10th Asian Regional Conference of IAEG (2015)

Experimental Study on the Formation and Evolution of Granular Mixtures Slope
Selection Result
Li Ning(1), Fu Rong Hua(2)(1) Chengdu University of Technology, Chinese,E-mail:79062693@qq.com(2) Chengdu University of Technology, Chinese
Abstract
The experiment simulation which was carried out in the slope model of our own
reproduces the movement process of granular slope particles and the accumulation process,studies its movement, accumulation and its fractal characteristics. It was found that the
average rules of a single particle migration distance is bigger than irregular particles,
particles migration distance and particle size of itself does not present a clear relationship,
and the morphology of particles in contact with the ground when one of the main factors
influences the particle migration distance; the worse the grain composition is, the greater
failure the slope angle of slope is, and vice versa; the side slope unstable particles controls
the critical angle; grain quality——particle size distribution fractal dimension increases withthe content of fine particles, and the fractal dimension decreases gradually since the slope
body is composed by an upper and a lower, suggesting that slope body evolution throughthe process of self-organization spontaneously and showing the self-organized criticality.
Keywords: grain body slope, movement characteristics, accumulation characteristics, fractal
characteristic
the formation of sand-sliding slope evolution as anevidence of Quaternary climate change in the Alpine
high altitude. Through a variety of advanced
geophysical methods (GPR) to detect the internalinterbedded structure of coarse particles, predicting
the rate of the rock weathering, then putting forward
the formation and evolution of sand-sliding slopemodel [ 2-5 ].Domestic study of sliding sand disasters
was only in its infancy and in the traditional
geomorphology it was classed as general weathering
debris deposits, yet the dedicated research haven’t
been conducted. With the great western development ,sand sliding hazard effects on the highway
construction is increasingly apparent, Liangguangmo
et al [ 6-9 ] studied the evolution of the formation ofsand -sliding slope , granular structure characteristics ,factors and particle motion model from theperspective of disaster science through field visits andlaboratory model test .Jiang Wei Liang et al [10-12 ]continued the research ideas of foreign scholars’ fromthe perspective of self-organized criticality, having
indoor systematic experimental study about its
dynamics, proposing sand granular layer and rub
blocking layer dual structure model [ 13 ] .

Preface
In the first slope zone of the Sichuan Basintransition to the Qinghai-Tibet Plateau and thehinterland of Tianshan Mountain, Qilian Mountains,formed a large number of grain body slopes by
scattered debris, commonly known as "slip sandslope." Especially in cold, drought, severe physicalweathering western region, this phenomenon isparticularly prominent. In the mass transportation ofwestern region, "slip of sand slope" is often existed as
road slope. Since the "mess" feature, Granular Slopeis sensitive to disturbance, so the Granular Slope on
the both sides of the road often caused silt buried
hazards to the road, usually with amazing speed
forward.
Foreign scholar study of sand-sliding slope began
in the middle of 20th century, it was limited to thenaked eye on the surface characteristics of theobserved slope, which made a number ofinconclusive or even contradictory opinions [1]. In the
21st century, Western scholars gradually from theperspective of Geomorphology and Quaternary
Geology proposing a "Alpine mode ", which regards

1

10th Asian Regional Conference of IAEG (2015)

1.Experimental Design
According to preliminary field investigation
combined with the actual situation of indoor venues
designed test platform dimensions with length 3.5m,
width 7m, height 3m, see Figure 1.
Top sand operating space

the particle shape characteristics of particle motion.
On this simulation platform, the test platform size in
Figure 1 changed to 9.6m in length, 3m in width,
6.8m in height, with slope of 45 and on the surface ofthe slope covered with mortar cement in advance). A
total number of 24 particles selected form former
materials with grain diameter of 3cm and 8cm. eachspecies take 6 caps regular in shape and 6 irregularity
in shape.
In slope movement, the time when the particles
reach the slope toe and the time of stop is different,
which is depends on the particle's mass, shape, path
differences. Table 2 gives each particle arrival time at
the foot of the slope.

