Damage to Mountain Tunnels
by Earthquake and its Mechanism
Toshihiro ASAKURA1, Kazuhiko TSUKADA1, Takeshi MATSUNAGA1
Shigeru MATSUOKA2, Kazuhide YASHIRO3, Yukio SHIBA4 and Toshio OYA4
1Dept. of Earth Resources Eng., Kyoto University
E-mail : [email protected]
2Tekken Corporation
3Railway Technical Research Institute
4Taisei Corporation
It is generally said that mountain tunnels are little damaged by earthquake. However, recent case studies
of the damage to mountain tunnels caused by earthquakes also show that they are likely to be damaged
when 1) the scale of the earthquake is large, 2) there are earthquake faults near the tunnel or 3) there are
special conditions.
We collected information on the tunnels which suffered damage from earthquake to study the damage
mechanism of mountain tunnels. We analyzed collected data, classified damage patterns and preformed
simulation analyses and model tests. Based on the study results, we concluded that we were able to classify
damage patterns of mountain tunnels by earthquake into following three patterns; 1) damage to tunnel
entrance and portal, 2) damage to tunnels at a fractured zone, 3) damage to tunnels by sliding of fault. We
were able to prove these mechanisms by the results of simulation analyses and model tests.
1. INTRODUCTION
As tunnels are surrounded by the ground, they have
good earthquake-resistance if the ground is stable
during an earthquake. Therefore, it is generally said
that the earthquake-resistance is not necessarily
required for tunnels in the stable ground. In the 1995
Hyogoken-Nanbu Earthquake, however, 10 tunnels
among at least one hundred mountain tunnels in
service in and around the disaster area had serious
damage to need repair and reinforcement. We
reconfirmed that if an earthquake was larger, even
mountain tunnels would have been damaged.
Damage survey of the regions affected by the 2004
Niigataken-Chuetsu Earthquake is still underway,
but so far it has been revealed that among over 100
mountain tunnels, approximately 50 were damaged,
including 25 or so that required repair and
reinforcement, as well as those that sustained minor
impacts.
There are few studies on the earthquake damage
mechanism of mountain tunnels. On the other hand,
more and more tunnels have been constructed
recently in the ground of low strength and low earth
covering, to require the establishment of a method to
design mountain tunnels in consideration of the
effect of earthquake. We performed this study to
acquire the basic knowledge of the earthquake
damage mechanism of mountain tunnels.
2. DAMAGE TO MOUNTAIN TUNNELS
BY EARTHQUAKE
(1) Past damage to mountain tunnels by
earthquake
Mountain tunnels and other structures have
suffered damage from large earthquakes. Table 1
outlines the damages to mountain tunnels caused by
large-scale earthquakes that happened in Japan, from
the 1923 Kanto Earthquake to the 2004
Niigataken-Chuetsu Earthquake.
Among them,
those that affected an extensive region by giving
heavy damages in some areas were the 1923 Great
Kanto Earthquake, 1964 Niigata Earthquake, 1978
Izu-Oshima-Kinkai
Earthquake,
1995
Hyogoken-Nanbu
Earthquake
and
2004
Niigataken-Chuetsu Earthquake. The damages
observed in the 1923 Great Kanto Earthquake, 1995
Hyogoken-Nanbu
Earthquake
and
2004
Niigataken-Chuetsu Earthquake are described below.
