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Assessment of Damages in Mountain Tunnels due to the
Taiwan Chi-Chi Earthquake
W.L. Wang1, T.T. Wang2, J.J. Su1, C.H. Lin1, C.R. Seng1, and T.H. Huang2
1 United Geotech Inc., Taipei, Taiwan
2 Department of Civi l Engineering, National Taiwan University, Taipei, Taiwan
Corresponding author
T.T. Wang
Department of Civi l Engineering
National Taiwan University
1 Section 4 Roosevelt Road
Taipei, Taiwan
Tel: +886 2 2363 0231
Fax: +886 2 2364 5734
Email: [email protected]
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Abstract
Tunnels, being underground structures, have long been assumed to have the ability to sustain
earthquake with little damage. However, investigations of mountain tunnels after the Chi-Chi
Earthquake in central Taiwan revealed that many tunnels suffered significant damage to various extents.
This work describes the findings of a systematic assessment of damages in the mountain tunnels in
Taiwan after the earthquake. It was found that among the 57 tunnels investigated 49 of them were
damaged. The damage patterns are summarized based on the characteristics and the distribution of the
lining cracks. This systematic investigation, involving geological conditions, design documents,
construction and maintenance records of these tunnels, has been conducted to assess the potential factor
that may have influences on the various damage patterns and the earthquake loading on tunnel
engineering. The results show that the degree of damage is associated with the geological condition and
structural arrangement of the tunnel. A tunnel passing through displaced fault zone will definitely
suffer damage. Extent of geological weak zone, distance from the epicenter, and existence of slope face
are also significant influencing factors. The seismic capacity of the tunnel is influence by its structural
arrangement, type if lining, invert setup, lining reinforcement, and others.
Keywords: tunnel damage, earthquake, lining cracks.
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1. Introduction
Mountain tunnels, being situated deep within rock layers, have generally been assumed to be
sustainable against damage from earthquakes. Previous studies have found earthquake damage in
tunnels to be localosed at sections with two important characteristics: those running through displaced
faults, which were damaged by shear forces that developed during the earthquake, and those near
surface slopes (especially at portal sections), which were damaged owing to slope failures (Dowding
and Rozen 1978, Yoshikawa 1981, Sharma and Judd 1991, Asakura and Sato 1996 and 1998). Most of
the design codes relating to earthquake mitigation for mountain tunnels are currently designed for use at
portals and sections near slope surfaces, and seldom for other sections, including deeper mined parts
and areas near intersections. Nevertheless, the Chi-Chi Earthquake incurred much damage on many
tunnels in central Taiwan, such as cracking, spalling of concrete lining and deformation of steel
reinforcement. These damages provide sufficient evidences to suggest that the effects of earthquakes
on tunnels should be further studied.
To study the damage influencing factors, the results of investigations of 57 mountain tunnels
affected by the Chi-Chi Earthquake were presented in this paper. For each tunnel the damage patterns
are examined on the basis of crack mapping results, and the degree of damage was assessed based on its
functionality after the earthquake. Tunnel damage, geological and geotechnical conditions and tunnel
structural characteristics are systematically investigated to evaluate the factors influencing tunnel
damage in an earthquake. This paper also discusses the seismic effects on tunnel engineering.
2. Brief description of the Chi-Chi Earthquake
On September 21, 1999, at 1:47 AM local time, a strong earthquake with a magnitude of 7.3 on the
Richter scale occurred near the town of Chi-Chi in central Taiwan (N23.78, E120.84), at a depth of
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approximately 7.5km. The island suffered catastrophic damage during the earthquake, with 2375 lives
being lost, over 10,000 people being injured and more than 30,000 buildings collapsed.
The Chi-Chi earthquake resulted from the reactivation of the Chelungpu Fault. The fault was long
ago identified as a thrust fault, running in a N-S direction for a total length of 60km, while dipping
eastward at an angle of 30° or less. However, visually identified surface ruptures following earthquake
indicated that the fault is extensive. It has a total length of 85km, including newly formed branches at
northern tip of the fault, as shown in Fig. 1. This growth of the fault represents the largest known
onshore thrust-faulting event of the 20th century.
Geologically, the fault is easily identifiable. The formation on the east of the fault, i.e., the hanging
wall, consists of late Pliocene Chinshui Shale and early Pleistocene shaley Cholan Formation, while the
west of the fault, the footwall, consists of gravelly late Pleistocene Toukershan Formation.
