Pre-augering is carried out in advance of sheet pile installation to loosen the sub soils to enable piles to be driven into ground conditions that might otherwise not be suitable for a sheet pile solution or would require an uneconomically heavy pile section.
The Bauer RTG RG 16T Telescopic Leader Rigs are fitted with either the MB20 or MB50 auger motors. A nominal 400mm diameter auger is then attached to the auger drive unit, the ground is then augured usually to the full pile depth at 600mm centres located at the position of the pile clutches, as shown in the sketch below.
Typically the intention is to loosen the soil rather than create an empty bore. The auger flights are rotated into the ground in one direction and counter-rotated to remove them leaving the sheared soil in place in the ground. A small amount of spoil is created to allow for the volume of the auger flights. This spoil needs to be removed from the pile line in advance of the sheet pile installation. Depths of up to 17.0m can be achieved using the MB50 motor.