㊨ WILEY

LTTTPfーヽ ▼'叩Tr‑lr ‑I 1'

rr‑ヤtpT I ′■ニー■･ Yー'‑I‑ L '‑ ‑ ､ 叫γ ■̀ ‥■ ‑t■ i ̀ '〜L" '■ '

‑ 〜.い ■̀‑L ト̀叫 卜'̀､叫一

I: / ′̀"pl "､'̀∴′' 一日..Jl̀‑1Y'､''' 一丁一打ー巾､W､'rlや ー ‑rrT･tlー'L‑YTLY.rYl【'J.和一叫｢‑｢けーlrrWJTT･A1rl,I‑･▲｢.∫1rュJ.17･I‑]･.1,It.‑･㌧‑.
'L

r

.'

‑

'J

'.

̲

▼ヽ

̲

̲

̲

̲

.̲∴

̲

.

.

‑

●

一

･

1･

.

I

･､

ROCEEDINGS OF THE

SECOND WoRLD CoNFERENCE ONJヽ̲■FL,qA･L■暮.Yヽ1

一一

CoNTROL
Ryoto, Jnpnn
Vわ一ume 2
.7‑

J■三

L●'■

L

一

一..･■'∴､

I.･/ ニー･‑一･.一･/ r

Edited by■

TakujlL Kobori Yutaka lnoue Kazuto Seto./ .

Hirokazu lemura Akira Nishitani･∴.､ーL..

‥

̲.

;I̲‑ノ

J

∴

ヽ̲̲̲､̲,.̲.̲.

̲...

/㌔.

.̲

.

̲.

L

̲

.
I

〜

.

̲

1

.

.

.

,.

.

"I

一

一

L

▲

▲1

..

ヽヽtI

J,I/JL,‑Seismic Response Controlof Un.derground Structures Using●

Seismic Isolation Deslgn Concept
Shigekj UNJOHu, Jun‑ichi HOSHIKUMAZ), Kazuhiro NAGAYA2),
Kazuhiko MURAI3) and Takeyasu SUZUKI4)
I Head, Earthquake EngineerLng Division, Earthquake DL･saster Prel′entL･on Lh･earch Center,

Public Works Lh.earch Institute, Ministry of ConstructL'on, Tsukuba.. Japan
2 Jie∫earch Engineer, dL･tto

3 vL･sL･tt･ng Research EngL･neer, ditto
4 Group Manager, Earthquake EngL･neerLng Lh･earch Group, TechnL･cal LhlearCh & Del′elopment

lnstL'tute, KumagaL'GumL'Co., Ltd, Tsukuba, Japan

ABSTRACT
Public Works Research Institute has conducted 3‑year joint research program on seismicisl)Ialion systems for underground structures to improve the structural perfomlanCe and thesafety during earthquakes･ This project has been made through the joint research program

bctweeII Public Works Research I)1Stitute, Public Works Research Center and 17 pnvatecompaTlics. Developed seismic isolation systems for the underground structures are madeby constructing the iso)ation materia)Swith )ow‑shear modulus around the undergroundstructures to absorb the effect of ground defonnation. Five kinds of seismic isolationmaterials have been developed and the analysts and design methods for the undergroundstructureswith the seismic iso)ation systems have beenalso studied and developed･

1. INTRODUCTION
UndergrL)u)1d structures such as tunnels and p)peJines are generaJly affected by thedisplacement and deformation of the surrounding groulld during earthquakes･ In general,

therefore, the underground structures are Jess illnuellCed by the effect of earthquakes than
the structures on the groulld in which the earthquake response is amplified through thestructures.
0]日he other hand, the undergrou)1d has recent)y been starting to be developed and to

be densely used especially in urban areas･ role underground structures are ofte)1 required tobe co)1StruCted at the sites where the effect of earthquake becomes critic･aHn the desigJl,such as the siteswith sufl soil conditio)lS, the sites where the ground condition is1 128

Seismic Response Control of Underground Structures Using Seismic Isolation Design Concept

draslicaHy changl)一g, and the sites where structureswith different vibrational characteristics
are constructed c】ose】y or joint】y･During the 1995

