Piles on Organic Silty Sand 6

[pelelo]

Engineers,

I was wondering if there would be any concern to design friction piles (steel, I beams) on Loose to very loose Organic silty sands. Organic content is around 90% and this organic is submerged. the thickness of the stratum is about 20 feet. Underneath there is a sandy layer (non organic), N values around 20 bpf.

If have never designed piles in organic materials, but not sure if there is a concern.

Please advise.

thanks.

 

[oldestguy]

Full submergence all the time seems to be helpful, but I'm not sure when it comes to acidic soil.. While double posting is frowned upon, I'd also post in the room "Corrosion engineering".

 

[SlideRuleEra]

IMHO, the piles will pass through the submerged loose organic silty sand as if it were not there, then quickly obtain bearing in the sandy layer 20' down. The only problem would be if the piles need lateral support for the 20' length that is in the submerged loose organic silty sand.

Actually driving steel piles in those conditions can be tricky. Sometimes just the dead weight of the steel pile can cause it to "sink" a considerable distance. Add the dead weight of the hammer, and "zero blows per 20 feet" is possible. Because of this, getting the pile positioned correctly horizontally can be a challenge. If practical, try to allow a "generous" horizontal tolerance on each pile location.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[HENRYZAU]

What's the pile load? If it's light there is a chance of using UC sections or tubes if corrosion is not a major concern, pH value? solfate content?

 

[MTNClimber]

Don't forget about pile downdrag. There will likely be a downdrag load on the pile from consolidation of the organics.

 

[PEinc]

....especially if there will be embankment placed above the weak organic soil layer.

http://www.PeirceEngineering.com

 

[L0k]

The pile will rely on end bearing plus the skin of non organic sandy layer, disregard the organic loose silty sand skin friction. A corrosion paint shall be applied on the steel pile section to protect corrosion at the 20 feet of organic silty sand layer.
Bored pile is not recommended unless a casing is used to protect caving in. In case using a temporary casing a top up of concrete may be required, in this case the tremie pipe should be staying in the hole to assure the intact concrete and it can be withdrawn after concrete top up.