Deep Ground Frost
Here in New England it’s not uncommon to find frost over 4 feet in the ground after a long cold winter. Before building a foundation all of the frost has to be removed from the sub-grade. You can let mother nature do the work and wait weeks or even months for the ground to thaw or you can remove it physically.
If you don’t remove the frost and you then build a foundation on top of the frozen ground you’ll face some serious problems. Once the ground thaws the structure will begin to settle and move. The structure will most likely be exposed to structural stresses that cause cracking and failure. So it’s absolutely imperative that the frost be removed prior to building the foundation.
Methods To Remove Ground Frost
There are several methods to physically remove the ground frost. We typically use two different methods depending on the depth of frost and area that needs to be corrected. If the frost isn’t all that deep and the area is relatively small the frost can be dug out of the ground using large excavators and earth moving equipment. Otherwise we use mobile ground heaters to help speed up the thawing process and drive the frost out of the ground.
Mobile Ground Heater
We use mobile ground heaters to thaw out deep ground frost over large areas. Mobile ground heaters are a rather simple piece of equipment that’s very similar to household boilers used to heat homes. The mobile trailer has a large oil or propane fired boiler, large fuel tanks and a large coil of rubber hose filled with hot water.
To thaw out the ground in a particular area the rubber tubing is rolled out on the ground spaced about 8 to 12 inches apart. The ground is then covered with insulating blankets. You can see an example in the adjacent photo showing the tubing and blankets. Then the boiler is started up and hot water circulates through the tubing. Typically the ground heater can remove about 6 inches of frost every 24 hours. So if you have 4 feet of frost it can take 8 days or more to completely thaw the ground.
Obviously this is not a cheap way of doing things. This particular piece of equipment cost $7500 per month to rent plus fuel! However, when time is of the essence this is the way to go. The important thing to realize is if you’re building in the winter or spring be sure you dig test pits. Be sure the frost is gone before you start building so you don’t run into problems later.