February 16, 2021
PDA or High Strain Pile Load Test is a dynamic pile testing method which allows technicians to assess the capacity of several piles in a single day. Pile Driving Analyzer (PDA) systems also evaluate shaft integrity, driving stresses, and hammer energy when monitoring installation. If you plan to use your PDA to test non-driven piles make sure to read about that application as well.
The strain transducers and accelerometers installation are very crucial to obtain a good PDA result. Align transducers with their sensitive direction parallel to the long axis of the pile. Arrange strain transducers so that when averaged their measurements cancel axial bending stresses.
Installation are very crucial to obtain a good PDA result. So in order to collect data, sensors must be installed tightly using right screw and bolt must be parallel with the pile.
As different hammer weights and systems will differ an unsuitable hammer might damage or dent the pile and thus the data collected might be inaccurate.
There are free-fall and hydraulic hammers, the pile tester must ensure that the ram stroke is hard enough to optimize the load transfer to the pile. This is one of the drawbacks when conducting the PDA test.
A textured or bumpy surface will be causing the impact distribution to be unequal and the data collected might be slightly wrong.
Pile tester must ensure the contractor to clear the surface of the pile and the tip of the PDA hammer too.
Now, using free-fall hammer does not guarantee the hammer will fall at the center of the pile.
It will be worse if its small diameter pile, it might slip!
Pile tester must check the position of the hammer by measuring it before proceed for the impact. This is not a problem for a hydraulic hammer but it is for a free fall hammer, hence it is important for the tester to confirm the position before conducting the test.
This might be not important, but the pile cushion might affect the performance of the hammer,
too thick and it will not perform well. Too thin and it might cause surface damage.
Pile tester must ensure the ram stroke force is high enough to optimize the transfer load considering the pile cushion.
Repeated pile blows will cause a degradation of pile material.
The pile performance will be reduced and can affect the data collected.
Ensure all details MUST be checked before proceeding with the first blow!
Sometimes the data collected by another technician is not of sufficient quality for good interpretation.
There is no shortcut, and experience matters here! But watch out for all the other pointers here, to prevent this problem.
This underprediction and overprediction causes deviation of data that could cost time, money.
Also, it cannot become the benchmark of pile test data.
This is unavoidable, the curve deviation will happened, it is recommended to conduct a static load test as a benchmark to these PDA tests.
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