Civil Engineering Reference
In-Depth Information
Basic piling methods
In this chapter, the main pile types and methods of installing them are described, with
details of currently available plant, pile types and proprietary methods. However, to
meet ever stricter environmental requirements and commercial pressures, piling plant
and methods of pile installation are constantly changing so that the text should be
regarded as an overview of the equipment and techniques in use. As with many fields
of engineering, descriptions of the latest equipment and methods offered by particular
manufactures are available on appropriate web-sites and scrutiny of the relevant sites
is advised for the latest information.
The two basic methods of installing piles are well known, namely driving them into
the ground, or excavation of the ground, usually by boring, and filling the void with
concrete. Other methods have evolved to cope with certain ground or groundwater
conditions, or to be more economic over particular (usually restricted) load capacities.
Over the years, methods have also evolved to overcome the need for temporary casing
during boring. Continuous flight auger (CFA) rigs developed to achieve this are now
well established. In this process the bore is supported by the spoil around the auger
right to the base of the hole until fluid concrete is pumped down the stem of the auger
to fill the bore as the auger is withdrawn. Some methods involve a combination of
driven and bored techniques, where a casing is driven or rotated into the ground fol-
lowed by in-situ concreting. There are also hybrid types of pile which bridge the gap
between vibro-stone columns and concrete columns, a stone-cement mix being vibro-
driven into the ground. Where the ground is amenable to boring by water jetting,
grouted columns can be produced which can be considered as a form of pile. Within
each category, variations exist associated with the particular proprietary method
in use.
A major advance is the degree to which piling rigs have become instrumented.
The piling operation is now, in general, highly monitored and some operations such
as concreting even carried out automatically where highly developed CFA rigs are
employed. This level of instrumentation raises the possibility of deciding on the pile
length as it is bored, i.e., the monitoring could eventually be sufficient to deter-
mine soil profile to a point where the ultimate capacity of the pile is assessed at the
drilling stage.
In another development, rigs can be located with high precision over a pile position
using GPS methods. The positioning of a rig with a high mast in this way requires
a different approach to the guidance of other mechanical plant, as a considerable
distance separates the receiving antenna on top of the (unstable) mast from the
