entrainment in rock avalanches

7/29/2019 Entrainment in Rock Avalanches

1/31

Entrainment of material in

rock avalanches


2/31

Equivalent

Fluid

Modelling: concept of equivalent fluid

Prototype Model


3/31

St.Vennant Equation, Lagrangian

Acceleration =

Gravityfrictionpressure term (P)

Moving

Coordinate

system

dx

dHgk

H

Tg

dt

dv

cossin

(Savage and Hutter, 1988)


4/31

Dynamic equilibrium of a column

T = resisting stress

Pressure term:

cosHds

dHkP

k

lateral pressurecoefficient


5/31

Material entrainment (Sassa, 1985)


6/31

Displacement of

alluvium, HopeSlide, B.C.

(1964)


7/31

Displacement of alluvium, Frank Slide, Alberta (1903)


8/31

Mt. Ontake rock avalanche, 1984(Voight and Soussa,1994)


9/31

Coal waste dump flow slidesource


10/31

Nomash Slide, Vancouver Island, B.C.

(Photos D.Ayotte)


11/31

Rock slide-debris avalanche

(Map: GSC)


12/31

Nomash River, Vancouver Island


13/31


14/31

Nomash River

debris deposit

proximal

distal


15/31

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


16/31

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


17/31

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


18/31

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)


19/31

2

tan)(V

uT

Voellmy model (Voellmy, 1955, Koerner, 1976)

Rapidly shearing,

saturated

undrained?

zone


20/31

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)


21/31

DAN 3D analysis

0m 1000m

measured trimline

simulated source slide

simulated entrainment zone


22/31

@ 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


23/31

frictional - Voellmy

NomashDAN 3D


24/31

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


25/31

Cervinara, Italy

measured trimline


- assumed 3600 m3 initial failure

0m 1000m


26/31

Cervinara, Italy

measured trimline


simulated entrainment zone

- assumed 3600 m3 initial failure

- assumed 2m maximum erosion depth

0m 1000m


27/31

Cervinara, Italy

0m 1000m

0s

3600m330s

49644m360s

75523m390s

75838m3120s

75864m3150s

75864m3180s

75864m3

@ 30s intervals:

simulated flow margin


28/31

Cervinara, Italy

simulated final erosion depth0m 2m


29/31

Cervinara, Italy


30/31

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


31/31

Huascaran, entrainment zone39 000 000/5 000 000 = 8 m average?

entrainment in rock avalanches

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