Project: Water Treatment Works at Hurleston
Customer: United Utilities
Main Contractor: Balfour Beatty
In 2003, Balfour Beatty Construction were in the process of upgrading Hurleston WTW, located just north of Nantwich off the A51, as part of a £6 million design and build contract. A major part of the contract was the construction of a new Clean Backwash/Interstage Pump/Sump Tank, alongside an existing 2-storey Control Building.
This required the installation of a temporary cofferdam, 25.2m x 14.4m x 5.0m deep. The soil profile was predominantly medium dense sand with a high water table, which, combined with the close proximity of the Control Building (1.75m from the face of the excavation) created extremely high soil pressures.
The decision was made to reduce the water table to below formation level using a well pointing system in order to alleviate some of the forces acting on the cofferdam. MGF designed a temporary cofferdam with a nominal sheet pile toe-in of 1.0m and two levels of frame.
The frames were designed to leave as much clear working space as possible, whilst also minimising deflection and movement of the supported soil to protect the integrity of the Control Building. For ease of construction, the upper frame was positioned above commencing level and the design allowed for the lower frame to be removed after the basic slab was cast, thus giving the customer a completely unobstructed working area to construct the RC Tank and Roof.
The MGF scheme enabled the customer to complete the job very quickly with the temporary works being installed in little over 2 weeks.
The vast working room provided and quality of service meant that progression with the permanent structure was unhindered.
The RC Tank and Roof slab were successfully completed for the required water test to be carried out in time for the deadline of an upcoming shutdown period.
Download the full case study PDF here: Balfour Hurleston.pdf