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501 WANG


									        Assessment of Damages in Mountain Tunnels due to the

                         Taiwan Chi-Chi Earthquake

    W.L. Wang 1 , T.T. Wang 2 , J.J. Su 1 , C.H. Lin 1 , C.R. Seng 1 , and T.H. Huang 2

    United Geotech Inc., Taipei, Taiwan

    Depart ment of Ci vil Engineering, National Taiwan Uni versit y, Taipei, Taiwan

Corresponding author

T.T. Wang

Depart ment of Ci vil Engineering

National Taiwan Uni versity

1 Section 4 Roosevelt Road

Taipei, Taiwan

Tel: +886 2 2363 0231

Fax: +886 2 2364 5734



   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.

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

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

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

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

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

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


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

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.

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

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.


   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.


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,, 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

     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


Yoshikawa, K. 1981. Investigation about past earthquake disasters of railway tunnels. Quarterly

     Reports of RTRI 22(3):103-111.

Table 1. Tunnel investigated and their damage types

                                                        Basic Information                                                                                                                           Damage Description

                                                                                                                   Distance to Che-Lung-Pu
                                                                                       Distance to the Epicenter

                                                                                                                                                                                                                           Concrete lining spalling

                                                                                                                                                                                                                                                                     Exposed reinforcement
                                                                                                                                                                                   Slope failure induced

                                                                                                                                                                                                                                                                                                                                  Rockfalls in unlining
                                Tunnelling Methoda

                                                                                                                                                              Sheared off lining

                                                                                                                                                                                                                                                                                                                Pavement cracks
                                                                                                                                                                                                                                                                                             Lining displaced
                                                                                                                                                                                      tunnel collapse

                                                                                                                                                                                                                                                                                                                                                                     Mined section
                                                                                                                                                                                                           Lining cracks
                                                                                                                                             Portal failure

                                                                                                                                                                                                                                                      Water inrush
       Tunnel and Location

                                                     Length (m)

                                                                                                                          Fault (km)
                                                                  Width (m)



