7.6.2.5 Ultimate compressive resistance by applying pile driving formulae
(1)P Pile driving formulae shall only be used if the stratification of the ground has been determined.
(2)P If pile driving formulae are used to assess the ultimate compressive resistance of individual piles in a foundation, the validity of the formulae shall have been demonstrated by previous experimental evidence of acceptable performance in static load tests on the same type of pile, of similar length and cross-section, and in similar ground conditions.
(3)P For end-bearing piles driven into non-cohesive soil, the design value of the compressive resistance, Rc;d, shall be assessed by the same procedure as in 7.6.2.4.
(4) When a pile driving formula is applied to verify the compression resistance of a pile, the pile driving test should have been carried out on at least 5 piles distributed at sufficient spacing in the piling area in order to check a suitable blow count for the final series of blows.
(5) The penetration of the pile point for the final series of blows should be recorded for each pile.
7.6.2.6 Ultimate compressive resistance from wave equation analysis
(1)P Wave equation analysis shall only be used where stratification of the ground has been determined by borings and field tests.
(2)P Where wave equation analysis is used to assess the resistance of individual compression piles, the validity of the analysis shall have been demonstrated by previous evidence of acceptable performance in static load tests on the same pile type, of similar length and cross-section, and in similar ground conditions.
(3)P The design value of the compressive resistance, Rc;d, derived from the results of wave equation analysis of a number of representative piles, shall be assessed by the same procedure as in 7.6.2.4, using ξ–values based on local experience.
NOTE Wave equation analysis is based on a mathematical model of soil, pile and driving equipment without stress wave measurements on site. The method is usually applied to study hammer performance, dynamic soil parameters and stresses in the pile during driving. It is also, on the basis of the models, possible to determine the required driving resistance (blow count) that is usually related to the expected compressive resistance of the pile.
7.6.2.7 Re-driving
(1)P In the design, the number of piles to be re-driven shall be specified. If re-driving gives lower results, these shall be used as the basis for ultimate compressive resistance assessment. If re-driving gives higher results, these may be considered.
(2) Re-driving should usually be carried out in silty soils, unless local comparable experience has shown it to be unnecessary.
NOTE Re-driving of friction piles in clayey soils normally results in reduced compressive resistance.
