ANALYSIS ON SLIDING MECHANISM OF ANALYSIS ON SLIDING MECHANISM OF TSAOLING ROCKSLIDE IN CHI-CHI TSAOLING ROCKSLIDE IN CHI-CHI

EARTHQUAKE EVENTEARTHQUAKE EVENT

Tien Chien ChenTien Chien ChenNational Pingtung University of Science & TechnologyNational Pingtung University of Science & Technology

Meei Ling LinMeei Ling LinNational Taiwan UniversityNational Taiwan University

Wang, Tau-Teh Wang, Tau-Teh National Pingtung University of Science & TechnologyNational Pingtung University of Science & Technology

22

ContentsContents

IntroductionIntroduction

Earthquake G-M Records Earthquake G-M Records

Ground Surface ProfileGround Surface Profile& Material & Material PropertiesProperties

Newmark's Method of Sliding BlockNewmark's Method of Sliding Block

Results and DiscussionsResults and Discussions

ConclusionsConclusions

33

IntroductionIntroduction

During the 1999 Chi-Chi earthquake, extensive slope failures were During the 1999 Chi-Chi earthquake, extensive slope failures were triggered by the earthquake in central Taiwan. triggered by the earthquake in central Taiwan.

A large-scale dip-slope slide in Tsao-Ling occurred, which involved A large-scale dip-slope slide in Tsao-Ling occurred, which involved mass movement of 120 million cubic meters. mass movement of 120 million cubic meters.

only 25-million cubic meters (20 %) of the sliding mass dropped into the only 25-million cubic meters (20 %) of the sliding mass dropped into the valley of the Ching-Shui River at the toe of the slope. The remaining valley of the Ching-Shui River at the toe of the slope. The remaining sliding mass of about 100-million cubic meters slid pass the Ching-Shui sliding mass of about 100-million cubic meters slid pass the Ching-Shui River, and landed on the remains of old landslide dam.River, and landed on the remains of old landslide dam.

Photo by Lien,2000

44

Residents who lived near the crest of the slope, flied with their Residents who lived near the crest of the slope, flied with their house on the sliding rock block and landed on top of the house on the sliding rock block and landed on top of the landslide dam through a distance of 3100 m away. 32 people landslide dam through a distance of 3100 m away. 32 people were killed and 7 survived after the “sliding-landing” process.were killed and 7 survived after the “sliding-landing” process.

Lansilde damLansilde dam

Landslide lakeLandslide lake

3.5 km

3.5 km

4.5 km4.5 km

Bird’s eye view of landslide lake, Tsao-Ling village, and the landslide Bird’s eye view of landslide lake, Tsao-Ling village, and the landslide area,area,..

N

E

69o +

-

Out-slope

55

View of landslide dam, 2002View of landslide dam, 2002

66

3 004 005 006 007 008 009 00

1 00 011 0 01 20 01 30 0

Ele

vatio

n, m

3 004 005 006 007 008 009 001 00 011 0 01 20 01 30 0

1999 landslide debris

1941 to 1942 prof ile surface 1979 prof ile surface

slip surface af ter 1999

before 1999 C H Y080

3 004 005 006 007 008 009 00

1 00 011 0 01 20 01 30 0

Ele

vatio

n, m

3 004 005 006 007 008 009 001 00 011 0 01 20 01 30 0

1999 landslide debris

1941 to 1942 prof ile surface 1979 prof ile surface

slip surface af ter 1999

before 1999 C H Y080

Seismic records of Taso-Ling areaSeismic records of Taso-Ling area

Ground acceleration records of strong Ground acceleration records of strong motion station CHY 080, CWBmotion station CHY 080, CWB

-10

-5

0

5

10

-10

-5

0

5

10

-10

-5

0

5

10

Acc

ele

ratio

n (

m/s

2)

V e rtica l, Z Ma x:7 .1 6 m/s2

Ho rizo n ta l, N-S MA X :8 .4 2 m/s 2

Ho rizo n ta l, E -W Ma x:7 .9 3 m/s2

Sta tio n :C H Y 0 8 0

20 25 30 35 40 45 50

Tim e E la p se (Se co n d s)

-10

-5

0

5

10Ho rizo n ta l, D ip Ma x:6 .4 7 m/s2

F ig . 10 Acce le ra tion reco rd o f sta tion CHY080(CW B).

