular sheet pile cofferdams to facilitate excavation for the construction of primary and final settlement tanks, an anoxic tank and an oxibox tank.

344 GU16N and GU21N sheet piles ranging from 6-10.5m in length were used for the project, creating approximately 200 linear metres of steel piling.

THE CHALLENGE

As the project took place within a live water treatment works with various services crossing underneath the site, the steel piles needed to be installed without the disruptive vibration or impact of more traditional piling methods.

Furthermore, the soil conditions were not ideal; beneath made ground and stiff clay, there was mudstone at depth in multiple areas. The size of the site also meant that the ground varied between the different cofferdam locations, requiring a tailored strategy for each section.

THE SOLUTION

To avoid disruption to the facility, the sheet piles were installed using the WP150 Silent Piler, an innovative press-in piler which is silent and vibration free.

The use of silent piling not only allows the works to be built in a vibration sensitive area, but it also reduces the environmental impact of the works.

To overcome the adverse ground conditions, the site was pre-augered as a driving aid to ensure smooth installation of the piles by loosening the mudstone.

The project took place over the course of 7 weeks. Numerous complicated internal moves were required to manoeuvre equipment and machinery between the different cofferdam sites without disrupting or damaging any existing services.

With the steel sheet pile cofferdams installed, it’s possible to excavate within and build the new tanks, increasing the capacity of the facility and benefitting those served by the sewage treatment works in the local area.