Principles of Ground Thawing

The Soil
Soil particles do not freeze, it is the moisture around the particles that freezes. Think about a bucket of pea gravel. If it is dry, it can be at –40°F and it is still as easy to move the stones around as if it were +70°F. Now fill the bucket with water to the top of the gravel and let it freeze. Now the whole thing is as hard as a rock! When we are thawing ground, we are thawing the water around the soil particles.

It takes a lot of energy to change snow or ice to liquid water.
If there is any snow or ice on the thaw site, remove it mechanically. It is far more efficient than trying to melt it with the heater. Save all of the energy for thawing the ground, not melting surface ice and snow.

Frozen ground is a great barrier for water flow.
Complete the Thaw. If you do not let the ground thaw all of the way down, the water that has melted will have no where to go, so it will stay on the surface. Once the frost has been fully removed, the water will drain back down to the water table, and the site will not be as muddy.

Heat Transfer

Water in its liquid form is a great conductor of heat. It is much better than air.
Think about the air in a warm oven. You can put your hands in a warm oven to get out a plate of food, even if the oven is at 200°F. If you put your hands in water that is at 200°F even for a couple of seconds you will scald yourself. The heater uses this 2 ways, first to transfer heat from heater to the ground, and then to transfer heat from the surface to the lower levels of ground.

Heat does not necessarily rise, it moves from warm things to cold things.
Sit on a steel bench in your underwear in winter and you will never forget this fact! The steel is cold, you are warm, the heat goes from you to the bench, even though the bench is below you. Hot air rises because it is lighter than cold air, and this is why some people think heat always rises.

It takes a lot of heat energy to change water from liquid to vapor.
If this water vapor escapes, it takes all of that heat with it. Rather than let it vent, convert the vapor into water so that it can go back down into the ground and continue the thawing process. When ground thawing, ALWAYS use a vapor barrier. Don’t let anyone tell you that because the insulating blankets have poly covering that they are good enough. They probably are not. Few things will slow a thaw more than if water vapor is venting. Another nice benefit is if you put the vapor barrier down before the hoses, it will keep the hoses much cleaner when the thaw is complete.

Thaw Plan

Remove all the surface ice and snow from the site.
Determine the depth of the frost.

Place a polyethylene vapor barrier over the frozen ground. Failure to do so will dramatically lengthen the time required to complete the thaw.
Place hoses on the area to be heated.
Spacing of the hoses is determined by the frost depth. Generally, use all of the hose on the reel, even if it is not needed. This will speed the thaw. Preheat heater to 180°F.

Place insulation blankets over the hoses.
Blankets should be poly clad. The more blankets the better, but they should provide an R factor of R15. If it is above 25 F and there is less than 2 feet of frost R10 is recommended.
Start the thaw. Do not stop until all of the frost is removed or the water will not be able to drain down to the water table.

HOSE LAYOUT

Hose Spacing
24" apart
16" apart
14" apart

Frost Depth
1' - 3'
4'
5'+

With this configuration and ideal soil conditions you can expect a thaw of 1' per day for the first 3' and 1/2' per day to 6'. Some overriding factors which slow the rate of thaw are:

1) Soil compaction - If the area to be thawed is compacted the rate of thaw may slow to 1/2' per day or less.
2) Soil moisture - If the moisture content in the soil is low as in the case of dry clay the rate of that will slow to 1/2' per day. The same is true for soil where the moisture content is very high. As in the case of saturated silt, the rate of thaw may slow to 1/2' per day or less.
3) Outdoor Temperature - The outdoor temperature can also effect the rate of thaw. If there are high winds and the temperature is at or below -30 F add hay bales on top of the blankets for further insulation.

These are general guidelines to follow for optimum performance under typical operating conditions. Extreme soil or weather conditions may call for different configurations. Always have your structural or civil engineer approve your plan.

Have questions? Call 888-612-HEAT(4328) or email us anytime.