Pile Driving Formula?

[SteelPE]

I have a project that requires the use of some very lightly loaded wood piles. I have done a project like this in a long time and there used to be a code reference that allowed for the calculation of the allowable pile capacity based upon a driving formula. The formula was written as follows:

R=2E/(s+c)

I went into the code and this formula is no longer listed. In place of this formula the code says that the pile capacity can be obtained by an approved driving formula. The local jurisdiction further places a FOS on this formula as 3.5. Now I am tasked with trying to figure out the original FOS of the formula (which I would like to use). Does anyone recognize this formula and what the FOS would be for the formula?

I believe the formula is called the EN formula and was developed by Wellington and was originally written as Qu=WH/(s+c). Further research suggests a FOS of 6 be applied to this formula. I guess the 2 located in the formula is throwing me for a bit of a loop.

 

[SteelPE]

I might have figured it out.....

E = W*h which is expressed in ft-lbs
s is in inches

So the 2 is coming from the unit conversion / FOS

Does this seem correct?

 

[WARose]

It does look like the old ENR formula.....which was: Pa= W*h/F(s+c).

You have just substituted "E" for W*h (ram hammer weight times the height the hammer falls).

If you will note there is an "F" in that formula.....that is your factor of safety. As you noted: they recommended a FS of 6 using it. (I think the "modified" ENR formula is much more widely used now. It also uses a FS of 6.)

I'd ask your geotech for some input as to which formula to use (and FS). If they do a lot of work in the area.....they've seen real results.

 

[Okiryu]

SteelPE, Japanese guidelines give the 2 shown in the dynamic formula for hydraulic hammers only. Appears that this is because hydraulic hammers are accelerated to 2g.

I assumed that the pile driving formulas perhaps are "normalized" to hydraulic hammers, therefore all the formulas have the 2 factor.

Then, there are "allowable" driving formulas which vary the factor "c" (from Prakash's pile foundation book: "c" is the additional penetration of the pile that would have occurred if energy losses during pile driving were zero). See attached extracts from the NAVFAC DM 7.2 manual for some allowable driving formulas.

Because these are "allowable" formulas, a FOS is included (which I assume it is built into the determination of the factor "c"). But, the general understanding is that the FOS is about 6 as you and WARose have indicated.

Anyways, I know that you already know this, but generally, these equations just serve as a guide to have an idea of the preliminary pile allowable capacities. Therefore, perhaps actual codes may be enforcing the use other methods to estimate pile capacites and that may be the reason you cold not find that equation in your current code.

 

[Okiryu]

SteelPE, just found this:

http://www.ce.udel.edu/courses/CIEG...Foundations - Part 2 (Piles-construction).pdf

Look at page 19 of the above link.

 

[BigH]

I thought that with FHWA, things have moved, if using dynamic formula, to the Gates Method. See:

http://www.dot.state.mn.us/research/TS/2014/201416.pdf

http://www.wsdot.wa.gov/research/reports/fullreports/610.1.pdf

http://www.google.com/search?q=lrfd...ng+formula&ie=utf-8&oe=utf-8&client=firefox-b

 

[Okiryu]

SteelPE, perhaps this is too late but I was trying to clean my PC during the holidays and found this old document from Wellington:

https://vulcanhammerinfo.files.wordpress.com/2017/08/wellington-formula.pdf

It just explains that based on experience the safe load is 1/6 of the ultimate load. See page 10 of the document.

I got this paper from the vulcanhammer website (

https://vulcanhammer.net/).

This website has lots of good stuff about pile driving...