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Fig. 3:
5 m long driven ductile iron piles stored ready for
delivery
The material was industrialised in the early 50’s
and provides a simultaneous combination of
everything a driven pile system needs:
■ ductility,
■ impact strength, and
■ corrosion resistance.
Added to this, there is excellent castability.
The conical plug-in joint is the most important
means of connection and is produced, together
with the barrel of the pile pipe, in a single cast
(Fig. 2); this makes things very much easier
on site. The piles are produced in 5 m long sections
(Fig. 3), which makes for easy handling,
and can be connected directly on site without
any welding or special tools. This also allows the
piles to be varied in length.
Bored piles of diameters � 500 mm or bored
micropiles [1] of diameters � 300 mm are economically
replaced in Austria by ductile iron
piles because ductile iron gives the best possible
combination of high loads with slender design.
Its modern material even allows the driven
ductile iron pile to score points over other preformed
driven piles in many respects.
2 Advantages of preformed driven piles
In special geotechnical engineering, there have
always been two means of support, bored piles
and driven piles. The advantages of bored piles
come to the fore when high loads and high
bending moments have to be withstood, e. g. in
multi-storey buildings and bridge abutments.
The disadvantage is the heavy and expensive
equipment needed for them. Where the
use of heavy equipment is not possible, e.g. on
gap sites or where the headroom or access is
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restricted, large sets of conventionally bored
micropiles are therefore employed. However,
both systems, bored piles and bored micropiles,
have a low installation rate per day and the boring
spoil fed out has to be disposed of. Over the
past few years, dumping costs have soared. With
contaminated soils, disposing of the spoil costs
several times more than the actual foundation.
Because of this, it is more and more frequently
being asked why the soil cannot be left where
it is.
High productivity is always wanted. With bored
piles, new techniques such as the SOB pile
(augered cast-in-place pile) have been developed
for this purpose. However, this system
shows little response to the actual foundation
soil present. Variations in load-bearing capacity
due to load-bearing soil layers of varying
thickness and compactness are a problem.
Concreting below the water table, the exposure
of concrete reinforcement, constrictions of the
column of fresh concrete due to expanding soil,
these are all added difficulties which have to be
factored into the design.
Given all these difficulties, reliance in special
geotechnical engineering is placed, wherever
possible, on precast driven piles. The precast
driven pile is usually manufactured industrially,
is subject to thorough quality control and, due to
the high degree of production by machine, there
is a reduction in human error on site.
As a representative of the precast driven pile,
the driven ductile iron pile has the advantage
that, due to its good strength-to-mass ratio, high
load-bearing capacities can be obtained using
only small and light-weight equipment. The pile
heads do not have to be trimmed and integrity
tests can be dispensed with.
3 The superiority of ductile iron
The most important materials for precast driven
piles are reinforced concrete, steel, wood and
cast iron, though the wooden pile is taking very
much of a back seat nowadays firstly due to its
limited length, but above all because problems
may be caused by the only limited consistency
in quality. It is true that wood does not rust but
it is subject to uncontrollable rot due to oxygen
in areas where the water table varies. In terms
of quantity, reinforced concrete and steel are
the leaders in precast driven piles, but as the
loads rise and the driven items become larger,
the equipment which has to be used very soon
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