Seismic Capacity Assessment of Sanyi Old Railway Tunnel

Seismic Capacity Assessment of
Sanyi Old Railway Tunnel
Jin - Hung Hwang , Chih - Chieh Lu
Department of Civil Engineering
National Central University
November 9, 2005

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Outline
Introduction
Basic Data of the Tunnels
Assessment Methods
Analysis procedure of MCSRD
Case analysis – Sanyi Old Railway Tunnel
Conclusion

Introduction
Underground structures are traditionally
considered to be more earthquake-resistant.
Extremely strong shaking might induce
damages of rock tunnel
 1995 Kobe earthquake
About 10 tunnels required countermeasures
 1999 Taiwan Chi-Chi earthquake
A total of fifty tunnels were reported to be
damaged
An important issue to tunnel engineers in
seismic active area

Basic Data of the tunnels
Topography
 DTM topography
 Max. overburden depth
Geology
 Gravel and soft rock formations
 Geotechnical parameters and wave velocities

Cross section and lining
 Cross section
 Lining thickness and materials
Current state of the tunnels
 Cracks
 Seeping of the ground water

Assessment Methods
The empirical method (Langefors and
Kihlstrom, 1963)
 Damage criterion
 Allowable PGV for concrete and brick linings
 Threshold PGA and JMA scale in the gravel
and soft rock formation
 Correlation of PGV with JMA intensity scale
 Assessment results

The Modified Cross-Section Racking
Deformation Method (MCSRD)
 Analysis procedure of MCSRD
 Case analysis-Sanyi old railway tunnels

Analysis procedure of MCSRD
Set up the grid mesh
Apply geostatic stresses
Excavate the tunnel and install the lining
support
Apply a seismic shear strain
Check the lining strength curves
Decide the allowable seismic shear strain
Calculate the allowable peak ground
velocity (PGV)

Step 2:Apply geostatic stresses
vσ
vh Kσσ 0= vh Kσσ 0=
vσ

Step 3:Excavate the tunnel and install
the lining support
vσ
vh Kσσ 0= vh Kσσ 0=
vσ

Step 4:Apply a seismic shear strain

Step 5: Check the lining strength curves
Mu
Pu
Vu
Pu

Step 6: Decide the allowable seismic
shear strain
 The allowable seismic shear strain is the shear strain
that just causes the lining internal forces reach the
limit state.
Mu
Pu
Vu
Pu

Step 7: Calculate the allowable peak
ground velocity (PGV)
......(1)....................asa V γυ ×=
is the allowable peak ground velocity
where, is the allowable seismic shear
strain
aγ
av
sV is the wave velocity of the ground

Case Analysis
Sanyi old railway tunnels
Input data
The enlarged deformation behavior of
tunnel
The distribution of bending moment, shear
force and axial force on the tunnel
Check the lining strength curves
The allowable peak ground velocity (PGV)
Seismic capacity of the tunnels

Input data
The parameters of the ground formation
Ground
formation
Unit weight
(KN/m3
)
E
(GPa)
c
(MPa)
φo Poison
ratio
Vs
(km/sec)
Vp
(km/sec)
soft rock 24 1.96 0.2 32 0.3 0.6 ~ 1.5 2 ~ 3
The cross section and strength properties of the linings
lining thickness (m) 0.3 0.45 0.6 0.8 1
cross section (m2
) 0.3 0.45 0.6 0.8 1
moment inertial (m4
) 0.00225 0.00759 0.018 0.0427 0.0833
lining strength (kg/cm2
) 140 、 210 、 280 、 350

The enlarged deformation behavior of tunnel
original
deformed
Shear direction

0.01剪應變
The distribution of bending moment,
shear force, and axial force on the tunnel
0.002剪應變 0.01剪應變Shear forceBending moment Axial force0.01剪應變

Check the lining strength curves
shear strain= 0.005
Mu (tf-m)
shearstrain= 0.001
-500
0
500
1,000
1,500
2,000
2,500
3,000
0 50 100 150 200 250 300
Mu (tf-m)
Pu(tf)
shear st r ai n=0
-500
0
500
1,000
1,500
2,000
2,500
3,000
0 50 100 150 200 250 300
Mu (tf-m)
Pu(tf)
-500
0
500
1,000
1,500
2,000
2,500
3,000
0 50 100 150 200 250 300
Pu(tf)
shear strain =0.005
0
50
100
150
200
0 50 100 150 200
Vu (tf)
Pu(tf)
Shear strain=0.002
0
50
100
150
200
0 50 100 150 200
Vu (tf)
Pu(tf)
shear strain=0
0
50
100
150
200
0 50 100 150 200
Vu (tf)
Pu(tf)

The allowable peak ground velocity (PGV)
Bending failure mode Shearing failure mode
0
0.2
0.4
0.6
0.8
1.0
1.2
10 15 20 25 30
ground velocity(cm/s)
Liningthickness(m)
fc'=140
fc'=210
fc'=280
fc'=350
0
0.2
0.4
0.6
0.8
1.0
1.2
30 35 40 45 50
ground velocity(cm/s)
liningthickness(m)
fc'=140
fc'=210
fc'=280
fc'=350

Seismic capacity of the tunnels
gravel formation

Seismic capacity of the tunnels
soft rock formation
bending failure mode shearing failing mode
JMA
scale
Lining strength(kg/cm2
) JMA
scale
Lining strength(kg/cm2
)
140 210 280 350 140 210 280 350
Liningthickness(m)
0.3 V V V V
Liningthickness(m)
0.3 V V V V
0.45 V V V V 0.45 V V V VI
0.6 V V V V 0.6 V V Ⅵ VI
0.8 V V V V 0.8 V VI VI VI
1.0 V V V V 1.0 VI VI VI VI

Summary of the assessed seismic capacity
JMA IV in gravel at least
JMA V in soft rock at least
One scale larger than that assessed by
the empirical method

Comparison with Field Performances
in the Past Earthquakes
1935 Hsinchu-Taichung Earthquake
 Historic iso-seismal map
 ML=7.1,JMA=VI,PGA≥400 gal
 Damage condition
1999 Chi-Chi Earthquake
 ML=7.3, iso-seismal map
 Estimated PGV, PGA and JMA scale
 JMA=IV~V
 No damage

Comparison
 Assessed JMA=IV~V at least
 JMA=VI in 1935 earthquake → serious damage
 JMA= IV~V in 1999 earthquake →no damage
 Agree field performance well

Conclusion
 A modified cross-section racking deformation
(MCSRD) method is proposed to assess the
seismic capacities of the tunnel structures. It is
easy ,fast, and able to automatically consider
nonlinear SSI effect and to consider complex
rock formation and irregular tunnel shape.

The assessed seismic capacities of Sanyi
old railway tunnels agree well with their
field performances in the past
earthquakes

Seismic Capacity Assessment of Sanyi Old Railway Tunnel

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