ETL 1110-2-544
31 Jul 95
Figure 26. Nonlinear stress-strain behavior was
simulated using the Modified Cam-Clay model. Also,
in the analysis, the permeability of the shell (rockfill)
was very high compared to that of the core (k = 10-7
cm/sec). The consolidation of partially saturated soils
in the core was simulated using a "homogenized" pore
fluid to account for the effects of water and air in the
void spaces. Separate analyses were conducted for two
different core conditions to account for the variations in
water content and dry density which may occur during
construction. These analyses accounted for a "stiff"
core (corresponding to 95 percent relative compaction
as determined by the Standard AASHO compaction test
and 1 percent dry of the optimum water content) and a
"soft" core (corresponding to 90 percent relative
compaction and optimum moisture content at the time
of placement).
d. Construction sequence. The analysis was
performed in three principal stages: (1) construction,
(2) reservoir filling, and (3) long-term seepage. The
construction represented a timespan of 3.5 years. The
construction of the cofferdam was accomplished by
introducing elements 1 though 16 as fill in two layers
(Figure 26). The remainder of the dam was con-
structed by the addition of five layers of additional "fill
elements." The construction was an undrained analysis
as it was assumed that excess pore water pressures did
not dissipate during the construction process due to the
relatively short timespan of the construction period.
The filling of the reservoir was modeled by the
application of the water pressures of the full reservoir
at the interfaces between the upstream and the core and
the impervious soil in the cofferdam zone. The
reservoir was assumed to be filled to elevation 990 ft.
Forces were applied to nodes connected to "shell"
elements to account for buoyancy due to submergence.
Figure 24. Plan and longitudinal views of New
The application of these pressures and forces is
Melones Dam
illustrated in Figure 27. Dissipations of excess
porewater pressures during reservoir filling were also
(3) Are the long-term stresses, calculated
neglected because it was presumed that the reservoir
assuming slow construction and assuming no excess
would be filled within a relatively short period. During
pore water pressure, the same as those calculated
the third stage, the long-term seepage stage,
taking into account the effects of consolidation?
fluctuations in the pool level were ignored as it was
assumed that the elevation of the pool remained at 990
c. Material model, properties, and finite element
ft. During this stage, as steady seepage was
code. The finite element code used in this analysis was
approached, deformations within the dam were
CON2D, and it has the ability to directly account for
influenced by the dissipation of excess porewater
the effects of consolidation. In the study, it was
pressures and seepage through the dam. In the
assumed that a plane-strain analysis would serve as a
analysis, stresses, strains, and porewater pressures
reasonable approximation of the performance of the
were calculated 5, 15, 50, and 80 years after the
dam in the center of the valley. The mesh is shown in
reservoir was filled.
A-22
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