          Shih-Gang Dam,        NA
1                                                     -            -          Y                 -                     0.0                                     ˇ                                                                                                                                                                                            C
     Water Conveyance Tunnel    TM
2       Highway 8, 13k+381       T                   20           6.5         N 35.1 12.0                                                                                                                                                                                                                                             ˇ                    A         A               A
        Highway 8, 27k+710
3                                   T                30           6.8         N 38.6 18.6                                                                                                                                                                                                                                                                  A         A               A
          Li-Lang Tunnel
4       Highway 8, 34k+668          T                50           3.2         Y 44.0 20.1 ˇ                                                                                                                ˇ                                                                                                                                               B         A               B
5       Highway 8, 34k+775          T                41           3.4         Y 44.0 20.1 ˇ                                                                                                                ˇ                                                                                                                                               B         A               B
        Highway 8, 35k+908
6                                   T                90           5.1         Y 44.8 19.8 ˇ                                                                                                                ˇ                                          ˇ                                                                                                    B         A               B
        old Ku-Kuan Tunnel
        Highway 8, 36k+908
7                                   T                90           7.5         Y 44.8 19.8 ˇ                                                                                                                ˇ                                                                                                                                               B         A               B
          Ku-Kuan Tunnel
        Highway 8, 38k+500
8                                   T                150          4.0         Y 45.9 21.5 ˇ                                                                                                                ˇ ˇ                                                                               ˇ                                                             C         B               C
     No.1 old Maa-Ling Tunnel
        Highway 8, 38k+500
9                                   T                365          5.1         Y 45.8 21.5 ˇ                                                                                                                ˇ ˇ ˇ ˇ ˇ                                                                                                                                       C         C               C
       No.1 Maa-Ling Tunnel
        Highway 8, 39k+075
10                                  T                60           7.5         Y 46.1 21.6 ˇ                                                                                                                                                                                                                                                                C         A               C
       No.2 Maa-Ling Tunnel
        Highway 8, 40k+830
11                                  T                245          7.5         Y 46.3 21.6 ˇ                                                                                                                ˇ                                                                                                                                               C         A               C
       No.3 Maa-Ling Tunnel
        Highway 8, 41k+311
12                                  T                100          7.5         Y 47.8 22.1                                                                                                                                                                                                                                                                  A         A               A
      No.4 Maa-Ling Tunnel
        Highway 8, 41k+311
13                                  T                100          4.0         Y 47.8 22.1                                                                                                                  ˇ ˇ                                                                               ˇ                                                             C         C               A
         No.4 old Maa-Ling
14      Highway 8, 42k+573          T                10           6.5         N 48.3 23.0 ˇ                                                                                                                                                                                                                                           ˇ                    C         C               C
15      Highway 8, 43k+040          T                15           6.5         N 48.3 23.0 ˇ                                                                                                                                                                                                                                           ˇ                    B         A               B
16      Highway 8, 45k+266          T                32           6.5         Y 48.5 22.8 ˇ                                                                                                                ˇ                                                                                                                                               C         B               C
       Highway 14, 37k+405
17                                  T                150          7.5         Y 19.7 12.0                                                                                                                  ˇ                                                                                                                                               A         A               A
         Shuang-Fu Tunnel
     Highway 14, 37k+981(L)
18                                  T                182          7.5         Y 19.8 12.2 ˇ                                                                                            ˇ                   ˇ                                          ˇ                                                                                                    C         A               C
          Gang-Lin Tunnel
     Highway 14, 38k+000(R)
19                                  T                249          7.5         Y 19.8 12.2                                                                                                                  ˇ                                          ˇ                                                         ˇ                                          A         A               A
          Gang-Lin Tunnel
     Highway 14, 39k+921(L)
20                                  T                158          7.5         Y 19.0 13.8                                                                                                                  ˇ ˇ                                                                                                                                             A         A               A
           Yu-Ler Tunnel
     Highway 14, 39k+921(R)
21                                  T                158          7.5         Y 19.0 13.8                                                                                              ˇ                   ˇ                                                                                                                                               A         A               A
           Yu-Ler Tunnel
       Highway 14, 45k+182
22                                  T                120          7.5         Y 15.9 17.5                                                                                                                  ˇ                                                                                                                                               A         A               A
          Pei-Shan Tunnel
     Highway 14, 48k+616(L)
23                                  T                129          7.5         Y 17.1 20.4                                                                                                                  ˇ                                                                                                                                               A         A               A
      No.1 Kuan-Yin Tunnel
     Highway 14, 48k+616(R)
24                                  T                129          7.5         Y 17.1 20.4                                                                                                                  ˇ                                                                                                                                               A         A               A
      No.1 Kuan-Yin Tunnel
     Highway 14, 48k+787(L)
25                                  T                123          7.5         Y 17.5 20.8                                                                                                                  ˇ                                          ˇ                                                                                                    A         A               A
      No. 2 Kuan-Yin Tunnel
     Highway 14, 48k+787(R)
26                                  T                123          7.5         Y 17.5 20.8                                                                                                                  ˇ                                          ˇ                                                                                                    A         A               A
      No.2 Kuan-Yin Tunnel
     Highway 14, 49k+253(L)
27                                  T                252          7.5         Y 17.6 21.2 ˇ                                                                                                                ˇ                                          ˇ                                                                                                    B         A               B
      No. 3 Kuan-Yin Tunnel
     Highway 14, 49k+253(R)
28                                  T                252          7.5         Y 17.6 21.2                                                                                                                  ˇ                                          ˇ                                                                                                    A         A               A
      No. 3 Kuan-Yin Tunnel
            Highway 16,
29                                  T                238          4.8         Y           6.1                         5.5                                                                                  ˇ                                          ˇ                                                                                                    A         A               A
           Chi-Chi Tunnel
            Highway 16,         NA
30                                                   580          7.5         Y           6.4                         5.3                                                                                  ˇ                                                                                                                                               A         A               A
      New Chi-Chi Tunnel (L)    TM
            Highway 16,         NA
31                                                   515          7.5         Y           6.4                         5.3                                                                                  ˇ ˇ                                                       ˇ                                                                                     C         C               A
      New Chi-Chi Tunnel (R)    TM