Top sand equipment

The left side of theglass retaining wallGri

The building
based on60°concretretaining wall

Table 2 Time Comparison Table of Particles Reach
the Slope Toe

The pipe support
at the bottom

Figure 1 Schematic Diagram of Bulk Solid
Stacking Test Platform

Particle

The

The

The

The

The

The total

numberleast time

averagelongestaveragetotal

averagevelocitytime（s） velocity

average

speed

（m/s）

（m/s）

time（s）

（m/s）

（s）

In this experiment, the material takes from theuniform of a Granular Slope in WenChuan County,
three kinds of materials was prepared, including thesmall gravel particles(1# ) with non-uniformity
coefficient of 3.8, the curvature coefficient of 1.24,
The gravel particles (2#) with the particle size of
about 6 ~ 10cm and the mixing gravel particles(3# )with the uniformity coefficient of 7, thecurvature coefficient of 1.16. The particle size
distribution of various materials showed in Table 1.
Three different graded granular materials test was
repeated nine times.

3cm Rules of

2.55

3.79

2.68

3.63

2.58

3.73

2.62

3.68

2.72

3.57

2.66

3.65

2.85

3.39

2.93

3.32

2.91

3.35

3.01

3.21

3.1

3.14

3.06

3.43

particlegroup
3cm Irregularparticlegroup
8cm Rules ofparticlegroup
8cmIrregularparticle

Table 1 Test sample of particle size distribution

group
Serial<80 <60

<40

<20

<10

<5

<2

<1

<0.5

<0.25 <0.074

For a better comparison, each group of particles arecarried out free-fall tests, for free-fall campaign, thereis,number1#

100 89.47

2#

100

3#

100 69.72

64.31 27.63 10.67 3.51 0.82

0.61

0.22

0.15

0

4.21 1.56

0.52

0.25

0

0

55.39 29.67 15.93 7.12 2.40

1.18

0.93

0.59

0

17.27 12.31

9.28

6.50

1
H  at2 （1）2

2 Experimental Results and Analysis
2.1 Characteristics of particle motion study
Experimental design in this large-scale simulation
platform Granular Slope ( through field observations
and experimental studies , combined with previous
research shows that granular particles in the plane
mainly have three kinds of movement, including
slipping, rolling and slip - scroll alternately [ 14 ].
In order to further analyze the movement of sandparticles slip characteristics, we selected four groupsof single particle rolling materials. By testing, we got
exercise time, the quality of the state of motion and

2

E 

1 2 1
1  2H 
H2
mv  ma 2 t 2  m 2  t 2  2m 2 （2）22
2  t tAmong them: H is the height of free fall ; t is time ; ais the acceleration ; E is the kinetic energy ; m is theparticle mass
Calculate the kinetic energy of each group
particles when they arrived at the bottom: the kinetic
energy of the 3cm rules particles is about 0.347J; thekinetic energy of the 3cm irregular particles is about210th Asian Regional Conference of IAEG (2015)

0.196J; the kinetic energy of the 8cm rules particles
and the 8cm irregular particles were 1.638J and1.501J respectively. Visible, for the same kind ofparticle size of particles, the kinetic energy of therules particles when reaches the bottom is larger than
the irregular one; for different size particles, thekinetic energy of the bigger particle size whenreaches its bottom is larger than the small one.
Because irregular particles use more energy whencontact with the slope, so the kinetic energy arriving
at the end is smaller.
The time and speed for each group of particle free
fall showed in the table 3.

approximation for uniformly accelerated motion.
2

distance（m）

12 y = 0.3554x + 2.7972x + 0.0146
2
10
R = 0.9778
8
6
4
2
0
0 0.5 1 1.5 2 2.5 3 3.5time（s）

The total average

The total averagetime（s）

speed（m/s）

3cm rules of particle group

1.15

5.91

3cmirregular particle groups

1.20

5.67

8cm rules of particle group

1.10

6.18

8cm irregular particle groups

1.25

5.44

10

distance（m）

Particle number2

y = 0.0279x + 3.4567x - 0.1155
R2 = 0.984

12

Table 3 The comparison table for particles free
fall stop time

8
6
4
2
0
0

0.5

1

1.5

2

2.5

3

3.5

time（s）

Figure 2 Distance - time curve of particle
movement ( above is 3 cm rule particles,
below is 3 cm irregular particles）

Compare Table 2 with Table 3, the fastest timethat the particles move to the slope toe is about 2times faster than free-falling. The kinetic energy of 4groups particles when they move to the slope toe
through free-fall were 1.748J, 0.963J, 11.464J,
8.996J( height of 6.8m), visibly，the kinetic energy ofparticles when arrive at the slope toe through theslope movement is about 0.143 ~ 0.204 times thanfree-falling.
Through the test data, found a certain relationshipbetween particles in slope movement time anddistance, with expression is as follows:

distance（m）

12

y = 0.0027x 2 + 3.3387x - 0.138
R 2 = 0.9933

10
8
6
4
2
0
0

0.5

1

1.5

2

2.5

3

3.5

time（s）
12

y = 0.0978x 2 + 3.0492x - 0.2196
R2 = 0.9932

10

distance（m）

s  xt 2  yt  z （3）Among them: s is the movement distance;
x, y, z for sports-related parameters ;t is the exercise time .

