Wood Pile Service Life

[AUCE98]

On a current industrial project, the client is wanting to reuse existing wood pile foundations for the support of a new storage silo. The piles are currently supporting a similar silo, the new one may be slightly heavier. My concern is the age of the piles and the expected service life of the new silo. The current foundations were installed in 1961, drawings indicate that they were treated, however I do not have the specifications which indicate with what or to what standard or how much. So, the piles have been in service for 52 years with no apparent signs of settlement or issue, however the anticipated service life of the new silo will be around 35 years. This would make them almost 90 years old all together. I know that if the piles are completely submerged below the watertable there is a likelihood that no biodegradation can occur, thus an unlimited service life. However, these piles are in an area where the water table may fluctuate 4-6 feet during the year. The mean water table elevation is approximately 4' below grade, right at the pile cap/pile interface. So decay can occur, just not sure how much.

My concern is that, although there has been no issue up to this point with the piles, I do not feel that I can arbitrarily assume that the capacity is the same 20 tons as indicated on the existing drawings. I am going to have the client open up a pit in a couple locations to expose the heads of the piles to look for any signs of decay and go from there.

My question is, is this a reasonable request, or should I assume that there is no issue with the piles and assume the capacity shown on the drawings?
Is there an estimate service life for treated piles?

As always thank you for your insight,

AUCE98
War Eagle...Big win last Saturday!

 

[BAretired]

I believe it would be prudent to examine the heads of two or three of the existing piles before concluding they are suitable for re-use.

BA

 

[hokie66]

Agree with BA. And congratulations on that win, improbable as it was.

 

[SlideRuleEra]

Concur with BA and hokie66, also. Treated piling from 1961 almost certainly used creosote as the preservative. The proper amount for the application you describe would have been 12 pounds per cubic foot, minimum retention. Take a look at "(Creosote) Performance: Proved By More Than 75 Years Service" on this page of my website:

http://www.slideruleera.net/TreatedWood.html

Creosote is as good as, or better than any wood preservative used today, it "just" has a number of environmental and health problems that have limited its use. I expect that your examinations will find the piling in excellent condition.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[GregLocock]

I assume there are some substantial costs involved in putting new piles in, perhaps you could specify an active measurement system for the new silo, and design it such that adding new piles if settling occurs would be easy if not cheap?

While that may be a cost effective solution I suppose it is not robust.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[AUCE98]

Thank you all for the advice. I will inspect some of the piles and go from there. As always, you all are very insightful and helpful. Thanks again and happy holidays!

 

[dik]

You may want to bore into the side and halfway through and examine the timber at the centre of the pile. Often retention is in the outer 'shell' leaving the core unprotected. Seal the hole appropriately.

Take a look at some old railway ties and see how the centre portion has rotted (albeit a far more serious exposure condition).

Another problem with trees is that they provide a protective extractive in the annual rings and above and below a site of 'injury'. This can interfere with preservative retention.

Dik

 

[racookpe1978]

Above, there was a recommendation to check midway down. Look at the top of course, the middle, but above and below the tide levels on several piles (6 to 12 ?) AND below the mud level on at least 4x to verify the old wood integrity is consistent.

The top holds the weight, but the middle holds up the top, and the bottom holds up everything else. Unseen.

 

[connect2]

Interesting thread currently doing a condition assessment of a port facility, 11,500 piles....or so, timber piles not treated installed in 1931. Can you do any load testing of the existing piles. Cut about 3' out of the pile and jack between the top of the pile and the underside of the pile cap? This is the best way if you can.

 

[SLTA]

There are testing groups that do only this, for good reason. The head of the pile may be awesome and totally rotted out 2' under. Our local SEA conference just had a talk on this. Talk to this guy: J. Darrin Holt, PhD, at FDH Engineering in Raleigh NC.

http://www.fdh-inc.com/