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Proceedings of the International Conference on
Advances and New Challenges in Earthquake
Engineering Research, Hong Kong Volume
SLOPE STABILITY AGAINST EARTHQUAKE
CONSIDERING THREE DIMENSIONAL EFFECT
I. Yoshida 1 , T. Kaneto 2 and M. Takao 2
Structural and Geotechnical Engineering Department, Tokyo Electric Power Services Co.,Ltd.,
Tokyo, JAPAN
2 Nuclear Power Engineering Department, Tokyo Electric Power Company
Tokyo, JAPAN
ABSTRACT
In order to discuss slope stability against seismic force considering three dimensional (referred as 3-d,
hereafter) effect, an evaluation method based 3-d dynamic FEM is developed. The model for the 3-d
dynamic FEM used in this study is composed of one 3-d model, four 2-d far field models and four 1-d
far field models. They are connected by viscous boundaries. In the proposed method, a sliding surface
is modeled by a set of planes or an oval. The problem to search the sliding surface with minimum
safety margin is formulated as optimization problem, in which objective function is safety factor, and
design parameters are parameters describing the sliding surface such as center and radius of the sliding
arc. The optimization problem is solved by using Genetic Algorithm, which attracts attention and is
widely used as practical global optimization method in various engineering problems recently. In 3-d
analysis, directions of excitation and sliding are also important, so that these directions for minimum
safety factor are also searched simultaneously. Several numerical simulation results show that safety
factor based on 2-d analysis tends to be conservative, though the response of 3-d model is larger than
that of 2-d model partially.
INTRODUCTION
After Kobe earthquake (1995), many Japanese aseismic design codes have been revised, and
design earthquake and spectra tends to become large. For the large design earthquake, we need to
estimate the limit state more carefully than before. If the limit state is examined under lots of
conservative assumptions, the obtained safety margin might be smaller than the level required in the
new design code. Consequently a lot of budget for the strengthening is needed irrationally. One of the
standpoints for more precise estimation is to consider three dimensional (referred as 3-d, hereafter)
effect of the slope. For the stability analysis of slopes, there are several methods, such as limit
equilibrium method and finite element method (FEM). However most of the method that have been
performed so far are based on two dimensional shape of slope and sliding surface.
In this paper, an evaluation method based on 3-d dynamic FEM is studied. Search of critical sliding
surface can be formulated as optimization problem hi which the objective function is the safety factor
of the sliding surface and design parameters are parameters which define the sliding surface. Genetic
Algorithm (referred as GA here) is used for the optimization. GA is one of the most prospective