7.5 Protection of piles

7.5.1 Piles shall be protected against attack by organisms, aggressive substances, corrosion and stray current where such risks exist.

The measure to be taken shall be considered and specified in the design.

7.5.2 Possible measures include:

  • the use of an adequate chemical steel composition;
  • the use of an adequate concrete or mortar composition;
  • cathodic protection;
  • organic or inorganic coatings or treatment;
  • concrete coating;
  • use extra material thickness;
  • use of permanent casings or liners.

7.5.3 Piles shall not be surface treated in such a way that the shaft resistance is reduced unless allowed or required by the design.

NOTE Negative friction can be reduced by the application of a suitable coating.

7.5.4 Timber piles for permanent structures shall only be used below the lowest anticipated ground water table or free water level during the life time of the structure unless adequate protection is provided.

7.5.5 For cast in place piles where the soil has a characteristic undrained shear strength less than 15 kPa a permanent casing or liner or other approved stabilising measures should be installed unless relevant experience has proven that it is not necessary.

7.5.6 The method of installing the liner shall be agreed.

7.6 Needs for driving assistance

7.6.1 The influence of driving assistance methods on the performance of the piles and safety of existing structures or potentially unstable slopes shall be considered in the design.

7.6.2 Any driving assistance such as predriving, preboring, water jetting, chiselling or preblasting shall be planned and be approved prior to start of work.

7.6.3 Driving aids should be carried out in such a manner that the bearing capacity of piles already in place or the safety of existing structures is not detrimentally affected.

7.7 Design for impact driving of prefabricated elements

7.7.1 General

7.7.1.1 Installation procedures, pile driving hammers, pile and hammer cushioning, pile size and length, and other factors affecting the driving stresses imparted to the pile shaft should be evaluated and taken into account when determining the driving criteria.

7.7.1.2 If there is the risk of overstressing the pile shaft a wave equation analysis should be carried out.

7.7.1.3 This analysis can be supplemented by stress wave measurements on site.

7.7.1.4 Driving stresses calculated, deduced or determined as outlined above in 7.7.1 should not exceed, at any point along the pile shaft, the values shown below in 7.7.2, 7.7. 3 and 7.7.4.

7.7.2 Prefabricated concrete piles

7.7.2.1 The transferred energy of the driving system should be chosen so that:

  • in compression:
    • the maximum calculated stress (including the prestress) during driving does not exceed 0,8 x characteristic concrete strength in compression at the time of driving;
    • in tension:
      • the calculated force should not exceed 0,9 × f × A minus prestress force, where:
      • f: the characteristic yield stress of the reinforcement;
      • A: area of the reinforcement.

7.7.2.2 Where stresses are actually monitored during impact driving, these may be 10 % higher than the values stated in 7.7.2.1.

7.7.2.3 When assessing the driving stresses, attention should be paid when driving from a hard layer into a soft layer as high tensile stresses may occur in the pile.

7.7.3 Steel piles

7.7.3.1 The transferred energy of the driving system should be chosen so that the maximum calculated stress in steel piles during driving should not exceed 0,9 x the characteristic yield strength of the steel.

7.7.3.2 Where stresses are actually monitored during impact driving, these may be 20 % higher than the values stated in 7.7.3.1.

7.7.4 Timber piles

7.7.4.1 The transferred energy of the driving system should be chosen so that the maximum compressive stress generated during driving should not exceed 0,8 times the characteristic compressive strength measured parallel to grain of the timber.

7.7.4.2 Where stresses are actually monitored during impact driving, these may be 10 % higher than the values stated in 7.7.4.1

7.7.4.3 Allowance should be made for reduction in section caused by drilling and notching details.

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