CHANNEL ISLANDS-BASED piling contractor Amplus used a variety of piling techniques to protect and allow investigation ofmedieval remains on a development in the centre ofBristol.
The firm, working for design and build contractor Stansells, carried out a phased programme of foundation construction to allow archaeologists as much time as possible to examine the medieval settlement, while keeping as close as possible to the programme requirements ofclient Royal Sun Alliance.
After the site was cleared, Amplus installed a 45m long contiguous pile wall comprising 600mm diameter,18m long CFA piles installed using a Soilmec CM45 rig. The wall forms the permanent support for the basement of the three-storey office and retail development, initially as a propped cantilever and then propped at basement and ground-floor level in the permanent structure. The basement was excavated, allowing the archaeological dig to be carried out.
Once this was finished, the firm installed 90, 600mm diameter and 18m long CFA piles using its Casagrande 425 rig. This is the first of its kind and was specially developed by Amplus and the Italian rig manufacturer. The new rig, used for the first time on this contract, can form up to 900mm diameter CFA piles to 25m depth and can be used for a variety ofbored piling systems.
Minipiles were specified to minimise damage in areas where the medieval settlement had been examined. Amplus used its new Casagrande C8 to install 110,250mm diameter and 20m long rock socketed minipiles through fill and alluvium and into the underlying bedrock.