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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
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.