New Steel Piles being driven in area with existing timber piles

[JenVal]

I am designing a new steel pile foundation for what is essentially a very large retaining wall in the Katrina-damaged areas around New Orleans. There is an existing timber pile foundation in the area, but it was damaged in the storm, and we aren't relying on it at all. My question it this: How close is it safe to drive a steel H-pile to a timber pile? I am reluctant to remove the timber piles, both as a matter of cost and because I fear that would greatly change the soil density in the area, reducing the effectiveness of the new piles. Thanks for the help!

 

[SlideRuleEra]

If you can expect the (abandoned) timber pile to remain in good condition for the intended lifetime of your new project, driving the steel pile withing 3 (nominal) pile diameters (or perhaps closer) of the timber piles should not be a problem.

Since I would expect the New Orleans area to have a very high water table (year-round) the timber piling (below the water table) should be, and remain is pristine condition indefinitely. If in doubt, perhaps you could sample the existing pile to verify condition.

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[BigH]

I'd be interested, from my perspective, on how the timber piling was damaged? Was it only in the upper reaches - or . . . Any thoughts?

 

[msquared48]

Don't discount the capacity of the wood pile here. They may still be able to be used if they were below the groundline and the waterline.

The reason I say this is that 28 years ago we did a foundation for a three story building just east of where the Kingdome stood in Downtown Seattle. That foundation consisted of 8" diameter steel piles in concrete pilecaps, all joined with an array of concrete grade beams.

During the construction, we ran into an old 18" diameter douglas-fir pile that had been there from the former building foundation since early 1900. As the pile was in a critical location, we had to do some adjusting, but decided to test the pile to see if we could use it. We welded up a test sleeve and proceeded to test the pile with the piledriver. It did not budge and performed better than the new steel pile. In fact, when the testing was done, the 8" pipe pile link from the pile driver head to the wood pile had folded like poured molasses - in a wavy pattern - in a classic failure pattern. It had to be cut off the pile driver head and I still have it in my office today. Works great as a waste basket.

Consequently, I have a lot of confidence in old pile in the ground that have been below the waterline continuously. Admittedly one experience does not a book make. Just don't throw out using the pile until you have tested it. It could save you some $$$.

Mike McCann
MMC Engineering

 

[BigH]

Mike - your comments are right on and that is what I was intimating by how/where were the timber piles damaged. By the way - he never indicated in the OP the type of steel pile (H-pile, open tube, closed tube) or the ground conditions. That information is crucial too.

 

[VAD]

JenVal:

Would your question be related to spacing to prevent possible heave of the wooden pile?. If so, then Slide Rule's answer of 3d would be appropriate. Would expect that the H-pile would be driven to a deeper toe elevation than the existing toe elevation of the wooden pile and if so there should be no problem if the wooden pile is not being relied on.

 

[JenVal]

First, thanks for the responses, everybody!
Second, the pile is a steel H-pile, and will be driven between 20 and 30 feet deeper than the existing wooden piles.
I have to admit that I don't know how the piles were damaged - I adopted this project late in the game, after the decision to go with steel had already been made.

 

[BigH]

At least you are using non-displacement piles . . .

 

[oldestguy]

It is common practice in my area when replacing highway bridges on piling to use what ever pile that the new investigation calls for and neglect that there are any piling still there. So far for hundreds of these no problems.