Table 1 Past damage of mountain tunnels by earthquake in Japan
Year, Name
1923
Kanto
1927
Kita-Tango
1930
Kita-Izu
1948
Fukui
1952
Tokachi-Oki
1961
Kita-Mino
1964
Niigata
1968
Toikchi-Oki
1978
Izu-Oshima-Kinkai
1978
Miyagiken-Oki
1982
Urakawa-Oki
1983
Nihonkai-Cyubu
1984
Naganoken-Seibu
1987
Chibaken-Toho-Oki
1993
Notohanto-Oki
1993
Hokkaido-Nansei-Oki
1995
Hyogoken-Nanbu
2004
Niigataken-Chuetsu
Magni
Epicenter
-tude
7.9
7.3
7.3
7.1
8.2
7.0
7.5
7.9
7.0
7.4
7.1
7.7
6.8
6.7
6.6
7.8
7.2
6.8
Tunnel Performance
Sagami Bay
Extensive, severest damage to more than 100 tunnels in southern Kanto
( Depth: unknown )
area
7km WNW of Miyazu, Kyoto
Very slight damage to 2 railway tunnels in the epicentral region
( Depth: 0km )
7km west of Atami, Shizuoka
Very severe damage to one railway tunnel due to earthquake fault
( Depth: 0km )
crossing
12km north of Fukui City
Severe damage to 2 railway tunnels within 8km from the earthquake fault
( Depth: 0km )
Pacific Ocean, 73km ESE off the Cape Slight damage to 10 railway tunnels in Hokkaido
Erimo ( Depth: 0km )
Near the border between Fukui and Gifu Cracking damage to a couple of aqueduct tunnels
Prefectures ( Depth: 0km )
Japan Sea, 50km NNE of Niigata City
Extensive damage to about 20 railway tunnels and one road tunnel
( Depth: 40km )
Pacific Ocean, 140km SSE off the Cape Slight damage to 23 railway tunnels in Hokkaido
Erimo ( Depth: 0km )
In the sea between Oshima Isl. and Very severe damage to 9 railway and 4 road tunnels in a limited area
Inatori, Shizuoka (depth: 0km )
Pacific Ocean, 112km east of Sendai Slight damage to 6 railway tunnels mainly existing in Miyagi Prefecture
City, Miyagi ( Depth: 40km )
Pacific Ocean, 18km SW of Urakawa, Slight damage to 6 railway tunnels near Urakawa
Hokkaido ( Depth: 40km )
Japan Sea, 90km west of Noshiro City, Slight damage to 8 railway tunnels in Akita, etc.
Akita ( Depth: 14km )
9km SE of Mt. Ontake, Nagano
Cracking damage to one hydraulic power tunnel
( Depth: 2km )
Pacific Ocean, 8km east off Ichinomiya Damage to the wall of one railway tunnel at Kanagawa-Yamanashi
Town, Chiba ( Depth: 58km )
border
Japan Sea, 24km north of Suzu City, Severe damage to one road tunnel
Ishikawa ( Depth: 25km )
Japan Sea, 86km west of Suttsu, Severe damage to one road tunnel due to a direct hit of falling rock
Hokkaido( Depth: 35km )
Akashi strait
Damage to over 20 tunnels, about 10 tunnels required repair and
( Depth: 18km )
reinforce
Kawaguchi-machi, Ojiya City
Damage to about 50 tunnels, of which 25 or so needed reinforcement or
(Depth: 13km)
repair.
The 1923 Great Kanto Earthquake caused the
biggest ever damage, which has still been worst in
the history of mountain tunnel in Japan. At that time,
there were about 149 tunnels, state-owned only
including some under construction, within about
120km from the epicenter, of which 62% that is 93
tunnels were damaged by the earthquake to the point
of needing repair. Among these, 25 tunnels suffered
significant damages that needed remedial measures
and rebuilding, such as collapse of whole tunnel and
entrance. Many suffered failure and burial of the
portal area, which was caused by major landslide and
slope failure.
The 1995 Hyogoken-Nanbu Earthquake1) affected
more than 20 tunnels, including those that suffered
minor damages, among over 100 that existed in the
damaged region. About 10 of the affected tunnels
suffered damages that required reinforcement or
repair. Several tunnels were found to have collapsed
at the linings due to the displacement of fractured
zones and faults in this disaster.
The 2005 Niigataken-Chuetsu Earthquake2)
affected about 50 mountain tunnels, including those
that suffered minor damages, among over 100 that
existed in the damaged region. About 25 of the
affected tunnels suffered damages that required
reinforcement or repair. The characteristic of this
earthquake was that while it was of the
epicenter-on-land type (M6.8), not all the tunnels
within a certain distance from seismic faults were
damaged. Instead, areas where the seismic faults are
supposed to have undergone significant sliding
(sliding length of 1.0m or more) suffered notable
damages.
Compressive failure
Shear crack
Spalling
Compressive failure
Spalling
Heaving
Damage to side wall
Damage to arch
Fault, fractured zone or water inflow
500m
Nunobiki Fault
Gosukebashi Fault
400m
Otsuki Fault
Ashiya Fault
(2) Damage patterns of mountain tunnels by
earthquake
We analyzed above-mentioned data and concluded
that we were able to classify damage patterns of
mountain tunnels by earthquake into the following
three patterns.
