1609
Technical Committee 203 /
Comité technique 203
considered. For the FEM analysis of the dam section, 15-node
triangular elements are used for generating finite element mesh.
The constitutive behavior of soil is modeled as HS small model.
The numerical values of soil properties considered for the
analysis are provided in Table 1. The axial stiffness (EA) of
geogrid (modeled as seepage barrier on the U/S face of the dam)
is taken as 1500 kN/m. The analysis is performed for reservoir
full condition with a free board of 2.0 m.
Table 1 Material properties of the soil considered for FEA
Parameter Description
Name Value
General
Material Model
Name HS model
Type of material behavior
Type Drained
Soil unit weight
Above phreatic level
γ
unsat
16 kN/m
3
Below Phreatic level
γ
sat
20 kN/m
3
Parameters
Secant stiffness in standard
drained tri-axial test
E
50
ref
2.0 × 10
4
kN/m
2
Tangent stiffness for
primary oedometer loading
E
oed
ref
3.601 × 10
4
kN/m
2
Power of stress-level
dependency of stiffness
m
0.5
Cohesion
c
′
ref
10 kPa
Friction angle
φ′
18
°
Dilatancy angle
ψ
0
°
Shear strain at which Gs =
0.722G
o
γ
0.7
1.2× 10
-4
Shear modulus at very
small strains
G
o
ref
2.7 × 10
5
kN/m
2
Poisson’s ratio
ν
0.2
Damping Coefficient
(Dynamic analysis)
ξ
5%
4.1
Stability under static condition
Fig. 1 shows the finite element model of dam section
(without using Geosynthetics as seepage barrier) with steady
state pore water pressure distribution within the body of the dam
section at reservoir full condition. It should be noted that there
are 465 15-noded triangular elements (no of nodes = 3887 and
average element size = 3.651 m) are used in discretization of
dam model. The factor of safety of the dam section at reservoir
full condition is obtained as 1.52.
Fig. 2 shows the finite element model of the same dam
section in which Geosynthetics are used as seepage barrier. The
elastic stiffness of Geogrid element is taken as 1500 kN/m. In
the modeling, uniformly distributed load system A is used to
simulate the hydrostatic pressure distribution on the U/S side of
the dam section at reservoir full condition. The Phreatic line is
assumed at ground surface. The factor of safety of the dam
section at reservoir full condition is obtained as 2.20. Hence, it
can be noted that the static stability of the dam section is greatly
enhanced with the use of Geosynthetics as seepage barrier.
4.2
Stability under dynamic loading
4.2.1
Sinusoidal input motion
For the stability analysis under dynamic loading, sinusoidal
input motion is given at the base of the dam section. A
parametric study is performed taking different values of
frequency (1, 2, 3, 4 & 5 Hz) and amplitude amplifier (0.02,
0.04, 0.06, 0.08 & 0.10). The time duration is taken as 20 sec.
The analysis of dam section is performed for both the cases in
which Geosynthetics are either not used or used as seepage
barrier. Fig. 3 shows the excess pore water pressure – time
history record at two different locations within the body of the
dam section (without Geosynthetics).
Fig. 4 shows the acceleration – time history record of the
crest of the dam section obtained for both the cases. It can be
noted that the provision of Geosynthetics greatly reduces the
crest acceleration and the reduction factor is almost 2.5.
Figure 3 Excess pore pressure at two different nodes (B, C)
within the body of the dam section (no Geosynthetics used)
for sinusoidal input motion (
f
= 5 Hz, A. amp = 0.02)
Figure 4 Acceleration – time history record of the crest
of the dam section (
f
= 5 Hz, A. amp = 0.02)
Figure 1 Steady state pore pressure (minimum value = 0
kN/m2, element 16 at node 387 and maximum value =
376.2 kN/m2, element 2 at node 65)
Figure 2 Steady state pore pressure (minimum value = 0
kN/m
2
, element 17 at node 5391 and minimum value =
376.2 kN/m
2
, element 1 at node 551)
