TM 5-852-4/AFM 88-19, Chap. 4
aspects of cold regions foundation design for a specific
small, local adjustments of site location based on
facility.
detailed knowledge of local conditions.
a. Climatic data. Some climatic data such as
(1) Specific weather information useful in
temperature information will provide direct input to the
foundation design includes mean, minimum, and
technical foundation design. Other data will provide
maximum daily air temperatures; precipitation (liquid and
indirect input, such as weather conditions which will be
solid); snow and ice depth on the ground; wind velocity
experienced during the construction period, including the
and direction; and frequency of storms or severe
lengths of the outdoor working seasons and of the
combinations of conditions. Air temperatures are the
specific periods over which protection against adverse
most important data; they are obtainable with a simple
temperature conditions will be required. Freeze and
recorded needing a minimum of attention.
thaw indexes are essential for computing depths of
(2) Even observations for a limited period
freeze and thaw and for estimating degradation or
such as a month, when compared with simultaneous
aggradation. Precipitation is an indicator of both outdoor
observations at the nearest regular weather stations, will
working conditions and of surface and subsurface
give valuable clues concerning the air temperature
drainage conditions. Snowfall amounts, the frequency
regime of the structure site.
and intensity of snow drifting, snow depths, and the
(3) Equipment,
installation
and
frequency and intensity of icing conditions are all
observational procedures should be in accordance with
important input elements affecting directly or indirectly
the guidance of the National Oceanic and Atmospheric
the foundation design. The deposit of ice and snow may
Administration Federal Meteorological Handbook No. 2,
178
Substation Observations . Greater technical detail is
frequently impose severe loads on structures and
177
available in Handbook No. 1, Surface Observations .
foundations. It is important to tabulate liquid and solid
b. Subsurface thermal regime.
Ground
types of precipitation separately. When snow drifting
temperatures with depth have been recorded for
patterns may be important to the operation and
numerous specific locations in North America and
maintenance of the facility, it is desirable to obtain aerial
Greenland, including a number of stations in
photographs in the spring after initial thaw has started to
10,25,29,37,99,101,102
. Data from such observations
Alaska
delineate sharply the natural patterns of seasonal
and air temperature records, together with detailed data
accumulation.
Information on wind directions and
on topography, elevation, snowfall and other site data,
velocities and the frequency of storms is essential in
permit approximate preliminary estimates of ground
design of structures and it is one of the determinants of
temperatures at new sites. However, it is very easy for
foundation design loading values. In mountain areas,
such estimates to be considerable in error unless all
structures may require design for velocities as high as
pertinent factors are accurately perceived and evaluated.
200 to 250 mpg, imposing severe foundation stability
For example, permafrost is found in the valley bottoms in
requirements. Often foundation uplift forces produced by
the Fairbanks, Alaska, area but is absent in valley
wind on specialized structures such as antennas offer
bottoms in the Knob Lake, Quebec, area in spite of a
the most critical foundation design problems in
lower mean annual temperature. One key reason for this
permafrost areas. If added footing weight and size or
is the much heavier snowfall in the latter area. Again, at
added depth of footing burial is required to resist uplift,
Kotzebue, Alaska, mean ground temperature in the
this may result in substantial revisions of the ultimate
gravel spit on which the village is located is about 29.7 F
design. Combinations of severe climatic conditions must
but it is about 24.5 ƒF in the silt and clay bluffs which are
also be investigated.
For example, severe icing
conditions combined with high wind may be critical for a
at only slightly higher elevation but are more removed
radio transmission tower. When there are no weather
from direct contact with the effects of the ocean.
records from' a station near the proposed site, it will be
(1) At new sites, ground temperature and
necessary to estimate conditions at the site from weather
freeze and thaw penetration information should be
records at the nearest available locations, taking into
obtained as early as possible in the site investigations, in
account such factors as latitude, elevation, exposure,
sufficient detail to demonstrate or verify the subsurface
and nearness to water bodies. Experience shows that
thermal regime.
Copper-constantan thermocouples
this estimation is difficult to accomplish with accuracy.
installed in foundation exploration holes or in holes drilled
Therefore, whenever the time and nature of the job
for this specific purpose provide the simplest means of
permit, arrangements should be made for collection of at
measuring subsurface temperatures. Readings with an
absolute accuracy of about 0.4C (3/4F) may be
least elementary weather data at the site itself at the
earliest possible time; even records for part of a year
obtained manually using a portable potentiometer.
may give invaluable checks on the accuracy of
When greater precision is needed than is obtainable with
estimates.
Sometimes design, maintenance and/or
thermocouples, thermistors of a select type, glass-bead
operational difficulties may be substantially simplified by
encased and properly calibrated, should be employed.
Careful techniques can readily produce data from ther-
3-4
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