The proposed construction of a steel framed house and brick garage on piled foundations posed a challenging problem as all plant and materials had to access the site through an opening 1.8m wide by 2.6m high. This restriction limited the type of piling rig to a mini rig which could pass through a single doorway, along with a small power pack ,1.2m wide, and a small grout pump for the pile concrete.

It was proposed to use 36no 250mm diameter grouted sectional flight auger piles up to 14.5m deep. All 55tonnes of sand and cement had to be carried in bags to the batching plant which along with the mini piling rig had to access through the restricted opening. The use of augered piles was necessary due to the fragile nature of the surrounding buildings some of which had already been renovated. In order to comply with Party Wall restrictions, we carried out vibration monitoring during the installation of the piles.

Problems were encountered during the installation of the piles due to 2m of brick rubble at the surface. This was excavated and removed after several attempts were aborted trying to bore through it. Obstructions at greater depth were also encountered which were due to the suspected presence of on old retaining wall as this site bordered onto the river great Ouse. These problems were overcome by installing additional piles and derating some of the original ones to minimise any additional costs.

The ground beams and pile caps were constructed in trenches excavated through the piling mat but due to the nature of the fill it was necessary to shutter the beams to contain the concrete and prevent excessive overspill.

Holding down bolts were cast into both ground beams and pile caps ready to receive the steel frame.

Initially various alternative methods of piling were considered but bored mini piles were decided on due to the necessity for a vibration less system.