Hyogo‑ken‑Jlanbu Earthquake, the damage to the undergroundstructures were relatively slight compar)ng the structures on the ground such as buildings

and bridges･ However, some of the underground structures such as subway station wereda)Tlaged destructiveJy･ At the Daikai‑Station of the Kobe High Speed Train, the RCcolumns were failed in shear and the upper slab was settled.
The damage to sewage systems such as cracks and dis】odgement of pipes were also

found. me Public Works Research lllStitute has been studied and developed the seismic
isolation systems for the underground structures to improve the seismic performance andthe safety by constructs)1g the isolation materialswith low‑shear modulus surrounding theunderground structures･ ne isolation materials absorb the deformation of the ground
durillg the earthquakes･ nis study was made through the joint research program between
Public Works Research hlStitute, Public Works Research Center, and 17 private compallies
including materialmakers, general contractors, design col‑Suiting firms･
In the Joint research program, major Objectives of the research and development are asfol]ows:

1) Development of Isolation Materia)s App)icab)e for the Seismic lso)atio)1 Systems2) Construction Methods of Seismic Iso)ation Materia)S3) Design Methods for Underground StructtJreSwith Seismic Isolation Systems
The final accomplishments of the research and development is compi】ed as the ''Draft

Mamal of Seismic isolation design for U)1derground Structures" in March 1998･

This paper presents the concept of the seismic isolation systems for the uJldergroundstructures and the outline of the draft design manual.

2. SEISMIC ISOLATION SYSTEMS FOR UNDERGROUNDSTRUCTURES

2.1 Concept of Seismic lsolatit7m Systems
ln general, u)1derground structures are subjected to the deformation through the interaction

between the ground and the structures. nerefore, when the stiff)less Of the structures are
increased, the f)exibiJily of the structures is decreased then the section force developed

against the same deformation iLHncreased･ Hence, the design to increase the sectioJI Or
number of reinforclng bars to ensure the earthquake force developed like usualstructures
is m)I effeclive in general. hl this case, it is effective to isolate the structures from thedeformatioJI Of the ground･mere are several ways to decrease the effect of ground defonnatioll tO be transmit tothe underground structures･ Major ways are the foJJowJngs :I) To make the underground structures flexible by decreasing the stifhleSS2) To decrease the effect of grou)1d deformation to be transmitted to the undergrouJld
structures

ne usual way, which has been employed for actua) submerged tun]1eJs and shie)dtunnels a)1d common utHity ducts, is the above 1) usi)1g neXibJe joiJltS. Whell the stiffnessof the joints are decreased, the ground deformation is absorbed at the joiJltS aJld theUNJOH, HOSlilKUMA, NAGAYA, MURAI and SUZUKl

1129

section force of the structures is decreased･ However, when the displacement developed at
the joints becomes excessive, there are cases in which such excessive displacement is not

acceptable or the specialwater‑proof joints are required depending on the performance)evel required to the structures during large earthqtJakes.

On the other hand, the above 2) includes the methods in which the seismic isolation

layer consisted of the materialSwith low shear modulus comparlng the surrou)lding soils
are constructed arot)nd the structures as shown in Fig.1. Since the shear deformation of theground is absorbed by the seismic isolation layer, the excessive displacement, which may
be developed at the specific joints, )s prevented by this methods. FurtherlnOre, Since theground deformation is absorbed, the isolation layer is effective to earthquake grounddeformation both il1 the 】ongitudina】 alld transverse directions.

Here, the method to decrease the effect of earthquakes by constructing the seismic
isolation layer around the undergroulld structures is defined as ‑TSeismic Isolation Systems

for Underground Structures'T.

Fig･l Concept of Seismic Isolation Systems for Underground Structures

2.2 Application or Seismic lsIIlation Systems
Th effect of earthquake is generally large for the underground structures under the
foIJowJng conditions based oil the past earthquake damage experiences･

1) Boulldary section where the ground conditions are critically changed
Tne effect of earthquakes on the underground structures becomes large at the sites
where the groulld coJldition is chang)ng from stiff ground to soft ground, Or from cut

groulld to embanked ground. The deformation and the strain is coJICentrated at tlle
boundary of the such sections with the cllaJlge Of grouJld conditions･1 130 Seismic Response Control of Underground Structures Using Seismic Isolation Design Concept

2) Connectioll Section of tu;o different structures
ne deformation is collCentrated at the connection section between sha爪and tunnels, or

junCtiol‑ections, by the difference of the vibrationalcharacteristics of two adjacentstructures.

