UFC 3-220-01N
15 AUGUST 2005
11-2.4.1
Free Water. If free water drawn to developing ice segregation can be
easily replenished from an aquifer layer or from a water table within a few feet of the
plane of freezing, heave can be large. However, if a freezing soil has no access to free
water beyond that contained in voids of the soil immediately at or below the plane of
freezing, frost heave will necessarily be limited.
11-2.4.2
Free Water in Permafrost Areas. In permafrost areas, the supply of
water available to feed growing ice lenses tends to be limited because of the presence
of the underlying impermeable permafrost layer, usually at relatively shallow depths,
and maximum heave may thus be less than under otherwise similar conditions in
seasonal frost areas. However, uplift forces on structures may be higher because of
lower soil temperatures and consequent higher effective tangential adfreeze strength
values.
11-2.4.3
Soil Water Content. The water content of soil exerts a substantial effect
upon the depth of freeze or thaw penetration that will occur with a given surface freezing
or thawing index. Higher moisture contents tend to reduce penetration by increasing
the volumetric latent heat of fusion as well as the volumetric specific heat capacity.
While an increase in moisture also increases thermal conductivity, the affect of latent
heat of fusion tends to be predominant, UFC 3-130-01 contains charts showing thermal
conductivity relationships.
11-2.5
Frost-Heave Forces and Effect Of Surcharge. Frost-heave forces on
structures may be quite large. For some engineering construction, complete prevention
of frost heave is unnecessary and uneconomical, but for most permanent structures,
complete prevention is essential. Under favorable soil and foundation loading
conditions, it may be possible to take advantage of the effect of surcharge to control
heave. It has been demonstrated in laboratory and field experiments that the rate of
frost heaving is decreased by an increase of loading on the freezing plane and that frost
heaving can be completely restrained if sufficient pressure is applied. However, heave
forces normal to the freezing plane may reach more than 958 kPa (10 tons per sq ft).
Detailed information on frost-heaving pressures and on the effect of surcharge is
presented in UFC 3-130-01.
11-2.6
Type of Structure. The type and uses of a structure affect the foundation
design in frost areas as in other places. Applicable considerations are discussed in
UFC 3-130-01.
11-3
SITE INVESTIGATIONS
11-3.1
General. In addition to the needed site investigations and data described
in the manuals for non-frost conditions, design of foundations in areas of significant frost
penetration requires special studies and data because of factors introduced by the
special frost-related site conditions. Detailed site investigation procedures applicable
for arctic and subarctic areas are described in UFC 3-130-02, Chapter 2, and UFC 3-
130-04, Chapter 4, and may be adapted or reduced in scope, as appropriate, in areas of
less severe winter freezing. Methods of terrain evaluation in arctic and subarctic
regions are given in UFC 3-130-01.
11-7
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