UFC 3-220-01N
15 AUGUST 2005
11-4.2.5
Granular Mats. In areas of significant seasonal frost and permafrost, a
mat of non-frost-susceptible granular material may be used to moderate and control
seasonal freeze-and-thaw effects in the foundation, to provide drainage under floor
slabs, to provide stable foundation support, and to provide a dry, stable working
platform for construction equipment and personnel. Seasonal freezing-and-thawing
effects may be totally or partially contained within the mat. When seasonal effects are
only partially contained, the magnitude of seasonal frost heave is reduced through both
the surcharge effect of the mat and the reduction of frost penetration into underlying
frost-susceptible soils. UFC 3-130-01 provides guidance in the design of mats.
11-4.2.6
solar radiation is very important in foundation design in permafrost areas. Corrective
measures that may be employed include shading, reflective paint or other surface
material, and sometimes live vegetative covering. In seasonal frost areas, it may
sometimes be advantageous to color critical surfaces black to gain maximum effect of
solar heat in reducing winter frost problems. UFC 3-130-01 provides guidance on the
control of solar radiation thermal effects.
11-4.3
Control of Movement and Distortion. The amount of movement and
distortion that may be tolerated in the support structure must be established and the
foundation must be designed to meet these criteria. Movement and distortion of the
foundation may arise from seasonal upward, downward, and lateral displacements, from
progressive settlement arising from degradation of permafrost or creep deflections
under load, from horizontal seasonal shrinkage and expansion caused by temperature
changes, and from creep flow, or slide of material on slopes. Heave may also occur on
a non-seasonal basis if there is progressive freezing in the foundation, as under a
refrigerated building or storage tank. If the subsurface conditions, moisture availability,
frost penetration, imposed loading, or other factors vary in the foundation area, the
movements will be non-uniform. Effects on the foundation and structure may include
various kinds of structural damage, jamming of doors and windows, shearing of utilities,
and problems with installed equipment.
11-4.3.1
Frost-Heave and Thaw-Settlement Deformations. Frost heave acts in
the same direction as the heat flow or perpendicular to the freezing plane. Thus, a slab
on a horizontal surface will be lifted directly upward, but a vertical retaining wall may
experience horizontal thrust. Foundation members, such as footings, walls, piles, and
anchors, may also be gripped on their lateral surfaces and heaved by frost forces acting
in tangential shear. Figure 11-5 shows an example of frost-heave forces developed in
tangential shear on timber and steel pipe piles restrained against upward movement.
In rivers, lakes, or coastal water bodies, foundation members, to which
floating ice may adhere, may also be subject to important vertical forces as water levels
fluctuate.
11-4.3.2
Controlling Frost Heave. Among methods that can be used to control
detrimental frost action effects are placing non-frost-susceptible soils in the depth
subject to freezing to avoid frost heave or thrust; providing sufficient embedment or
11-14
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