pole foundation on bad soils

[johndeng]

We have building signs (typical gas station signs) on bad soil. 8' top soil SPT value at 10, below that all peat and silt. I can only use concrete tube foundation (3 feet diameter) since pad footing wont work. I may use 5' deep concrete tube foundation, so I have 3 feet soil (with 1000psf capacity) below bottom. Wind load will resist by lateral soil.
Will this be ok since vertical weight is small? Or it's better to replace top 10 feet with good soil?

Thanks

 

[ishvaaag]

What to say? It is like to say I know what to do but someone or myself don't want to. Problem is only a problem if it holds (even potentially) a solution. Yours has. So do all there your best to deal with the question because nature is no respecter of just good intentions.

 

[johndeng]

ishvaaag, thanks. Looks like you dont like any of the ideas?
The only answer is to put on piles, right?