Seismic Capacity Assessment of Sanyi Old Railway Tunnel

Seismic Capacity Assessment of Sanyi Old Railway Tunnel

Jin - Hung Hwang , Chih - Chieh LuDepartment of Civil Engineering

National Central UniversityNovember 9, 2005

DATE: 10th Nov, 2010CET Hall

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Outline

IntroductionBasic Data of the TunnelsAssessment Methods Analysis procedure of MCSRDCase analysis – Sanyi Old Railway TunnelConclusion

IntroductionUnderground 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

damagedAn 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 meshApply geostatic stressesExcavate the tunnel and install the lining

supportApply a seismic shear strainCheck the lining strength curvesDecide the allowable seismic shear strainCalculate the allowable peak ground

velocity (PGV)

Step 1:Set up the grid mesh

Analysis procedure of MCSRD

Set up the grid meshApply geostatic stressesExcavate the tunnel and install the lining

supportApply a seismic shear strainCheck the lining strength curvesDecide the allowable seismic shear strainCalculate the allowable peak ground

velocity (PGV)

Step 2:Apply geostatic stresses

v

vh K 0 vh K 0

v

Analysis procedure of MCSRD

Set up the grid meshApply geostatic stressesExcavate the tunnel and install the lining

supportApply a seismic shear strainCheck the lining strength curvesDecide the allowable seismic shear strainCalculate the allowable peak ground

velocity (PGV)

Step 3:Excavate the tunnel and install

the lining supportv

vh K 0 vh K 0

v

Analysis procedure of MCSRD

Set up the grid meshApply geostatic stressesExcavate the tunnel and install the lining

supportApply a seismic shear strainCheck the lining strength curvesDecide the allowable seismic shear strainCalculate the allowable peak ground

velocity (PGV)

Step 4:Apply a seismic shear strain

Analysis procedure of MCSRD

Set up the grid meshApply geostatic stressesExcavate the tunnel and install the lining

supportApply a seismic shear strainCheck the lining strength curvesDecide the allowable seismic shear strainCalculate the allowable peak ground

velocity (PGV)

Step 5: Check the lining strength curves

Mu

Pu

Vu

Pu

Analysis procedure of MCSRD

Set up the grid meshApply geostatic stressesExcavate the tunnel and install the lining

supportApply a seismic shear strainCheck the lining strength curvesDecide the allowable seismic shear strainCalculate the allowable peak ground

velocity (PGV)

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

awhere

Analysis procedure of MCSRD

Set up the grid meshApply geostatic stressesExcavate the tunnel and install the lining

supportApply a seismic shear strainCheck the lining strength curvesDecide the allowable seismic shear strainCalculate the allowable peak ground

velocity (PGV)

Step 7: Calculate the allowable peak ground velocity (PGV)

......(1)....................asa V

is the allowable peak ground velocity

where, is the allowable seismic shear straina

av

sV is the wave velocity of the ground

Case AnalysisSanyi old railway tunnels

Input dataThe enlarged deformation behavior of

tunnelThe distribution of bending moment, shear

force and axial force on the tunnelCheck the lining strength curvesThe 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

0.0001剪應變 0.002剪應變 0.01剪應變

The distribution of bending moment, shear force, and axial force on the tunnel

0.0001剪應變 0.002剪應變 0.01剪應變Shear forceBending moment Axial force0.0001剪應變 0.002剪應變 0.01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 strai n=0

-500

0

500

1,000

1,500

2,000

2,500

3,000

0 50 100 150 200 250 300Mu (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(t

f)

shear strain=0

0

50

100

150

200

0 50 100 150 200

Vu (tf)

Pu(t

f)

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)

Lin

ing

thic

knes

s(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)

linin

gth

ickn

ess(

m)

fc'=140

fc'=210

fc'=280

fc'=350

Seismic capacity of the tunnelsgravel formation

Seismic capacity of the tunnelssoft 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

Lin

ing thickness (m

)

0.3 V V V V Lin

ing thickness (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 leastJMA V in soft rock at leastOne 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

Thanks for your attention