                                                            Basic Information                                                                                                                           Damage Description

                                                                                                                       Distance to Che-Lung-Pu
                                                                                           Distance to the Epicenter

                                                                                                                                                                                                                               Concrete lining spalling

                                                                                                                                                                                                                                                                         Exposed reinforcement
                                                                                                                                                                                       Slope failure induced

                                                                                                                                                                                                                                                                                                                                      Rockfalls in unlining
                                   Tunnelling Methoda

                                                                                                                                                                  Sheared off lining

                                                                                                                                                                                                                                                                                                                    Pavement cracks
                                                                                                                                                                                                                                                                                                 Lining displaced
                                                                                                                                                                                          tunnel collapse

                                                                                                                                                                                                                                                                                                                                                                         Mined section
                                                                                                                                                                                                               Lining cracks
                                                                                                                                                 Portal failure

                                                                                                                                                                                                                                                          Water inrush
        Tunnel and Location

                                                         Length (m)

                                                                                                                              Fault (km)
                                                                      Width (m)



      Highway 21, 54k+326(L)       NA
32                                                      462           7.5         Y 14.2 21.8                                                                                                                  ˇ                                                                                                                                               A         A               A
           Da-Yuan Tunnel          TM
      Highway 21, 54k+326(R)       NA
33                                                      444           7.5         Y 14.2 21.8                                                                                                                  ˇ                                                                                                                                               A         A               A
           Da-Yuan Tunnel          TM
      Highway 21, 66k+940(L)       NA
34                                                      185           7.5         Y           8.5                      19.9                                                                                    ˇ                                                                                                                                               A         A               A
           Shue-Sir Tunnel         TM
      Highway 21, 66k+940(R)       NA
35                                                      185           7.5         Y           8.5                      19.9                                                                                                                                                                                                                                    A         A               A
           Shue-Sir Tunnel         TM
       Highway 21A, 17k+303
36                                     T                128           7.5         Y           9.3                      20.2                                                                                                                                                                                                                                    A         A               A
        No. 1 Huan-Hu Tunnel
       Highway 21A, 17k+253
37                                     T                61            7.5         Y           9.3                      20.2                                                                                                                                                                                                                                    A         A               A
        No. 2 Huan-Hu Tunnel
            Highway 149,           NA
38                                                      505           7.0         Y 31.1                                  7.0                    ˇ                                                             ˇ ˇ                                                       ˇ                                                                                     C         B               C
          Tsao-Ling Tunnel         TM
            Highway 149,
39                                     T                52            7.5         N 32.0                                  3.7                    ˇ                                         ˇ                   ˇ                                                                                                                                               C         C               C
         Ching-Shue Tunnel
           Tou-6 highway,
40                                     T                100           6.5         Y 15.5                                  7.2                                                                                  ˇ ˇ                                                                                                                                             A         A               A
       No. 1 Tu-Cheng Tunnel
           Tou-6 highway,
41                                     T                290           6.4         Y 15.3                                  7.6                                                                                  ˇ ˇ                                                                                                                                             B         B               A
       No. 2 Tu-Cheng Tunnel
           Tou-6 highway,
