Throughout Canada, the climate results in frost damage to buildings, roads, and
equipment every winter. Smaller buildings and roads are particularly affected
by ground movements due to frost heave.
As the ground freezes, water is drawn from the lower unfrozen soil to the frost
front where it freezes forming a series of ice lenses as the frost penetrates
In the change from liquid to solid, water expands 9% in volume.
Fine grained soils, particularly silty soils are frost susceptible, as their
pore structure allows the capillary movement of water but is fine enough to
support ice lensing. Clays impede water flow and so the development of ice
lenses is retarded. A sandy soil will allow frost to penetrate deeper than a
clayey or silty soil.
Annual frost penetration depth at any location is determined by the balance
between the supply of heat from the interior of the earth(latent heat) or the
structure and the rate at which it is lost to the atmosphere.
Frost penetration depth is affected by the latent heat of fusion and moisture
migration as a result of thermal gradients. High thermal gradients can
cause moisture migration, which, in turn, may induce undesirable shrinkage of
fine-grained soils supporting footings
The large ground heaves are a result of ice segregation and ice lenses which
form under the following conditions:
1). frost susceptible soils, 2). ground water, 3). freezing temperatures in the
Elimination of any one of these factors will eliminate frost heave for all
Therefore, frost heaving can be avoided by removing one of the 3 factors
necessary for its foundation.
The use of: 1). granular backfills, 2). good drainage 3). footings below the
depth of frost penetration or insulation for shallow slabs and footings
Presentation by Derek Xia, an expert in the field of frost heave
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The most economical method to prevent frost heave is insulation (Styrofoam by
Dow Chemical), The insulation retards geothemal heat loss in the earth, thereby
reducing the depth of frost penetration.
The insulation layer should be buried at a sufficient depth to prevent its
damage by traffic and to protect it against chemical deterioration under
sunlight. Generally 200mm to 300mm of fill or fill plus pavement is considered
For heated structures, it is advantageous to maintain the floor slab as low as
possible relative to the outside grade, this will permit maximum flow of heat
to occur from within the building to the soil beneath the foundations.
In unheated structures, a continuous insulation mat must be provided beneath the
entire area of both floor and footings.The insulation required is
significantly reduced if clean, nonfrost susceptible fill is provided beneath
the floor. Even though the nonfrost susceptible fill may freeze, ice lenses
will not develop,and consequently, frost heave will be within generally
Robinsky E.I., Bespflug K.E., Design of Insulated Foundations Journal
of the Soil Mechanics and Foundations Division, Vol. 99, No. 9, September 1973
Penner E. Experimental Pavement Structures Insulated with a Polyurethane
and Extruded Polystyrene Foam National Research Council of Canada ,
Typical Thermal Properties of Selected Materials
|Portland cement concrete
|Bituminous or asphalt concrete
|Typical unfrozen fine grained soil (w=30%)
|Typical frozen fine grained soil (w=30%)
|Typical unfrozen coarse grained soil (w=10%)
|Typical frozen coarse grained soil (w=10%)