v120 y

Design is unacceptable if degree of utilization is > 100%

Notes on Example 13.5

O The maximum set of 6mm per blow has been arbitrarily assumed for this example.

© The formula for energy transfer is a standard used by industry.

© This form of the Hiley formula is one of many variants that are used in the industry. It represents a simplified form of the equation with fewer constants required to specify the hammer performance than may be required for other variants.

© Correlation factors are those specified in Annex A of EN 1997-1 for between 15 and 20 piles tested.

© On the basis of the requirements of EN 1997-1 the pile tests indicate that the piles do not fully comply with DA1 but with a utilization factor of 102% are likely to be regarded as adequate. Note: traditionally a factor of safety of 2.0 is often applied to provide safe capacities from driving formulae, an equivalent global factor of safety of 2.34 is implied by the DA1 calculation.

© The same design action is calculated for DA2 as for DA1-1.

© DA2 indicates that the design is unacceptable with a utilization factor of 111%.

© The UK NA to BS EN 1997-1 provides larger correlation factors to those given in Annex A of EN 19997-1 and therefore both the characteristic and design resistances are reduced.

© The utilization factor for DA1 to the UK NA is much greater than 100% and would suggest that the piles would be unsatisfactory if the design set was 6mm per blow. This would imply that a lower set would be required giving an inferred global factor of safety much higher than 2.0. However, it could be argued that the reliability of pile driving formulae to properly predict pile performance is low and therefore the current practice by some contractors of adopting a global factor of safety of 2.0 may be too optimistic.

® By splitting the base and shaft components lower levels of utilization can be calculated but these are still higher than is acceptable. Also it is not technically possible to identify from pile driving formulae the proportion of capacity derived from the base and the shaft, thus in practice advantage cannot be taken of the reduced factors.

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