FOUNDATION CONTRACTOR Branlow has just finished upgrading the foundations of a pre-war hangar for British Aerospace.
The Warrington-based company installed groups of 250mm and 300mm diameter augered piles through 16 existing concrete bases to depths of up to 20m to cope with the anticipated extra loads caused by increased aircraft production.
British Aerospace is upgrading its Broughton factory near Chester to cope with increased demand for the European Airbus. The internal modifications for the new facility, which include additional lifting machinery, are expected to impose extra loads of up to 700kN on each concrete base.
Because foundations were installed from inside the working hangar, Branlow had to cope with restricted access, headroom and working space, as well as numerous services both above and below ground. This meant that a flexible working approach was needed, with many of the bases requiring individual solutions.
The client also imposed strict environmental restrictions, namely noise, vibration, exhaust emissions and particularly dust, which it monitored closely as work was carried out next to where Airbus wings are built.
Working for main contractor Clugston Construction, the company started piling in mid-January and finished at the end of last month.
Dynamic pile load tests carried out by Testconsult before the main works showed settlements of 1.6mm occurred at working load and 2.6mm at one- and-a-half times working load. Branlow said that recoveries of over 90% were observed, indicating that movement was predominantly due to elastic compression of the pile.
Branlow is also installing 60, 300mm diameter and 8m deep temporary piles to form a 20m long contiguous piled retaining wall for a 4m deep excavation. The piles are heavily reinforced using 219mm diameter circular hollow sections to resist bending stresses in the unrestrained, cantilevered piles which are being built using a specially modified concrete mix that ensures easy installation of the tubes. A further 20 piles are also being installed to support the pile caps for temporary columns required for major alterations to the front of the building.
Branlow said this work is enabling the main contractor to complete the excavation works faster and more economically than traditional methods such as underpinning, down to a maximum of 4m.