8
6
4
2
0
0

The expression regression curves of the distancetime curve of each group particles, as is shown in the
Figure 2 and 3, were consistent with the formula 3.
Visibly, the distance and the time of particles
movement on the slope shows a parabola relationship,
and coefficient of determination reached 0.99. The
constant x in the equation values is between 0.0027 ~0.3554, because v  ds/dt 2xt  y , so the particle
motion acceleration value is the 2x, namely theacceleration valueis between 0.0054 ~ 0.7108,

0.5

1

1.5

2

2.5

time（s）

3

3.5

Figure 3 Distance - time curve of particle
movement ( above is 8cm rule particles,
below is 8cm irregular particles）
The figure shows the connection for each data
pointed in the local regression equation. There is acertain shift indicated sometimes, the move velocityof particle changes a lot, namely the acceleration is3

10th Asian Regional Conference of IAEG (2015)

large. During this time, the particle jumping motion
may be occur.
In addition, the test also observe and record the
movement of the particles when they arrived at theslope toe, found that the placement is located between
1.55 ~ 9.95m away from the foot of the verticaldistance. Most of the particles are concentrated tostop near the central axis, but the placement of therule particles appears more dispersed than theirregular particles.
Statistical results showed that the average
distance that rules 8cm particles move from the footto the static of the slope is 6.09m, the maximum
average migration distance of rules 3cm particles is
6.21m, corresponding to the particle size of theaverage transport distance of irregular particles is
4.69m and 5.53m respectively. Thus, the averagetransport distance of rule granules is larger thanirregular granules. But test data shows that migration
distance of particles and particle size in itself does notshow a clear link. Perhaps the reason is that the slope
is steep, particles fell on the ground after collision
with slope in the process of movement. Before thecollision with the ground, the tangential velocity issmall. Watch the video replay showed that Shape ofparticles in contact with the ground is one of the main
factors affecting the particle migration distance.

5

7
9
11
13
Stacking sequenceslope angle/°

20
10
0
3

15

Figure7 3# Angle changes before the collapse
The average slope of 1# sample's upper , middle
and lower part before slumping was 35.88 ° ,38.27 °, 33.73 °, the total average gradient was
35.96 ° ; the average slope of sample's upper ,middle and lower part after slumping was 36.66 °,37.34 ° , 35.25 °, the total average gradient is
36.42 °, which increase 0.46 ° than it before
slumping.
The more uniform the sand grain particle is, thewider the slope angle of the slope destruction
becomes; the less uniform the sand grain particle is,the smaller the slope angle of the slope destruction
becomes; on the whole, the angle of slope changes
little before and after the collapse.
( 2 ) Analysis of influence factors
By a single curve analysis, the slope angle of thesame parts in the accumulation process constantly ups
and downs. The angle fluctuation after the collapse
was larger than before the collapse, which isconsistent with the observation of the test site.
Judging from stacking on slope, the large andsmall particles are not evenly distributed. Someregions only spread with large particles, while someother regions with fewer large particles. The
nonuniformity of their distribution makes theinstability of side slope. Under the same condition of
the disturbance, the stability of the large particles area
is better than the area composed of fine particles forthe large particles can deeper embedded into the slope,particles. The heavier the non-uniform degree of theparticles is, the more diversity and complexity of theslope stability is. Large particles can form theskeleton effect supporting pressure from external
while Small particle have the filler effect improving

lower

50
40
30
°

20
10
0
slope angle/

lower

30

1

(1) The accumulation process change in slope angle
slope analysis
By large-scaled physical simulation experiments,
got the slope angle of upper, middle, and lower part of
1 #-3 # test materials slope in the process ofaccumulation before and after the collapse, the changeof the typical as shown in figure 6, 7.
middlemiddle40