The Chi-Chi earthquake caused significant ground deformation. GPS survey results indicated that
an area east of the fault with a width of about 15km was displaced north-westwards, with a maximum
horizontal displacement of 9.06m (10m horizontal displacement was measured on the ground), and
vertically uplifted by around 9.8m at the Shihkang Dam, near the north tip of the fault line. Fig. 1.
shows the surface rupture and peak ground acceleration (PGA) contour caused by the earthquake.
3. Damages to mountain tunnels
Following the earthquake, a systematic investigation was conducted on 57 tunnels located in central
Taiwan. Firstly, quick visual inspections were performed within a couple of days of the earthquake to
gather preliminary information on tunnel damage. Detailed surveys were then performed for tunnels
that were significantly damaged, using lining crack mapping, photo recording, and measuring of the
major crack characteristics (including width, depth and relative displacement direction). Non-
destructive inspection methods, such as ground penetration radar (GPR), were also used in several
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severely damaged tunnels. Fig. 2 indicates the locations of the investigated tunnels and the intensity of
the earthquake on the ground surface.
Various types of damage were observed, including lining cracks, portal failure, concrete lining
spalling, groundwater inrush, exposed and buckled reinforcement, displaced lining, rockfalls in unlined
sections, lining collapses caused by slope failure, pavement or bottom cracks, and sheared off lining.
Table 1 lists the basic information and damage conditions of the investigated tunnels.
Tunnel damage differs in magnitude and location among different sites in central Taiwan. To study
the factors influencing damage, the tunnels are divided into 3 categories, according to their location
relative to the displaced Chelungpu Fault: passing through the displaced fault, located in the hanging
wall, and located in the footwall and other areas, as shown in Fig. 3. The numbers of tunnels suffering
various types of damage are plotted in Fig. 4. Lining cracks and portal failure are clearly the most
commonly observed types of damage suffered by mountain tunnels following the earthquake.
Huang et al. (1999) suggested assessing the degree of damage to a tunnel based on its functionality
after earthquake. Considering the potential hazard to vehicles, the degree of damage can be evaluated
according to the width and length of cracks in mined sections of typical traffic tunnels, as presented in
Table 2. Meanwhile, in this paper the degree of damage to the portal section can be accessed by the
stability of the slope above the tunnel. For simplicity, the same damage evaluation standards are also
adopted herein for water conveyance tunnels. Among the 57 tunnels investigated, only 8 are classified
as totally undamaged, while the other 49 tunnels suffered various degrees of damage, as summarized in
Table 1. Table 3 lists the degree of damage to tunnels in different categories. The tunnels passing
through the displaced fault zone suffered catastrophic damage, and the lining was sheared off.
Meanwhile, for the 50 tunnels in the hanging wall group, 5 tunnels (10%) are classified as undamaged,
21 tunnels (42%) were lightly damaged, 11(22%) moderately damaged and 13(26%) severely damaged.
Finally, for the 6 tunnels in the footwall and other areas, 3 (50%) suffered no damage at all, 2 (34%)
were lightly damaged and 1 (16%) was severely damaged. Evidently, the tunnels located in the hanging
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wall area suffered more damage than those in the footwall area.
4. Classification of damage patterns
Numerous damage conditions were observed in the tunnels, and some of the major patterns with
significant characteristics are illustrated below.
4.1. Sheared off lining
All buildings, bridges, roads, tunnels or other structures lying across the displaced fault zone were
destroyed, regardless of their size and stiffness, when the Chelungpu Fault line underwent shearing. The
Shihgang Dam and its water conveyance tunnel are the best examples of this type of failure.
Investigations by Chang and Chang (2000) revealed that this gravitational type Shihgang Dam was
displaced 7.8m vertically and 7.0m horizontally towards the north, destroying the dam’s water retaining
function. The dam’s water conveyance tunnel was also sheared off at a point 180m downstream from
the inlet because of the displaced fault. The tunnel was separated roughly 4m vertically and 3m
horizontally, as displayed in Fig. 5(a), causing the tunnel to fail. Furthermore, severe spalling of the
concrete lining and cracks developed along the tunnel, as illustrated in Fig. 5(b).
4.2. Slope failure induced tunnel collapse
When surface slopes fail during an earthquake, tunnels can be damaged by the failure surface at
sections near the slope face. Figs. 6(a) to 6(c) illustrate two representative cases from tunnel located at
Sta. 42k+573 of Highway No. 8 and the Chingshue Tunnel of Highway No. 149A. The damage
patterns are presented Fig. 6(d).
