Civil Engineering Reference
In-Depth Information
Cohesive strata
Granular strata
Setting up the rig
Screwing in the
compression
auger head
Drilling down into
the bearing layer
and introduction of
the steel cage
Fill the tube and
its upper hopper
with concrete
Unscrewing and
tube withdrawal as
the pile is filled
with concrete
Completed pile
Figure 3.6
Atlas piling system: installation process.
and granular strata to a maximum depth of 22m, providing piles ranging in diameter
from 360 to 560mm. To achieve the torque of perhaps 250 to 350 kNm required
at the auger, power requirements are relatively high. Whilst the pile is environmen-
tally friendly in that it reduces the amount of potentially contaminated spoil that
needs disposal, set against this there may be an increase in atmospheric pollution from
the more powerful plant employed compared with a traditional auger pile machine.
It has been found that when screw displacement augers are used in dense granular
deposits the rate of auger wear is high and in extreme cases this can make the pile
uneconomical.
The Omega pile introduces a variation at the concreting and auger removal stage.
After screwing the auger into the ground and displacing the soil to the full depth
of the pile, the auger is rotated in the same direction on extraction as for instal-
lation. This then leaves a straight-shafted pile of the diameter of the outer auger
diameter, but producing a small amount of spoil. Similarly, in the Fundex pile, a
flighted casing is pulled vertically out of the bore at the time of concreting, leaving
a straight shafted pile. In this pile, however, if required, the casing can be left in
place to give protection to the concrete shaft in aggressive ground conditions. In the
patented 'Screwsol' piling system by Bachy Soletanche, a fin extends from the main
hollow-stem auger to create a helically threaded pile that typically extends the central
350mm diameter shaft to 500mm diameter across the threads with minimum spoil
production.
