Post on 11-Jan-2016
description
Post-event reconstruction of the short-lived Siaolin landslide dam
Advisor: J.J. DongPresenter: Y.S. LiDate: 2010/10/14
莫拉克颱風引致之堰塞湖地形與水文參數分析-以小林村堰塞湖為例
Outline
• Introduction• Methods• Results• The characteristics and failure mechanisms of
the Siaolin landslide dam• Conclusions• Future works
Introduction(1/3)• Formation of landslide
dams :
• Longevity of landslide dams:
(Casagli and Ermini,2003)
(Costa and Schuster,1986 )
Stability
Introduction(2/3)
• Stability of landslide dams :
(Dong et al.,2009)
(Dong et al.,2009)
DBI :
log b d
d
A HDBI
V
bA
dH
dV
: catchment area
: dam height
: dam volume
Discriminant analysis: 2.94log 4.58( ) 4.17( ) 2.39log( ) 2.52s d d dD P H W L
P
dH
dW
dL
: peak flow
: dam height
: dam width ( along the valley)
: dam length( across the valley)
Ds > 0 : Stable
Ds < 0 : Unstable
(Dong et al.,2009)
(Ermini and Casagli,2003)
Introduction(3/3)• Why ? The database of landslide dams is incompleteness.
→ Lacked for systematic data gathering on process, characteristics, control measures, and effects of landslide dams. (Costa and Schuster, 1986)
→ The forming and breaching of rainfall triggered landslide dam is beneficial to understand the impact of extreme weather on surface process relates to landslide dam. (Kroup, 2004)
→ Detailed documentation of processes of dam failure remained scare. (Kroup, 2002)
• So … Morakot event.
→ The Siaolin landslide dam.
→ Reconstruction of the shape of landslide dam.
ASTM→ Grain size distributions of dam materials .
2. Field investigation
MethodsReconstruction of dam geometry
TopographyDebris budget of
landslideInflow rate and
overtopping time
1. Aerial photographs 1. Laboratory works
2. Debris budget
DTM.
Field investigation & Laboratory works.
Kriging.
2. Inflow rate is 2974cms. → overtopping time.
1. Water level. →Water volume. (based on DTM)
, , ,1ls channsl ls i F E ls slopeV V F V V (Hungr and Evans,2004)
Volume of debris entered the channel.
Initial volume of a landslide.
volume expansion due to fragmention.
Volume of debris deposit on the slope.
Volume of the entrained materials.
Results(1/5)• Topographic Analysis
• Laboratory works Sample NO. 1 2 3 4Wet Unit Weight (kN/m3) 20.1 20.6 21.3 21.7 Water Content (%) 3.4 1.7 1.8 1.8Specific Gravity 2.85 2.56 2.80 2.71Atterberg Limits (%) LL=24.1
PI=7.5LL=23.1PI=3.6
LL=25.6PI=7.7
LL=29.5PI=7.8
Fines Content (%) 40 50 39 52Soil Classification SC SM SC SC
t
wW
sG
cF
Fine grain particles
Lower Hydraulic conductivity
Overflow
●
●
EL. 440
EL. 420
Results(2/5)• Volume and debris budget of landslide
, , ,1ls channsl ls i F E ls slopeV V F V V 25.21 million m3 2.23 million m3
13.33% 15.41 million m3
15.31 million m3
Reference value
Results(3/5)• Dam height
●
EL. 410
●EL. 440
●
EL. 420No.11 Bridge
0.0E+000 2.0E+007 4.0E+007 6.0E+007W ater storage (m 3)
370
380
390
400
410
420
430
440
450
460
470
Ele
veat
ion
of
lake
's w
ater
leve
l (m
)
12.4E+06 m 3
W ater storagewhen the elevation of dam crest
= 415 mPredicted overtopping time
0 100 200 300Time (m in)
370
380
390
400
410
420
430
440
450
460
470
Ele
veat
ion
of
lake
's w
ater
leve
l (m
)
P redicted overtopping tim ewhen the elevation of dam crest
= 415 mPredicted overtopping tim e
69 m in
Q=2974 cms
Results(4/5)• Reconstruction of the shape of landslide dam
0 100 200 300 400 500 600 700 800 900D istance (m )
350
400
450
500
550
600
650
Ele
vatio
n (m
)
AD-AD Cross-SectionTopography before the forming of the landslide dam
Topography after the breaching of the landslide dam
D am crest
O vertopp ing po in t (EL.415m )
Results(5/5)The total dam volume is 15.34 million m3 .
15.31 million m3
The maximum thickness of deposition is 60 m.
The breached dam volume is 7.36 million m3.
The maximum thickness of erosion is 41 m.
The characteristics and failure mechanisms of the Siaolin landslide dam
• Characteristics欄位名稱 結果堰塞湖天然壩座標 X=120°38'52" ; Y=23°10'19"
發生年 2009/08/07-2009/08/09
名稱 旗山溪堰塞湖誘因 降雨導致崩塌土石堵塞淇山溪河道集水區面積 354067960.758m2
水系次數 3
平均流量 30.14cms
尖峰流量 2974cms
上游坡降 約 7.6%下游坡降 約 1.0%壩體組成材料與地質 SC 、 SM 、糖恩山砂岩 ( 上新世 )山崩移動土塊量 25210743.35m3
山崩發生源面積 627294m2
山崩水平滑距 2916.69m
比高 875m
壩高 damA=27.36m ( 平均壩高 )damA=54m ( 縱剖面最高點的壩高 )damA=44m (Breaching point 壩高 )damA=60 m( 最大壩高 )
壩長 damA=1553.6m
壩寬 damA=486.68m ( 平均壩寬 )damA=760m( 縱剖面最高點的壩寬 )
湖水深 35m
湖面積 73350 m2
壩體積 damA=13179396.26m3 ; damB=2161888.972m3
湖體積 9876559.36 m3
壽命 約 44 分鐘
• Failure mechanisms DBI=3.2 ; Ds= -0.37 Unstable
Matrix-supported.
Overtopping
FS=3.46
Piping
FS=3.46
SlopeXX
Conclusions
• The total volume of landslide dam is estimated to be 15.34 million m3, the dam height of breaching point is 44m, the maximum dam height is 60m, the dam length(along valley) and dam width(across valley) is 1554m and 760m.
• According to dam materials and estimated geometry and hydrologic parameters:→ The Siaolin landslide dam is classified as unstable and failure
mechanism is dominated by overtopping.
Future works
• 3D landslide dam.
• Collecting the data of landslide dams during Morakot typhoon.
Thanks for your attention !