42                                     T                140           5.3         Y 15.2                                  7.8                                                                                  ˇ                                                                                                    ˇ                                          B         B               A
       Shuang-Lung Tunnel (E)
           Tou-6 highway,
43                                     T                90            5.3         Y 15.2                                  7.8                                                                                  ˇ                                                                                                                                               A         A               A
      Shuang-Lung Tunnel (W)
           Tou-6 highway,
44                                     T                80            4.5         Y 15.2                                  7.8                    ˇ                                                             ˇ ˇ                                                                                                                                             B         B               B
      No. 1 Shuang-Tung Tunnel
           Tou-6 highway,
45                                     T                120           4.5         Y 15.2                                  7.8                                                                                  ˇ ˇ                                                                                                                                             A         A               A
      No. 2 Shuang-Tung Tunnel
         Chi-Chi line railway,
46                                     T                350           5.0         Y           6.1                         5.5                                                                                  ˇ                                                                                                                                               A         A               A
             No. 1 tunnel
         Chi-Chi line railway,
47                                     T                1400          5.0         Y            <1                          11                                                                                  ˇ                                                                                                                                               A         A               A
             No. 2 tunnel
         Chi-Chi line railway,
48                                     T                250           5.0         Y           4.5                      15.9                                                                                    ˇ                                                                                                                                               B         B               B
             No. 3 tunnel
         Chi-Chi line railway,
49                                     T                150           5.0         Y           5.5                      16.4                                                                                    ˇ                                                                                                                                               B         B               B
             No. 5 tunnel
       Da-Kuan power station,
50                                     T                 −            −           Y           8.5                      19.9                                                                                    ˇ                                                         ˇ                                                                                     C         C               A
           headrace tunnel
     New Tien-Lun power station,   NA 10600
51                                                                    5.0         Y             40                     18.6                                                                                    ˇ                                                         ˇ ˇ                                                                                   C         C               A
           headrace tunnel         TM
        Mountain line railway,     NA
52                                    7540                            9.1         Y             55                     11.1                                                                                    ˇ ˇ                                                                               ˇ ˇ                                                           C         C               A
          No. 1 San-I Tunnel       TM
        Mountain line railway,     NA
53                                    260                             9.1         Y             50                     10.1                                                                                                                                                                                                                                    A         A               A
          No. 2 San-I Tunnel       TM
        Mountain line railway,     NA
54                                    520                             9.1         Y             49                     10.1                                                                                                                                                                                                                                    A         A               A
          No. 3 San-I Tunnel       TM
        Mountain line railway,     NA
55                                    455                             9.1         Y             49                     10.1                                                                                                                                                                                                                                    A         A               A
          No. 4 San-I Tunnel       TM
      Old mountain line railway,
56                                     T                230           5.0         Y             59                     14.5                                                                                    ˇ ˇ                                                                                                                                             A         A               A
          No. 1 San-I Tunnel
      Old mountain line railway,
57                                     T                730           5.0         Y             58                     13.1                                                                                    ˇ ˇ                                                                                                                                             A         A               A
          No. 2 San-I Tunnel
Note: a. Tunnelling method: T means traditional tunnelling method, NATM means New Austria Tunnelling
      b. Damage classification refers to Table 2 and texts for details.

Table 2. Tunnel damage classification chart for emergency investigation
           phase (Huang et al. 1999)

     Tunnel          Damage                                                                              Traffic
                                                         Damage description
 classification        level                                                                            strategy

    No              No damage No damages detectable by visual inspection.
immediate                                                                                               Normal
  danger                        Light damages detected on visual inspection, no effects on traffic     operation
                      Slight       c        c
                                (w <3mm, l <5m).

                                Spalling, cracking of linings (w>3mm, l>5m), exposed
                                reinforcement, displacement of segmental joints, leaking of water.
              B     Moderate                                                                              with
                                Some disruption to traffic.

                                Slope failure at openings, collapse of main tunnel structure, up
                                heave or differential movement of road and road shoulder,
              C       Severe    flooding, damaged ventilation and lighting system in long tunnels.

                                Total disruption of traffic.

