7.8 Structural design of piles
(1)P Piles shall be verified against structural failure in accordance with 126.96.36.199.
(2)P The structure of piles shall be designed to accommodate all the situations to which the piles will be subjected. These include:
- the circumstances of their use e.g. corrosion conditions;
- the circumstances of their installation e.g. adverse ground conditions such as boulders, steeply inclined bedrock surfaces;
- other factors influencing driveability, including quality of joints;
- for precast piles, the circumstances of their transportation to site and installation.
(3)P During structural design, construction tolerances as specified for the type of pile, the action components and the performance of the foundation shall be taken into account.
(4)P Slender piles passing through water or thick deposits of very weak soil shall be checked against buckling.
(5) Normally a check for buckling is not required when the piles are contained by soils with a representative, undrained shear strength, cu, that exceeds 10 kPa.
7.9 Supervision of construction
(1)P A pile installation plan shall form the basis for the piling works.
(2) The plan should give the following design information:
- the pile type;
- the location and inclination of each pile, including tolerances on position;
- pile cross-section;
- for cast-in-situ piles, data about the reinforcement;
- pile length;
- pile number;
- required pile load carrying capacity;
- pile toe level (with respect to a fixed datum within or near the site), or the required penetration resistance;
- installation sequence;
- known obstructions;
- any other constraints on piling activities.
(3)P It shall be specified that the installation of all piles is monitored and records are made as the piles are installed.
(4) The record for each pile should include aspects of construction covered in the relevant execution standards, EN 1536:1999, EN 12063:1999, EN 12699:2000, such as the following:
- pile number;
- installation equipment;
- pile cross-section and length;
- date and time of installation (including interruptions to the installation process);
- concrete mix, volume of concrete used and method of placing for cast-in-situ piles;
- weight density, pH, Marsh viscosity and fines content of bentonite slurry (when used);
- for continuous flight auger piles or other injection piles, volumes and pumping pressures of the grout or concrete, internal and external diameters, pitch of screw and penetration per revolution;
- for displacement piles, the values of driving resistance measurements such as weight and drop or power rating of hammer, blow frequency and number of blows for at least the last 0,25 m penetration;
- the power take-off of vibrators (where used);
- the torque applied to the drilling motor (where used);
- for bored piles, the strata encountered in the borings and the condition of the base if the performance of the pile toe is critical;
- obstructions encountered during piling;
- deviations of position and direction and as-built elevations.
NOTE EN 14199 on the execution of micro-piles is in preparation.
(5) Records should be kept for at least a period of five years after completion of the works. As-built records should be compiled after completion of the piling and kept with the construction documents.
(6)P If site observations or inspection of records reveal uncertainties about the quality of installed piles, investigations shall be carried out to determine their condition and if remedial measures are necessary. These investigations shall include either performing a static pile load or integrity test, installing a new pile or, in the case of a displacement pile, re-driving the pile, in combination with ground tests adjoining the suspect pile.
(7)P Tests shall be used to examine the integrity of piles for which the quality is sensitive to the installation procedures if the procedures cannot be monitored in a reliable way.
(8) Dynamic low strain integrity tests may be used for a global evaluation of piles that might have severe defects or that may have caused a serious loss of strength in the soil during construction. Defects such as insufficient quality of concrete and thickness of concrete cover, both of which can affect the long term performance of a pile, often cannot be found by dynamic tests and other tests, such as sonic tests, vibration tests or coring, may be needed in supervising the execution.