4.3. Longitudinal cracks
Longitudinal cracks in the concrete lining were developed in some tunnels, and were generally
extended. The crack length often exceeds the diameter of the tunnel, as illustrated in Fig. 7(a). This
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damage pattern can be further classified into 3 types, singular crack at the vault of the crown,
symmetrical cracks, and non-symmetrical cracks, as shown in Figs. 7(b) to 7(d). Most of the singular
cracks and symmetrical cracks are of the open and non-sheared types. The No. 1 San-I railway tunnel,
New Chi-Chi Tunnel on Highway No. 16 and the headrace tunnel of New Tienlun power station are the
most representative examples of this type of damage.
4.4. Transverse Cracks
Cracks in the concrete lining also developed perpendicular to the direction of tunnel axis, as
illustrated in Fig. 8. These cracks were generally observed above the road, and were characterized by
the spalling or relative displacement of the lining. The No. 1 San-I railway tunnel and the No. 1
Maaling Tunnel on Highway No. 8 are the most representative examples of this kind of damage.
4.5. Inclined Cracks
Singular cracks inclined at 30~60° to the horizontal develop in concrete lining at one side of the
tunnel and generally terminating at the segmental joints, as illustrates in Fig. 9. Damage of this type
was found in the No. 1 San-I railway tunnel.
4.6. Extended Cross Cracks
Inclined cracks in the concrete lining develop at variable inclinations and run continuously, possibly
crossing segmental joints, along the concrete lining segments and around the tunnel, as illustrated in Fig.
10(a). The No.1 Shuangtung Tunnel, shown in Fig. 10(b), and the West Shuanglung Tunnel of Tou-6
highway are typical examples of this kind of damage.
4.7. Pavement or bottom Cracks
Cracking of the pavement or the bottom of the tunnel usually runs continuously over a long distance,
as shown in Fig. 11(a), such as in the Shuanglung Tunnel of the Tou-6 highway. More serious damage
may also occur in the form of up heaving, such as the adit of the No.1 San-I railway tunnel, as shown in
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Fig. 11(b).
4.8. Wall Deformation
Fig. 12(a) shows tunnel damage caused by significant inward deformation of the sidewalls. The
deformation caused numerous cracks in the concrete lining on the inner face of the sidewalls and
collapse of the side ditch, such as in the adit of the No.1 San-I railway tunnel shown in Figs. 11(b) and
12(b).
4.9. Cracks that develop near opening
It is very common to see cracks developed near an opening such as electronic niche, fireplug and
fire extinguisher niche, refuge and so on. These cracks illustrated in Fig. 13(a) are usually localized and
limited within a few meters. However, as those openings become large and are arranged symmetrically,
the cracks can extend from both sides and join together. The collapse at the large refuges of the No. 1
San-I railway tunnel is an example, as shown in Fig. 13(b).
5. Study of the possible influences related to tunnel damage
Based on the above damage patterns, possible causes of tunnel damage are investigated. For each
damaged tunnel, relevant geological investigation reports, design documents and details on
construction and maintenance were collected. Details of each section of the damaged tunnels were
systematically investigated to examine possible factors controlling the occurrence of a certain type of
damage. Table 4 illustrates an example of such an investigation, focusing on the 8 damaged sections in
the No. 1 San-I railway tunnel.
The major factors associated with increased damage include: tunnel being located adjacent to
surface slopes or portals, tunnel running through faults, absence of concrete lining, unusual or
unfavorable concrete lining conditions, steep sidewalls, absence of invert, and so on. These factors are
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listed in Table 5 corresponding to the damage patterns, and can be broadly classified into 3 major
categories, as discussed below.
5.1. Earthquake intensity at each tunnel
The intensity of seismic force experienced by each tunnel differs owing to their different distances
from the displaced fault zone and the epicenter of the earthquake. The distance to the ground surface or
to nearby slopes also influences the seismic effect. Seismic waves propagate in the ground and lose
energy because of dispersion and ground resistance, causing tunnels to be under greater seismic forces
if they are closer to the displaced fault zone or the epicenter. Additionally, when seismic waves reach
the ground surface, they release energy due to reflection or refraction, and thus tunnels near the surface,
and especially those near slope faces, will absorb a greater seismic energy.
