FOUNDATION CONTRACTOR May Gurney is using an integrated foundation and retaining wall system for the top-down construction of a new basement car park for a hotel in Manchester's Chinatown.
Internal columns and some of the perimeter retaining wall piles have elements of the superstructure steelwork cast in place and positioned to very high tolerances.
Structural elements link to allow the steel framework and precast floors to be built as soon as the 6m deep basement is excavated.
The system allows the floor slabs to be built rapidly, without the need for falsework, and forms a permanent prop to the retaining walls.
Design was developed by close collaboration between May Gurney, contractor Allenbuild and consulting engineer BJB. More than 3300, 600mm diameter rotary bored piles make up the cantilever retaining walls and 100, 1050mm diameter rotary loadbearing piles are being installed for the internal columns that will support the car park superstructure at ground level.
Steel sections are installed in the open holes of the internal column piles using a specially developed guide frame, which allows accurate positioning to 25mm in plan at 6m below piling level.
One of the biggest challenges for May Gurney was dealing with significant obstructions when installing the retaining wall piles, said May Gurney northern piling manager Jim Blackwell.
The site was originally home to a bank and Victorian brick and iron foundations had to be rotary cored to 5m depth in advance of piling.
Coring was chosen over excavation to reduce disturbance of surrounding utilities and to save time and money, said Blackwell.