Proceeding of the 2018 DFI-EFFC International Conference on Deep Foundations and Ground Improvement, Rome, Italy, (DFI, EFFC)
The Importance of Energy Evaluation on an Individual Pile Basis
Julian P. Seidel, Technical Director
The relationship between hammer energy, pile capacity and pile movement (ECM relationship) is the common basis of all pile termination/acceptance criteria. The energy delivered to a pile has historically either been assumed to be equal to the hammer potential energy, or has been assumed to be some fraction of the potential energy to account for various and wide-ranging losses in hammer drop and transfer through the helmet/cushioning system. With the advent of Pile Driving Analyzer (PDA) testing which became common in the early 1980s, true energy delivery to the tested pile could be measured. However, regardless of whether energy losses were ignored, estimated or measured, it was and remains today effectively universal practice to assume that hammer efficiency and delivered energy does not vary. This is an assumption which is significantly incorrect and has significant consequences on achieved pile capacity. This paper shows by way of a number of longitudinal studies of PDA energy measurement through projects that delivered energy routinely and randomly varies by 35% or more. The consequence of this degree of energy variability on pile capacity is established by reference to the normalized bearing graph approach. The study concludes that effective pile driving control and pile acceptance criteria should account for energy variability on an individual pile basis.
|article #3023; publication #1040 (ROME-2018)|