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Frost heave — what it is and what to do about it

By Erin ParkerFrost heave is a common problem that rears its ugly head this time of year in northern Michigan.   Frost heave is a very sneaky thing — it comes alive only during periods of cold weather and works slowly and quietly in the ground where you can’t see what’s happening.    

It is especially active on those clear starry nights when the temperature drops down toward zero, and when it is able to expand and extend its fingers deeper into the ground.   Frost heave is a serious enemy and it has the potential to displace or destroy just about any type of structure sitting on, in, or even above the ground.

Actually, the phrase “frost heave” can be misleading, since it implies that frost-related movement happens quickly and violently.   I prefer to use the the phase “frost action,” since the movement that occurs in freezing soil is actually a relatively slow and gradual process.   I’ve also heard the term “frost jacking” used — this is probably because frost action can “jack” posts right out of the ground!

Whatever you want to call it, it’s important to understand frost heave in order to prevent it.

Frost HeaveThis picture was taken in a basement I looked at not too long ago. See the badly cracked and dislocated blocks in the corner? This damage was caused by frost heave which took place over a period of several winters. Just imagine the immense force it took to break these  concrete blocks in  half and push them  inward  like this.

The property owner  said  that the problem  ”seemed to get a little worse very year.”   While he had no idea what was causing this problem, he knew it was bad and that he needed to get it fixed!

If you’ve ever encountered a problem like this, you probably already know how frustrating, difficult and expensive to fix it can be.   Please be advised: the worst possible thing you can do is to hire a contractor to fix the structural damage caused by frost heave without first understanding and correcting the root cause of the frost heave problem.

The rest of this post will be dedicated to: 1) an  explanation  of what frost heave is, and 2) a brief outline of basic solutions for preventing future frost heave problems.

Frost Heave: What is it?
Frost heave results from one simple thing — water freezing in the soils near the surface of the ground.   Unfortunately, if you live in northern Michigan, you can never completely escape frost heave, since all soils have some moisture in them, and therefore all soils will exhibit some degree of frost action.

However, certain conditions are known to lead to significant amounts of ice formation, and consequently, significant frost heave.   In most cases, frost heave only becomes a  serious problem when the following two elements are present:

  1. Poorly drained, or frost-susceptible soil (e.g., silts and loams)
  2. A supply of water to feed ice lense formation

When a combination of poorly drained, frost-susceptible soil and a water source are present, ice begins to form in the soil during periods of low temperatures.   The colder it gets, the faster the ice crystals within the soil will grow.

Frozen water (ice) takes up about 10% more space than liquid water, so the soil mass begins to grow and push upward and outward.   As long  as a supply of water is available, more and more ice will continue to form in the soil resulting in ongoing expansion.

These ice formations, which are commonly referred to as “ice lenses,” can far exceed a 10% increase over original volume.   These growing ice/soil masses exert extremely damaging pressure on structures, such as the basement wall shown above.

Frost Heave: What to do about it?
As indicated above, a combination of poorly drained, frost-susceptible soil and a water source need to be present to create a frost heave problem.   The goal for either new construction, or to fix an existing frost heave problem, is to eliminate both of these elements from the area near the structure.

Soils: Remove poor soil (i.e., silt or clay) down to frost depth (42″ in northern Michigan). Replace the poor soil with clean fill sand within 10′ of the foundation. Make sure the fill sand has a low percentage of fine material. The best way to ensure you are getting good material is to order the fill sand from a reputable aggregate supplier.

Water: Eliminate sources of excess water. Install gutters and direct the downspouts away from the foundation. Make sure the final grade slopes away from the foundation. Consider installing a footing drain.

By understanding frost heave and by taking the steps outlined above, you can greatly reduce the potential for frost heave to cause damage to your structure.

In the example indicated above, the basement wall had been backfilled with  frost susceptible  soil, the grade sloped toward the wall, and drainage from the roof was not directed away, but allowed to pond right  against the basement wall!

In addition to the frost heave problem shown in the photo, this also caused water to leak into the basement every time it rained.   These problems had to be fixed  (by a combination of backfill replacement and regrading) so the repaired masonry would not be damaged in the future.

As always, if you have any specific questions about frost heave, or about any other type of problem or concern you may be having, I'd love to hear from you! Please feel free to contact me at parkerengineer@gmail.com.

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