(d)

N

E 69o +

-

Out-slope

-10

-5

0

5

10

-10

-5

0

5

10

-10

-5

0

5

10

Acc

ele

ratio

n (

m/s

2)

V e rtica l, Z Ma x:7 .1 6 m/s2

Ho rizo n ta l, N-S MA X :8 .4 2 m/s 2

Ho rizo n ta l, E -W Ma x:7 .9 3 m/s2

Sta tio n :C H Y 0 8 0

20 25 30 35 40 45 50

Tim e E la p se (Se co n d s)

-10

-5

0

5

10Ho rizo n ta l, D ip Ma x:6 .4 7 m/s2

F ig . 10 Acce le ra tion reco rd o f sta tion CHY080(CW B).

(b)

-10

-5

0

5

10

-10

-5

0

5

10

-10

-5

0

5

10

Acc

ele

ratio

n (

m/s

2)

V e rtica l, Z Ma x:7 .1 6 m/s2

Ho rizo n ta l, N-S MA X :8 .4 2 m/s 2

Ho rizo n ta l, E -W Ma x:7 .9 3 m/s2

Sta tio n :C H Y 0 8 0

20 25 30 35 40 45 50

Tim e E la p se (Se co n d s)

-10

-5

0

5

10Ho rizo n ta l, D ip Ma x:6 .4 7 m/s2

F ig . 10 Acce le ra tion reco rd o f sta tion CHY080(CW B).

(c)

-10

-5

0

5

10

-10

-5

0

5

10

-10

-5

0

5

10

Acc

ele

ratio

n (

m/s

2)

V e rtica l, Z Ma x:7 .1 6 m/s2

Ho rizo n ta l, N-S MA X :8 .4 2 m/s 2

Ho rizo n ta l, E -W Ma x:7 .9 3 m/s2

S ta tio n :C H Y 0 8 0

20 25 30 35 40 45 50

Tim e E la p se (S e co n d s)

-10

-5

0

5

10Ho rizo n ta l, D ip Ma x:6 .4 7 m/s2

F ig . 10 Acce le ra tion reco rd o f sta tion CHY080(CW B).

(a)

Earthquake G-M RecordsEarthquake G-M Records

77

The strong ground motion records of station CHY080 of the Central Weather Bureau The strong ground motion records of station CHY080 of the Central Weather Bureau located just north to the crest of Tsaoling,located just north to the crest of Tsaoling,

In order to consider properly the effects of ground motion, the short-time Fourier transform In order to consider properly the effects of ground motion, the short-time Fourier transform of seismic record was conducted to illustrate the landslide initiation time. Figure 2 shows of seismic record was conducted to illustrate the landslide initiation time. Figure 2 shows the seismic wave arrived at 29 sec., the main shock was at 32 sec. the seismic wave arrived at 29 sec., the main shock was at 32 sec.

Fig. 2 The short-time Fourier transform of N-S ground motion

88

Ground Surface Profile & Material PropertiesGround Surface Profile & Material Properties

Average slope angle is 12o

Before landslideAfter landslide

Distance (m)

Elev

atio

n (m

)

Ground surface profile for seismic analysis

A large dip slopeA large dip slope The dip angles of The dip angles of

slope ranged from slope ranged from 12 to 14 degree, and 12 to 14 degree, and the main sliding the main sliding occurred in the shale occurred in the shale formationformation

99

Material Material propertiesproperties

The photograph The photograph was taken in 17was taken in 17thth November 2002, November 2002, it can be seen in it can be seen in the front of photo the front of photo that water that water seeping down seeping down slope along the slope along the interface of the interface of the two formations.two formations.

