1.
Seismic Capacity Assessment of
Sanyi Old Railway Tunnel
Jin - Hung Hwang , Chih - Chieh Lu
Department of Civil Engineering
National Central University
November 9, 2005
4.
Outline
Introduction
Basic Data of the Tunnels
Assessment Methods
Analysis procedure of MCSRD
Case analysis – Sanyi Old Railway Tunnel
Conclusion
5.
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
6.
Basic Data of the tunnels
Topography
DTM topography
Max. overburden depth
Geology
Gravel and soft rock formations
Geotechnical parameters and wave velocities
7.
Cross section and lining
Cross section
Lining thickness and materials
Current state of the tunnels
Cracks
Seeping of the ground water
8.
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
9.
The Modified Cross-Section Racking
Deformation Method (MCSRD)
Analysis procedure of MCSRD
Case analysis-Sanyi old railway tunnels
10.
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)
12.
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)
14.
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)
15.
Step 3:Excavate the tunnel and install
the lining support
vσ
vh Kσσ 0= vh Kσσ 0=
vσ
16.
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)
18.
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)
19.
Step 5: Check the lining strength curves
Mu
Pu
Vu
Pu
20.
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)
21.
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
22.
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)
23.
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
24.
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
25.
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
26.
The enlarged deformation behavior of tunnel
original
deformed
Shear direction
27.
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
30.
Seismic capacity of the tunnels
gravel formation
31.
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
32.
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
33.
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
34.
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
35.
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.
36.
The assessed seismic capacities of Sanyi
old railway tunnels agree well with their
field performances in the past
earthquakes
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