Tnerefore, the application of the seismic isolation systems is effective such boundary

sectionswith different ground conditions or different structuralconditions as shown in
Fig･2･ The concentration of the deformation and the strain is absorbed by the seismiciso)ation layer and the seismic performance of the underground structures can be
improved･

Also, the transmission of shear deformation can be decreased by the seismic isolation
layer, the effect of earthquakes is decreased for the transverse direction of the structureswith wide section in which the surrounding shear stress is critical in the seismic design･
Furthermore, when it is required to prevent water from coml)1g in the structure

depending on the required performance of the structures･ the application of the seismic

isolation )ayerwith a water‑proOf function is effective both for the increase of theearthquake resistant performance and the water‑proof perfonnallCe･
l l I l I l竜 一｣= l∽ I 白

爾

ﾇ6

ﾆ

F柳菷

妨'6

6

/i
l

sheHdD霊ngTunne昌.
t

StifFSoiI●

2.3 Seismic Isolation Materials
seismic isolation materials applicable to the uJ1derground structures are required to havethe perfonnances of seismic isolation functions and the function as the back fin lnaterialS･
rrne development of the seismic isolation materials have been made for the shield‑driving
tunnels and the open‑cut type tunnels･ The required perfonnal‑CeS are aS follows:i) Low shear modulus and high shear deformability

2) High durability･ long‑terln Stability, and small volumetric changes
3) High constructionablity (for example for shield‑driving tunl1e】S : lraJ‑sponabi】ity bypumplng ln a liquid state and high filling‑up performance4) WatertightlleSS5) No dilution by ground water

6) No contaminants
Based on the above required perfonnallCeS, in the joint research program, 5 kinds of theseismic isolation materials were developed as shown in Table l･ The material

characteristics inc)udil1g meChaltical one･ such as shear modulus, durabiny, walertightness,
creep. and collStruCtionablitv were tasted usin廷develoDed materials･薄ﾂ

UNJOH, HOSHIKUMA, NAGAYA, MURAI and SUZUKI

lJ31

Table 1 Seismic Isolation Materials Developed

ConstructionMethods 膝6

ShicldDrivingTunncl 7

ﾆ

F柳葷

F7&

ﾂ

MaterialContents

ﾇBﾖ& 66Dﾖ F7& ﾂ eiSgPhtal,itaeTdabPsOonttainndgc,?,rye;tJith

Urcthan‑bascdMatcrial 標&WF

轅友

fﾇ

6

Silicon‑basedMatcrial

踐免

襷逍

6

免

襾

友

ﾇ薮"

ﾇ

F

W"

Open‑CutTypeTunnel 犯 V胞'V&&7$ﾖ F7& ﾂ goo.lyylPsT,tcaydi;nape‑typeliquidrubberwith
PrecastRubberPanel

V&&W'Fﾅ 6ﾖ FV g6 VFFVGF W7v友 W&WF

ﾇ蒙W'&W6問

Fig.3 shows examples of the mechanical properties of the developed materials obtained
through the hollow cylindricalcyclic shear tests･ meal】 materials were tested by the same

testing Jnethods.

To simulate the actual condition ill the tests, the surface soiHayerwith about 3m areassumed for the open‑cut type lunnels･ And for the shie)d driving tu11ne】S, the surface layer

with about 2() m was assumed･ me)1 the confined pressures were selected as O･5, 1･5 and
3･5 kgI'/cm2･ me cyclic loading rate is assumed as 1 Hz considering the llatural period or
the surracc layer. The strain range tested was assumed up to lO% coJISidering the largedcfl)rmatil)n during the large earthquakes based on the analytical results.

Fig･3 shows that the shear modulus and damplng ratio for Urethan‑based material,

Silicon‑based materia) andLiquid Rubber material are ahnost constant in the range of thestmiTl teStCd. And the confinement dependency was not found.

