Insulation to Prevent Frost Heave in Pipe Rack Piles

[CANeng11]

We are having an issue with frost heave in a truck loadout piperack in Northern Alberta. The piles are steel piles that were originally driven 14ft below grade according to the drawings we have. The site has been shortening the pipe stands every spring the past few years to deal with the frost heaving and I would estimate its heaved at least a foot, probably 2.

One solution that was proposed to me was to install insulation around the piles, extending about 3 meters around the piles and at a depth of about a foot. Does anyone have any experience with this method? Or any other suggestions? We have looked at replacing the piles with screw piles, but the layout of the pipe rack makes this difficult.

 

[Canuck67]

Have you determined whether your piles are heaving due to frost heave, or frost adhesion, or combination of both?

There are several Canadian guides online that touch on the design criteria for insulated foundations. I don't have any links handy, however, I believe Dow has an online guide and also search for the original technical publication by Robinsky and Bespflug in 1973.

You will need to specify the correct type of insulation for below grade installation (S701 - Type 4 extruded polystyrene usually)

Generally I design for 1" thickness of insulation being thermally equivalent to 1ft. of frost cover. Extend insulation out far enough so that the 'path' of 'escaping heat' is at least equivalent to the frost depth.

Depending on how far north you are in Alberta, frost depth could be quite deep .... 8'++. I am guessing that frost adhesion is also likely and issue, in which case you will need to evaluate how to provide a slip surface between the native soil and surface of the pile. This could be problematic as several methods such as greasing the exterior of the pile would be difficult and would reduce the pile capacity unless it was endbearing.

Your project geotech should be able to help you out with your specific location.

 

[Bendog01]

We are currently working on a proposal in Saskatchewan. We have been instructed by the geotech to install 150mm void forms (also known as frost cushions)under all grade beams and pile caps to prevent uplifting by soil heaving.

 

[CANeng11]

So there is still an issue with frost adhesion even if you reduce the frost penetration with the insulation?

 

[Canuck67]

There still may be a problem with frost adhesion as your steel pile is going to be a massive thermal bridge past the insulation, it will be like a frozen popsicle stuck in the ground. It will be minimized, but not eliminated.