Design of Friction Piles
Design of Friction Piles
(OP)
I have a site with 20 feet of very soft silty sands with thin interbedded clay layers (N values of 2 - 4), followed by a compact becoming dense to very dense silty sand with trace gravel. This strata extends to 100 feet where we stopped drilling, assuming we would go with a friction type pile and not a standard end bearing to rock or till.
Water table is at 3 foot depth.
I have determined that the site will not support standard spread footings without undue settlement, and was going to look at the ability to use driven piles. As we normally have rock at less than 50 ft I do not have a lot of experience in designing piles based on friction and end bearing (i.e belled, or even screw type piles.)
The building is a large sports complex with a slab on grade and large spans.
My questions are this, what is procedure I should use to analyse the pile type required given my SPT information, and what are the types of piles that might be appropriate in this situation.
Thanks in advance.
Water table is at 3 foot depth.
I have determined that the site will not support standard spread footings without undue settlement, and was going to look at the ability to use driven piles. As we normally have rock at less than 50 ft I do not have a lot of experience in designing piles based on friction and end bearing (i.e belled, or even screw type piles.)
The building is a large sports complex with a slab on grade and large spans.
My questions are this, what is procedure I should use to analyse the pile type required given my SPT information, and what are the types of piles that might be appropriate in this situation.
Thanks in advance.





RE: Design of Friction Piles
RE: Design of Friction Piles
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RE: Design of Friction Piles
A common technique for a large project is to have a preliminary contract to drive a series of marked index piles (say 4 to 10) on the job site to determine pile length and driving conditions. If they will be heavily loaded, perform load test(s) on selected piles. Both the pile type (timber, concrete, steel, etc.) and the driving equipment should be as close as possible to materials and methods intended for production piles. The index piles are often extracted after the test program, but may be abondoned in place and (if successful) sometimes incorporated into the work.
www.SlideRuleEra.net
RE: Design of Friction Piles
www.SlideRuleEra.net
RE: Design of Friction Piles
But, my likely choice would be the Franki-pile (expanded base piles) as used extensively in the New Jersey area with similar sounding soils. Almost all the casinos in Atlantic city are so founded.
I humbly beg to differ with my friend SRE about the use of H-piles - viz., non-displacement piles. I have seen them driven "forever". One case in point was in Richmond BC. They never seem to "set up". A very experienced structural engineer of great repute once had them driven to over 150 ft - as they never stopped. Chellis' book (original pile bible) talks about this. In such cases, you could put flanges between the webs in order to give some "bearing".
A great book to check out would be M.J. Tomlinson's Pile Design book (Viewpoint Press). Much better than Bowles. Tomlinson was/is with Wimpey and has a wealth of practical experience.
The bottom line is that you don't have to found on rock or till to get a good pile.
RE: Design of Friction Piles
the reference material as suggested is much appreciated also.
regards.
RE: Design of Friction Piles
RE: Design of Friction Piles
http://www.fhwa.dot.gov/bridge/geosoft.htm
It's a pretty good program. However, be careful of using the option to just use the SPT blow counts if you have very fine sands or silty sands. And I think the format of the output is poor.
RE: Design of Friction Piles
RE: Design of Friction Piles
RE: Design of Friction Piles
RE: Design of Friction Piles
Please don't knock the programs - DRIVEN, for example, incorporates accepted procedures required for use on highway projects eligible for federal funds. As such, these programs may not be entirely accurate or flexible, but will get one into the ballpark of the desired answer. Naturally, engineering judgement is required, and a hand check - often made more practical by using a spreadsheet - based on elementary theory is a good idea. Also, as Panars has noted above, the output format from certain applications can leave much to be desired.
geomtl,
I am personally very reluctant to specify driven H-piles in friction applications, due to the low displacement of the cross-section. This can lead to poor fetching at the toe of the pile.
Having just (literally) returned from a short course on augered cast-in-place and drilled displacement piles, I believe that these types of piles might be very effective in these conditions.
Hope this helps,
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Design of Friction Piles
A great reference is Pile Foundation Analysis and Design by Poulos & Davis. Also the NAVFAC DM7.02 provides easy solutions.
jdonville,
It was a pleasure meeting you at the DFI conference.
RE: Design of Friction Piles
As for Poulos and Davis - I have it and it is a great book but I think that Tomlinson's would be more practical and reasonable for the question at hand. It also has better and more detailed example problems.
RE: Design of Friction Piles
We ofter have a FOS of 2 on piles and yes ther is as much judgement as anything that goes into such designs, the cheief of which is familiarity with you area;s geology and past work.
There is still alot to be learned and I agree with Big H the computer solutions despite how admirable are only good to give comparisons, the true understanding of what to do depends on firts can I get my pile to a certain depth, this should be one's first attempt at understanding pile driving and the strata that one is working with.
I have to go - beer time
Regards
RE: Design of Friction Piles
Likewise.
Jeff
Jeffrey T. Donville, PE
TTL Associates, Inc.
www.ttlassoc.com
RE: Design of Friction Piles
http://www.vulcanhammer.net/download/
This site also has a calculator for pile capacity, but it's restricted to academic use (uses the Dennis and Olson Method.)
RE: Design of Friction Piles
I'm learning alot!
Another excellent reference:
PileBuck www.pilebuck.com/books
Very good text with examples.
Cheers