1) Damage to tunnel entrance and portal
2) Damage to tunnels at a fractured zone
3) Damage to tunnels by sliding of fault
Detailed damage patterns are shown below.
a) Damage to tunnel entrance and portal
Tunnel entrances and portals are likely to suffer
from earthquake because they often exist in the loose
ground where earthquake motion is amplified and the
ground deforms to a large extent. The damage to
tunnel entrances and portals include the inclinations
of and cracks in portal walls and cracks in the lining
near tunnel entrances. This damage pattern is the
most popular except for damage caused by landslides
around tunnel entrances.
Typical examples are the damages to the Imaihama
Tunnel at the 1978 Izu-Oshima-Kinkai earthquake
and the Higashiyama Tunnel at the 1995
Hyogoken-Nanbu earthquake. ( Photo 1 )
The Higashiyama tunnel was constructed with
concrete blocks in 1928. The geology is a relatively
loose quaternary formation. Its earth covering is less
than 10m. In this tunnel, existing cracks expanded;
new cracks occurred in the portal wall and some
cracks with spalling occurred at the shoulder of the
arch along the tunnel axis at the earthquake.
b) Damage to tunnels at a fractured zone
If a tunnel is constructed in the ground whose earth
covering is large, it generally has good
earthquake-resistance due to the stiff rock mass.
However, a few tunnels with large earth covering
have also suffered damage from earthquake.
A typical example is the damage to the Rokko
Tunnel at the 1995 Hyogoken-Nanbu earthquake.
The Rokko Tunnel is a long railway tunnel in
Mesozoic granite with a length of over 16km. There
were troubles when the tunnel was constructed
Fig.1 Damage patterns observed in the Rokko
Tunnel 1)
Koyo Fault
Photo 1 Cracks in the portal wall of the Higashiyama
Tunnel 1)
16,250m
300m
200m
100m
0m
For Shin-Osaka
For Okayama
Fig.2 Longitudinal profile and damage locations of
the Rokko tunnel 1)
②アーチ部ひび割れ
Crack
①クラウン部圧ざ
Compressive failure
③側溝部損傷
Damage
下り線
上り線
④路盤コンクリート浮き上り
Heaving
⑤中央通路側壁コンクリート傾斜
Inclination
Fig.3 Damage to the Myoken Tunnel (Schematic
illustration) 2)
because of a number of fractured zones at high
pressure water.
1) Compressive and shear failure with spalling at
the arch
2) Compressive failure with spalling at joints
between the arch and side wall
3) Spalling of the lining at longitudinal construction
joints
These damage patterns are superimposed in Fig. 1.
Fig. 2 shows the longitudinal profile of and
earthquake damage locations in the Rokko Tunnel.
Almost all damage locations coincide with fractured
zones. The Myoken Tunnel, which was affected in
the 2004 Niigataken-Chuetsu Earthquake, was found
to have suffered the following damages shown in
Fig. 3, which were comparable to the Rokko Tunnel:
5cm
8cm
Upstream
( Sandstone
and mudstone )
5.1
m
10
.5m
Crack
Downstream
( Granite )
Fig.4 Damage to the lining of the Shioyadanigawa
River Diversion Tunnel ( Schematic illustration ) 1)
Photo 2 Damage to the lining of the Shioyadanigawa
River Diversion Tunnel 1)
1) Compressive failure at the crown (about 50m
long) and spalling of concrete
2) Cracks parallel to or slanted to the tunnel axis
3) Upheaval of side wall concrete (about 40mm)
and cracks in invert concrete
In-depth survey is still underway at the Myoken
Tunnel, but the soft site condition is supposed to have
been one of the causes of damages, considering the
fact that the bottom heading and side drift methods
had been employed in the construction work.
c) Damage to tunnels by sliding of a fault
Earthquake fault crossing sometimes causes severe
damage to tunnels by sliding of the fault at
earthquake. There are some examples of damage
such as those of the Tanna Tunnel at the 1930
Kita-Izu earthquake, Inatori Tunnel at the 1978
Izu-Oshima-Kinkai earthquake, hydraulic power
tunnel at the 1984 Naganoken-Seibu earthquake and
Shioyadanigawa River Diversion Tunnel. ( Fig. 4,
Photo 2 )
The downstream portal of the Shioyadanigawa
River Diversion Tunnel is near the Suma fault and
the middle of the tunnel crosses the Yokoo-yama
Fault. Near the Suma Fault, ring cracks occurred at
the earthquake. At the Yokoo-yama Fault, the
upstream side of the tunnel moved 8 cm to the right
and 5 cm upward relatively to the downstream, and a
number of cracks occurred in the arch, side wall and
invert concrete. The ground of the downstream side
Fig.5 Analysis model
Table 2 Analysis conditions ( in the normal state )
Earth covering
5m
Location of foundation bed
Lower end of tunnel side wall
Thickness of tunnel lining
45cm
Surrounding ground
Sandy soil
Young’s modulus of ground
E=0.75kN/mm2
Modulus of subgrade spring
k=25.7N/m3 （k=1/2×1×E-3/4）
Strength of concrete
f’ck=18N/mm2
Young’s modulus of concrete
Ec=24kN/mm2
Unit weight of concrete
γ=23.5N/mm3
of the Yokoo-yama Fault consists of granite, whereas
the upstream side consists of sandstone and
mudstone of the Miocene. ( Fig. 4, Photo 2 )
In the following Chapters, we show the results of
numerical analyses and model tests to reproduce the
above-mentioned three earthquake damage patterns
and discuss the earthquake damage mechanism of
tunnels.
3. THE DAMAGE MECHANISM OF
TUNNEL ENTRANCES AND PORTALS
We performed numerical analyses to reproduce
earthquake damage patterns of tunnel entrances and
portals.
(1) Analysis model
The dynamic behavior during an earthquake of
tunnel entrances and portals, which often exist in the
loose ground with low earth covering, is greatly
influenced by the dynamic behavior of the ground
because mountain tunnels have a smaller unit weight
than that of the surrounding ground. Therefore, we
used the seismic deformation method.
Analyses were performed by frame analysis where
a tunnel was modeled by beams and the ground by
springs. Fig. 5 shows the analysis model of a
standard single truck railway tunnel. Table 2 shows
analysis conditions in the normal state.
We supposed three earth pressure modes in the
normal state shown in Table 3 because it was
impossible to estimate the real earth pressure acting
on the tunnel lining.
Table 3 Earth pressure modes in the normal state
Model
B
Horizontal
Assumption for
pressure
pressure
load setting
None
None
Assuming that ground is stable.
K0=0.5
Assuming that φ is about 30゜.
K0=0.2
( As a load between A and B )
Loosen
Model B
Model C
Hight of loosen
bedrock H=3.87m
Hight of loosen
bedrock H=3.87m
K0=0.5
K0=0.2
σt=-0.9N/mm2
σt≒0N/mm2
σt=-0.4N/mm2
σt=-2.8N/mm2
σt=-4.7N/mm2
σt=-3.6N/mm2
( Dead load only )
Model
A
Vertical
Model A
bedrock
C
None
k=51.4N/m3 （k=1/2×2×E-3/4）
Seismic intensity
0.2
Velocity of shear elastic wave
109.5m/s
Natural period of subsurface layers
0.41s
Ground level displacement
1.23cm
During earthquake
Modulus of subgrade spring
Ground level
Load of loosen bedrock
At rest
Table 4 Analysis conditions ( during earthquake )
5m
Lateral pressure
Lateral pressure
Load caused by
displacement of ground
Fig.7 Bending moment diagram and the maximum
tensile stresses
δv
δ
δ
δh
δh
5.9m
Foundation bed
Fig.6 Analysis model ( during an earthquake )
Table 4 shows analysis conditions during an
earthquake. In this analysis, we assumed a horizontal
seismic intensity of about 0.2 to study mainly an
qualitative damage mechanism of tunnel entrance
and portal.
We calculated the ground level
displacement from that intensity and converted it into
nodal forces to use for the analysis model. ( Fig. 6 )
(2) Result of the analyses
Fig. 7 shows the bending moment diagrams and the
maximum tensile stresses in the normal state and
during an earthquake. In the normal state, the
deformation modes were different from each other
but the maximum tensile stresses at the lining were
small and no cracks occurred on the lining. On the
other hand, during an earthquake, all the bending
moment diagrams roughly looked alike regardless of
the mode of earth pressure. The maximum tensile
stresses of the tunnel lining occurred almost at the
same location on the shoulder of the arch, and the
maximum tensile stresses exceeded the tensile
strength. ( When the compressive strength is
18N/mm2, the tensile strength is 1.6N/mm2. ) This
result roughly agreed with the actual locations of
cracks caused by an earthquake at tunnel entrances
and portals, and proved that cracks could occur on
the shoulder of the arch at tunnel entrances and
portals at an earthquake of the horizontal seismic
intensity of about 0.2.
d
δv
d
Strain:γave=δ/d
Strain:γave=δv/d=δh/d
a) When an angle of incidence of shear wave is vertical
b) When an angle of incidence of shear wave is 45゜
against the vertical line.
Fig.8 Analysis models
Table 5 Analysis conditions
Young’s modulus of ground
500N/mm2
Poisson’s ratio of ground
ν=0.3
Young’s modulus of concrete
Ec=26kN/mm2
Compressive strength of concrete
f’ck=18N/mm2
Tensile strength of concrete
ftd=1.9N/mm2
Poisson’s ratio of concrete
ν=0.167
4. DAMAGE MECHANISM OF TUNNELS
AT A FRACTURED ZONE
We performed numerical analyses to reproduce
damage patterns of tunnels at a fractured zone at an
earthquake.
(1) The analysis model
At the Rokko tunnel, cracks which were slanted to
the lining occurred at the earthquake. Therefore, we
used a FEM code which was able to simulate
generation and growth of cracks. Fig. 8 shows the
analysis model. Table 5 shows analysis conditions.
We mainly focused on grasping the crack mechanism
of the lining qualitatively and simplified the modes
of shear deformation of the ground during an
Width of crack ( mm )
Width of crack ( mm )
Large
Cracks occured
0.015
Average shear
strain =1800µ
Small
Enforced displacement
a) When the angle of incidence of shear wave is vertical.
Width of crack ( mm )
Average shear
strain =1800µ
Large
0.028
Cracks occured
Small
Enforced displacement
Width of crack ( mm )
Average shear
strain =1800µ
Large
0.028
Cracks
occured
Small
Cracks
occured
Initial earth pressure
0.028
Average shear
strain =1800µ
Large
Small
Fig.10 Distribution of width of crack
b) When the angle of incidence of shear wave is 45゜
against the vertical line.
Cracks occurred at the arch crown and the center of
the invert when the ground is vertically compressed.
On the other hand, cracks occurred at the springline
of both sides when the ground is horizontally
compressed. We performed parameter studies by
changing intensity of shear deformation, we found
that the intensity affected only the width and depth of
cracks but did not the location of cracks.
From these results, we found that tunnels tend to
have cracks and compressive failures at the crown of
the arch and the springline at a fractured zone by a
large bending moment caused by earthquake.
However, the direction of crack was only vertical to
the lining and we were not able to reproduce cracks
slanted to the lining like those observed at the Rokko
and Myoken Tunnel.
Enforced displacement
b) When the angle of incidence of shear wave is 45゜
against the vertical line.
Fig.9 Distribution of width of crack
earthquake into the following two cases; a) when the
angle of incidence of shear wave is vertical, and b)
when the angle of incidence of shear wave is 45゜
against the vertical line.
(2) Effect of shear wave
Fig. 9 shows the distribution of crack width when
the average shear strain of the ground caused by
shear wave is 1.8*10-3. The crack width is calculated
by the following equation on the assumption that one
crack occurs on one element.
Width of crack = Plastic strain of the element ×
equivalent length of the element
a) When the angle of incidence of shear wave is
vertical.
As the shear strain of the ground reached 6.3*10-4,
cracks occurred at the joint between the invert and
side wall and at the shoulder of the arch at the same
time. As the shear strain became large, the width of
crack became wider the crack penetrated the lining
when the shear strain reached 1.8*10-3.
(3) Effect of initial load acting on the lining
If the strength of the ground around the tunnel is
low as in a fractured zone, an initial load like the
squeezing earth pressure may sometimes act on the
lining. We analyzed other cases with some initial
load enforced on the lining.
The direction of the earth pressure was assumed to
be horizontal.
An equally distributed load
( 80kN/m2 ) was applied at the boundary first and
then a shear strain corresponding to the deformation
caused by earthquake was added.
Fig. 10 shows the distribution of width of crack
when the average shear strain of the ground caused
by a shear wave is 1.8*10-3, where the angle of
incidence of shear wave is 45゜against the vertical
line. As the shear strain became larger, a relatively
wide crack occurred inside the springline. We
performed parameter studies by changing the
intensity of initial earth pressure, and found that the
intensity affected only the width and depth of cracks
but not the location of cracks. From these results, we
found that when mountain tunnel suffered damage
from the shear deformation caused by an earthquake,
cracks slanted to the lining like those observed at the
Rokko Tunnel occur depending on the mode of initial
earth pressure acting on the lining.
Enforced
Displacemen
Inside
Photo 3 Tunnel lining test unit
Enforced
displacement
Legend:
Alluvium assumed
( To be slided )
Outside
Crack
Crack with a gap
Loaded area
Fig.12 Crack chart ( model test )
Dilluvium assumed
( Immovable )
Sliding
direction
Upstream
( Prototype )
Soft rubber supported
( Alluvium assumed )
Hard rubber supported
( Dilluvium assumed )
Enforced
displacement
( Model )
Strut ( Steel plate )
Fig.11 Modeling of sliding of fault
Table 6 Property of model
Lining
Spring
Material
Mortal
Compressive strength
f’ck=18N/mm2
Young’s modulus
Ec=26kN/mm2
Thickness
t=2cm
Width
w=60cm
Material
Cylindrical rubber
Modulus of
K1=1,900 (N/mm) ( hard type )
subgrade spring
Modulus of
K2=80 (N/mm) ( soft type )
subgrade spring
5. DAMAGE MECHANISM OF TUNNELS
BY SLIDING OF A FAULT
We performed model tests to reproduce damage
patterns of tunnels by sliding of a fault.
(1) Testing model
We used a 1/30 scale tunnel lining test unit that
models the Shinkansen standard tunnel ( Photo 3 ).
The test unit consists of loading bolts, cylindrical
rubbers and a reaction frame. After a lining made of
mortar was set in the test unit, step loading was
carried out with displacement controlled. At all
points except the loading point, the cylindrical
Inside
Downstream
Fig.13 Crack chart ( Shioyadanigawa River
Diversion Tunnel )
springs made of hard rubber simulating the ground
were set to induce subgrade reaction proportional to
deformation. Fig 11 shows the modeling of sliding
of fault, and Table 6 the properties of the model.
To simulate faults, we changed the type of rubber
at the center of the model. The rubber on one side
was hard ( supposing Diluvium ) and that on the other
side was soft ( supposing alluvium ). The tunnel
section was closed by a strut made of steel.
Load were applied by enforcing displacements on
the side wall of Alluvium side to simulate rightward
slipping of a fault.
(2) Result of the test
Fig. 12 shows the crack chart of the lining obtained
from the model test. Cracks followed the processes
of, 1) occurrence near the fault from the left side wall
to the arch, 2) extension to the tunnel axis, 3)
rightward slipping of shear cracks and 4) occurrence
of a number of parallel cracks to final tunnel fracture.
Fig. 13 shows the crack chart of the
Shioyadanigawa River Diversion Tunnel at the part
of crossing the Yokoo-yama Fault. Cracks followed
the processes of , 5) rightward-slipping of shear
cracks occurred along the Yokoo-yama Fault, and 6)
occurrence of a large number of diagonal cracks
crossing the Yokoo-yama Fault. We found that the
mode of cracks of the model test was similar to that
observed at the Shioyadanigawa River Diversion
Tunnel.
6. CONCLUSION
We conclude that we can classify damage patterns
of mountain tunnels by earthquake into the following
three patterns;
1) Damage to tunnel entrances and portals
2) Damage to tunnels at a fractured zone
3) Damage to tunnels by sliding of a fault.
We have proved these mechanisms based on the
results of simulation analyses and model tests.
REFERENCES
1) Asakura, T., Shiba, Y., Sato, Y. and Iwatate, T.: Mountain
Tunnels Performance in the 1995 Hyogoken-Nanbu
Earthquake, Special Report of the 1995 Hyogoken-Nanbu
Earthquake, Committee of Earthquake Eng. JSCE, Jun.
1996.
2) Japan Society of Civil Engineers Tunnel Engineering
Committee Niigataken Chuetsu Earthquake Special
Subcommittee: Report by Japan Society of Civil Engineers
Tunnel Engineering Committee Niigataken Chuetsu
Earthquake Special Subcommittee, June 2005.