Steel Soldier Pile Corrosion Protection 1

[RVSWA]

I have a soldier pile wall with W12x40 (ASTM A992) retaining a maximum of 7 ft. Because this wall will be permanent, I have been asked to provide protection against corrosion. I have always understood that corrosion of steel embedded in soil is negligible (unless ph of soil is really low) because of the lack of oxygen. Below the excavation the piles will be encased in concrete so my point of highest stress will be protected. However, a soldier pile wall creates an interesting region above the excavation that has moist soil on one side and ample oxygen on the other. Can anyone direct me to some good literature and possibly throw out their thoughts on corrosion and possible corrosion protection in this region of my piles?

 

[dik]

Just finished a system exposed to high temperatures (used for a slag pit) and the owner has opted for 'active' cathodic protection.

Dik

 

[civilperson]

Use excess thickness of 1/8" for corrosion allowance with 20-40 year life.

 

[PEinc]

You did not describe the exposure of the soldier beams. Are the beams exposed? Is there a concrete facing attached to the front of the beams? Are there precast lagging planks or panels installed behind the front flanges?

In my experience, exposed soldier beams are usually coal tar epoxy coated or galvanized. If the beams will be covered over by the facing, the beams are sometimes left bare. Sometimes, as civilperson said, the beam thickness is increased for sacrificial thickness.

Go to FHWA's geotechnical publications web site to see available design and practice manuals for anchored retaining walls.

 

[DRC1]

As you stated, corrosion is not typically a problem. In some areas it canbe. Rail projects and coal power plants are always suspect as the coal ash degrades into an acid that can accelerate corrosion of the steel.
For more typical applications, I would suggest an HP 10x57.
It is more steel, but it will give you a little more thickness than the W 12x40 - about .05 inches, which combined with a higher section modulus, will probably allow a 1/16 to an 1/8 of corrosion or rust. Generally rusting slows after a skin is formed. The surface could be protected with a rust inhibatve paint, or for more bucks a578W weatering steel can used, although this may need to be ordered on a rolling, which requies some lead time. If you are using timber lagging, the steel will probably outlast the lagging, even with treatment.

The benefit of using the HP section is constructability. Th HP,s are heavy and can be driven with an impact or vibro. They can work through obstructions and the helments of the impacts and the jaws of the vibros are designed to fit them. Some W shapes drive well, many don't. For soldier pile walls, I always use HP sections.
One caveat, Because H-piles are square, many sections are not compact, so check to be sure the pile will work structurally for you application.

Good Luck

 

[SlideRuleEra]

An added benefit of HP sections is that both the web and flanges are essentially the same thickness. This is intentional - they were intended to withstand corrosion.

Consider the details of the proposed W12x40:
Flange Thickness: 0.515"
Web Thickness: 0.295"

Compare those numbers with HP10x57 that DRC1 suggested:
Flange Thickness = Web Thickness =0.565"

The flanges on the W12x40 will be worthless if the web is gone.

If cost is critical and a lighter member will carry the load, even the HP10x42 has superior thickness when compared to a W12x40.

You also asked about a reference for steel pile corrosion. See "NBS Monograph 58 Corrosion of Steel Pilings in Soils". You can download it from this page of my website:

http://www.slideruleera.net/Steel-Piling.html

http://www.SlideRuleEra.net

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