5.2. Condition of the surrounding ground
Most mountain tunnels run through very hard ground, and a few tunnels pass through the displaced
fault zone and fractured zones. Seismic waves propagate faster in hard and dense materials, and thus
less energy will be released at places where the tunnels lie in ground that is harder than the tunnel
structure, meaning that such tunnels will tend to deform with the ground and suffer less damage. On the
other hand, if the tunnels lie in relatively weaker ground they will absorb larger amounts of energy and
thus suffer greater damage. Concrete linings can particularly be damaged easily by ground
displacement or ground squeeze where soft and hard grounds meet, as soft and hard grounds behave
differently during earthquakes.
Any unfavorable events such as cave-in or collapse during tunneling would extend the plastic zone
around the tunnel, weaken the surrounding rock and cause excessive vibration when seismic waves pass
through. In addition, if the ground has previously experienced vertical stress from loosening, plastic
stress owing to squeezing, inclined stress or any other weakening processes, tunnels in these areas will
suffer greater damage to their concrete linings during an earthquake.
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5.3. Seismic capacity of the tunnel
The seismic capacity of tunnels can be assessed by studying the amount of damage sustained, a
higher seismic capacity implies less substantial the damages should be. Based on a general review of
the 57 tunnels investigated, the seismic capacities of tunnels depend on structural arrangements such as
cross sections and refuge openings, the presence of linings and inverts, the presence of lining
reinforcements, lining thickness, and any unusual conditions such as porous structures, presence of
cavities and serious concrete deterioration in the linings.
6. Concluding remarks
Among the 57 tunnels investigated in central Taiwan, 49 tunnels suffered various degrees of
damage after the Chi-Chi earthquake. The most and often serious damages were found on the east of the
Chelungpu fault line (hanging wall) while damages on the footwall and other areas suffered less. The
most severely damaged tunnel sections in the hanging wall are those close to surface slopes or portal
openings, while sections with a thick overburden generally suffered less. Nevertheless, however badly
the tunnels were damaged, they remained relatively unscathed when compared to surface structures.
The extent of damage to tunnel linings was influenced by the position of the tunnels in relation to
fault zones, ground conditions, and closeness to the epicenter and surface slopes. Additionally, the
presence and type of lining and lining reinforcement, and any unusual condition in the linings are also
important influence factors. It is difficult in a short time to gather the basic data of damaged tunnel,
especially information on ground conditions, support structure designs and unusual construction events
immediately after an earthquake. It is deemed necessary to establish a database of basic information on
existing tunnel structures and damage assessment.
To prevent slope failures and fault displacements from damaging tunnels, efforts should be made to
avoid passing through active faults and avoid placing tunnels too close to slope faces when planning
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future tunnels.
The effects of earthquakes on mountain tunnels have seldom been investigated. Up to now, no
established methods can be employed for assessing and evaluating tunnel stability during earthquakes,
and design codes for earthquake protection in tunneling are lacking. To ensure the functionality of
existing tunnels and enable future tunnels to withstand earthquakes, further investigation of the above
topics is necessary.
Acknowledgment
The Highway Bureau, MOTC, the Taiwan Railway Administration and RSEA Engineering
Corporation are appreciated for providing valuable information on the tunnels, helping in on site
investigation, and assisting in other various tasks.
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Reference
Asakura, T. and Sato, Y. 1996. Damage to maintain tunnels in hazard area. Soils and Foundations,
Special Issue, 301-310.
Asakura, T. and Sato, Y. 1998. “Mountain tunnels damage in the 1995 HYOGOKEN-NANBU
Earthquake,” Quarterly Reports of RTRI 39(1):9-16.
Chang C. T. and Chang, S. Y. 2000. Preliminary inspection of dam works and tunnels after Chi-Chi
Earthquake. Sino-Geotechnics 77:101-108.
Dowding, C. H. and Rozen, A. 1978. Damage to rock tunnel from earthquake shaking. Journal of the
Geotechnical Engineering Division, ASCE 104(GT2):175-191.
Huang, T. H. et al. 1999. Quick investigation and assessment on tunnel structures after earthquake, and
the relevant reinforced methods (in Chinese). Report for the Public Construction Commission,
Taipei, Taiwan.
National Central University, Department of Earth Science and Institute of Geophysics,
[email protected], Chi-Chi Earthquake Report.
Sharma, S. and Judd, W. R. 1991. Underground opening damage from earthquakes. Engineering
Geology 30:263-276.
