TM 5-852-4/AFM 88-19, Chap. 4
2.
Bearing capacity factors based on a smooth base (base shear stress = 0) and D/B greater than 4.
3.
recommended in paragraph 4-8f(1).
U. S. Army Corps of Engineers
Figure 4-61b. Bearing capacity formulas1. (Ultimate bearing capacity of deep foundations in c-∅ material.)
system for wall and column loads is separate, as
tensile stresses. The amount of steel reinforcement in
illustrated in figures 4-24, 4-27 and 4-28. Choice may
concrete members should be sufficient to prevent
depend on either structural or economic factors, or both.
cracking of concrete and the consequent exposure of
(10) A pier is a prismatic or cylindrical
steel to moisture. To prevent foundation uplift, bases of
column that serves, like a pile or pile cluster, to transfer
footings should be large enough to resist frost heave
load to a suitable bearing stratum at depth, as illustrated
uplift through passive soil reaction of the base
in figure 4-61b. It may be noted in figure 4-61b that the
projections against overlying materials, or pier-type
bearing capacity increases as the square of the radius of
foundations should extend to sufficient depth to resist
the pier in two of the three factors making up the total
such uplift through skin friction or adfreeze bond on
bearing for the circular pier, thus suggesting rapid
lateral surfaces. Uplift resistance contributed by dead
increase of bearing capacity with diameter of pier.
load from structure and weight of foundation should be
(11) However, it should also be noted that
taken into account. When practical, surfaces in contact
the ultimate frost heaving force which can be developed
with the frozen soil may be battered so that heave of the
on a pier or on the stem of a footing is a function of the
frozen layer will tend to reduce the contact and thereby
surface area of the member in contact with the
minimize heaving forces. It is also desirable that vertical
seasonally frozen ground and hence of the diameter of a
foundation members extending upward through the
cylindrical member. The frost heaving force is capable
annual frost zone from underlying pads be as small in
of fracturing members which are weak in tension and
cross section as possible to minimize the total heave
which are solidly anchored below the seasonal frost
seasonal frost zone during thaw, care must be taken to
zone. Footing or pier members in the seasonal frost
avoid column instability in thinned-down members. Frost
zone which may be placed in tension by frost heave
heave forces may be estimated as described in
forces should be made strong enough to resist such
paragraph 4-31.
4-94
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