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).

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.

The application of these pressures and forces is

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

ft. During this stage, as steady seepage 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.

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