I am now making review of some PDA tests for 305x305x180kg/m grade 55 steel H-piles. The pile length is about 35m with general geology consisting of fill (8m, gravelly to sandy), alluvium (4m, sandy), grade V weathered soil (sandy)
From the PDA (PAK model) records of 5 piles, it was recorded that the transferred energy ratio (EMX/PE) are about 120% . The testing contractor claimed that such abnormal readings are "due to additional acceleration applied to the hammer ram after rebound". I would like to seek the opinions from any experienced partitioner. Thank you very much!
I have seen higher than 100% readings before, and they may be correct. Almost always the higher than 100% values come when the hydraulic hammer is operated at less than full stroke. In fact, the lower the hammer setting the more likely this will happen (and conversely, at high hammer settings it is unlikely that this should occur, if as others point out the dynamic data is of good quality). The simple explanation is that many (and perhaps even most) of the hydraulic hammer makers use proximity switches to get an average velocity over a short distance (typically 75 mm). The real velocity at the bottom of the measurement will be higher due to continued acceleration of the fall. In addition the proximity switches are usually placed some distance above the actual impact point (several reasons for this), so there is additional potential energy associated with this extra distance and again the ram continues to accelerate over this distance making the real final impact velocity higher than the "average" velocity over the proximity switch locations. Thus the real kinetic energy is higher than indicated, and since there is good transfer for steel piles the PDA dynamic test result can in fact be higher than that indicated by the hammer energy monitor. Again this is most likely at low strokes where the extra distance below the bottom sensor is a significant fraction of the total reduced stroke.
I might also add that there could be an error in the proximity switches, and of course you have to be careful of the units (if the dynamic test is in kN-m and the hammer monitor is in kip-ft, then the dynamic test to hammer energy may also exceed 100% if you just divide the numbers and do not take into account the different units!!!)