1010

Table 2. Material properties of Tsao-Ling area.

Item Shale Reference Source

Total unit weight t (kN/m3) 25.8 Lee,2001

Peak friction angle, p (o) 36.8 Lee,2001

Peak cohesion, cp (kPa) 664 Lee,2001

Residual friction angle, r (o) 13.4 Lee,2001

Residual cohesion, cr (kPa) 0 Lee,2001

Submerged friction angle (o) @ w=2% 19 Yeng,2000

Submerged friction angle (o) @ w=4% 14 Yeng,2000

Friction angle (o) (long-term submerged) 2.0 to2.8 Lin,1983,Yeng,2000

Cohesion (kPa) (long-term submerged) 0 Yeng,2000

Material parametersMaterial parameters

1111

W

S

N

m acp

R

aN

p

l

acp=m

lC +〔(g cos12°+aN) tanΦP- gsin12°〕

acr= ( g cos12°+aN) ) tanΦr

P(air pressure，Δp= 1/2 ρ V2，P = Δp･ l )

m acp+ S = R

R = C l + m (g cos12°+aN) tanΦp Out-slope

into_slope as

aN,as: acceleration

12o

Ground surface

E

69o

- +

+

-

-

aN

Newmark's Method of Sliding BlockNewmark's Method of Sliding Block

a

V

D

acp

Elapsed time Elapsed time

acr

as

1212

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60 70 80 90 100

Elapsed time, Sec.Acc

eler

atio

n co

mpo

nent

par

apel

le to

slo

pe s

urfa

ce (m

/sec

2)

-15

-10

-5

0

5

10

New

mar

k cr

itica

l acc

eler

atio

n (m

/sec

2)

7.Ad(=As+g.sin12-Acr）

3.Newmark critical Acp

Case ofp=30o

Results and DiscussionsResults and Discussions

N Out-slope

into_slope as

aN,as: acceleration

12o

Ground surface

E

69o +

- +

+

-

-

Out-slope

aN

aass vs.vs. a acpcp

slidingstatic

Depending on the Depending on the acceleration aacceleration aNN of of

earthquake the critical earthquake the critical acceleration aacceleration acpcp is not a is not a

constant.constant.

The down-slope The down-slope

acceleration acceleration ad could be could be determined from determined from

formula: formula: aass+g.sin12o-+g.sin12o-

aacrcr

g

gs

gN

acr

Down-slope ad=as+g.sin12O-acr

acp=m

lC +〔(g cos12°+aN) tanΦP- gsin12°〕

1313 Newmark’s acceleration increased as Newmark’s acceleration increased as pp increasing increasing

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 90 100

Elapsed time (sec)

Dow

n sl

ope

velo

city

, m/sec

-3000

-2000

-1000

0

1000

2000

3000

Dow

n sl

ope

disp

lace

men

t, mVelocity at 30 degree

Velocity at 25.6 degree

Velocity at 20 degree

Velocity at 15 degree

Displacement of 30 degree

Displacement of 25.6 degree

Displacement of 20 degree

Displacement of 15 degree

（ Case of p=15o-30o ； r=2.8o ）

Down-slopeDown-slope acceleration vs. displacement acceleration vs. displacement

1414

The short-time Fourier transform of Z-direction ground motion

0

50

100

150

200

250

300

0 10 20 30 40 50 60 70 80 90 100

Elapsed time (sec)

Dow

n sl

ope

velo

city

, m/sec

-3000

-2000

-1000

0

1000

2000

3000

（ Case of p=15o ； r=2.8o ）

Result of Result of the short-time the short-time Fourier transform of Fourier transform of vertical direction (Z) vertical direction (Z) seismic record shows seismic record shows the initiation time of the initiation time of rockslide about at 37 rockslide about at 37 secoend.secoend.

The result coincides The result coincides with the result from with the result from Newmark’s method.Newmark’s method.

