(Helical) Pile design in clay - drained and undrained calculation

[kiskertlugas]

Hi all.

I have a project where the helical piles shall be installed in stiff medium clay. I only have drill logs and consistency. I have to work with table correlations. GWL is very high, (at about -0.3m)

Loads:
factored DL is 100kN
factored LL is 60kN
total factored load: 160kN

In ALL guideline, helical iles are designed using undrained parameters. I don't see why the drained condition is not dealt with. 2/3 of the toal load is DL, I think drained condition shall be checked.

Can anyone name a reason why drained conditions are not checked in guidelines (for clay)?

Thanks for any comments.

 

[PEinc]

Yes. IMHO, helical anchors and piles usually have relatively low capacities compared to other types of piles and anchors. If you design using undrained properties with cohesion, you will usually calculate higher capacities. If you use drained properties without cohesion, the lower capacities may steer people away from helicals. Manuals and guidelines for helicals are usually written by companies that manufacture and/or sell helicals. It is in their best interest to show design methods that give higher capacities.

http://www.PeirceEngineering.com

 

[litayoon]

Thanks a lot for your valuable information.

.

 

[dik]

Had a project a few years back... supported a 1m thick slab and six 400,000 lb transformers on helical piles... not just for low capacities... Transformers were the size of a small house and cooling oil for each was 1-1/2 tanker cars... on a sorbweb drainage basin...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[PEinc]

How many helical piles supported the 400 kip load and concrete slab? Helical DL?

http://www.PeirceEngineering.com

 

[dik]

I don't recall now... I'll see if I can dig it up... each pile had 3 or 4 flights of augers... only error was that for simplicity, I cut the supporting tube on an angle for installation... I should have used a flat plate with a round BAR 'spike'... the bevelled tube 'wandered' when being installed; the spike would have prevented it.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik