NEW SEISMIC ISOLATION DESIGN FOR URBAN TUNNELS INCONSIDERATION OF SLIP AND ITS APPLICATION TO ANACTUAL SHIELD‑DRIVEN TUNNEL
Takeyasu SUZUKI
Chuo Fukken Consultants Co., Ltd., 2‑ll, Nihonbashi Oodenma‑cho, Cuo‑ku, TOKYO 103‑0011, Japanlsao TAKATORI
Public Works Research Center, 1‑6‑4, Titoh, Taitoh‑ku, TOKYO 110‑0016, Japanlchiro OKADA
Nippon Civic Engineering Consultant Co., Ltd., Nishi‑nlPPOri, Arakawa‑ku, TOKYO 116‑0013, Japan

Ryqji HAGIWARA
Chiba National Highway Work Oがce, Kanto Regional Development Bureau, MinistlT OfLand, InPastructure

and Transport, Japan, 5‑27‑1, Tendai, Image‑ku, Chiba‑ski, CHIBA 263‑0016, Japan
ABSTRACT: A new seismic isolation technology ln Which a slip easily occurs between a stmcture andits peripheral soil or back‑filling material has been developed･ Such slip takes place by coatlng the outersurface of structure with a particularsilicone palnt Of water emulsion type with kinetic friction coefficients as

low as 0.15. In this paper, seismic design method of urban tunnels in consideration of slip is described first･Then, seismic isolation design is applied to an actual shield‑driven tunnel･ Seismic isolation design isconducted, focuslng On the tunnel portion at connections with vertical shafts. In this design, authors propose

the combined use of an isolation layer and segments coated with slipplng material, for the purpose ofminirmzlng cost and improvlng isolation effect.Asa result, this technology lS Proven tO be more effective
and less expensive than the conventional measures.

1 INTRODUCTION

comenced a three‑year JOlnt research prq】ect to

The Hyogo‑ken Nanbu Ea血quake of January 1995

underground structures. The design method wasdamaged not only building and bridge structures but

established, as well as the development of seismic

develop the seismic isolation technology forunderground structures, Some of which such as theisolation materials and construction methods uslng

Daikai Station on the Robe Rapid Transit Railway

these materials, for the seismic isolation structure of

were heavily damaged (Suzuki 1996)･ It is?Ssential

underground structures. They were compiled andto guarantee the operation of corrmunlCations,published in September 1998 as "The Undergroundelectnclty, gas and water supply, and other lifelines

Stmcture Seismic Isolation Design Method Manualin regions Struck by large earthquakes. To achieve(Dra町'(PWRI et al. 1998).

this goal, the safety from strong earthquakes ofutility tunnels thatare typical underground structures

This technology was applied to the connections with

provided to concentrate these lifeline services should
be preserved. In addition, while the earthquake

both a departure and an amival vertical shafts ofresistance of underground stmctures must be

shield‑driven tunnel, in the construction of the No. 1
Nakagawa utility tunnel, Nagoya (Unjoh et al･

improved, the public is demanding that the cost of1999). The seismic isolation design fわr the tunnel

their constmction be reduced.

was conducted in 1988

and its constmction work

was camied out at the departure shaftin 1999 and at
The seismic isolation structure that was

the departure shaftin 2000. The effectiveness ofdeveloped fわr underground structures is a structure

the completed isolation structure was verified bythat can sharply reduce the effect of earthquakes byconductlng a large scale in‑situ loading experimentforming aflexible seismic isolation layerarOund the(Unjoh et al. 2000).

outer periphery of an underground structure to

insulate the underground structure from deformation

The largest problem in this technology, however, lS

of its peripheral grPund (Suzuki & Tamura 1995)･

costliness of the isolation material, which is a

The research on selSmic isolation f♭r undergroundmixture of siliconerubber material and fly ash. In

structures was initiated by a few englneerSorder to reduce construction cost,therefore, a new

individually at the end of 1980S (Suzuki 1990,

seismic isolation system, in which a slip easily

Takeuchi 1994, Kawashima 1989). Right a洗er theoccurs between a stmcture and its peripheral soil orearthquake, the Public Works Research Institute of
the Ministry of Construction, the Public Works

back‑filling material by coatlng the outer surface of

Research Center and 17 pnvate companies havedeveloped (Suzuki 良 Katsukawa 2001a).

the structure withparticular

paints, has been

2

ELASTIC SEISMIC ISOLATION LAYER

L Lo o 4 2 0 0 ′0 4 2

AND SLIP MATERIAL●SⅠSM0‑7(a u /〜)9'SntnpOMJVaqS■ ◆ ▲ uE4ﾓ ﾓR 8uE4ﾓ ﾓ2 8uE4ﾓ ﾓ

The typical material to formelastic seismic isolation
layer is the silicone‑based isolation material. By

mxlng two types Of liquid A and B immediately..●亳

before Injection, the injected material that filled avoid becomes solid mbber in the undergroundi一■■ 劔 劔劔

‑坪◆

circumstance. Liquid A is the mixture of silicone oil◆◆and fly ash, in which fly ash is a filler used toincrease the volume. Liquid B, on the other hand, isll

the catalyst. This isolation matedal is elastic, shear

0.0001▲i

modulus of which can be controlled. Fig.1 shows
shear

6ﾂ

冤 汎ﾈ

0.001

2

▲▲i

0.0

lll

1

0.

1

1

Shear Strain, †moduli obtained from hollow cylindricalFig.1 Strain‑dependent shear moduli ofdynamic simple shear tests on the silicone‑based

silicone‑based seismic isolation

isolation matedal, SISMO. There is no strainmaterial (SISMO).

dependency ln Shear moduli as shown in the figure.

SISM0‑I through 7 in the figure denotes a productnumber for the seismic isolation material, where
慧EFur… ilntkhrgof/ucgmh27 at the end mean values of shew

The slip material developed for undergroundstructures is a particularsilicone palnt Of water
emulsion type･ Photo･l shows the spray coatlng On

shield segments with the palnt. Segments coatedwith such slip matedal are called "slip segments" inthis paper. When backfilling materialsare Injectedduring shield ddving to a tail void, which exists in
between segments and their peripheral ground, thepalnt absorbs water血.om backfilling materials or its

peripheral ground･ A lubricant layer composed offillers with small particles and water is formed
between a film of the palnt andthe outer surface ofsegments. Kinetic friction coefficients of the

Photo.1 Spray coatlng On Shield segments withslip material.

material obtained by hollow cylindrical dynamic

tTestData

sheartests are summarized in Fig.2. As shown in the‑ApproximationFomulaユ')uap!J aou o!)3!Jh3!)au!X

figure, It is clear that the coefficient is dependent on

effective confined pressure. The kinetic friction

coemcient used in seismic isolation design,
therefore, is glVen by the approximation fomula in
the fbllowings (Suzuki & Katsukawa 2001b).
FL ‑ 0.142+ 0.615exp(13.941g)

0

0 .4

3

(1)

where, FL and J denotes kinetic friction coefficientand effective confining pressure, respectively.

3

SEISMIC ISOLATION DESIGN METHOD NCONSⅡ)ERATION OF SLIP

0.0

0. 1

0.2

0.3

0.4

0.5
つ

Effective Co fining Pressure, G (N/mm‑)

The method of seismic isolation design inconsideration of slip on the outer surface ofsegments is

Fig･2

Kinetic加･ction coefficients of slip material

axISymeteric model.

fundamentally identical with thatapplied to the seismic isolation layer. The computercode "EASIT", which is a computer program ofaxISymmetdc丘nite element model. 也 the upperstatic analysis based on axISymmeteric finite

part of the figure, a tunnel is constructed crosslng

element model, is used in the design (Suzuki 1996).

the boundary between a soft soil deposit and a stiff

Fig･3 illustrates a schematic representation of thesoil deposit. The lower part of the figure represents

the axISymmetedc modeling of the ground andGround Surface

tunnel condition in the upper part, ln Which a tunnel

center line is set to be a symmetric axis. It isessential, therefore, that a special consideration

should be taken in modeling the effects of groundsurface, boundary conditions

and seismic load.

Then, if a method to convert seismic load in theaxISymmeteric model to make ground displacement∬Ound a mnnel equal in boththe upper and lower

figures is defined, a simplified procedure, evaluatlng
three‑dimensional interaction
tunnel, can be developed.

e飴cts

aroundaSuch a conversion

technique was developed and it was co°ed as thecomputer program "EAS汀" (Suzuki 1996)･ Thus,

the interaction between a tunnel body andsu汀Ounding soil can be ngorously evaluated byfinite elements with a specified stress‑strain
relationship.
l
1

A slip on the outer surface of segments is taken into

Fig.3

Schematic illustration f♭r axIS)Ⅶ皿etdc

modeling used in EASIT

consideration by applying a bilinear approximation
to the shear stress ‑ strain relationship of thin丘nite

elements covenng slip segments. The approximation

I 7f

is illustrated in Fig･4, in which 7f denotes the critical‑‑AGs

shear stress, which is coincident with frictional
stress glVen in the fbllowlng equation:
Tf‑FL･C'(2)1γ

where, FL andロ･ denotes kinetic friction coefficientand effective confining pressure, respectively. In theseismic isolation design, the effective confiningpressure at a tunnel center is calculated丘rst. Then, akinetic friction coefficient of slip segments adopted
is calculated using equation (1). Iteration analyses∬e ca汀ied out with a judgment whether a slip occurs

or not on the outer surface of slip segments.

Fig.4

Bilinear shear stress ‑ strain relationshipfor elements covenng slip segments
modal vectors as shown in Fig.5(C).

Fig.5 shows a schematic illustration to demonstrate aprocedure of analysis conducted in the seismic
isolation design. Prior to an axISymmeteric丘nite

4 GROUND AND TUNNEL CONDITIONS

element analysis uslng EAS汀, ear山quake response

analyses of surface deposits are camied out first, as

The seismic isolation design method shown in theshown in Fig.5(a). These are one‑dimensional

multiple reflection analyses with eqi‑linear

previous chapter was applied to the shield‑driven
tunnel planned as a utility tunnel in Chiba National

technique･ Then, the earthquake input motion at

Highway

bedrock (denoted by E+F in the figure) and values ofDevelopment

soil stiffness and damplng factor of surface deposits

Infrastructure and Transport, Japan. The outercan be obtained. The multiple degree of freedom

diameter of the tunnel is 5450 孤. The thickness of

system (MDOF) is fわrmed in the next step andshield segments is

modal analysis is carried out as shown in Fig.5(b).

longitudinal section which illustrates soil profiles

Then, a single degree of freedom system (SDOF) forand a longitudinal alignment of the shield‑driven

Work

Office,Bureau,

275

Kanto

Ministrym. Fig.6

RegionalofLand,

shows thefundamental mode of vibration of the surface deposit

tunnel, including vertical shafts. The total length ofis derived. Static external forces or seismic

the tunnel is

5.4

km. The constmction of sevenaccelerations loaded to the axISymmetric model isshafts, whichare composed of 2 departure (EITl,

calculated, by multiplying response maximum

E7T7), 1 amival (E4T4) and 4 intermediate shafts

acceleration obtained by the SDOF system by the(E2T2, E3T3, E5T5 and E6T6), ∬e planned in thisMultiple rene ctio A analysis

2E

usmg e qli‑le ne aLiZ:血en

十I
Desl酢Earhquake

I叩ut Mロ血nconverged soil S此ess
Eq山valent血mping factor, heq
÷士Earthquake input

EI IF ⊂‑ E+F a;hTi'JaTieALpov:k(1〕 Earthquake reSP OnSe andySis of swface deposit

岬AxiSyrEtmeteric bite element m叫ySis using EASIT

甘[4,]1β1

Response acceler血on spectnutt

Modehg MDOF system Mロdal吐ndysis andTl

SDOF system(2) MQdal analysis and forma血of SDOF system

Fig.5lb]1βSa(Tl･heq)(句Max. feSPOnSe OfSDOF sStem弧d calcul血on of
野Oumd acceleratin as extemd force uSed血EASIT

Flow of analytical procedure conducted in the seismic isolation design

Tota一 Length L=5414m

TL=650mL=1081mL=1031mL=946mL=1059mL=647m1
l iflTl

4S%C"/E3'3 艇/E5'5 ぴ▲‑‑YA 辻ﾓBｲ箚覿

蜥ﾒﾘ,BI..‑....‑i‑醍 偬 ｢罎粐篦

油壷排i≡

盛垂仙

Fig.6

匹r粐罎

剪

I‑::

Longitudinal section to represent soil profiles and tunnel alignment

section as shown in the figure. The tunnel is aligned

occu汀ed at plate boundary deep ln the ocean. The

deeply, in order to avoid the influence ofTYPE‑2 ea血quake motion, on the contrary, lS theliquefaction in shallow sand layers, Asl and Dsl andmotion onglnated from a near‑field earthquake. Boththe tunnel is driven through diluvial layers. The

types of ea血quake input motions are considered inearthquake resistant perfomance of the tunnel,

the seismic design.

therefわre, lS relatively high in the ordinary tunnel

Results of earthquake response analyses of surface
portion, even though a large ea血quake motion is set

as a seismic lnput in a seismic design. The seismic

performance agalnSt a large earthquake for thetunnel portion at a connection with a vertical shaft,on the contrary, is not necessarily high in general.

The authors made the seismic isolation design,
therefore, Only focuslng On Such connections.

soil deposit at the vertical shaft, E7T7are illustrated
in Fig.8, in order to describe representative results ofanalyses at 7 sha氏S. Converged shear moduli shownin (b) in the figure were used in the formation of a
MDOF system for modal analysis and for anaxISyrrmetriC

finite element model. Converged

damping factors, On the contrary, were used to
calculate the equlValent damplng factors, heq for a
5

EARTHqUAKE RESPONSE ANALYSESSDOF system of fundamental mode of shear
vibration･ The predominant period of the SDOF

Ea血quake response analyses of su血ce soil

system or surface soil deposit at E7T7 is 1.63 s fordeposits were camied out uslng a representative soil

TYPE‑I and 1.65 for TYPE‑II earthquake motions.

profile close to each vertical shaft･ Input earthquake
motions used in the analyses are illustrated in Fig･7･The equivalent damplng factor, heq lS O･13

for

TYPEII and O･ 14 for TYPE‑II earthquake motions.

These are usually adopted in seismic design of road

Then, ground acceleration profiles shown in Fig.8(d)bridges as Level 2 earthquake input motions･ The

was obtained by SDOF analyses. Inthis case,there

TYPE‑1 motion denotes a large earthquake motion

is no large difference of acceleration profile between

‑

l

鳴

5

10

0

lJ

15
Time

l

l

20

25

30

0

剿ﾂ

5

I

10

(S)

鳴

15
Time

I

20

25

30

(S)

Fig.7 Input earthquake motions (2E) used in earthquake response analyses of surface soil deposits

shear Modulus (N/mm∠)
0 IOO

200

300

400

Acceleration (gal)Damplng Factor
0.00

0 100200300400500

0.25

0

相田"ItltI"H!tlt"tltI"田垂:畏5●誕‥(a) soil profile

Fig.8(b) shearmoduli(C) damping factors(d) acceleration profile calculated

Dynamic properties obtained from earthquake response analyses of surface soil deposits

and acceleration profiles used as an extemal force in axISyrr‑etric analyses for E7T7

0

50

100

1

50

200

Distance丘om the imer wa皿of a vertical sha允(m)Fig.9

Axisymmetric丘nite element mesh fわr E7T7

the two types of earthquake input motions.

modeled. The seismic load, which is a product ofseismic acceleration given by Fig.8(d) and ground

6

AXISYMMETRIC ANALYSES BY EASIT

mass, is loaded to each nodal polnt With the special
procedure of conversion on loading constructed for

EASIT (Suzuki 2000).

Modelingand cases in analyses
After

丘nishing earthquake response

analyses of

surface deposits at every vertical shaft,axISymeteric fimite elementanalyses uslng EASIT

Three cases of connection structures at verticalsha氏s as shown in Fig.10 are dealt with in thewere camied out. Fig.9 illustrates an example of aanalyses. The case of seismic isolation layer denotes

fimite element mesh, modeling ground, tunneland
verticalshaft, E7T7･ As shown inthe figure, surface

that a seismic isolation layer composed of SISM0‑5

ground in a range 200 mfrom a vertical shaft is

thickness of 70 孤 covenng segments and with ashown in Fig.1 is applied to the connection with a

B ackfilling material

Back丘111ng matenal

S示itnlIlよ;叩▲sCgmLLnL ILn)ngt(a) Rigid Cormection

Fig. 10▲

slip segmemts(b) Seimic Isolation Layer▲(C) Isolation Layer + Sl申Segments

Cases on JOlnt Structures With a汀ival and intemediate sha触considered in analyses(tr[3)luaI)aUt!Tds!Q(u3) u2‑93qds!Q
∠U420

8

6

4

2

0
0

20

40

a)

80

0

1(氾120 140 160

Distancefrominner wa皿ofvertical shaft(m)

20

40

60

80

1(カ120 140 1成)Distancefrominner wan of vertical shaft(m)(a) Tunnel displacerrEnt distribution(a) Tunnel displaceI化nt distribution

伽Ⅹ10‑6u!t2])SaJ.
u!t!J)S･du(ロ

0

20

40

60

80

棚 加

0

1(氾120 140 160

II‑

｣LI

‑1

l

1

喜.●L

0

1

剪

20

40

60

80

100120 140 160

仲) Tunnel straindistribution仲) Tunnel straindistributionOd)9310Jat!SuaL

20

Distancefrominner wan of a vertical shaft(m)mstancefrominner wa皿ofvertical shaft(m)価 (邑93,05･dLuO3

山 03 鮒 の 仰 加‑日日Isolationhyer‑

40

yep‑

60

80

100

TYPE‑Ⅰ

120

140

160

0

20

40

60

80

1CO

120

140

160

Dktancefrominner wa皿of vertical sha氏(m)Distancefrominner wall ofvertical sha允 (m)(C) Tunnel axial force distribution(C) Tunnel axial force distnbution

2 2 1. 5 0 5育)冒)u!of50的u!uado

Loo 0 5 0

0

20

40

60

80

100120 140 160

Dktancefrominner wall of vertical sha允 (m)':i: :i(d) Distribution of opening atring joints
3(tu)'ds!pa^!)t!tq(u3).ds!pa^!)t!pv

0

0

00 4

0

5

10

15

20

htancefrominner wall ofvertical shaft(m)

0

5

10

15

20

Distancefrominner wall of vertical shaft(m)(e) Relative disp･ between seg汀Ent and peripheral so且

Fig.ll Results ofanalyses at E5T5 due

to tensile defamation

Fig.12

Results ofanalyses at E5T5 due

to compressive deformation

0 ′LU 4(u ) uaua3t!tds!Q(∈3) uaua3dlds!Q

JTY蒜‑tTl
一一一一一一一一.‑.RigidConnect.

‑‑‑ⅠsolationLayer‑Ⅰso.Layer+Slip

0

20

40

60

80

100

120

140

0

20

60

80

100

120

140

(a) Tunnel displacement distribution(a) Tunnel displacement distribution
600xl0‑6

3.Oxl0‑3
u!t!J)Sat!SuaL

40

Distance from inner wall of vertical shaft(m)Distance from inner wall of vertical sha允(m)2211O 50505

0

20

40

60

80

100

120

0

140

20

40

60

80

(N1)93JOJ'duou

211 0 5 0 5 0

40

60

80

140

■:i.･.去100xlO3(Nq)9310JaT!SuaL

20

120

(b) Tunnel strain distribution(b) Tunnel strain distribution

0100

Distance from inner wall of vertical shaft(m)Distance from inner wall of vertical shaft(m)

100

120

0 ∠U 4

0 0 0

140

0

Distance from inner wall of verticalshaft(m)

20

40

60

80

100

120

140

Distance from inner wall of vertical shaft(m)(C) Tunnel axial force distribution(C) Tunnel axial fわrce distribution(u )S)u!orJo叫u!uado

0

20

40

60

80

100

120

140

Distance丘･om inner wall of vertical sha允(m)(d) Distribution of opening at ring joints̲ ̲ゝ̲̲f=;I‑;=I=‑‑Ls(u ).ds!pa^!)t2ta出

2 2 LLoo 5 0 5 0 .5 0(u ).ds!pa^!t ZP由一一一一一一RigidConmect.

‑一一ⅠsolationLayer

00 8 .4‑Ⅰso.Layer+Slip…一……HlTYPE叫

‑

0

5

10

15

20

Distancefrom inner wall of vertical shaft(m)(e) Relative disp･ between segment and peripheral soil
Fig･13Results ofanalyses at E4T4 due

to tensile defbmation

0

"ﾕ

5

10

15

20

Distancefrom inner wall of vertical shaft(m)(d) Relative disp. between segment and peripheral soil
Fig.14

Results ofanalyses at E4T4 due

to compressive defamation

total length of 10.9 m from the tunnel mouth. The

thin elements covenng slip segments, a slip

case of isolation layer +slip segments, on thephenomenon at the outer surface of slip segments is

contrary, denotes that seismic isolation layer isevaluated in EASIT as described in Chapter 3. The

applied to the COnneCtion only within the reglOn Of

critical shearstress denoted by 7f Was Set tO be O･35

2･4 mfrom the tunnel mouth (2 segmentrings) andN/rr‑2, because values of y'which is a product of athat slip segmentsare assembled from the thirdring･

kinetic触ction coefficient and an effective confining

Giving a bilinear shear stress ‑ strain relationship tostress, Were ranged from O･32 through O･35 N/rr‑2

for 7 verticalshafts. The results of analysesare

shown in Fig.1 1(d). The water resistance of shield‑

described on two connections withvertical shafts,

driven仙mel becomes much higher, because theE5T5 and E4T4 which represent dynamic behaviors

seismic isolation layer is composed of waterof intemediate shafts

resistant material.

and

an

amiValshaft,

respectively･The above mentioned results of analyses meanSthat

the effect of combination of isolation layer and slip

Results at E5T5

Fig.1 I summarizes results of analyses by EASIT due

segments on seismic isolation is identical to or a

to TYPEII earthquake Input motions in case oflittle larger thanthe effect of seismic isolation layer･

tensile deR)nation at E5T5, at which血e largest

Due to the examination made by血e authors, theresponse

Fig.12

seismic isolation layer was more effectivethanthe

those in case of compressive

nexible segment. Thus, the new connection

sumizeswasobtainedin7

shafts.

difference instructure, a combination of isolation layerand slip

displacement distributions between Fig.1 1(a)andsegments, becomes a new earthquake resistantFig.12(a), originatedfromthe difference in axial

method in place of previous methods with higher

stifhess. It is a characteristic feature in shield‑driven

perfomance and lower cost･

deformation. There is a clear

tunnelsthatthe stiffness in tensile deformation isremarkably small compared to compression, because

Results at E4T4

nng JOmtS absorb displacement o山y in tensile

Figs.13and 14 summarize results of analyses due todeformation. Thus,the tunnel displacement sharply

TYPE‑II earthquake Input motions atthe amiVal

decreases at the comection in case of tension, while

sha允, E4T4 uslng EAS汀in case of tensile andit decreases gradually in case of compression. Due tocompressive deformation, respectively. There is a

血e abso叩tlOn Of displacement by the seismic

simdarisolation layer and slip segments, there is a clear

displacement distribution and tunnel strain at E4T4

tendency inthe distributions of tunnel

difference in displacement distribution betweenthe

with血ose at E5T5. It is clear, however,血at血ecase of rigid connection and other two cases oftensile force of segments canbe largely reduced byseismic isolation in both tensile and compressive

applying seismic isolation todefbmations.

showninFig.13(C). This is originated from the

The axialstrain or axial force generated in tunnel

amiValshafts. The skin plate of a shield‑ tunnelingsections is remarkably reduced by applying themachine composed of steel is le氏underground at theseismic isolation, compared to a case of rigid

tunnel mouth after excavationand concrete lining lS

血e connection as

structural difference between intermediate andcomection, as shown in Fig.1 1(b), (C), Fig.12(b) andplaced inside of the plate. Therefore, there is no nng(C). Al血ough也e tensile stress of segments and bolts

JOlntS Which can absorb tensile displacement till 5.3

at nng JOlntS exceeds its allowable design value inm toward the groundfromthe mouthofthe tunnel,

case of rigid connection,the maximum tensile force

while 2 segment血gs (2.4 m) ∬e assembled insideconnection, in both cases of seismic isolation andthe plate. Inthis section,the stifhess of tunnel liming
for tensionand compression is identicaleach other,

combination of isolation layer + slip segments,andand it is much higher than血e tensile stifhess ofthe tensile stresses of bo血segments and bolts wereshield segment mg.

was reduced to a half compared to the case of dgid

settled down within their design values. The

other hand, to one fourth. The reduction rate in case

Fig.13(d) illustrates the opeming of ring joints
obtained from theanalyses. As mentioned above,theof combination of isolation + slip segments is larger

opening lnltlateS at the polnt 5.3 mfrom the tunnel

maximum compressive fわrce was reduced, on血e

血an that in case of seismic isolation layer, because

mouth. The maximum value of openlng, 3.5 mmin

the isolated length and absorbed displacement iscase of rigid connection, can be reduced by thelarger inthe former case as shown Fig.ll(e)andseismic isolation to a half, lower than its limited

Fig.12(d). 也 case of compressive defamation,

value.

however, the compressive stress of segments was

settled within allowable design value, even in case

Figs･13(e) and 14(d) show relative displacementof rigid comection.

distribution between segments of concrete limingand
peripheral soil. The small

The openlng Ofring JOlntS exceeds its limited value

amount of relative

displacement of 0.2 孤 can be seen at the tunnelof 2 rrm in case of rigid connection. It canbe

mouth in bothtensile and compressive deformation.

reduced to a half in both cases of seismic isolation as

It denotes the stmin absorpt10n by back fillingmaterialfomed between tunnel lining and concrete
wall of a vertical shaft. In tensile defomation shown(zuAuJN)S aJ)Sal!Sua1

in Fig.13(e),血e relative displacement generates
o山y within the skin plate in both cases of seismic

isolation. Thus, no slip occurred in tensile

deformation, although a slip occurs during
compressive deformation as shown in Fig･14(d)･
1

Sincethere is not a large differenceinrelative

2

3

4

5

6

7

6

7

Vertical Shaft No.

displacement between the two cases of seismic(a) Rigid connection

isolation at E4T4 even in compressive defomation,
axialforceand strain of segments and lining of both(luJuJN)S aJtSal!SuaI㍍H叩 i i 引

0 6 2 8 40 0 0 0 0 0 0 0 0 0cases are almost identical.

Summ打Y Of resultsand examinations
As a result of analyses by EAS汀, it was concluded

that no seismic measuresare necessary for vertical1

sha氏s No.3 and 6 (E3T3 and E6T6), because every

comections of residual 5

3

4

5

Vertical Shaft No.

ten of stress or displacement is withinthe design
values in both tensile and compressive defomations.
However, seismic isolation should be applied to血e2仲) Seismic isolation layer(zu VN)S aJtSal!SuaI[九川rrl.̲

0 6 2 8 40 0 0 0 0 0 0 0 0 0 0

sha氏S, in which thebeanng capaclty ln tensile stress of segment, tensilestress ofbolts f♭r mg JOlntS Or Openmg Of血g JOlntS
is over the design values. Fig.16

山ustrates anexample of the effect of seismic isolation tothe
reduction of山mel tensile stress of segments. As
1

2shown inthe figure,the tensile stress of segments is
reduced to the value lower than the design value by

the application of seismic isolation. The effect of the

3

4

5

6

7

Vertical Shaft No.

(C) Isolation layer + Slip segments
Fig.16

Reduction in axial stress of segments

seismic isolation on the reduction in tensile stress ofsegments is almost identical in bo血seismic isolation

cases. Little difference in seismic isolation effects
between two seismic isolation cases also can berecogmized even in tensile stress of bolts and(喜一d〓S

openmg of血g JOlntS.
00 4

Fig.17 summarizes the totallength of area where aslip generated on outer surface of slip segments, in
仙e case of combination of isolation layer and slip

segments. The largest length , 16.8 m occurs at No.5

1

7

3

4

5

6

7

VerticaI Shaft No.

sha允. 0山y small mount of length lower than 10 m
occurs at other fわur sha氏S.

2

Fig.17

Slip generated on outer surface of slip

segments at each vertical shaft

SEISMIC ISOLATION STRUCTURES

Due to the facts that the seismic isolation effect isalmost identical in the two seismic isolation cases
and that the total length, which is necessary to use

slip segments, is relatively short, the cost

perfbmance of the combination of isolation layerand slip segments is much higher than the seismic

isolation layer alone･ Thus, the authors proposed that

selSmC isolation structures adopting the
combination of isolation layer and slip segments
should be applied t0 5 vertical sha触.