United Geotech, Inc. 1999. Assessment and recommendation report for Emergency repair work of
Tsao-Ling Tunnels at Highway No. 149A and Yun-Chia Tunnel at Tsao-Rei Highway after Chi-
Chi. Design document for Taiwan Highway Administration Bureau, Taipei, Taiwan.
United Geotech, Inc. 1999. Investigation and assessment report on the tunnels damaged under Chi-Chi
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Earthquake in central Taiwan (5 volumes for Highway No. 8, No. 14, No. 16, No. 149 and Tou-6
highway, respectively), Taipei, Taiwan.
Wang, W. L. and Wang, T. T. 2000. A Study on the Damage of San-I No.1 Railway Tunnel Impacted by
Chi-Chi Earthquake. Annual Celebration Conference for the reorganization of the China Institute
of Technology, 279-288, Taipei.
Wang. W. L., Wang, T. T., Su, J. J., Lin, C. H., Seng, C. R. and Huang, T. H. 2000. The seismic hazards
and the rehabilitation of the tunnels in central Taiwan after Chi-Chi Earthquake. Sino-Geotechnics
81:85-96.
Yoshikawa, K. 1981. Investigation about past earthquake disasters of railway tunnels. Quarterly
Reports of RTRI 22(3):103-111.
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Table 1. Tunnel investigated and their damage types
Basic Information Damage DescriptionDamage
classification
No.
Tunnel and Location
Tun
ne
lling
Met
hoda
Le
ngth
(m
)
Wid
th (
m)
Lin
ing
Dis
tan
ce to
the
Epi
cent
er
(km
)
Dis
tan
ce to
Ch
e-L
ung
-Pu
Fa
ult
(km
)
Po
rtal
failu
re
Sh
ea
red
off
linin
g
Slo
pe
failu
re in
duc
edtu
nne
l co
llap
se
Lini
ng
crac
ks
Con
cret
e lin
ing
spa
llin
g
Wa
ter
inru
sh
Exp
ose
d re
info
rce
me
nt
Lini
ng
disp
lace
d
Pa
vem
ent c
rack
s
Roc
kfal
ls in
un
linin
gse
ctio
n
Ove
rall
Min
ed s
ect
ion
Po
rtal
s
1Shih-Gang Dam,
Water Conveyance TunnelNATM
- - Y - 0.0 ˇ C
2 Highway 8, 13k+381 T 20 6.5 N 35.1 12.0 ˇ A A A
3Highway 8, 27k+710
Li-Lang TunnelT 30 6.8 N 38.6 18.6 A A A
4 Highway 8, 34k+668 T 50 3.2 Y 44.0 20.1̌ ˇ B A B5 Highway 8, 34k+775 T 41 3.4 Y 44.0 20.1̌ ˇ B A B
6Highway 8, 35k+908old Ku-Kuan Tunnel
T 90 5.1 Y 44.8 19.8 ˇ ˇ ˇ B A B
7Highway 8, 36k+908
Ku-Kuan TunnelT 90 7.5 Y 44.8 19.8 ˇ ˇ B A B
8Highway 8, 38k+500
No.1 old Maa-Ling TunnelT 150 4.0 Y 45.9 21.5 ˇ ˇ ˇ ˇ C B C
9Highway 8, 38k+500
No.1 Maa-Ling TunnelT 365 5.1 Y 45.8 21.5 ˇ ˇ ˇ ˇ ˇ ˇ C C C
10Highway 8, 39k+075
No.2 Maa-Ling TunnelT 60 7.5 Y 46.1 21.6 ˇ C A C
11Highway 8, 40k+830
No.3 Maa-Ling TunnelT 245 7.5 Y 46.3 21.6 ˇ ˇ C A C
12Highway 8, 41k+311
No.4 Maa-Ling TunnelT 100 7.5 Y 47.8 22.1 A A A
13Highway 8, 41k+311No.4 old Maa-Ling
T 100 4.0 Y 47.8 22.1 ˇ ˇ ˇ C C A
14 Highway 8, 42k+573 T 10 6.5 N 48.3 23.0̌ ˇ C C C15 Highway 8, 43k+040 T 15 6.5 N 48.3 23.0̌ ˇ B A B16 Highway 8, 45k+266 T 32 6.5 Y 48.5 22.8̌ ˇ C B C
17Highway 14, 37k+405
Shuang-Fu TunnelT 150 7.5 Y 19.7 12.0 ˇ A A A
18Highway 14, 37k+981(L)
Gang-Lin TunnelT 182 7.5 Y 19.8 12.2 ˇ ˇ ˇ ˇ C A C
