Blow count criteria of steel pile.
Blow count criteria of steel pile.
(OP)
A distinct advantage of driven steel piles (open end pipe, closed end pipe, or H-piles) is the ability to readily confirm the capacity during installation.
I have a question on this. As a general guideline, is there an equation to correlate the blow count (of the final 12" penetration, for example) and the skin friction capacity for open end piles?
Thanks,
I have a question on this. As a general guideline, is there an equation to correlate the blow count (of the final 12" penetration, for example) and the skin friction capacity for open end piles?
Thanks,





RE: Blow count criteria of steel pile.
RE: Blow count criteria of steel pile.
RE: Blow count criteria of steel pile.
Qa = 105*(e*Eh)^0.5*log (250/s)/4
where e is the hammer efficiency; Eh is the driving energy in kJ, s is the set in mm/blow.
We used to use 40mm/blow as the maximum rate at capacity. This corresponds to a Qa = 91kN. (I don't know why it is independent to soil condition).
40mm/blow is about 7.6bpf. Comparing to other suggested final sets, I find this driving criteria is too loose.
RE: Blow count criteria of steel pile.
RE: Blow count criteria of steel pile.
Testing should be appropriate to the scope and risk involved in the work. Load testing, PDA monitering and restrikes may be prudent on some projects. However on many jobs in defined soil conditions with known properties, and relatively light loads, which constitute a large portion of pile work, PDA monitering, wave equation analysis or a good static analysis, are often sufficent for a successful project. Note I do not reccomend the use of dynamic formulas or driving equations for design. For more information on pile driving, go the Pile Driving Contractors Association website www.piledrivers.org
RE: Blow count criteria of steel pile.
My work is with the Ohio DOT and we use PDA testing on every structure with driven piles. We use a safety factor of 2.0 because of our extensive history with PDA testing.
RE: Blow count criteria of steel pile.
First, even though my family business put the ENR formula in its literature for many years, I'm inclined to agree with Panars that the Gates formula is more accurate. That being said, my preferred use for this or any other dynamic formula is to make an initial hammer selection to then be refined by the wave equation analysis.
Once you've done that, you should run some kind of static analysis to get an idea of the resistance of the pile. That information (taking into consideration set up, plugging and other phenomena) can then be entered into a wave equation analysis. More than the estimated static resistance of the pile should be entered to develop a "bearing graph" or range of blow counts and resistances, which becomes the "equation" you're looking for if you don't use a PDA.
The PDA, when operated and interpreted by knowledgeable personnel, is obviously the next step up, if the economics of the job call for it. For very large projects a static load and/or Statnamic test can be added.
As far as expense is concerned, if you can use the DOS wave equation program WEAP87, it and the documentation that goes with it can be found at
http:
That page also links to my collection of driven pile books for download, including the 1997 FHWA manual on the subject.
http://www.vulcanhammer.net
http://www.vulcanhammer.info