Pile Design and Construction Practice, Fifth edition

54 Types of pile
The Fundex pile also installed by Fundex group (versions of this and the other types are
available from American Piledriving Inc in the USA) is a form of screwpile (see Section
2.3.5). A helically screwed drill point is held by a bayonet joint to the lower end of the piling
tube. The latter is then rotated by a hydraulic motor on the piling frame and at the same time
forced down by hydraulic rams. On reaching founding level, a reinforcing cage and concrete
are placed in the tube which is then withdrawn leaving the sacrificial drill point in the soil.
This limits the disturbance at the pile base. The Tubex pile also employs the screwed drill
point, but the tubes are left in place for use in very soft clays when ‘waisting’ of the shaft
must be avoided. The tube can be drilled down in short lengths, each length being welded to
the one already in place. Thus the pile is suitable for installation in conditions of low headroom,
for example, for underpinning work. This pile can also be installed with simultaneous
grout injection which leaves a skin of grout around the tube and increases bearing capacity.
The speciality of the Vibro pile (from Terracon in the Netherlands) is the method used to
compact the concrete in the shaft by alternate upward and downward blows of a hammer on
the driving tube. The upward blow of the hammer operates on links attached to lugs on top
of the tube. This raises the tube and allows concrete to flow out. On the downward blow the
concrete is compacted against the soil. The blows are made in rapid succession which keeps
the concrete ‘alive’ and prevents its jamming in the tube.
2.3.3 Shell types
Types employing a metal shell generally consist of a permanent light gauge steel tube in
diameters from 150 to 500 mm with wall thickness up to 6 mm and are internally bottom
driven by a drop hammer acting on a plug of dry concrete (care being taken not to burst the
tube). The larger diameter tubes are usually fabricated to the estimated length and handled
into a piling frame with a crane. Smaller diameter, spirally welded tube can be manually
placed on the rig leader and welded in sections to produce the required depth during
installation. On reaching the bearing layer the hammer is removed, any reinforcement
inserted, and a high slump concrete placed to produce the pile. Working loads up to 1200 kN
are possible.
In France cased piles varying in diameter from 150 to 500 mm are installed by welding a
steel plate to the base of the tubular section to project at least 40 mm beyond the outer face
of the steel. As the pile is driven down, a cement/sand mortar with a minimum cement
content of 500 kg/m 3 is injected into the annulus formed around the pile by the projecting
plate through one or more pipes having their outlet a short distance above the end plate. The
rate of injection of the mortar is adjusted by observing the flow of mortar from the annulus
at the ground surface. The working load is designed to be carried by the steel section. The
working stress permitted of 160 N/mm 2 is higher than the value normally accepted for steel
piles using EN24-1 steel, because of the protection given to the steel by the surrounding
mortar. Steel H or box sections can be given mortar protection in a similar manner.
The well-known Raymond ‘Step-Taper’ Piles which consisted of helically corrugated
light-steel shells are no longer available. The ‘TaperTube’ pile (Figure 2.28), a steel shell
similar to the Monotube but without the flutes, has been developed by DFP Foundation
Products and Underpinning & Foundation Constructors of the USA. It uses a heavier wall
thickness of 9.5 mm in 247 N/mm 2 grade hot-rolled steel to form a 12-sided polygon tapering
from 609 to 203 mm at the cast steel point over lengths of 3 to 10 m. Where tube extensions
are needed the top of the polygon can be formed into a circle for butt welding; this provides