19Highway 14, 38k+000(R)
Gang-Lin TunnelT 249 7.5 Y 19.8 12.2 ˇ ˇ ˇ A A A
20Highway 14, 39k+921(L)
Yu-Ler TunnelT 158 7.5 Y 19.0 13.8 ˇ ˇ A A A
21Highway 14, 39k+921(R)
Yu-Ler TunnelT 158 7.5 Y 19.0 13.8 ˇ ˇ A A A
22Highway 14, 45k+182
Pei-Shan TunnelT 120 7.5 Y 15.9 17.5 ˇ A A A
23Highway 14, 48k+616(L)No.1 Kuan-Yin Tunnel
T 129 7.5 Y 17.1 20.4 ˇ A A A
24Highway 14, 48k+616(R)No.1 Kuan-Yin Tunnel
T 129 7.5 Y 17.1 20.4 ˇ A A A
25Highway 14, 48k+787(L)No. 2 Kuan-Yin Tunnel
T 123 7.5 Y 17.5 20.8 ˇ ˇ A A A
26Highway 14, 48k+787(R)No.2 Kuan-Yin Tunnel
T 123 7.5 Y 17.5 20.8 ˇ ˇ A A A
27Highway 14, 49k+253(L)No. 3 Kuan-Yin Tunnel
T 252 7.5 Y 17.6 21.2 ˇ ˇ ˇ B A B
28Highway 14, 49k+253(R)No. 3 Kuan-Yin Tunnel
T 252 7.5 Y 17.6 21.2 ˇ ˇ A A A
29Highway 16,
Chi-Chi TunnelT 238 4.8 Y 6.1 5.5 ˇ ˇ A A A
30Highway 16,
New Chi-Chi Tunnel (L)NATM
580 7.5 Y 6.4 5.3 ˇ A A A
31Highway 16,
New Chi-Chi Tunnel (R)NATM
515 7.5 Y 6.4 5.3 ˇ ˇ ˇ C C A
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Basic Information Damage DescriptionDamage
classification
No.
Tunnel and Location
Tun
ne
lling
Met
hoda
Le
ngth
(m
)
Wid
th (
m)
Lin
ing
Dis
tan
ce to
the
Epi
cent
er
(km
)
Dis
tan
ce to
Ch
e-L
ung
-Pu
Fa
ult
(km
)
Po
rtal
failu
re
Sh
ea
red
off
linin
g
Slo
pe
failu
re in
duc
edtu
nne
l co
llap
se
Lini
ng
crac
ks
Con
cret
e lin
ing
spa
llin
g
Wa
ter
inru
sh
Exp
ose
d re
info
rce
me
nt
Lini
ng
disp
lace
d
Pa
vem
ent c
rack
s
Roc
kfal
ls in
un
linin
gse
ctio
n
Ove
rall
Min
ed s
ect
ion
Po
rtal
s
32Highway 21, 54k+326(L)
Da-Yuan TunnelNATM
462 7.5 Y 14.2 21.8 ˇ A A A
33Highway 21, 54k+326(R)
Da-Yuan TunnelNATM
444 7.5 Y 14.2 21.8 ˇ A A A
34Highway 21, 66k+940(L)
Shue-Sir TunnelNATM
185 7.5 Y 8.5 19.9 ˇ A A A
35Highway 21, 66k+940(R)
Shue-Sir TunnelNATM
185 7.5 Y 8.5 19.9 A A A
36Highway 21A, 17k+303No. 1 Huan-Hu Tunnel
T 128 7.5 Y 9.3 20.2 A A A
37Highway 21A, 17k+253No. 2 Huan-Hu Tunnel
T 61 7.5 Y 9.3 20.2 A A A
38Highway 149,
Tsao-Ling TunnelNATM
505 7.0 Y 31.1 7.0 ˇ ˇ ˇ ˇ C B C
39Highway 149,
Ching-Shue TunnelT 52 7.5 N 32.0 3.7 ˇ ˇ ˇ C C C
40Tou-6 highway,
No. 1 Tu-Cheng TunnelT 100 6.5 Y 15.5 7.2 ˇ ˇ A A A
41Tou-6 highway,
No. 2 Tu-Cheng TunnelT 290 6.4 Y 15.3 7.6 ˇ ˇ B B A
42Tou-6 highway,
Shuang-Lung Tunnel (E)T 140 5.3 Y 15.2 7.8 ˇ ˇ B B A
43Tou-6 highway,
Shuang-Lung Tunnel (W)T 90 5.3 Y 15.2 7.8 ˇ A A A
44Tou-6 highway,
No. 1 Shuang-Tung TunnelT 80 4.5 Y 15.2 7.8 ˇ ˇ ˇ B B B
45Tou-6 highway,
No. 2 Shuang-Tung TunnelT 120 4.5 Y 15.2 7.8 ˇ ˇ A A A
46Chi-Chi line railway,
No. 1 tunnelT 350 5.0 Y 6.1 5.5 ˇ A A A
47Chi-Chi line railway,
No. 2 tunnelT 1400 5.0 Y <1 11 ˇ A A A
48Chi-Chi line railway,
No. 3 tunnelT 250 5.0 Y 4.5 15.9 ˇ B B B
49Chi-Chi line railway,
No. 5 tunnelT 150 5.0 Y 5.5 16.4 ˇ B B B
50Da-Kuan power station,
headrace tunnelT − − Y 8.5 19.9 ˇ ˇ C C A
51New Tien-Lun power station,
