Frost box?

[mark416]

Hello All;

How would one go about protecting an underground pipe from the effects of frost if the pipe happens to be within the frost penetration zone of the soil. I have the Army TM 5-852-5 report “ARCTIC AND SUBARCTIC CONSTRUCTION: UTILITIES, Chapter 12: Thermal Considerations”, where it provides solutions with insulation. (Is this called a “frost box”?) However, is there any other technical solutions besides the TM 5-852? The client does not want to spend the money to heat or steam traces the pipes. However, would encasing the pipe in concrete be ok to prevent the pipe from freezing? How would you protect the pipes from up-heaving due to the frost?

Many thanks,
Mark.

 

[CarlB]

Whaqt is the pipe carrying?

In Anchorage, AK the frost depth is 10 feet (usually maximum penetration under pavement or other surface cleared of snow)

-waterlines are placed below 10 feet usually, though sometimes shallower and protected with some insulation scheme.

-sewer lines are provided with at least 5.5 feet of cover, rarely are there freezing problems, likely due to the relatively warm contents. When pipe has to be placed a little shallower, sheet of board insulation can be placed over pipe to help prevent freezing; when very shallow "Arctic pipe" is necessary, which is pre-insulated pipe with 2" or more annular insulation.

-Storm drains are placed at any depth (City requires 4 feet minimum cover, State does not); whether there are freeze-up problem depends on particular inlet design, air flow, timing and frequency of runoff, etc.

A "Frost box" is probably a term for a variation (enhancement) of the sheet insulation over the pipe, where vertical insulation is placed along the pipe to better protect the pipe & contain the heat.

See also thread378-217830

 

[civilperson]

Anything built without a heat source will freeze in a frozen environment. Insulation only slows the transfer of heat/cold. Your client needs to understand this. By building in the permanent region, eiher always frozen or always thawed, the effect of frost heave becomes inconsequential.

 

[oldestguy]

Here is a thought.

the depth of frost penetration depends on a lot of things. One factor is the presence of water in the soil. As that material is at 32 degrees, it gives off heat of fusion. That heat release slows down the migration of that freezing front. As an extreme of this, take the depth of frost at a lake as compared to soil on land. The higher the percent of water, slower the frost penetration.

At my woods cabin location where rock is shallow, I had the contractor backfill the water line trench with clay instead of rock. Pipe is at the usual "frost depth", but so far no problems. Clay contains lots of water usually. Not a perfect solution (see the comment below), but every little bit helps

then look at the ground surface. If you have snow cover, that helps. Long grass and leaves make quite a difference.

For your question about concrete encasement, that is a darn good heat transfer medium and very low water content. It is likely to be a poorer protection than ordinary soil.

Beware of a sheet of closed cell plastic foam right over the pipe, since cold can migrate around the ends, but making the distance to the pipe longer.