A v a l a n c h e

D y n a m i c s

a n d

D e f e n ce

Table 1.Summary of chutes

Table 2.Summary ofparticles

Chute No.LengthWidthInclinationLocation
mmdegree

ParticleWeightDiameterBulk densityMax. Number
gmmkg/m³

1
2
3
4
5*
6*
7*
8*
9*
10

20
20
40
20
2
2
2
2
2
2

1.0
0.9
0.4
0.9
0.05
0.075
0.1
0.125
0.15
0.05

30
40
40
30
free
free
free
free
free
free

Shinjo
Tohkamachi
Tohkamachi
Nagaoka
-
-
-
-
-
-

TTB 1
TTB 2
TTB 3
PB
GB 1
GB 2
SFP 1
SFP 2
SFP 3
SFP 4
PP

2.5
2.2
2.0
7.0
45
25
0.0033
0.0008
0.0002
0.0026
0.11

38
44
38
40
43
43
6
3-4
1.5-2
5
5

64
37
52
155
750
445
8.2
13.2
16.8
22.3
600

30000
2000
2000
2000
1000
2000
2700
15000
18000
7500
1200

*Halfpipe chutes.

3. RESULTS

3.1 Head-tail structure

Fig.3 shows typical examples of the side views of TTB ava-
lanches andGB avalanches, etc. at the window 18m down
from the starting position.These pictures are successive
snapshotstakenbyahighspeed videocamera inevery
0.25sec.TheTTBavalanchesoflightparticleshavea
head-tailstructure.In the GBavalanches ofheavy parti-
cles,however,thehead-tail structure isnotformedyet,

*Bulkdensities forTTB,PBand GB are theoretically
given by the closest packing.

but the particles are scattered at the front end as well as at
the rear end. These results are similarto those of SFP and
PP avalanches on reducedscale in comparison with TTB
and GB avalanches.

3.2 Variation of velocity

The variation of the front velocity of a TTB avalanche from
start is shown in Fig.4. In the avalanchesfirst, the velocity
increases with distance from the start point and then the
steadyoneisalmostreached.On theotherhand,GB
avalanchesare still accelerating during theseexperiments.

Fig.2 Particles used in theseexperiments.Fig.3 Side views of model avalanches.

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