Effect of coating on Steel Piles

[humanengr]

I'd like to inquire if anyone can advise on whether the external coating on steel piles would have an effect
on the skin friction and the performance of the pile.
In this case the production steel piles may be galvanized or epoxy coated. Would pile tests using uncoated
steel have a material effect on the test results?
My preference is to use test piles identical to production piles. However, this question has come up in order to try
to expedite the pile testing.

 

[humanengr]

I should have mentioned the steel piles will be installed in a soil profile of mostly stiff clay with possible
layers of sand or loose sand.
Some of the steel piles will be helical piles which are sensitive to the installation torque. It seems possible the increased friction of bare steel against the clay would have an effect on the installation torque.

 

[JAE]

A few articles on this subject:
Never Galvanize Steel Pile

Dealing with Piling Corrosion

In Ground Performance of Galvanized Steel

All of the above deal primarily with the corrosion aspect of the piling - not the skin-friction aspect.

Texas DOT recommendations for coatings:

https://ftp.dot.state.tx.us/pub/txdot-info/brg/geotechnical/steel-pilings.pdf

It seems that a big concern is that as you drive the piling, some of an applied epoxy, or other coating might come off and this creates an accelerated corrosion potential in the pile...more so than if it was uncoated.


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[SlideRuleEra]

Some of the steel piles will be helical piles...

Are the other steel piles driven, such as H-pile?

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[MotorCity]

Coated or uncoated, the test piles should be identical to the production piles, otherwise whats the point of testing? Test results will show real data of the pile performance - good or bad.

 

[humanengr]

SideRuleEra:
Other piles will be driven steel round HSS

 

[epoxybot]

Well, the surface energy of plain steel (probably over a 1000 dynes) is going to be far far higher for bare steel than the surface energy of an epoxy (45 Dynes). In water saturated ground it probably makes a big difference. Perhaps more so initially and may extend primary settlement, under certain "Driven" friction pile conditions. Geotech is not my area but I have seen companies that adfertize (Hey, I just made a new word)"Adfertize"..., I have seen companies that adfertize epoxy coatings to counteract down-drag. I can see how a lower energy surface created by the epoxy coating would reduce skin friction & aid the installation of a helical piles. Zinc is about 780 dynes.

Since the pile capacity of helical piles can be correlated to the installation torque, I think it would be essential for indicator/test piles to be the same as production piles. A lower energy surface blade should reduce drag as the blades of the helical pile shear through cohesive soil.

 

[SlideRuleEra]

humanengr - As the excellent references JAE provided indicate, coatings on driven steel pile are typically not a good idea. IMHO, hot-dip galvanizing would, more or less, survive driving and would increase skin friction because of the rougher galvanized surface.

For epoxy... abrasion during driving would probably make it ineffective as corrosion protection. Since the epoxy would likely be "gone", I suppose the affect on skin friction would be minimal. But if epoxy is no longer present, no point in using it.

With steel H-pile, one anti-corrosion step is to specify (A36) steel with increased copper content (or to just use an available higher corrosion resistant steel alloy). Extra copper helps... a little. With HSS, probably not an option for either method.

For steel piling that extend above the ground line, one technique is to dig down a short distance after driving and paint the pile with bitumastic for a couple of feet both below and above the ground line. This is the where the worst corrosion is likely. With an HSS, could not get the bitumastic to the inside surface.

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[humanengr]

The epoxy coating is Fusion Bonded Epoxy. The application process results in "chemical cross linking".
My understanding is FBE will be more resistant to removal by abrasion during driving or, in the case of helical piles, during installation.

 

[ATSE]

Getting a little off track now.
With all due respect to JAE - whose opinion should be heavily weighted - I must take exception to one of the attachments.
The first article from APE regarding HD galv on helical piles makes a few questionable claims, and should be compared with other data and technical opinions on the matter arguing to the contrary.
Otherwise, the other links are good.
Back on track now.
Pile friction has wide scatter, even when controlling for all the variables (as if that's possible with geo-structural). The persuasion to match test piles with production piles is prudent.

 

[JAE]

ATSE - no problem - just found those links quickly and pushed them on here.

I guess to some extent pile installation is monitored during the hammering and isn't the actual in-place capacity of the pile determined by blow counts, dynamic monitoring, etc.? So the effect of any coating would simply be reflected in the on-site results correct? Need some geotechnical folks to weigh in.

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[SlideRuleEra]

Fusion Bonded Epoxy is intended for driven piling. Will the inside of the HSS be coated, too? Why not call the manufacturer and ask about helical piling.

Friction driven piling "set" after driving has been completed. Typically takes overnight, or so. Load capacity is increased after "set" when compared to load capacity immediately upon completion of driving. That's why a load test (performed well after driving of the test pile and reaction piles) is sometimes used to calibrate blow count and PDA results.

To extract friction piling, Contractors can break "set" by driving the pile down a few inches before extraction. Handy for removing the reaction piles.

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[Okiryu]

Is this a countermeasure against negative friction? That's the only reason I have seen coated piles. But anyway, if you have a testing program already in place, why not test both coated and uncoated piles?

 

[dik]

FBE is good stuff... I've used it for driven as well as screw piles. The screw piles supporting 6 - 400K transformers (still no movement or settlement). I usually use HDG for a couple of feet below the soil line... great references JAE...

Dik