8.4 Prefabricated piles

8.4.1 General The specific directives given for handling, pitching and storing the piles shall be followed. Where no specific directives are given the pile elements shall be handled and stored so that they are not overstressed. Where specified, one or more piles shall be restruck after a specified period to determine the effects of time on pile bearing resistance (see subclause 7.8.1). If the driving criteria is not fulfilled on restriking, the bearing resistance of the pile shall be reassessed (see ENV 1997-1,

8.4.2 Prefabricated concrete piles The head of a prefabricated concrete pile which is being impact driven should be protected with a pile cushion to ensure that the impact stresses are reduced and spread evenly on the pile top. The specific instructions given for joining the pile elements shall be followed.

8.4.3 Steel piles The head of a top impact driven steel pile should be covered with a close fitting steel helmet to prevent damage to the pile top. The base of a bottom driven pile shall be strong enough to resist the impact forces of the hammer and to contain the force of the plug material (see Welding and cutting of steel elements The pile top shall be cut square to the pile axis before top driving. If edge preparation or cutting of the steel elements is necessary this shall be done in accordance with EN 29692. Unless otherwise specified in the design, for structural steels in accordance with ENV 1993-5 and EN 10248, joint preparation, welding processes, and the description of the welding procedure, shall be in accordance with the Table 1. For other steel grades, requirements shall be specified. When lengths of pile are to be butt-jointed on site, adequate facilities shall be provided for supporting and aligning them prior to welding. The lengths shall be secured in such a manner that eccentricity or angle between the axes of the two segments shall be in accordance with the design and the relevant standards.

Welding operations shall not be performed where affected detrimentally by vibration. The metal deposited by welding shall, as a minimum, have the mechanical characteristics equivalent to the minimum specified for the base material. Special care shall be taken in order to make sure that the stresses and distortion due to the welding are minimised. Welding shall be carried out by appropriately experienced operators. Testing and inspection of welds shall be in accordance with Table 1 unless otherwise specified.

Table 1 — Welding testing and inspection criteria for piles and pile details in structural steels
Welding Testing and inspection of welds
Type of joint Type of weld Joint preparation Type of electrode Welding process according to
EN ISO 4063
Description of welding procedure Acceptance class for defects EN 25817 Type of testing Extend of testing
butt joint / lap joint a EN 29692 EN 29692 EN 499 111
EN 288-2 D Visual 100 %
butt joint / lap joint b EN 29692 EN 29692 D Visual 100 %
a for structural welds
b for non – structural welds


8.4.4 Timber piles Before driving, precautions to prevent brooming shall be taken.

NOTE This may be done by trimming the head of the pile square to the axis and fitting it with a steel or iron ring or by an alternative method shown to be effective. When it is necessary to employ piles formed by two or more lengths the butting surfaces should be cut square to ensure contact over the whole cross sectional area of the pile. The joint should be secured by means of a proven method. See Figures A.8 and A.9 of annex A. After driving, the heads of piles should be cut off square to sound wood and treated with preservative before capping.

8.4.5 Combined piles

When driving, care should be taken not to overstress the joint between the pile elements of different materials.

EN 12699:2001 Execution of special geotechnical work – Displacement piles