Continuouse Flight Auger Piled Retaining Wall

As a result of severe flooding in early August 2008 which undermined the centuries-old limestone embankment, a section of wall and footpath collapsed into the River Arra at Newcastle West, Co. Limerick.

Ground Conditions

The embankment consisted generally of sandy gravel over moderately strong limestone at approximately 4m depth below existing road level.

Piling proposal

Considering the restricted access for the piling as a result of maintaining traffic flow on the N69, the use of large rotary piling rigs to drill rock sockets was precluded. Odex piling was eliminated over concern that drilling with air may further undermine the remaining quay wall. The chosen solution was to install 450mm diameter continuous flight auger piles at 600mm centres nominally socketed into the limestone bedrock. Once all piles were sufficiently cured the piles were drilled through the centre of the piles with a 175mm DTHH forming a 2m rock socket. This method ensured that compressed air used to drill the rock socket did not permeate through the fill/existing quay wall. The 175mm diameter bore was reinforced and filled with a 40N grout. The piling was completed within the 2 week programme.