Geoscience Reference
In-Depth Information
seismic analysis of geotechnical works both in research and practice. It is about the time
to explore the next level of knowledge in the discipline of geotechnical engineering. The
timeisripetodiscussthefundamentalaspectofmechanicsofassemblageofsoilparticles
as related to the soil behavior under cyclic loading among the geotechnical earthquake
engineers and researchers. Thus, the paper begins by discussing this fundamental aspect
of analysis. Some of the findings useful in practice of seismic analysis are also reviewed
with respect to the seismic analyses of embankments, embedded structures and soil-pile
systems.
The paper then discusses the emerging trends in the fundamental conceptual frame-
work for seismic design of geotechnical structures. One trend is centered round the con-
cept of performance. There is an important paradigm shift from structure-oriented to
service-oriented approach. The other trend demands a new approach readily applicable
for designing large urban area against combined hazards such as those due to tsunamis
and earthquake motions. The paper concludes with a proposal that will be useful for
designingnewandlargegeotechnicalworksthathavetomeettherapidlygrowingsocial
and economic demands in Asia and those for redevelopment of urban areas around the
world.
2. Assemblage of soil particles
A granular material consists of an assemblage of particles with contacts newly formed
or disappeared, changing the micromechanical structures during macroscopic deforma-
tion. Among various constitutive models proposed for granular materials, a model that
characterizes a structure of the assemblage of particles has capability to reproduce the
distinctive behavior of granular materials due tothat structure (Iai and Ozutsumi, 2005).
Stress in granular materials as defined for continuum is given by a certain average of
contact forces between the particles. In assemblage of spherical particles, the contact
force
P
k
canbepartitionedintothedirectionofcontactnormal
n
k
andtangentialdirection
t
k
as (seeFigure 13.1, left)
P
k
=
Fn
k
+
St
k
(13.1)
Macroscopic stress is given by taking an average over the contact forces within the
representative volume element
R
having volume
V
as (e.g. Thornton, 1989)
2
V
σ
kl
=
r
(
Fn
k
n
l
+
St
k
n
l
)
(13.2)
R
where
r
denotes radius of spheres.
Before taking the average over all the contacts of random orientation, a structure can be
identified by systematically grouping the contacts according to the orientation. The first
level of structures is identified by choosing those pairs of a contact force and a contact
