Pile Design and Construction Practice, Fifth edition

36 Types of pile
Figure 2.16 Fabrication yard for steel tubular piles at Milford Haven.
silt or soft clay trapped in the interior during driving. In some circumstances the soil plug
within the pile may itself develop the required base resistance (Section 4.3.3).
The facility of extending steel piles for driving to depths greater than predicted from soil
investigation data has already been mentioned. The practice of welding-on additional
lengths of pile in the leaders of the piling frame is satisfactory for land structures where the
quality of welding may not be critical. A steel pile supported by the soil can continue to
carry high compressive loads even though the weld is partly fractured by driving stresses.
However, this practice is not desirable for marine structures where the weld joining the
extended pile may be above sea-bed level in a zone subjected to high lateral forces and
corrosive influences. Conditions are not conducive to first-class welding when the extension
pile is held in leaders or guides on a floating vessel, or on staging supported by piles swaying
under the influence of waves and currents. It is preferable to do all welding on a prepared
fabrication bed with the pile in a horizontal position where it can be rotated in a covered
welding station (Figure 2.16). The piles should be fabricated to cover the maximum
predicted length and any surplus length cut off, rather than be initially of only medium
length and then be extended. Cut-off portions of steel piles usually have some value as scrap,
or they can be used in other fabrications. However, there are many situations where in-situ
welding of extensions cannot be avoided. The use of a stable jack-up platform (Figure 3.7)
from which to install the piles is then advantageous.