Short Battered Piles

[spartanz2001]

Does anyone have any ideas of why battered piles should be limited to lengths of over 15 ft? I have a few theories but I was wondering if any one had solid information on this subject.

I am currently working on a bridge project where we would like to use piles at the abutments in lieu of drilled shafts but we have only 10 feet from the bottom of the footing to bedrock (excavation to bedrock is not an option due to other site constraints).

The State's Bridge Design Manual states that piles under 15 ft in length SHOULD not be battered but there is no explanation of why.

 

[Qshake]

spartanz2001,

No matter what you're state's bridge manual says, AASHTO sets a minimum steel pile length of 10'. Often, if a state agency can't get 10' naturally, they will drill out the amount(10 or more feet) with "pre-bore".

So depending on what the costs are in your area, you may wish to consider using the drilled shafts since you may have to drill the steel pile holes and seat them in with sand.

As for the greater than 15' limit, I suspect it's due to the reliable properties of the overburden at that shallow depth.

Good Luck.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[spartanz2001]

Thanks for the input Q-Shake.

I agree with your assessment of pile lengths and AASHTO Code but my question is more related to BATTERED piles. I was wondering if their ability to resist horizontal loads is compromised when their length is less than 15 ft.

As for the overburden at the site, the piles would be end bearing on rock so I wouldn't think that the overburden would be an issue.

 

[PEinc]

The overburden could be the only thing that keeps the battered piles from spreading sideways or moving apart under load. If there is insufficient overburden, there may not be sufficient lateral support for the piles, especially if there is shallow rock.

 

[Qshake]

PEinc,

Thanks for the clarification. That is exactly what I was trying to get across.

With a shallow bearing strata, and with the fact that most engineers dismiss the upper 10-15' as disturbed or potentially disturbed it reasons that engineers would discount the lateral confinement necessary to develop a reaction to the applied lateral load.



Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[spartanz2001]

I got it...that does make sense for the battered pile. I will check with our Geotech regarding the existing soils and their ability to provide confinement (borings showed good fill material).

Thanks for your help!

 

[cage]

I don't see why the lateral support requirements are any different for vertical vs battered piles. Both are subject to axial load and probably flexure.

cage

 

[BigHarvey]

If you have problems with horizontal loads and have to used drilled foundations then think about barrettes ( rectangular piles ) oriented in the right direction instead of circular piles which have the same inertia in all directions

 

[BSC111]

Why would you want to batter these shorts? Prolly can get adequate lateral capacity with plumbs with fixity at cap and pinned connection at rock.

An array of fairly heavy tipped H piles ought work ok for what is prolly a rather smallish bridge.

Short stiff tip bearing batter piles under lateral load either buckle and fail or lift the structure as they rotate about their tips. A solution that tends to look good on paper but often not that hot. If the batters are longer and less stiff they deflect and so shed some load. But still iffy.

BSC

 

[PEinc]

spartanz2001, Qshake, BSC111,

What's with the green, underlined, advertising links in your posts? Did you put them in there intentionally or do they pop up automatically when you type a certain buzz word? I think these advertisements are very annoying.

 

[PEinc]

Well, I guess I got my answer on my own! My above post just had a phrase automatically turned into an advertising link. Sorry, guys.