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Author:
Lawrence Shek
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2003-04-08 |
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Dear all,
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!
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Follow-up:
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Author:
Bengt H. Fellenius
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2003-04-15 |
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If you get a transferred energy that is larger than the stated rated or potential energy from the hammer, you have an error somewhere in your system or the data. You cannot, must not, rely on any of the information or analysis based on your data until you have located that error.
It can be so simple that the information you have on the hammer is just wrong. Ram weight is off, or ram travel or height-of-fall is wrong. (I wish you had provided identifying information on the hammer with your question). Your gage calibration may be off, or the driving is bending the pile (Forces F1 and F2 are different). But then the PDA error signals should have alerted you to this.
The "testing contractor's explanation that the large ratio value is "due to additional acceleration applied to the hammer ram after rebound" is ludicrous. The hammer bounces as a response to the pile head springing back up due to reflections of the force wave in the soil, particularly from the pile toe. If so, the accelerometer at the pile head indicates a "negative" velocity and the transferred energy value starts reducing from that time on. This can sometimes cause concern for having too small values of transferred energy (when the inspector want to apply a specific value of energy ratio and fails to understand the mechanism), it can never cause the transferred energy to increase. It is so basic that the explanation from the "Testing Contractor" is an attempt to pull the wool over your eyes -- hardly professional, he knows better.
April 15, 2003, Bengt H. Fellenius
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Return
to subject 'Dynamic Pile Testing'
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Follow-ups:
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Subject:
Energy Transferred Ration greater than 100% as recorded in PDA 