Pile Design and Construction Practice, Fifth edition

126 Piling equipment and methods
Air or water
Compressed
air
Discharge
pipe
Lifting ring
Spider
Riser pipe
Manifold
Air inlet holes
Spider
Jetting nozzle
Cutter head
Figure 3.39 Airlift for cleaning-out soil from steel tubular piles.
broken rock can be removed by lowering the airlift device shown in Figure 3.39 down the
tube, the soil or broken rock in the plug being loosened by dropping or rotating the riser
pipe. A reverse-circulation rig with a rotating cutter (Figure 3.34) is an efficient means of
removing soil if justified by the number and size of the piles. Crane-mounted power augers
of the type shown in Figure 3.25 can only be used for cleaning after the pile has been driven
down to its final level where there is space for the crane carrying the auger to be manoeuvred
over the pile head. The self-erecting crawler rigs are more manoeuvrable and with the
other methods described above can be used to drill below the pile toe and so ease the driving
resistance. However, drilling below the toe also reduces the shaft friction and the method
may have to be restricted to end-bearing piles. This aspect is discussed further in the section
on piling for marine structures (Section 8.3). Because of the delays involved in alternate
drilling and driving operations, it is desirable that any drilling to ease the driving resistance
should be restricted to only one operation on each pile.
Difficulties arise when it is necessary to place a plug of concrete at the toe of the cleaned-out
pile to develop high end-bearing resistance, or to transfer uplift loads from the superstructure
to the interior wall of the hollow pile through a reinforcing cage. In such cases a good bond
must be developed between the concrete filling and the interior of the steel pile. This
requires any adherent soil which remains after removing the soil plug to be cleaned off the
pile wall. A sandy soil can be effectively removed by water jetting or by airlifting, but an
adherent clay may require high-pressure water jets to remove it. A rig can be used for this
purpose that comprises a central airlift pipe and a base plate with jetting nozzles around the
periphery. The assembly can be half-rotated as necessary and wire strand ‘brushes’ can be
attached to the plate. However, the process is tediously slow since the jets tend to drill