Consolidation settlement of piles/caissons

[LRJ]

I was wondering whether anyone knew of a good method to calculate the settlement of piles and/or caissons, specifically the long-term primary and secondary consolidation.

I've created something in spreadsheet format using basic consolidation theory as a start and essentially reducing the load based on the caisson friction. However, I was wondering what else was out there (besides FEA).

Thanks in advance for any help.

 

[HENRYZAU]

Deep foundations normally terminate in competent founding materials and thus primary consolidation is not applicable. However recompression is likely to be expected, and secondary compression is also expected but should be very small.

 

[LRJ]

I agree with what you say. However, do you know of a good method to perform this calculation check?

 

[ATSE]

Calculation of pile settlement is addressed by Terzaghi, Peck, Mesri text, Section 52.5.
Fellenius also has some free downloadable papers / publications that are real helpful, but not quick or easy.
The main simplification is the equivalent rigid footing for the pile group at a specific depth below the pile cap - usually 2/3 the pile length for friction piles. The it's soil mechanics (as if no piles but a recessed mat foundation).

 

[LRJ]

I'd seen that simplification, but I found it rather crude. I was looking for a simplified method which also considered the frictional component explicitly, and how this affects the settlement calculation.

 

[fattdad]

I'd think the simplified but, "Crude" approach is the industry standard; however. Confusing how to find a simpler method to what's already pretty straightforward.

f-d

ípapß gordo ainÆt no madre flaca!

 

[Okiryu]

For settlement of pile groups look at Poulos and Davis. They proposed a method which considers spacing, length vs diameter, interaction pile/soil. There are charts for this method...

 

[Okiryu]

Here is the link to download Poulos and Davis book:

http://research.engr.oregonstate.edu/usucger/PandD/PandD.htm

 

[ATSE]

The settlement from the friction component is nearly zero.

 

[fattdad]

to ATSE,

The, "Friction" of a pile transfers an increased vertical load on the adjacent and underlying soils. That transfer of stress WILL lead to some compression, consolidation, or otherwise settlement. Not sure of your comment, but it doesn't resonate with me as written.

Then again. . .

f-d

ípapß gordo ainÆt no madre flaca!

 

[ATSE]

fattdad - we don't disagree. The friction mechanism I am referring to is the interface between the pile and soil, which requires a very small displacement to engage. As the load is dumped from the pile skin to the soil, settlement will occur in the soil mass as a function of the effective stress ratios.
Going back to the original post, the question is about consolidation and piles. Consolidation is considered apart from, and not because of, the friction interface. That is, the consolidation settlement is from the soil (imaginary footing) near the bottom portion of the pile, not an interface slip.

 

[LRJ]

That's my chief gripe with a simplified 'imaginary footing' kind of method: it doesn't properly consider the frictional mechanism. Moreover, the frictional resistance will create an elevation in pore-water pressure. Over time, that PWP will dissipate, and therefore the soil adjacent to the pile wall will also consolidate, i.e. it's not just the soil beneath the pile, or along a specific portion of it, which consolidates.