Coating Sheet Piling We are design 3

steelbeam · Jul 20, 2017

Coating Sheet Piling
We are designing cofferdam sheeting that will extend through a continuous layer of peat and terminate a minimum of 2 ft. in hard clay.
The sheeting is not in a body of water but will be used to construct an access road to a new sewer line through a marsh area. The geotech
recommends that the sheeting should be coated because of the organic peat. My question is what is the difficulty in getting the sheeting
coated? I don't believe sheeting manufacturers are set up to do this additional work before shipping them to the job site? I would like
to hear from anyone who has been through this.

Thanks in advance for any help or information/suggestions.

dik · Jul 20, 2017

HDG is often used for coating for sheet piling. Having peat may be somewhat acidic and may affect the longevity of HDG. You might check with a DOT group in your area and see how they address the soils.

Dik

oldestguy · Jul 20, 2017

That recommendation sounds far fetched. I'd put the geotech on the spot and ask for what installations they know of where this has been done. What PH did they measure? I've seen galvanized perforated drain pipes steel sheet metal completely gone in peat, but that was after many many years. If this is permanent and of real concern go with a heavier weight sheet pile. Cathodic protection???

DETstru · Jul 20, 2017

Whenever I've had to deal with corrosion with sheet piles I always just use a thicker sheet and consider some amount of it "sacrificial."
Though I've never done them in highly corrosive environments.

I've gotten buy-off on this method many times from AHJ's and have even had corrosion analysis done from a third party (seemed like a bunch of hand waving to me though...).

SlideRuleEra · Jul 20, 2017

Agree with oldestguy and DETstru, use thicker sheeting. This is the usual approach in the really corrosive sea water environment. Bitumastic coating can be used on both steel sheeting and H-piles. However, this type coating cannot withstand the abrasion with soil during pile driving. What is often done is to stop pile driving about 2' to 4' short of final depth. Paint this area of the piling plus another 4' or so that will be above the ground line. Then complete driving the pile. There is no point in painting any deeper, the coating will be removed by soil friction. Later, the remainder of the above ground portion of the piling is painted with the same product.

Hot dip galvanizing might survive driving well enough, but could be difficult to find a galvanizer who can dip long sheets. Also, the zinc coating may interfere with the threading of steel sheet piling interlock. For the cost of HDG, can probably buy much thicker sheets.

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