2218
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
CDSS (Sand)
CDSS (Clay)
Sand (FLAC)
Clay (FLAC)
Seed & Idriss curve
ATERIA
O VERSU
UDE
soil characteristics used in the model as defined by the shear
modulus degradation (G/Gmax) and damping ratio (D) curves.
▼
Stratum
Soil Parameters for Effective Stress Analysis
I (4.3m (14ft) thick)
=726 kg/m
3
,Vs=122 m/s, c=4.8 kPa,
=15
o
II (21.3m (70ft) thick )
=807 kg/m
3
,Vs=186 m/s, c=5.8 kPa,
=20
o
III (23.5m (76ft) thick)
=888 kg/m
3
,Vs=300 m/s, c=5.8 kPa,
=20
o
IV (58.0m (190ft) thick)
=1000 kg/m
3
,Vs=335 m/s,
=35
o
Figure 1. Soil stratigraphy for the study site (Not to scale).
Figure 2. Soil dynamic characteristic curves
2.2 Characteristic of Earthquake Input Motion
The peak ground acceleration (PGA) of the earthquake motion
is 0.48 g with a duration time of 40 sec. As indicated from the
power spectra of input velocity and input acceleration as shown
on Figure 3, the highest frequency component of the input
motion is less than 10 Hz with the majority of the frequencies
are less than 6 Hz. The input motion is applied at the depth of
105m (350ft).
Figure 3. Acceleration time history and power spectrum of input
motion.
2.3 Two-Dimensional Numerical Modeling
Kuhlemeyer and Lysmer (1973) state that for accurate
representation of wave transmission through a model, the spatial
element size,
l, must be smaller than approximately one-tenth
to one-eighth of the wavelength associated with the highest
frequency component of the input wave, i.e.,
l
≤
or
f
≤Cs
/(
10
l), where
is the wavelength associated with the
highest frequency component that contains appreciable energy;
and Cs is speed of propagation associated with the mode of
oscillation. Since the majority of the frequencies of input
motion are less than 6.0 Hz, a 1.83m (6ft) x 1.83m (6ft) mesh
size is selected for the modeling. The maximum frequency that
can be modeled accurately for this element size is 6.7 Hz. The
frequency of Dynamic excitation to the FLAC model was
specified using the compliant-base deconvolution procedure
(Mejia and Dawson, 2006). The input excitation was specified
as a stress time history at the base of the model as a function of
mass density
, shear wave velocity
Vs
at the half-space depth
(105 m (350 ft) below seafloor) and input shear particle velocity
v
. Figure 4 demonstrates the FLAC mesh with rectangular and
triangle shapes for this two-dimensional analysis. The free-field
on vertical sides and quiet boundary conditions at the bottom
are applied in the soil domain.
Stratum I (Clay)
Stratum II (Clay)
Stratum III (Clay)
Stratum IV (Sand)
Water depth-200 ft