011 the I)tllCr halld, Asphalt‑based material has the strai‑1 dependcllCy ln Which when thestrain incrcascs the shear modu】us decreases and the damplng l11CreaSeS･ The confineTTleTlt
depcl‑dc一一cy is found at the slllall straiJl range but is )lot remarkablc･

For Precast Rubber Panel, the straiTl dependeJICy and confinement dependency arcrt)u‑ld･ SiTICe the precastrubber pancHs made by bi)‑ding the rubber tips by resi1‑, theprecastrubber panel has the vt)id inside the panel. The strain depelldellCy is devclt)Fed by
the resiTI Characlcristics is changed in the high strain range then the shear moduJus
decreases.

Seismic isolatiol‑ design of the underground structures has lo be made based on the

malerial characteristics as above mentioJled. Some materials have other dynamic

characteristics such as velocity depelldency. They are also obtaiJ‑ed through the necessary
tests.

2.4 CtmstructiOn Methods
Fig･4 shows the outline of the construction methods of seismic iso】atio]1 materia)S･ For theshield‑driving lull)lets, the same cl)I‑StruCtion methods of the backfi】Ho the tale void isappHcable. The materia】s are illjected to the tale void from the inside of the tunnels alld
the seismic isoJatil川layer has constructed art)und the structures. To prevent the imf)Ow of

the isl)]atil)]1 materials toward the shieJd maclline alld to construct seismic isulatioll layer

1 132

Seismic Response Control of Underground Structures Using Seismic Isolation Design Concept(∈uJ161)SnlnPOVqJt:aエS巾lソ】 2 1 1 Lh O 5 0 5 0

I/' 4 3 2 1

八%)o!le正6U!dEt!Q
○q 剴ﾓ
A

汎

剩

ｦﾆﾆﾂ

｢

!□q

00 000

綏ｶdR

剪

ｲ

I

I

A

冤■.一

I

劔=3.Std/a

劔

l

l■■

l

l
l ∫ 凵｡ ｲ

I剪

I

∫

○▲

l

I

I

一

〜

LH l7‑

I

●▲ 鳴

B

2

llI
▲■

i
10

一

10

ﾂ 僮 fP 傳!..よ 剪

3

10

3

白

10

B 貞6ｷ"" (/cL ー′(∫

鳴

1

10

O

10

一

10

3

Shear Strain

10

2

10

l

1010

Shear Strain(a) Asphalt‑based Material(∈uf16王sn一nPO≡Jt2aLJS
1 1 2006420(%)o!tetj6U!du)t20

ll O■一 △■● ロ■' 冤JHLTII =0̲SkzE/‑ =L.SkLE/‑ =3.5k‑/‑ 劔 I

54321 0 0 0 0 0 0日日川lll 劔● ▲ ■ 冫I=0.3klf/a q一=LSkd/cd qt=3.5bf/cJ 剪

】 劔剪

l 唐

白 EL

一

■

一

10‑3

10

■

■

l

I
10

一

2

10

1

10

O

lot.

10‑)

10‑2

10‑L

10‑0

Shear Strain

Shear Strain(b) Urethan‑based Materialsn(uJuJ 6q)snlnPOMJdauS
ll 2 0 8 6 AT 2 0.｣tl 劔ll1 僣ll(%)o!lt2t]6U!duJt20

I

5 4 3 20 0 0 0‖

l諜 ﾂ 8=3. 6ｷFb
a 4｢
信; 剴ﾓ

○

爾 噸 綏ｶB 爾 蔬ﾅ6ｶB R｢ 蔘2 FB

ｲ

l
10‑.

ﾂ

10‑J

i

10‑7

101'

101.

