Entrainment in Rock Avalanches
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Transcript of Entrainment in Rock Avalanches
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Entrainment of material in
rock avalanches
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Equivalent
Fluid
Modelling: concept of equivalent fluid
Prototype Model
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St.Vennant Equation, Lagrangian
Acceleration =
Gravityfrictionpressure term (P)
Moving
Coordinate
system
dx
dHgk
H
Tg
dt
dv
cossin
(Savage and Hutter, 1988)
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Dynamic equilibrium of a column
T = resisting stress
Pressure term:
cosHds
dHkP
k
lateral pressurecoefficient
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Material entrainment (Sassa, 1985)
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Displacement of
alluvium, HopeSlide, B.C.
(1964)
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Displacement of alluvium, Frank Slide, Alberta (1903)
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Mt. Ontake rock avalanche, 1984(Voight and Soussa,1994)
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Coal waste dump flow slidesource
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Nomash Slide, Vancouver Island, B.C.
(Photos D.Ayotte)
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Rock slide-debris avalanche
(Map: GSC)
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Nomash River, Vancouver Island
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Nomash River
debris deposit
proximal
distal
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ROCK SLIDE
COARSE
DEBRIS AVALANCHE
DEPOSITION
0 400 800 1200 1600 2000 2400
DISTANCE (m)
200
400
600
800
1000
ELEVATION(m)
0 400 800 1200 1600 2000 2400
DISTANCE (m)
-1500-1000
-5000
500
10001500
YIELDRATE(m3/m)
ROCK
DEBRISEROSION
0 400 800 1200 1600 2000 2400
DISTANCE (m)
0100000200000300000400000500000600000700000
VOLUME
PASSING(m3
) ROCKDEBRIS
TOTAL
DEPOSITS
Nomash
River
Profile
Yield rate
(m3/m)
Volume balance
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0 200 400 600 800 1000 1200DISTANCE (m)
500
600
700
800
900
1000
1100
1200
ELEVATION(m)
ROCK SLIDE
COARSE
DEBRIS
LAKE
DEPOSITION
0 200 400 600 800 1000 1200
DISTANCE (m)
0
20000
40000
60000
80000
100000
VOLUME
PASSING(m3) ROCK
DEBRIS
TOTAL
EROSION
0 200 400 600 800 1000 1200DISTANCE (m)
-750-500-250
0250500750
YIELDRATE(m3/m)
ROCK
DEBRIS
DEPOSITS
AVALANCHE
Eagle pass slide, B.C. Interior
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Material entrainment:
1.Increases volume2. Lubricates base of the slide
3. Increases mobility
EAGLE
NOMASH
1x104
1x105
1x106
1x107
1x108
1x109
1x1010
1x1011
VOLUME (m3)
0.1
1
0.2
0.3
0.4
0.5
0.60.70.80.9
TANa
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Entrainment of material from path
Acceleration =
Gravityfrictionpressure -momentum correction
Moving
Coordinate
system
m
v
dt
dm
dx
dHgk
H
Tg
dt
dv
cossin
(Hungr, 1995)
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2
tan)(V
uT
Voellmy model (Voellmy, 1955, Koerner, 1976)
Rapidly shearing,
saturated
undrained?
zone
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0 500 1000 1500 2000 2500
DISTANCE (m)
0
100
200
300
PA
THWIDTH(m)
300
400
500
600
700
800
900
ELEVATION(m)
WIDTH
EROSION
0 500 1000 1500 2000 2500
DISTANCE (m)
0
10
20
30
40
VELOCITY(m/s)
FRONT
TAIL
Model with material entrainmentNomash River slide, 1999
Source volume: 370 000 m3Entrained debris: 400 000 m3
Frictional Voellmy (0.05, 400)
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DAN 3D analysis
0m 1000m
measured trimline
simulated source slide
simulated entrainment zone
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@ 30s intervals:
0s
3600m3
30s
49644m3
60s
75523m3
90s
75838m3
120s
75864m3
150s
75864m3
180s
75864m3
0m 1000m
- assuming rheology changes following
interaction with path material
(frictional - Voellmy)
NomashDAN 3D
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frictional - Voellmy
NomashDAN 3D
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Cervinara, Italy
- shallow failure in anartificial cut
- transformed into a
large debris avalanche
by stripping up to 2m
of
surficial material from
its path- large increase in
volume influenced
extent of impact areaCourtesy Prof. F.M. Guadagno, Italy
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Cervinara, Italy
measured trimline
simulated source slide
- assumed 3600 m3 initial failure
0m 1000m
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Cervinara, Italy
measured trimline
simulated source slide
simulated entrainment zone
- assumed 3600 m3 initial failure
- assumed 2m maximum erosion depth
0m 1000m
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Cervinara, Italy
0m 1000m
0s
3600m330s
49644m360s
75523m390s
75838m3120s
75864m3150s
75864m3180s
75864m3
@ 30s intervals:
simulated flow margin
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Cervinara, Italy
simulated final erosion depth0m 2m
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Cervinara, Italy
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Huascaran, 1970
Source:
5 million m3 rock
9 million m3 ice
Entrainment:
39 million m3 debris
Total:
53 million m3 deposits
8.214
39
source
entrained
V
VER
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Huascaran, entrainment zone39 000 000/5 000 000 = 8 m average?