ETL 1110-2-355
31 Dec 93
consider the base rigid, and the preliminary analysis
suggestions for use of battered piles are defined in
can be performed using a rigid base analysis tool,
EM 1110-2-2906. In using battered piles, consider-
such as the computer program CPGA (Hartman et al.
ation must be given to geometric constraints from
1989). This program performs the pile analysis for
adjacent pile-founded monoliths and sheetpile cutoffs.
two- and three-dimensional loading conditions. For
These constraints can be assessed using the computer
subsequent foundation design and any structural con-
program CPGI (Pile Group Interference Check, CASE
crete design, the pile cap should be treated as a
computer program X0086). Generally, piles from one
flexible base. Therefore, the pile foundation and
monolith should not extend into the area beneath an
structural analysis must be performed using a pro-
adjacent monolith because of the possibility of
gram that will consider the internal stiffness relation-
ship of the structure. The same flexible base analysis
can be used to analyze the piles and the concrete
(2) Pile head fixity. If it is not practical to use
structure. This is possible using the computer pro-
battered piles to resist the lateral loads because of
gram CWFRAME (Jordan and Dawkins 1990) or
geometric constraints, all vertical piles may still be a
other frame analysis or finite element applications
possible solution, but lateral deflections may become
which include pile elements. A complete SSI finite
critical. If lateral deflections are too high using verti-
element model can be useful for this analysis, though
cal piles with a pinned condition at the pile head, the
it is usually much more complicated.
pile may be embedded deeper and analyzed as fixed
at the pile cap. Pile head fixity is discussed in
EM 1110-2-2906. Refer to Castella (1984) for more
f. Pile stiffness coefficients. Before beginning
information on pile head fixity.
any detailed pile analysis, the pile stiffness coeffi-
cients should be determined by performing single pile
(3) Lateral subgrade moduli. When an accept-
analyses based on available soil data or previous pile
able initial layout is achieved based on pile forces
tests with similar soils and conditions. These coeffi-
and stresses, a comparison of calculated pile head
cients are essentially linear springs that approximate
deflections to those seen in test results or assumed in
the nonlinear behavior of the soil-pile foundation.
the pile stiffness coefficient analysis must be made.
Normally, it is desirable to perform a parametric
Since the pile/soil stiffness degrades with deflection,
analysis where the bounds in variability of the coeffi-
the calculated deflections seen in analyses should
cients can be captured. Once determined, these
compare with the deflections assumed or generated in
coefficients are input to the various programs chosen
the selection of the pile stiffness coefficients.
for the pile group analysis. See EM 1110-2-2906 for
a further discussion of stiffness coefficients.
6-3. Soil founded. The analysis of the foundation
includes checking for resultant location, sliding, uplift
tance in pile foundations is dependent upon the pile
(flotation), differential settlement, and bearing failure.
type, strong axis orientation and batter angle, and on
One of the single most important elements in the
the assumed or experimental lateral subgrade moduli
design of a soil-founded U-frame lock is the assump-
used in design.
tion regarding the distribution of the effective base
pressure.
(1) Pile orientation. Lateral loads are most effi-
ciently resisted by battered piles. However, battered
a. Pressure distribution. There are two basic
piles are more difficult to drive and result in a more
approaches used in determining the distribution of
complicated layout to design and construct. Addi-
base pressures. One is a soil spring approach and the
tionally, battered piles tend to dramatically change the
other is an assumed pressure distribution. The spring
pile force distribution. If the lateral loads are not
method is discussed in paragraph 7-3e. The assumed
significant, the designer should consider using all
pressure distribution approaches are a uniform distri-
vertical piles. If the lateral load is significant, piles
bution and a stepped distribution with appropriate
with unequal stiffnesses about the orthogonal axes
corrections for eccentric loading. The methods pre-
(H-piles for example) can be turned to increase stiff-
sented have been derived from analysis of instrumen-
ness in the direction of the load or they can be bat-
tation data where base pressures were measured and
tered. The preliminary batter slope and number of
compared with conventional calculations. A tool
battered piles can be determined by using force vec-
available to compute base pressures is the CASE
tors or similar methods. Capacities, limitations, and
computer program 3DSAD (Tracy and Kling 1982).
A-11
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