■

ﾈ爾

■●

10‑一

■

10‑'

Shear Strain● ■■■■

10‑2

10

t

lO

O

Shear Strain(C) Silicon‑based Materials(uJuJ16王snlnPOLqJ｡0エS〜

ll2 0 8 6 4 2 0】

lH
l

ｴ

H l

l

D姪ｴ

〔コ■■

ﾗ

Cﾓ

剴ﾓ2ﾆ

絣

劔棉C

ｶH

冀t/d｣

冤

ﾂﾒ

免

+ql Aq+ ■〇一 剴ﾘ ｲ ｶBﾂﾓ 綏&bﾄｦ4｢ ﾓ2 $ﾂ Hlo!)｡∝6uJdEt2Q

q

白

I 倚ｳ

E)

ﾂ

鳴

1

I
10‑.

l 綿

10‑2

r

f

l

10‑'

ﾂ

10‑L

10‑一

10‑0

白
10‑3

■

ｸ

免ﾂ
10

2

10

t

10‑0

Shear Strain

Shear Strain(d) Liquid Rubber Materials(uJuh6王snrnpoMJdaLJS〜

訓 40 30 20 1 0 0

Jlr

冤tll

川t

Oq A■

b

&b 7" $R

剪
●▲■

E)

l

ﾘ

ﾂ

爾 噸 &b

ﾖﾂ綏$R x 蔘2絽G ﾆb

o!lt2正6uJduJt20

劔

321 0 0 0 ハV

■■

A

̀1

I

ll

2

劔

Jr

○

I一

10

10‑'

10‑3

10‑I

10‑●

10‑'

10‑‡

10

■

10ーO

Shear Strain

Shear Strain(e)Precast Rubber Panel
FI'g･3

Dynamic Mechanical Properties of Seismic Isolation Materials Developed

UNJOH, HOSHIKUMA, NAGAYA, MURAI alld SUZUKl

1133

cerlain]y in the tale void, the shield machine requlreS the innow prevention devices but notimportant remodeling･ For the open‑cut type tunnels, the seismic isolation layer can beconstructedwith the constructioll Of the tunnels. In the joint research project, bothconstruction methods are verified through the construction tests of the seismic isolation
layer.

･l‑〜

8年Ckfit‑I‑□ [≡≡蛋表書≡∋
普(a) Shield Driving Tunnels
Fig.4(b) Open‑Cut Type Tunnels

0utline of Construction Methods

3. VERIFICATION TESTS OF THE EFFECTIVENESS OF SEISMIC
ISOLATION SYSTEMS

3.1 Test Models
To verify the effectiveness of the seismic isolation systems, the modeHests were madeusmg large shake table aHhe Public Works research lnstitule.
Fig. 5 shows the scale of the model. Tunnel is assumed to be constructed at the change

sectiol‑ Of ground collditions. ne tunnel was the almost 1/70 size of actual structureswitha diameter of 70mm and the thickness of 2mm･ The ground was made of Silicon where
the soft soil was assumed to have the shear modulus of lkgf/cm2, and the stiff soil was
assumed to have the 20kgf/cm2･ seismic isolation layer was assumed to have the thickness
lOmm and the shear modulus of O･05kgf/cm2･

ne model was subjected to the silluSOidalground motion and the rat‑dom earthquakegrou)ld motion. Since the natural frequency of the lnode】 was 6.5Hz, the sinusoidalwave

with the natural frequency of the ground was lnPuHO the shake table.

3.2 Test Results

Fig･ 6 shows the typical test resuJts･ In the right side section where the ground co)1dition is1 )34

Seismic Response Control of Underground Structures Using Seismic Isolation Design Conceptchanged, the seismic isolation layer is constn]cted･ The strain in the tunnels in thelongitudinal direction developed at the change section of the ground conditions wasdecreased by 30% by employing the isolation layers. TTIis was thealmost expected
effectiveness through the analysis･

Fig.5

Model for Shake Table Tests

4. CONCLUDING REMARKSThe preceding pages presented an outline of 3‑year joint research program on seismic
isolation systems for underground structures to improve the structural perfonnance and thesafety during earthquakes･ mere is an idea of the seismic isolation system for theunderground structures Ions time ago, but the isolation materials and the collStruCtion
methods applicable for the systems had not yet been deve】oped. ¶lrOugh tl‑e joint research

program, 5 kinds of seismic isolation materials have beel‑ developed and the analysts anddesign methods for the ullderground structures with the seismic isolation systems havebeen also studied and developed･ The fillalaccomplishment is complied as a 'IDraft

Manual for Seismic lsolatiol‑ Design of Underground Structuresr.･ Since the draft manuaHs
I‑0w ullder prilltil一g, it will be available in around June.

