Irzternational Sy叩榔tum

The Eneas ofSu如GeoLogy

on Set'smt'c Motiotl
ESG 1992, ODAWARA, JAPANPREDZCTZON OF GROU和紙OT工ONS AT ASFZGARA VALLEY
uSZNG

TEE

EXTEmEDQUASI‑THREE‑DZ蛇NSZONALGROUND

HODEL

Takeyasu su2:uki and Sat.oshi flara
Znst･

const･

Tech･･

Kumagai

Gumi

Col,

Ltd･′1043

Shimoyama,

oni9akubo′ Tsukuba City′エbaraki pref･ 300‑22′ JapanINTRODUCTION

As a practical model which evaluates ground motions ofirregularly bounded surface ground during earthquakes, thequasi‑t･hree‑dimensional ground model was proposed (Tamura andsuzuki･ 1987)･ Zt･ was extended to the model which can takefundamental through arbitrary n‑th mode of shear vibrations
into consideration (suzuki and Unami･ 1991) and is capable ofconducting non‑linear analysis adopting the equivalent linear
method (suzuki 1991)･ This paper provides the prediction
results of the earthquake ground motions of Ashigara valleysites using computer code ･･EXQ3D･･ which was coded by theauthor for the ext.ended model.
舶ODELZ村G

The modeling procedure used is a simplified hybred model of

two‑dimensional finite elements and mass‑spring‑damper sys‑
tems･ As illustrated in Fig･1, Soil masses are connectedeach other by a finite plate element･ The model is tvo‑
dimensional one but it can deal with three‑dimensionasl soil
profiles and boundary conditions of a surface ground. Boththe time for computation and the effort for modeling are muchless than those by 3‑D finite element procedure. The areamodeledlinearistheanalysisr叫‑
isof3･O

carriednon‑lineaとanalysis

iskmx

l･5

km

alo叩theoutforaweakevent′appliedforastrong

event.

valley･A

whereasasincethesurface of the layer named as os‑2 is regarded as the rigid
base in modeling･ the response at KD2 is correspondent withthat of RRl except for the existence of phase difference dueto the travelling time from xRl through KD2･. The input
ground motions are applied with the consideration of wave

propagation from a epicenter with the velocity of 1500 m/see.
COXPtJTED RESULTS AND DZSCtJSSZON
peak

accelerations′velociues

anddisplacements

atxslandxs2 Computed by ''EXQ3D･･ are summarized in Table l･ Comparing
the computed peak values with observed ones at RSl for asmall event･ computed responses in EW direction are muchsmaller than observed ones and the analysis does not neces‑sarily glVeS a good simulation･ For a strong eventr however.
thecomputedresponses

at

bothKSlandxs2

brought

about

reasonable ground responses which represent the predominantvibrations orlglnated from the geological condition of thevalley; the ground motions in EW direction. which is thedirection of major axis of predomonant vibrations･ are highlyamplified.

‑147‑

CONCLUDZNG RE紙ARRS''EXQ3D'l was applied for t･he predict･ion of eart･hquake groundmotions

atAshigara

Valleyprediction

sites･

The

predominantvibrations orlglnat･ed from t･he geological struct.ure of t.heblind sites Were obtained through the analysis for a strong
event･

工t

wasconflmed

that

theproposed

methodiscapableof comput･ing effect･ively t･he eart･hquake ground not.ions ofirregularly bounded

3‑D surface ground･

Table 1 Computed Peak Accelerat･ions, Velocities and Displace‑ment,s at. RSl and KS2!

I白▲●lﾂ綿ﾂ⊃;●;

Total syste■ of EXQ3D ■odel･M〕 [!]･lC] [書].【K, [;]=‑lM] [当日

1. FtJnda■ental )ode of shear yibration syste■･MIL･[;]'Ll lcl‖[折【Kl.t!r=‑【MI,･lg+

2. Second lode of shear Vibration systeb(a) Irregularly botJnded three‑dilenSional surface ground･Ml"lgl 【cJ"lYirl lK72打Iニー【M増]Plate Ele■ent I++
N.月th Jo°e of shear vibration systel･Mr何て[cr聞こ【Kr,[汀ニー[Mr･[幻K',A:.. K{;:..
(b) n‑th lode of shear yibration systeL in EXq3D lodel

Fig･l A Schemat･ic Diagram t10 Represent･ t.he Ext̲ended Quasi‑t‑hree‑dimensional Ground Model
REFERENCE Sl･ C･ Tamura and T･ Su2:uki (1987), A Quasi‑t.hree‑dimensional
Ground Model for Eart･hquake Response Analysis of Underground

託kr;訂u吉…;I. ,9%h:･1 , J,0,u̲ri｡.Inst･ Ind喧し生し一･ Universi‑ty of
2･ T･ Suzuki and X･ Unami (1991). The Ext.ended Quasi‑t.hree‑dimensional Ground Model for Earthquake Response Analysis of三器…三ur:訂1y Bounded Surface Ground･ Proc･ JSCE (to be3･ T･ Suzuki (1992), An Approach t.o Analy2:e Seismic Hot̲ionsof=rregularlyBounded

Surface

Ground,

功理工(t.o be appeared)‑148‑

Earthq.

Enq.

St.rue.