alternative foundations for poles
alternative foundations for poles
(OP)
Hi all,
I'm looking for alternative foundation designs for 70 ft tall poles resisting axial, lateral and moment at base. The soil is medium to dense silty sand with phi of 28 to 30 degrees. Also at one of the location of the poles, peat was found in between the sand layer; this one definitely calls for piles or driven shaft foundation.
Any suggestions are warmly appreciated in advance.
Thanks.
I'm looking for alternative foundation designs for 70 ft tall poles resisting axial, lateral and moment at base. The soil is medium to dense silty sand with phi of 28 to 30 degrees. Also at one of the location of the poles, peat was found in between the sand layer; this one definitely calls for piles or driven shaft foundation.
Any suggestions are warmly appreciated in advance.
Thanks.





RE: alternative foundations for poles
RE: alternative foundations for poles
RE: alternative foundations for poles
There are a number of good books on this subject. Google it.
RE: alternative foundations for poles
I am reading quite a few literature on bored piles and driven piles as two alternatives.
The problem with piles from my preliminary calcs was the uplift force vs the uplift resistance. From the geotech report, the uplift resistance per pile is, I think, calculated as a fraction of skin resistance and the wt. of the pile. Which gives rise to a question: "Can I also incorporate lateral soil resistance to uplift due to overturning moment for both piles and driven shafts?"
RE: alternative foundations for poles
RE: alternative foundations for poles
If the sand is truly dense, you may have difficulty getting driven piles down to the penetration required for uplift.
If you use drilled piers or ACIP piles be aware that excessive soil removal can loosen the sand and reduce the capacity of adjacent previously-installed piles or piers.
Get a geotechnical engineer to help with the analyses.
RE: alternative foundations for poles
Thanks for your response. Regarding the uplift capacity, does negative friction have any effect (positive or negative) on it? Based on the values provided from the geotech, the uplift capacity of single timber pile (FS=3) is greater than the compressive capacity (FS=2).
Thanks
RE: alternative foundations for poles
RE: alternative foundations for poles
I'm confused, though, with your uplift forces. What's causing an uplift force? Are you trying to resolve a moment using a couple? Because the approach taken in all the literature I've seen uses a couple developed horizontally, using a kind of passive pressure.
RE: alternative foundations for poles
I am currently looking at helical piers too. Lateral loads is not a concern. The only problem is the axial capacity of piers in liquefiable soil depth. I'm assuming the piers to be unbraced on the entire portion of the liquefiable soil depth. I'm trying to find the increase in capacity by adding sleeves. Do you have any suggestions?
JedClampett,
Thanks for the info. Drilled shafts was actually the first option we've looked into. With a single drilled shaft, the concept of uplift forces is not valid, I guess. I was referring to a pile group which when subjected to moment, will produce tension in one-half and compression in other half of the pile groups.
RE: alternative foundations for poles
RE: alternative foundations for poles
However, I'm not sure if there is any way we can quantify the force (due to heave and thaw) that we should design the wall for.
Anyone has any thoughts on this one?
Thank you.