Pipe Pile Design 1

[RiverBeav]

Design a structure on piles in a coastal environment subject to liquefaction and just had some basic questions on pile design in general:

1) What code governs steel pipe pile, H Pile, or concrete filled pipe pile design. Reading old threads on Eng Tips and they talk about a corrosion allowance for the wall thickness, and they mention 0.08 mm/year or something similar, as a low end. What code is that specified in? They then talk about the design life of the structure as being only 50 years . . . is there a standard of care specified for what design life would be appropriate. I presume you would simply base your design capacity on the pile shape subtracting out the thickness from corrosion based on corrosion per year

2) What goes into determining wall thickness on a pipe pile. We haven't got a full geotechnical report yet, but know the general capacity of an 18" diameter pipe pile is 245 to 280 kips. I know the basics out of the IBC: 5 to 10 feet of unbraced length is required, and that IBC has further guidelines based on the selected hammer for the pile. But a 10'-0" tall column with a 1/4" wall is easily good for 245 kips. Yet neighboring projects have 1/2" wall or are 16" driven pipes with concrete and a full rebar cage.

2) What factors determines whether you should place concrete into the pipe pile (already understand that for this pile type it would be driven closed ended and cleaned out before concrete placement). Does it just increase the load capacity of the pile. Is the design based on the composite shape or the concrete only (for instance, if you would suspect that the steel would eventually rust away)?

3) What would make you choose an H-pile over a pipe pile? Is it simply between availability, price or a local preference, or is there an engineering reason for one over the other?

3) How does liquefaction affect the unbraced length of the pile? If you have deep deposits of sand and very tall piles, treating the piles as totally unbraced columns would require very large piles just to have a kl/r less than 200.

Mostly looking for a design reference on these. I have CRSI's Drilled Piers design guide, but looking for something similar that covers steel and concrete filled pipe piles. We don't own L-pile and will have the geotechnical engineer cover that.

 

[Settingsun]

Is this a structure in the water so the piles have an exposed length, or are the piles fully buried?

1) Can't help with code specifics as I'm not American. We have a piling code that is referenced in the building code so pretty straightforward. If there's no equivalent US document, steel piles may just be governed by the steel code. You could also take guidance from the bridge code. 0.08mm/year is at the low end for the tidal/splash zone in an aggressive environment but about OK for permanently submerged if there's no accelerated corrosion, and about midrange for milder tidal/splash environments. I've seen holes in marine piles that indicate average localised corrosion of 0.3-0.5mm/year. Much less for buried piles once well underground even though the groundwater will be salty. You should document what you've allowed for.

2a) Wall thickness has many factors eg strength, robustness, durability and installation. You mentioned 1/4" being plenty but take away 4mm corrosion from your item #1 and it looks a bit skinny. If the pile can be hit by boats or floating debris, you might go thicker or fill with concrete. You also go thicker if there's going to be hard driving. Buried pile installed by vibrating or small hammers means you can go thin.

2b) Concrete fill is underwhelming with regard to strength increase compared with effort. Usually better to go with a thicker steel wall IME. The reasons for fill include getting end bearing capacity, sockets for tension capacity, making connection to the superstructure, and robustness.

3a) Pipe piles have the same strength in all directions and only corrode on one face. H-piles can be quite compact and good for hard driving.

3b) Liquefaction will usually mean the pile is unbraced over the liquefied length and impose loads on the pile. If these piles are fully buried and 18" diameter, you must have around 50' of liquefaction if you're worried about kL/r>200?

 

[1503-44]

This may help. There may be a newer version.
See Attached, or download from here,

https://vdocument.in/download/navfac-dm-72-foundation-earth-structurepdf

Others

https://db1.ientry.com/us_army_corps_coastal_engineering_manual.pdf

https://www.fema.gov/sites/default/files/2020-03/frm_p1coast.pdf

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[HTURKAK]

Dear RiverBeav ,

I will try to respond your questions based on my experience,

1- The selection of H-pile, Pipe pile or concrete filled steel pipe pile depends choice, availability of material, const. speed. I would prefer steel pipe pile and if necessary , i would increase the wall thick and dia. rather than filling with conc.

Some codes suggests corrosion rate .. For the atmospheric corrosion rate, may be taken as 0,01 mm per year in normal atmospheres and as 0,02 mm per year for marine conditions. I have copy and pasted the relevant table of Eurocode 3 Design of steel structures — Part 5: Piling

2- I will suggest the use of 0.4fy for the axial load capacity of pile +CA.

2a- The top 2-3 meters could be concrete filled . I would prefer steel pipe pile without concrete fill.

3- The pipe pile is better for corrosion resistance, stiffness in both direction and end resistance due to plug formation.

4- The layer which could liquify during a seismic event , could be assumed without lateral soil support.

I will suggest you to look a novel practice API RECOMMENDED PRACTICE 2A-WSD (Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms )

 

[RiverBeav]

Thanks for the responses! These piles would be 100% buried but are about one block from the ocean, and the soils they are going through are corrosive. Talked to the geotech yesterday, and he was going to give guidelines about the corrosion.

Note that some of the questions related to things I was seeing on other projects. On one major project that I am peripherally involved in has I think 12" pipe piles that are anywhere between 70 to 120 feet long in a river soil with high liquefaction potential. I just see the drawings and the geotech report, but never was involved in the actual design. I suspected that the geotech must have determined that only certain layers in the soil profile was liquefiable.

Thanks

 

[Settingsun]

Report back when you hear from your geotech (I'm nosy).

Here are the Australian code guidelines:

 

[1503-44]

Cathodic protection with buried anodes?

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[ATSE]

The chloride exposure should not be underestimated, nor rules of thumb applied.
Just based on field observation near the coast at many Naval military bases (I am not a corrosion specialist), even a minor amount of chloride exposure (1 mile away from the ocean) can significantly accelerate section loss.
I have had good luck with passive anodes, but not a risk-free or simple execution.
Also, here in California, Caltrans defines and approves of CISS piles - cast in steel shell - are these are somewhat common outside of the transportation industry. You can go one step more robust and use the steel shell as a driving tool and as permanent casing, and reinforce the infill concrete as if the steel section corroded to the 50-year life. This requires a bounded design (all designs should be bounded, btw), but it is not as expensive as you might think.