Pullout test on driven pile 1

[jonastp]

Hello,

We made an pullout test (ASTM D3689)on a driven pile with success. The criteria used for the acceptance of the pile is the elastic lengthening + 5mm. I calculated the elastic lengthening with PL/AE, but the bridge engineer says that the elastic lengthening should take into account the soil resistance!? I do not agree with that, but the piles are not accepted until we can give an answer to that, and I do not have arguments. I do not know where to begin either to calculate the ''elastic lengthening'' taking soil resistance into account....

The pile is 14'' diameter pipe pile with 0.375'' wall thickness (356mm x 9.53mm).

Anybody has input to direct me??

Thank you very much in advance.

Jonathan

p.s. You can find the test data joined (in french but it's mostly straightforward)

 

[SlideRuleEra]

Jonathan - This is a really interesting question. I have been working on it this weekend, and have a PROPOSED solution for you:
At 1000 KN, Calculated Elongation Subtracting Soil Resistance = 18.4 MM. (Compared to the measured 12.77 MM)

I've worked with your data the old way (paper / pencil, graphical approach). See the attached 4 pages (8.5 megabytes, sorry).

Page 1: The higher the load, the closer measured elongation approaches theoretical elongation (31% @ 50 KN compared to 55% @ 1000 KN). This is reasonable. Under light loading even theoretical elongation is not enough for the pile to "break free" of skin friction at any location. As load increases, elongation slowly allows more and more of the pile to break skin friction. You can make use of this trend.

Page 2: At 1000 KN, skin friction is minimal (for the test range of 0 KN to 1000 KN). Look at the last test increment (950 KN to 1000 KN). For a 50 KN increase in force the pile elongated 0.92 MM. Draw a line with that slope all the way from 0 KN to 1000 KN. That line predicts pile elongation IF soil resistance had been constant at the minimal test value observed (from 950 KN to 1000 KN).

Page 3: This graph is just a check of Page 2 to make sure that a data collection error did not invalidate the Page 2 calculation. Result was a reasonable, slightly lower calculated elongation = 17.2 MM.

Page 4: Another check, exactly the same as Page 3, but using even more data. Result, as expected, a still lower but reasonable calculated elongation = 16.4 MM.

Review the graphs, it is difficult to provide a word description. Realize these results apply only for the 0 KN to 1000 KN test range, not a general solution. This proposal makes use of available data - no doubt a more accurate solution can be obtained... but only by performing additional (expensive) tests.

Questions or Comments welcome.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[jonastp]

Thank you very much SlideRuleEra,

Your input on my problem is extremely helpful!

 

[dcarr82775]

The elastic lengthening must take into account the soil resistance. If you assume uniform resistance along the embedded length you get 100% of the load at the top of the embedded portion of the pile and 0% at the base. So taking L = L/2 accounts for the soil resistance. You then add whatever 'free' length you have above grade. It is a pretty big assumption, but you can't get much more involved than that unless you instrument the length of the pile to determine when the load is zero.

 

[L0k]

Hi Jo, you may not get the answer unless you install the strain gauges on the side of the pile to read the strain movement and the skin friction as well.
The test showed in the elastic condition, the permanent deflection is 0.66mm and it was not failure yet. The elastic deflection (PL/AE) is only valid if soil resistance is measured.
The load is P at the ground surface and it is zero at the end/tip of the pile.

 

[Panars]

It looks like you have unloading measurements, so why not use the slope of the unloading curve to determine the elastic lengthening? The movement of the top of the pile as the load is removed is only due to the elastic movement of the pile. The fact that you have significantly less than 5mm of movement after the test is complete tells me that you do have a successful test.