1515

0

20

40

60

80

100

120

140

160

180

200

0 10 20 30 40 50 60 70 80 90 100

Elapsed time (sec)

Dow

n sl

ope

Vel

ocity

, m

/sec

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

Dow

n sl

ope

disp

lace

men

t, mVelocity at 2 degree

Velocity at 6 degree

Velocity at 8 degree

Velocity at 12 degree

Displacement of 2 degree

Displacement of 6 degree

Displacement of 8 degree

Displacement of 12 degree

φp=30o

Sliding Velocity and Distance under various Sliding Velocity and Distance under various residual friction angleresidual friction angle

As a result, the critical As a result, the critical acceleration decreased acceleration decreased from peak to residual from peak to residual state, the slid rock block state, the slid rock block gained velocity and gained velocity and displacement.displacement.

The sliding velocity of The sliding velocity of rock mass could be rock mass could be larger than 200 km/hr larger than 200 km/hr (56 m/s) at the “ jumping (56 m/s) at the “ jumping point” as point” as rr was lower was lower

than 6than 6oo..

1616

Does air cushion exist?Does air cushion exist? 4 air densities (i.e. 1.2, 100, 500, and 1000 4 air densities (i.e. 1.2, 100, 500, and 1000

kg/mkg/m33) were tested to illustrate the effect of ) were tested to illustrate the effect of “air cushion”.“air cushion”.

0

250

500

750

1000

1250

1500

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 5000

Distance (m)

Hei

ght (

m) B

A

C

?

0

250

500

750

1000

1250

1500

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 5000

Distance (m)

Hei

ght (

m) B

A

C

?

1717

Does air cushion exist?Does air cushion exist? Results show the rock block will fall into valley until the Results show the rock block will fall into valley until the

density of 1000 kg/mdensity of 1000 kg/m3 3 is reached. Air, in the is reached. Air, in the circumstance, is acted a incompressible-like medium circumstance, is acted a incompressible-like medium (such as water), since the rock block was flied over valley (such as water), since the rock block was flied over valley In reality.In reality.

0

250

500

750

1000

1250

1500

0 250 500 750 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 5000

Distance (m)

Ele

vati

on (m

)

Air density1000

Air density 500

Air density 100

Air density1.204

B

A

C

1818

ConclusionsConclusions In the result of short-time Fourier transform on In the result of short-time Fourier transform on

ground motion record shows the initiation time of ground motion record shows the initiation time of Tsaoling rockslide about at Tsaoling rockslide about at 37 second37 second of record. of record. WhichWhich is coincidence with the time calculated by is coincidence with the time calculated by Newmark’s method analysisNewmark’s method analysis..

Result shows the shear strength of Tsaoling rockslide Result shows the shear strength of Tsaoling rockslide plane degraded far from peak strength, the shear plane degraded far from peak strength, the shear strength is strength is close to residual strengthclose to residual strength and and significant significant to the velocity of sliding blockto the velocity of sliding block. .

Under this circumstance ofUnder this circumstance of rr lower than 6 lower than 6oo, the , the sliding velocity of rock block could be higher than 200 sliding velocity of rock block could be higher than 200 km/hr (56 m/s), which dimmed the occurrence of km/hr (56 m/s), which dimmed the occurrence of ““sliding-flying-landing” processsliding-flying-landing” process for the sliding rock for the sliding rock block possible with such high velocity.block possible with such high velocity.

1919

From the comparison in the location of From the comparison in the location of deposition and the result of analysis, air cushion deposition and the result of analysis, air cushion effect could be existed in Tsaoling rockslide effect could be existed in Tsaoling rockslide case.case.

Having well representative material parameters Having well representative material parameters and good quality ground motion record, and good quality ground motion record, a simple a simple prediction modelprediction model, e.g.. Newmark’s method, , e.g.. Newmark’s method, also also could achieve a well estimation on rockslide could achieve a well estimation on rockslide sliding behavior. sliding behavior.

2020

Thanks for your Attention……Thanks for your Attention……