piles can overcome some of the problems encountered with the flexibility
of slender H-sections. Steel tube piles can be manufactured in seamless
spirally welded, or lap-welded. There is no difference between the two
types of welding with respect to the allowable driving stresses. Tubes
are manufactured in sizes from 0,30 to 2 m outside diameter and with wall
thickness ranging from 6-12 mm for the smallest diameters, to 10-25 mm
for the largest diameters. Steel tube piles can be produced with increased
wall thickness than standard sections, when it is necessary to accommodate
high axial loads or bending moments, or in the case of corrosion. When
driving into very stiff clays, dense granular soils or rock, the pile
toe can be protected from buckling by a stiffening ring or different types
of proprietary cast-steel shoes. An internal stiffening ring should be
used where the pile is supported mainly by skin friction. In very hard
driving conditions the toe protection should consist of a thicker wall
pile section about one to one-and-a--half pile diameters in length, butt-welded
to the main pile.
are normally installed by top driving but in difficult ground conditions
they can be installed by a combination of "drill-and-drive".
can be driven either closed or open ended. Also open-ended piles tend
to plug, especially in cohesive soils or when impact hammers are used.
As hollow piles are driven into cohesive soil layers, cohesion can prevent
the soil from entering the pile base, and displacement will then occur
unless the plug of soil is removed. In granular soils, steel tube piles
can be installed more easily by vibratory hammers, which have a lower
risk of plugging, whereby the speed of installation is increased. However,
it should be assumed that in most soils even open-ended tubular piles
perform as displacement piles.
not the plug needs to be removed during driving depends on the soil type,
the pile diameter and the installation method. The tendency of plugging
is largest in long piles with small diameter, driven into cohesive soils.
Removing of the plug facilitates pile penetration but may be time-consuming
and costly. Open-ended steel tube piles have generally a lower bearing
capacity than closed-end piles.
can be reduced by jetting, where water,
air or grout is flushed to the pile base during driving, by pre-drilling
(soil loosening) or pre-coring (soil removal).
at depth may not necessarily be observed as heave at the ground surface,
but may cause significant lateral soil movements. The depth, at which
soil displacement occurs, can be difficult to predict but is usually concentrated
to cohesive soils.
piles may be driven closed-ended through cohesive soil containing cobbles
and small boulders, but heave is then more likely to occur. This pile
type performs well in resisting impact and bending loads, and large-diameter
sections can be used to carry considerable loads. This has led to their
extensive use for marine structures, where long, unsupported pile elements
are commonly used at large water depth.
piles of high tensile steel are used for marine structures (jetties and
piers), where high lateral forces from the berthing impact of ships or
wave action must be resisted. Due to their circular section, tubular piles
are less affected by waves and currents than box
piles, or H-section piles. Also, the use
of high tensile steel gives often better economy with respect to weight
of material and hence reduced shipping and handling costs. The piles can
be manufactured of material with different strength properties: the upper
part and the lower section in mild steel, and the center section in high
tensile steel. Thus the more expensive high tensile steel is used in the
highly stressed zone close to the sea bed, and facilitates welding of
bracing steelwork to the upper section.
for marine applications have usually large diameter and are therefore
often driven open-ended to resist lateral and uplift loading. However,
the base resistance of open-end piles can be low in loose to medium dense
granular soils. Excessive penetration depth can be avoided by welding
H- or T-sections to the circumference.
conditions permit, it is preferable to drive box or tube piles with a
closed end, since this permits inspection of the pile shaft after driving,
and usually gives higher pile bearing capacity. After driving, the pile
shaft is filled with concrete. This method is frequently used when corrosion
may be a problem (marine structures). Alternatively, piles may he driven
open-ended and can, if required, be cleaned over their full length and
concreted. If long piles are driven, a convenient method is to drive the
first section open-ended. The following sections can be provided with
a base plate. The upper part of the pile, which may he subject to corrosion,
remains empty and can be cast with concrete. The stresses along the pile
cross-section can be shared between the steel casing and the concrete
core, thereby increasing the capacity of the critical pile section. However,
the cross-sectional area of steel in a hollow pile is likely to be governed
by driving stresses rather than by the compressive stress from the working