31 Dec 93
performed using computer program CPGA (Case Pile
Generally speaking, for U-frame locks, greater
Group Analysis) (Hartman et al. 1989) for this pur-
concentrations of piling should be located beneath the
pose, or if a two-dimensional monolith is being eval-
heavier portions of the monolith such as the lock
uated, a flexible base analysis can be performed using
walls and less dense concentrations beneath lighter
CWFRAM. The final decision, which will be based
areas like the chamber floor. Also, tension piles may
on cost, can be made using the refined pile layout
be needed at the center of the chamber floor to pro-
compared with a soil founded configuration.
vide resistance against uplift during maintenance or
other dewatered conditions. Tension anchors could
6-2. Pile founded.
also be used in this regard, and the use of drains can
help reduce uplift forces. Preliminary pile analyses at
this stage could be performed using CPGA (Hartman
a. General. The pile foundation design devel-
et al. 1989) which assumes an infinitely rigid base
opment should follow a procedure that conforms to
and allows for two- or three-dimensional analysis.
the normal submittal phases for civil works design
For U-frame locks, the rigid base assumption is not
projects. During the feasibility phase of the project,
necessarily correct but is satisfactory for determina-
the determination for use of a pile foundation should
tion of preliminary pile quantities for costing pur-
be made, the most economical type of pile to use
poses. Preliminary pile layouts should be developed
must be decided, and an approximate cost of the
for the major types of monoliths that comprise the
foundation should be projected. The actual detailed
lock so that accurate costs can be obtained. Calcula-
design of the pile foundations should occur during the
tion of pile loads and some refinement in the layout
preparation of design memorandums for the project.
can be accomplished using CWFRAME (Jordan and
The final pile layouts for all monoliths should be
Dawkins 1990). This program analyzes two-
developed so that only minor refinements and addi-
dimensional plane sections through the lock and
tion of details are required during the development of
accounts for the flexibility in the base of the lock
plans and specifications.
structure. This will give a more accurate distribution
of pile forces for a U-frame lock than will CPGA
b. Types of piles. There are many different
(Hartman et al. 1989). However, three-dimensional
types of piling that can be used for a U-frame lock
effects must be accounted for independently and
foundation, each with its advantages and disadvan-
added to the two-dimensional CWFRAME (Jordan
tages. Common types of piling include: steel H-piles,
and Dawkins 1990) results. This flexible base behav-
steel pipe piles, precast concrete piles, cast in place
ior verification is particularly important for monoliths
concrete piles, mandrel driven piles, and timber piles.
that may require tension piling under the lock floor to
For a detailed discussion of the types of piles and
resist uplift during dewatering.
how to evaluate them, see EM 1110-2-2906.
d. Final pile layout and analysis. If the pile
c. Initial pile layout. Determination of the
layouts were properly developed during the feasibility
initial pile layout should be made in the feasibility
phase of the project, they can be used as a good
stage. Preliminary layouts for costing purposes can
starting point for development of the final layouts.
be accomplished by using conservative lateral and
Lastly, after an acceptable pile layout is determined
vertical capabilities for a single pile and applying
based on assumed critical cases, all load cases should
these values to resist the total lateral and vertical
be checked for effects on the pile layout and the base
loads for the worst load cases. This gives a very
rough idea of the total quantity of piling required.
Piles should be located in grid patterns relative to
e. Rigid versus flexible base. The designer
concentrations in foundation forces, geotechnical
should determine the relative rigidity of the lock base
considerations, and pile-driving tolerances. The grid
with respect to the pile foundation. This can be
should be established so that no pile interferes with
accomplished by running some simple parametric
studies in which the pile forces for a simplified flex-
pilings under adjacent monoliths or with sheetpile
ural model are compared with the rigid base results.
cutoffs. Computer program CPGI (Pile Group Inter-
For U-frame locks, most monoliths should be ana-
ference Check, CASE computer program X0086) can
lyzed as flexible base structures unless it can be
shown that the rigid base results closely approximate
also consider the effects of close pile spacing on
the flexible base. Initial design estimates could
design criteria, particularly for friction piles.