headrace tunnelNATM
10600 5.0 Y 40 18.6 ˇ ˇ ˇ C C A
52Mountain line railway,
No. 1 San-I TunnelNATM
7540 9.1 Y 55 11.1 ˇ ˇ ˇ ˇ C C A
53Mountain line railway,
No. 2 San-I TunnelNATM
260 9.1 Y 50 10.1 A A A
54Mountain line railway,
No. 3 San-I TunnelNATM
520 9.1 Y 49 10.1 A A A
55Mountain line railway,
No. 4 San-I TunnelNATM
455 9.1 Y 49 10.1 A A A
56Old mountain line railway,
No. 1 San-I TunnelT 230 5.0 Y 59 14.5 ˇ ˇ A A A
57Old mountain line railway,
No. 2 San-I TunnelT 730 5.0 Y 58 13.1 ˇ ˇ A A A
Note: a. Tunnelling method: T means traditional tunnelling method, NATM means New Austria TunnellingMethod.
b. Damage classification refers to Table 2 and texts for details.
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Table 2. Tunnel damage classification chart for emergency investigationphase (Huang et al . 1999)
Tunnel
classificationa,b
Damage
levelDamage description
Traffic
strategy
No damage No damages detectable by visual inspection.No
immediate
dangerA
SlightLight damages detected on visual inspection, no effects on traffic
(wc<3mm, lc<5m).
Normal
operation
B Moderate
Spalling, cracking of linings (w>3mm, l>5m), exposed
reinforcement, displacement of segmental joints, leaking of water.
Some disruption to traffic.
Operable
with
regulations
Dangerous
C Severe
Slope failure at openings, collapse of main tunnel structure, up
heave or differential movement of road and road shoulder,
flooding, damaged ventilation and lighting system in long tunnels.
Total disruption of traffic.
Not
operable
Note: a. Classification of a tunnel is based on its functionality (Traffic condition for road tunnels, ability towithstand water pressure for water conveyance tunnels) and extent of damage in the tunnel.
b. Classification of a tunnel should be based on the least safe section being assessed to be conservative.c. W means width of crack, L means length of crack
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Table 3. Damages of mountain tunnels caused by Chi-Chi Earthquake(after Wang et al. 2000)
LocationNo. Of tunnels
assessed
Tunnel
classificationDamage level
Tunnel
damaged
Damaged
in portal
Damaged
in mined
section
A Slight - - -
B Moderate - - -Displaced fault
zone1
C Severe 1 - 1
A Slight 26 32 35
B Moderate 11 9 8Hanging wall
area50
C Severe 13 9 7
A Slight 2 3 2
B Moderate - - -Footwall and
other areas6
C Severe 1 - 1
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Table 4. Assessment example on damages influencing factors, No. 1 San-I railway tunnel (after Wang and Wang2000)
Secti
on
Location Dama
ge
typea
Overburde
n (m)
Adverse
geological
condition
Rock mass
classificatio
n (RMR)
Constructio
n hazard
Auxiliary method Convergenc
e (%)
Support
stress
Openingc
Concrete
condition
A Approx.
161k+300
4,9 45 San-I
Fault zone
(19) – Cement grouting (5
times)
4.1 – Large
refuge
Local cavern
existing
B Approx.
