UFC 3-220-01N
15 AUGUST 2005
other anchorage to resist movement under the lifting forces; providing sufficient loading
on the foundation to counterbalance upward forces: isolating foundation members from
heave forces; battering tapering members within the annual frost zone to duce
effectiveness of heave grip; modifying soil frost susceptibility; in seasonal frost areas
only, taking advantage of natural heat losses from the facility to minimize adfreeze and
frost heave; or cantilevering building attachments, e.g., porches and stairs, to its main
foundation.
11-4.3.3
Permafrost. In permafrost areas, movement and distortion caused by
thaw of permafrost can be extreme and should be avoided by designing for full and
positive thermal stability whenever the foundation would be adversely affected by thaw,
If damaging thaw settlement should start, a mechanical refrigeration system may have
to be installed in the foundation or a program of continual jacking may have to be
adopted for leveling of the structure. Discontinuance or reduction of building heat can
also be effective. Detailed guidance is given in UFC 3-130-01.
11-4.3.4
Creep Deformation. Only very small loads can be carried on the
unconfined surface of ice-saturated frozen soil without progressive deformation. The
allowable long-term loading increases greatly with depth but may be limited by
unacceptable creep deformation well short of the allowable stress level determined from
conventional short-term test. Present practice is to use large footings with low unit
loadings; support footings on mats of well-drained non-frost-susceptible granular
materials, which reduce stresses on underlying frozen materials to conservatively low
values; or place foundations at sufficient depth in the ground so that creep is effectively
minimized. Pile foundations are designed to not exceed sustainable adfreeze bond
strengths. In all cases, analysis is based on permafrost temperature at the warmest
time of the year.
11-4.4
Vibration Problems and Seismic Effects. Foundations supported on
frozen ground may be affected by high stress-type dynamic loadings, such as shock
loadings from high-yield explosions, by lower stress pulse-type loadings as from
earthquakes or impacts, or by relatively low-stress, relatively low-frequency,
steady-state vibrations. In general, the same procedures used for non-frozen soil
conditions are applicable to frozen soils. Design criteria are given in UFC 3-220-03A
and UFC 3-220-09. These criteria also contain references to sources of data on the
general behavior and properties of non-frozen soils under dynamic load and discuss
types of laboratory and field tests available. However, design criteria, test techniques,
and methods of analysis are not yet firmly established for engineering problems of
dynamic loading of foundations. Therefore, the senior engineer of the organization
should be notified upon initiation of design and should participate in establishing criteria
and approach and in planning field and laboratory tests.
All design approaches require knowledge of the response characteristics
of the foundation materials, frozen or non-frozen, under the particular load involved. As
dynamic loadings occur in a range of stresses, frequencies, and types (shock, pulse,
steady-state vibrations, etc.), and the response of the soil varies depending upon the
load characteristics, the required data must be obtained from tests that produce the
same responses as the actual load. Different design criteria are used for the different
11-15
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