This research is olle Of the first steps to realize a new earthquake resistallt StruCture･ We
are plann)ng to study furthermore about the practicalapplication of the isolation systems
and the verification tests uslng full‑scale structures should be studied.

UNJOH, HOSIIIKUMA, NAGAYA, MURAl and SUZUKl‑W 一一‑一一W 友

ﾇ6

ﾆ

1135

F鑓

thoutlsolation(oLut. uJ)ut. tZJlS一t2!XV

300

200

Distance (cm)(a) Strain Distribution in Tunnel Model in The LongitudinalDirection(Sinusoidal Input : 6･5Hz, 150gal)
2500

2000
(oLU!L J)U!?JISlt2!×V

1 500
1 000

500
0

‑500
rl‥HL 【H■ーh

0 50 00 0

‑2000

∴十°十
守.:'..

lf･･i= ‑I:L=･l t'f･i ttT･=J] I:;.‑=J l;;･･= ';= LT:T,: ‑i=･== tfi.:

‑2500

1.5

0.5

Time (S)(b) Strain Response(SinusoidalInput : 6.5Hz, 150gal)(oJu!uJ)u!t2jlS一t?!XV

6 4 20 0 0 0 0 0

2 4 6 08 0 0 0 0 0 0

0

1

1.5

2

2.5

3

Time (S)(C) Strain Response (Earthquake Wave)
FI'g.6

Test Results of Shake Table Tests

3･5

4

4･5

1136

Scismic Response Control of Underground Structures Using Seismic Isolation Design Concept

ACKNOWLEDGMENTS
This study was made the joint research program between Public Wl)rks Research Institute,
PubHc Works Research Center and 17 prlVate firms･ The authors thankal] members of thejoi)1t research program who have conducted research and development eagerly･ Illparticular, Mr･ Isao TAKATORI, Director of the Public Works Research Center for theirfaithful co)1tribution to the joint research program.

REFERENCES

1) Public Works Research Institute : Report of The Disaster Caused by the 1995 Ilyogo‑ken Nanbu
Earthquake, Journal of Research, Public Works Research Institute, Vol･33, March 1997 (inEnglish)2) Public Works Research Institute, Public Works Research Center, 17 Private Firms : Report of
The Joint Research on Seismic Isolation Design of Underground Structures Vol･l and Vol･2,
Joint Research Report, No.154 and 192, November 1996 and December 1997, (ln Japanese)

3) Public Works Research Institute, Public Works Research Center, 17 Private Firms : Report of
The Joint Research on Seismic Isolation Design of Underground Structures, ‑ Draft Manual for
Seismic Isolation design of Underground Structures ‑, Joint Research Report, March 1998 (Under
Printing)

4) Unjoh, S., Hoshikuma, J., Nagaya. K, and Murai, K: Development of Seismic Isolation Systems
for Underground Structures and the Mechanisms of Seismic Isolation, 7th US‑Japan Workshop
on Earthquake Disaster Prevention forLifeline Systems, November

4‑7, 1997, Seattle,

Washington5) Suzuki, T, and Tanaka, T : Research and : Development on the Seismic Isolation Systems

applied to Urban Tunnels (Part‑1: Development of Seismic Isolation Materials and Construction
Methods), 7th US‑Japan Workshop on Earthquake DJ'saster prevention for Lifeline Systems,
November 4‑7, 1997, Seattle, Washington
6) Tanaka, T, and Suzuki, T : Research and : Development on the Seismic Isolation Systems
applied to Urban Tunnels (Part‑1: Effects of Seismic Isolation and Seismic design), 7th US‑Japan

Workshop on Earthquake Disaster Prevention for Lifeline Systems, November 4‑7, 1997, Seattle,
Washington
7) Unjoh, S., Hoshikuma, ∫., Nagaya. and K, Murai, K: Draft Manual for Seismic JsoJation Designof Underground Structures, 30th UJNR Joint Meeting, May, 1998, Gathersbarg