Note: a. Classification of a tunnel is based on its functionality (Traffic condition for road tunnels, ability to
          withstand 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

Table 3. Damages of mountain tunnels caused by Chi-Chi Earthquake
           (after Wang et al. 2000)

                  No. Of tunnels      Tunnel                       Tunnel    Damaged
   Location                                         Damage level                         in mined
                     assessed      classification                  damaged   in portal

                                         A             Slight         -          -          -

Displaced fault
                        1                B            Moderate        -          -          -

                                         C             Severe         1          -          1

                                         A             Slight        26         32         35

Hanging wall
                       50                B            Moderate       11         9           8

                                         C             Severe        13         9           7

                                         A             Slight         2         3           2

 Footwall and
                        6                B            Moderate        -          -          -
  other areas

                                         C             Severe         1          -          1

Table 4. Assessment example on damages influencing factors, No. 1 San-I railway tunnel (after Wang and Wang
Secti    Location     Dama      Overburde      Adverse       Rock mass      Constructio        Auxiliary method         Convergenc       Support     Opening        Concrete
  on                    ge         n (m)      geological    classificatio    n hazard                                      e (%)          stress                   condition
                       typea                  condition       n (RMR)
  A       Approx.       4,9         45        San-I             (19)            –         Cement grouting (5                4.1             –          Large     Local cavern
         161k+300                             Fault zone                                  times)                                                       refuge      existing
  B       Approx.       4,9         35        San-I             (14)          Cave-in     Cement grouting                   0.3b            –          Small         Good
         161k+360                             Fault zone                       and                                                                     refuge
  C      161k+375      3,5,9      25~35       San-I           (27~30)           –         –                                 0.3b        8 tons in      Small        Cavern
           ~410                               Fault zone                                                                                  bolts        refuge       existing
  D       Approx.       3,9         120           –             (43)            –         –                                 1.5             –          Small     Local cavern
         164k+740                                                                                                                                      refuge      existing
  E      164k+758       3,5         125           –           (46~67)           –         –                               1.5~1.8       23.5MPa          –           Good
           ~810                                                                                                                            in
  F      164k+842        3       130~150          –             (19)            –         Cement grouting                   2.3             –            –          Cavern
           ~880                                                                                                                                                     existing
  G      165k+600      3,4,5     105~110          –           (35~37)        Squeezing    Forepoling, cement              3.6~5.5           –            –          Cavern
           ~660                                                             and support   grouting, ring excavation                                                 existing
                                                                              damaged     and re-supporting
  H       Approx.       3,9         125        Fractured        (28)            –                     –                     2.5             –          Small        Cavern
         165k+800                                zone                                                                                                  refuge       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.

              Table 5. Summary of factors influencing tunnel damage

                                           Damage Typea
                                                          1    2     3      4     5     6     7      8     9
Possible Factors

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.

       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

   Figure 3. Tunnels location relative to Chelungpu thrust fault

Figure 4. The numbers of tunnels suffering various types of damage

Figure 5. Damage pattern - sheared off lining. (a) sheared off damage at the water conveyance
          tunnel of Shih-Gang Dam; (b) sketch of sheared off lining damage.

Figure 6. Damage pattern — slope failure induced tunnel collapse. (a) photo of Chi-Shu
          Tunnel before Chi-Chi Earthquake; (b) photo of Chi-Shu Tunnel after Chi-Chi
          Earthquake; (c) slope failure induced tunnel collapse at Sta. 45k+573 of Highway
          No.8; (d) sketch of damage pattern.

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) typical
         mapping result of symmetrical cracks; (d) typicla mapping result of non-symmetrical

Figure 8. Damage pattern — transverse cracks

Figure 9. Damage pattern — inclined cracks

Figure 10. Damage pattern — extended cross cracks. (a) sketch of extended cross cracks; (b)
         extended cross cracks observed in No.1 Shuang-Tung Tunnel.

Figure 11. Damage pattern — pavement or bottom cracks. (a) sketch of pavement of bottom
           cracks; (b) bottom cracks observed in the adit of No1. San-I railway tunnel.

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.

Figure 13. Damage pattern — cracks nearby the opening. (a) sketch of the cracks nearby the
           opening; (b) lining collapse occurred above the refuge of No.1 San-I railway


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