161k+360
4,9 35 San-I
Fault zone
(14) Cave-in
and
collapse
Cement grouting 0.3b – Small
refuge
Good
C 161k+375
~410
3,5,9 25~35 San-I
Fault zone
(27~30) – – 0.3b 8 tons in
bolts
Small
refuge
Cavern
existing
D Approx.
164k+740
3,9 120 – (43) – – 1.5 – Small
refuge
Local cavern
existing
E 164k+758
~810
3,5 125 – (46~67) – – 1.5~1.8 23.5MPa
in
shotcrete
– Good
F 164k+842
~880
3 130~150 – (19) – Cement grouting 2.3 – – Cavern
existing
G 165k+600
~660
3,4,5 105~110 – (35~37) Squeezing
and support
damaged
Forepoling, cement
grouting, ring excavation
and re-supporting
3.6~5.5 – – Cavern
existing
H Approx.
165k+800
3,9 125 Fractured
zone
(28) – – 2.5 – Small
refuge
Cavern
existing
Notes:a. Damage types: 1) sheared off lining, 2) slope failure induced tunnel collapse, 3) longitudinal cracks, 4) transverse cracks, 5) inclined cracks, 6) extended cross cracks,7) pavement or bottom cracks, 8) wall deformation, 9) cracks nearby the opening.
b. Section B and C were located close to breakthrough point Sta. 161k+385, the monitoring results might not reflect the actual tunnel behavior.c. The large refuge is 4.5m in width and 3.5m in height, the small one is 2.0m in width and in height, and the excavation size of tunnel is 11m in width and in height.
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Table 5. Summary of factors influencing tunnel damage
Damage Typea
Possible Factors1 2 3 4 5 6 7 8 9
Passing through displaced fault zones ∇
Passing through faults, fractured zone and unfavorable
ground condition • ∇
Interface of hard and soft ground ∇
Nearby slope surface or portal ∇ ∇ ∇ ∇
Unfavorable events such as cave-in, collapse occurred
during construction • • • •
Anomaly such as lining cracks occurred before quake • •
Badly structural arrangementsb • • ∇
Absence of lining •
Plane concrete lining • • • • • • • ∇
Steep sidewalls, absence of invert, etc. • ∇ ∇
Deteriorated lining material • •
Cavity existed behind lining ∇ •Notes:a. Damage types refer to Table 4.
b. Arrangements such as opening, refuge, and so on, especially symmetrically located in both sidewalls.
c. ∇ presents significant influence, • presents moderate influence.
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Figure 1. Intensity of Chi-Chi earthquake felt at different locations in Taiwan(after National Central University, 2001)
Figure 2. The location of tunnels investigated and the earthquake intensity on ground surface
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Figure 3. Tunnels location relative to Chelungpu thrust fault
Figure 4. The numbers of tunnels suffering various types of damage
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Figure 5. Damage pattern - sheared off lining. (a) sheared off damage at the water conveyancetunnel of Shih-Gang Dam; (b) sketch of sheared off lining damage.
Figure 6. Damage pattern — slope failure induced tunnel collapse. (a) photo of Chi-ShuTunnel before Chi-Chi Earthquake; (b) photo of Chi-Shu Tunnel after Chi-ChiEarthquake; (c) slope failure induced tunnel collapse at Sta. 45k+573 of HighwayNo.8; (d) sketch of damage pattern.
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Figure 7. Damage pattern — longitudinal cracks. (a) sketch of longitudinal cracks damage; (b)typical mapping result of singular crack at the vault of the crown; (c) typicalmapping result of symmetrical cracks; (d) typicla mapping result of non-symmetricalcracks.
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Figure 8. Damage pattern — transverse cracks
Figure 9. Damage pattern — inclined cracks
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Figure 10. Damage pattern — extended cross cracks. (a) sketch of extended cross cracks; (b)extended cross cracks observed in No.1 Shuang-Tung Tunnel.
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Figure 11. Damage pattern — pavement or bottom cracks. (a) sketch of pavement of bottomcracks; (b) bottom cracks observed in the adit of No1. San-I railway tunnel.
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Figure 12. Damage pattern — wall deformation. (a) sketch of inward deformation of sidewall;(b) inward deformation of sidewall in the adit of No.1 San-I railway tunnel.
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Figure 13. Damage pattern — cracks nearby the opening. (a) sketch of the cracks nearby theopening; (b) lining collapse occurred above the refuge of No.1 San-I railwaytunnel.