Piling Settlement in the news

[unclesyd]

We have in our area a new Interstate Bridge that was commissioned in December 2007 and they have close off 2 lanes of the three available lanes on one span due to a little piling settlement. The settlement is reported as 1" which is stated as no problem and should be expected. According to fishermen the gap between the bridge deck and support looks larger than one inch.
Would one expect a 1" settlement of piling in 5 months?

I drove over the bridge on Wednesday and if the surveying was being done at night we would have a Laser light show on the bay. One has to be quite suspicious as the DOT isn't always forthcoming, don't want to frighten the public.

 

[DRC1]

I would not expect 1" of settlement in 5 months. Generally pile foundations, if properly designed and installed exhibit little settlement. Where is the Bridge?

 

[unclesyd]

It's the new I-10 bridge over Escambia Bay in Pensacola Florida.

http://www.pnj.com/apps/pbcs.dll/article?AID=/20080507/NEWS01/80507019

I know if one has that kind of settlement on a land building it would alsmost be panic time. We had one large building at work where there has been a 1/16" settlement in 50 years and even that caused several discussions.

 

[MichSt]

Must be some downdrag forces on those piles. We typically see/expect very little if any settlement in pile supported foundations. Any new updates on this structure?

 

[DRC1]

Drown drag, while increasing the structural load in the pile, does not significantly induce additional settlement.

 

[MichSt]

Really?? I'm no geotech, but if the down drag force exceeds the capacity of the pile won't that induce settlement??? I mean, if you significantly increase the structural load via down drag past the pile capacity you'll have some significant settlement, whether it's deformation of the pile or settlement of the pile, right?

 

[unclesyd]

Here is all they will say about the problem but as I posted previously there is still a lot of surveying going on at times.
The FDOT has has and will use the umbrella of national security not to release information.

http://www.escambiabaybridge.com/I-10LaneClosures053008.pdf

 

[unclesyd]

It has turned out to be a little more than just a shim job as first proposed.

http://pnj.com/apps/pbcs.dll/article?AID=/20080621/NEWS01/806210321

 

[DRC1]

MichST
Sorry I lost track of this thread. Piles develop tip resitance and side friction. At some point the pile develops sufficent capacity to carry dead loads. In order to develop this capacity, the pile must move downward relative to the soil. At some point, (Refered to as the neutral axis) the pile has sufficent capacity, and the soil above this point moves downward wrt the pile. This causes down drag. As additional loads are added to the pile, more of the the pile no moves downward and the down drag is replaced by positive friction.
Another misconception is that downdrag only occurs in soft soils. Actually it occurs in all soils, and only a small amount of settlement is needed to achive full friction. Thus soils that exhibit large settlements do not impose any more downdrag than if they had only settled slightly.
The concept is based on the work of Fellenius and is detailed in the Canadian Foundation Manual.
This concept is somewhat contrary to current practices by many designers working with AASHTO.

 

[jorton]

I'm no geotech either, but I think down drag can cause significant movement. We (the company I work for, not me personally) were involved with a bridge widening job some years back. They drove new psc piles near the existing ones, pulling them down several inches in the process. The deck was stiff enough that the beams did not settle under self weight, but they would bang down against the cap every time a truck went over. It made quite an impression on my boss; he has drilled in into our heads to never repeat the mistake. Our DOT no longer lets us drive psc piles near existing ones. They use caissons (or drilled piers depending on where you're from) instead.