H Pile Capacity Determined from Driving Data 5

[psnyder]

I am trying to calculate what the maximum allowable vertical load per pile is for some 10x42 H-piles that were driven 57 ft yesterday for a small rural bridge abutment. Reference is being made to the ENR equations (from Lindeburg's CERM) for a MKT model 7 double-acting air hammer. I have the specs for the hammer, but am unsure what figures to use for the driven weight vs. striking weight. There are two pile capacity equations: one for driven weight < striking weight and another for driven weight > striking weight. Driven weight = weight of hammer + pile(?), Striking weight = rated energy per blow in ft-lbs(?). Any help is appreciated. Thanks

 

[Qshake]

If a pile was driven to refusal it usually meant 2xDesign Bearing.

One way to know for sure is to test it, per the ASTM standards. They have a quick compression test and your local geotech can provide the info if not the entire procedure.

I've not known anyone to back into the value from hammer energy before. But then most everything I've done with pile has been driven to rock upwards of 120'+ below grade.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[PEinc]

psnyder did not say that the pile was driven to refusal or to rock. If it wasn't, then the ENR formula, or other formula such as Gates' formula, could be used. These formulas need at least the weight of the hammer ram and its stroke (or the hammer energy) and the weight of the pile. Knowing the pile set, you can calculate the capacity or, knowing the required capacity, you can calculate the required set or blows per inch.

Now, before anyone gets on the anti-dynamic driving formula bandwagon or soapbox, remember that these formulas have been used for about a hundred years and I haven't noticed all of the old buildings falling over. Are the formulas accurate and exact? No. Are some formulas better than others? Probably. Are there more exact ways of determining or proving the pile capacity? Yes. But these formulas have been and are commonly used, especially for small jobs nowadays.

For bridge abutment piles, the bridge owner or designer may want you to use some other method such as dynamic PDA testing, WEAP analysis, static load test, etc. Check the project specs.

Also, the ASTM D-1143 Quick Static Pile Load test has been revised recently and is not a quick as it used to be.

http://www.PeirceEngineering.com

 

[BigH]

PEinc - my thoughts match yours. When driving piles, you need a quick way at the time of driving to judge (and that is the operative word) as to whether the pile is driven "good" enough or needs to be driven further. Sites in the boonies often do not have the time or money for anything more sophisticated. I've attached some pages from a ppt I recently gave to some client's civil engineers. The stick man is mine - the other information from Tomlinson and Bowles and a WSDOT paper. (see Olson and Flaate's iconic paper on comparative results from pile load tests - ASCE GT Journal - late 60s.)

 

[PEinc]

Good stuff, BigH. Nice stick man!

http://www.PeirceEngineering.com

 

[mdhshanwil]

Very nice summary, BigH.

 

[psnyder]

Thanks to all. I ended up using the ENR formula before getting any replies. Because of the poor soils, I designed the piles based on friction capacity and the calculated theoretical capacity matched the capacity that we ended up getting in the field. We ended up getting about 115 blows/ft after driving the piles another 15 feet (which is what I designed the final depth to be based on friction capacity). I saved the attachment from BigH in my personal archives. Thanks again.

PAUL S SNYDER, P.E.

 

[vulcanhammer]

The Olson and Flaate paper can be found here:

http://www.vulcanhammer.info/drivability/Olson-Flaate.pdf

One other option is to use a wave equation analysis to "back figure" the capacity. That's fallen out of fashion with CAPWAP, but it's an option if you have the familiarity with the method to do it.

http://www.pz27.net

 

[BigH]

vulcanhammer - wasn't there a follow up paper, too? I remember plotting all this stuff - from two papers and then seeing that if one applied a specific safety factor - he failed, like 0% of the time . . . Thanks for the link - appreciate it.

 

[vulcanhammer]

I think it's one of the papers linked here:

http://www.vulcanhammer.info/drivability/tti/

I am in the process of posting a lot of "classic" material on driven piles and especially offshore technology, so check back from time to time.

http://www.pz27.net

 

[BigH]

I'd love to work with you on this - but much of mine, sadly is in storage in Toronto. Let me know if I can help. BigH