Fig.18

Schematic illustration for the seismic

isolation structure at No.5 vertical shaft(E5T5)

̲. ▲ †■ p Ipp(a) enlarged section at the tunnel mouth

Fig･19(b) seismic isolation structure proposed

Schematic illustration for the seismic isolation structure at an arrival shaft, E4T4

Fig.18 illustrates a schematic representation of the

REFERENCES

seismic isolation structure designed for theconnection with No.5

sha氏. This represents the

Kawashima, K. et al. (1989), Research on the

structure at departure and intemediate shafts. Slipdevelopment of seismic design technology fわr

segmentsare assembled from the mouth through theunderground structures, Joint Research Reports of

20th segment nng which means 24 m in total length

at No.5 shaft, while from the mouth through lothsegmentring (12 m) at No.1, 2 and 7 shafts.

PffW, No.29, pp.208‑235 (in Japanese)･
PWRI et al. (1988), Report on joint research on thedevelopment of seismic isolation materials fわr use in

the seismic isolation design of undergroundFig.19 illustrates a schematic representation of theseismic isolation structure proposed for theconnection with No.4

a汀ival sha允. The seismic

isolation layer is famed covenng concrete lining
and segments inside the skin plate, and it is also

formed covenng one segmentring outside the skinplate. From there, slip segmentsare assembled for

10 segment dngs (12 m).

structures (Part 3), Underground Structure Seismic
Isolation Design Method Manual (Draft), Joint
Research Reports ofPW7U, No.21 1 (in Japanese).
Suzuki, T. (1989), Model vibration tests on seismic
isolation structure for shield‑driven tunnels, Proc.
the 20th Earthquake Englneerlng Symposium, JSCE,
pp.565‑568 (in Japanese)･

Suzuki, T. and Tamura, C. (1995), The seismic
isolation structure and the effect of seismic isolation
for shield‑driven tunnels, Proc. JSCE, No.525/Ⅰ‑33,

pp.275‑285 (in Japanese).

8

CONCLUSING REMARKS

Suzuki, T. (1996), Damages of urban tunnels due tothe Southem Hyogo ea血quake of January 17, 1995

In this paper, authors presented a seismic isolationand the evaluation of seismic isolation Effect, Proc.

design method and its application to connections

the llth World ConjTerence on Earthquake
Englneerlng, Acapulco, Mexico･

with vertical shafts of an actual shield‑driven tunnel.
The conclusions derived in this paper can be

Suzuki, T. (2000), The axisymmeteric finite elementsummarized as follows:model developed as a measure to evaluate(1) The seismic isolation design in consideration ofslip on outer surface of segments was applied to an

Proて･ the 12th World Conference on Earthquake

actual shield‑ddven tunnel fわr the丘rst time.

Englneerlng, Auckland, New Zealand, 2000.
Suzuki, T. and Katsukawa, T. (2001a), Development(2) Almost same effect of seismic isolation as theapplication of seismic isolation layer can be obtainedby the combination of isolation layer and slip

earthquake responses of seismically isolated tunnels,of the lubricant palnt applied tothe seismic isolation
for tunnels, Tunnel and Underground, Vol.32, No.6,

Segments ･

pp.43149 (in Japanese).

(3) The number of rings where slip segments should
be assembled is at least 10 for 4 departure andverification tests on the seismic isolation of slip type

Suzuki, T. and Katsukawa, T. (2001b), Proposal andfor underground structures, Proc. JSCE, No.689/Ⅰ‑

intermediate shafts and20

for one intermediate

sha允, while it is 10 f♭r an a汀ival sha允.

(4) The cost perfbmance of the combination ofminimum isolation layer and slip segments is muchhigher than the application of seismic isolation layer

57, pp.137‑151 (in Japanese).

Tekeuchi, M. et al. (1994), Experimental study on
the reduction in cross‑sectional stress of shieldtunnel, Proc. JSCE, No.483/Ⅰ‑26, pp.1071116 (inJapanese).

or a special nexible segment, which is the standard

Unjoh, et all (1998), Seismi? respopse.Control ofconventional seismic measure.

underground structures uslng SelSmC designconcept, Proc. the 2nd lnt. ConjTerence on Structural

Control, Kyoto, Vol.2, pp.1 12711 136, 1998.