Piling Options in Permafrost

[KootK]

What are attractive/unattractive piling options in permafrost? Can screw piles be installed? Driven steel? Drilled concrete piers? CFA?

This is a total rookie question but, here we go: is the piling design method to rely on competent soil below the frost depth? Or do you actually rely on the permafrost soil itself for resistance? I suppose one has no choice but to rely on the permafrost for lateral load resistance.

Anybody know of a good article covering permafrost pilings?

If anyone wants more context, please refer to this thread: Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[fattdad]

During the early 80s I worked on the North Slope. We designed and installed pile foundations for municipal buildings, like schools, gyms, fire houses, etc. We also designed slabs on grade for the benefit of warehousing.

Here's what I have to say about buildings. . . The greatest risk is the conditioned air thawing the permafrost to depth. It may take a few decades, but beware! The use of piles allows for the first floor of the structure to be elevated and the cold winter air to keep the flux of coldness from such long-term thawing. If you don't have conditined air, then this may not be relavent.

We used pile foundations for structures. The piles were rough cut and installed in holes drilled using a highway auger. They'd often go to 15 or 20 ft and it'd be frozen for the full depth. We'd keep the cuttings from the hole, mix them with water and use the slurry for pile backfill. We'd install thermisters to the pile to look at temperature as a gauge of ice development and setup. We'd often take samples of the slurry and measure the freezing point to make sure salinity was not affecting the freezing poing.

Got to be careful about load-bearing slabs. They can be designed, but require insuation layers and gravel. (Graven is often hard to find and expensive in the permafrost.) Water tanks are very problematic as the heat sink of all that water wants to thaw the permafrost. Cryoanchors are thus needed below many ground supported structures.

I can't provide design details, as I've been out of the business for too many decades. Just sharing a bit of my former experience.

Good luck and dress warm!

f-d

ípapß gordo ainÆt no madre flaca!

 

[KootK]

Thanks fattad. So what pile type was it that you were using? This "building" will really be batteries in a shelter about the size of a shipping container. The shelters won't be conditioned but presumably, the batteries would emit heat. Would you still be concerned about permafrost melting in this scenario? Lastly, can you make a recommendation regarding the amount of air space that might be required between the structure and grade?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

Yes still be concerned about the permafrost melting, not only from the battery heat but also from the steel warming from the sun. I would intend on having the main support platform some distance off of the ground to allow the natural temp air to run clear underneath the structure.

I'm assuming by his rough cut description of the piles they were timber (as noted by someone in the other thread). I have seen steel pipe piles used in northern work however I haven't done any design myself.

 

[KootK]

Are pipe piles screw piles Jayrod? Or just driven RHS?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

Not screw, and not driven as far as I was led to believe. Basically the same installation method as has been described by others but instead of timber just RHS pipes. Drill a hole, place the pile, backfill with slurry. Doesn't give you a whole lot of faith does it?

 

[fattdad]

Helicals or driven piles don't make sense for permafrost. You have no idea how difficult it can be to just drill through some permafrost. We'd always use a highway auger to make a 18 to 24 in diameter hole. Drop in a rough-cut timber pile and backfill with slurry.

a couple of feet (maybe 3) would be sufficient for air space.

f-d

ípapß gordo ainÆt no madre flaca!

 

[CarlB]

This report has some general information on Kotzebue soils and material sources.

http://www.brooks-alaska.com/kotzebue/documents/finalFS/KotzFeasStudy_AppA_ExistingConditions.pdf

In Kotzebue city, shallow souils are primarily silt and organic silt.
Auger freeze-back pile are often used in this material. There is a concern of warming permafrost in the region; this can be mitigated with deeper piles, or if heavy loaded & critical structure, use of thermosyphons.
Driven steel piles (vibratory) have been more commonly used in permafrost area recently, dpending on soils and capacity. Pre-drilling a pilot hole is typically required.