Drilled Pier Frost Heave

[ChiEngr]

Hello,

I am currently designing concrete drilled piers, and per the geotech report, the recommendations incur a 1600 psf design stress for potential frost heave. The recommendations also state that placing friction reducing material can be considered as an alternate option to prevent damage resulting from adfreezing and potential for frost jacking. Does anybody have prior experience with this? My first inclination is to remove the soil around the drilled pier and replace with non-frost susceptible fill like crushed stone (say 2 ft all around), but I am not sure that this is the best solution.

 

[ANE91]

I need more detail to wrap my head around the problem, because 1600 psf is 11 psi, which is not a lot of stress for the concrete but can definitely generate a ton of upward force.

Is this a confining radial stress or an axially compressive stress or both or what? How big is the drilled shaft?

ASCE 32 says something along the lines of replacing FSS with NFSS down to the depth of frost, below the bottom of the drilled shaft. Problem solved.

Disclaimer: I don’t work in the cold north.

EDIT: 1600 psf is upward pressure acting on the face of the shaft. Liner works great, as others have noted.

 

[ChiEngr]

Diameter of the pier is 2.5 ft, depth to frost is 3.5 ft - which results in an upward load (based on circumference of the pier) of around 44 kips. I would have to go very deep in the shaft embedment below the frost depth to get an adequate uplift resistance via skin friction.

 

[canwesteng]

A liner with some material to break friction on the upper portion of the pile is what I've done in the past.

 

[ChiEngr]

A liner with some material to break friction on the upper portion of the pile is what I've done in the past.

Do you have a specific product in mind?

 

[canwesteng]

Last time it was just a sonotube with plastic wrap along the outside. 12' frost depth, piles started sat 6' below grade, so only a 6' piece of sonotube.

 

[BAretired]

Last time it was just a sonotube with plastic wrap along the outside. 12' frost depth, piles started sat 6' below grade, so only a 6' piece of sonotube.

That sounds like a good idea, and the cost should not be excessive.

In Alberta, frost depth is variable, sometimes taken to be about 4'-0" for heated to 6'-0" for unheated buildings . Typical soil is glacial clay. Grade beams are usually underlain by 4" void form, but no special precautions are typically taken to protect piles from frost jacking. I am not aware of any local cases of concrete piles frost jacking, however regions with frost susceptible soil near the surface may be exceptions.

 

[ChiEngr]

That sounds like a good idea, and the cost should not be excessive.

In Alberta, frost depth is variable, sometimes taken to be about 4'-0" for heated to 6'-0" for unheated buildings . Typical soil is glacial clay. Grade beams are usually underlain by 4" void form, but no special precautions are typically taken to protect piles from frost jacking. I am not aware of any local cases of concrete piles frost jacking, however regions with frost susceptible soil near the surface may be exceptions.

Thanks BAretired!

 

[jayrod12]

Just two provinces over from BA we routinely provide greased and poly lined sonotubes for the top 6 feet of unheated piled structures to mitigate frost heave.

Our frost depth is 6-8 feet depending on who you ask and what the situation is. We also generally don't provide many piles shorter than 20 feet unless they have nothing on them.

 

[BridgeSmith]

If you have FSS, you can't count on lateral support from the soil. If you need a 2.5' diameter shaft for the lateral load, isn't the length of the shaft going to be more than twice the frost depth anyway?