TM 5-852-4/AFM 88-19, Chap. 4
serted. The building is still giving good service more
communication antenna towers, however, must usually
than 20 years after erection although the one jack
maintain fixed orientations at all times and normally
requires periodic adjustment and occasionally an
require fixed types of foundations. Bridge piers and
additional section has to be removed from the top of the
abutments are normally thought of as fixed types of
pile. In figure 4-39 the rapid jacking out of the ground of
structures but recent observations of such construction
porch posts embedded only in the annual frost zone is
in Alaska have shown that considerable seasonal
48
movements may occur . Figure 4-41 shows observed
contrasted with the performance of the permafrost
movements of a bridge pier in central Alaska.
embedded piles supporting the building itself. These
Nevertheless, such facilities must be designed for
porches became unusable and had to be reconstructed.
h. Figure 4-40 shows the rapid settlement of a
permanent stability, accepting small cyclic seasonal
deflections due to thermal stresses. Water and POL
wooden garage building on a grossly inadequately
storage tanks may accept considerable movement and
ventilated foundation', "0. The greater displacement of
distortion if properly constructed and may therefore be
the west side as compared to the east may have resulted
supported either on "floating" or fixed types of
from the effect of the late afternoon sun on the west side.
foundations, provided long range thermal stability is
Degradation of the permafrost was finally nearly arrested
assumed.
by discontinuing heating of the building. In spite of
j.
When components such as exterior loading
extreme differential distortion of the building it was then
platforms, porches or unheated wings are attached to
used for some years for storage with very little further
heated structures which are stable supported, the
distress. It was finally moved to a new foundation and
potential exists for severe differential movements
reconditioned; it is still in use more than 20 years after its
between the facility components (fig 4-39).
Such
original construction.
i.
Power transmission line towers can often
conditions must be carefully studied and precautions
must be taken in design to ensure that structural damage
tolerate several inches of upward and downward
will not occur. To achieve this, the foundation of the
seasonal movement (depending on the tower design)
attached or unheated facilities should be provided with
provided there is no progressive tilting, heave or
the same
settlement. Therefore, it is often possible for such
towers to be economically sup ported on footings resting
on pads of free-draining granular materials. Radar or
U. S. Army Corps of Engineers
Figure 4-39a. Wood frame residence 32 x 32 feel on wood pile foundation, Fairbanks, Alaska73,180. See figure 4-25 for site
conditions. See figure 4-12b for degradation of permafrost, 1948-1957. (North side elevation.)
4-62
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