2.2 Study on accumulation characteristics of slopes

upper

upper
50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
stacking sequence

Figure6 1# Angle changes before the collapse

410th Asian Regional Conference of IAEG (2015)

the density of sand pile. The Smaller the granular is,
the higher compactness of the sand heap becomes andthen the greater shear strength is. More Large grainedmaterials mean higher compressive strength. The lesslarge particles contain, the more small particles in thesame volume, causing more space and poorer stability;
when the large particles content is more, the sand ismore dense and the weight of unit volume is greater;when the size of the particles volume arrive at a
certain ratio, the gap in sand will be filled with small
particles, the density can reach maximum .The resultsthat Jiang hongying got through the different ratio ofcompressive strength test also verified this point ofview.
When the slope is large-scale instability, themajority of the subsequent slump occurred in the fineparticle level which is formation after the firstlarge-scale instability, suggesting that the fineparticles play a controlling role in the stability ofsand-sliding slope. The fine particle level in the slope
is formed by the separation of the fine particles whichcause the fine particle gathered and infiltrated tounder part of the slope. With the stacking of fineparticles, the content of fine particles also constantly
increases. When the slope collapse on a large scale,slipping particles can bring fine particles out of theslope, the fine particles content of slope would reduceat this time, when reduces to a species degree (Whenthe regulatory role of the fine particles severely
weakened), the sand stacked again, and repeat above
processes.

M(r  R)  R 
  MT
 RL 

3 D（4）

Among them： R is the particle size;
M (r<R) is particle size less than R pellet quality;
RL is the maximum particle size;
MT is the total mass of particles;
D is the dimension.
Calculating the fractal dimension of different
parts of the slope in this experiment , sampling a totalof 13 groups, sampling in each set of upper, middle,
lower part of the three parts of the slope, sampling a
total of 39 times. The specific fractal dimension are
shown in table 3, figure 8.
1. The quality of particles soil slopes deposits -- thedistribution of particle fractal dimension
Fractal dimension values in Figure 8 were
between 2.0 and 3.0, and the fractal dimension
increases with the increasing of the slope height, thefluctuation difference of the lower part of the curve isbigger, the upper is small. The average fractal
dimension value of the upper slope is 2.3706; theaverage fractal dimension value of the central
measurement point is 2.3607. Fractal dimension are
all above 2.2377, indicating that the heap size
composition of the sand has a good fractal structure,
the structure of the sand conforms to the fractal
distribution.
2. Distribution of Granular Slope deposits granularity
Granular Slope particle buildup is obvious
distributed, although the accumulation distribution
along its height direction is quite different. The
content of fine particles decreases from top to toe ofslope, while coarse particle content gradually
increases.
3. Quality of the particles slope debris - relevance
between particle size fractal dimension andgranularity
Heap fractal state during the test is as shown in
the figure 8, the fine particles gradually reduce fromtop slope to bottom while the coarse particles isincreasing. Particles presents sorting characteristics
in the process of accumulation, Thus the quality ofthe particles slope debris -- particle size fractal
dimension increases with the increasing of thecontent of fine particle. Fractal dimension decreases
from top to bottom, indicating that the slope evolved

2.3 Study on fractal characteristiccs of particle
Sampling from different parts of the accumulationbody during the process of experimental, followed by ascreening test and weighing, to study sand particles’
fractal characteristics by use of the fractal model ofparticle size distribution which raises by d Yler et alunder the assumption that particle density is under thesame conditions.

510th Asian Regional Conference of IAEG (2015)

through process of spontaneous self-organization,
embody the self-organized criticality. Particle
composition of the slope deposits can be characterized
by the fractal dimension value of size, the higher thedimension points is, the more accumulation of fineparticles in composition have, whereas the smaller thefractal dimension is, the smaller the fine grains are.
Test each measuring point data basically reflect thisrule, see Table4.

3 Conclusions

1, The average transport distance of a single ruleparticles is larger than the irregular particles for
irregular particles consume relatively more energy
during movement after makes contact with the rearslope due to its irregular shape , so the kinetic energy
is relatively small , its migration distance is evensmaller .
Migration distance, the size of the particles andthe particles themselves exhibit no obvious link.
Maybe the reason is that slope was too steep, theparticles collide with slope during movement, thenfalling on the ground, and its tangential velocity issmall in front of collision with the ground.
Observe from the test, the horizontal offset
direction is not keep the single constant, during its
movement process, the slope conditions on the offset
direction particles play a decisive role because of thedifferent slope conditions affecting the offset
direction of the particles. Also with the constantdownward motion of the particles, the verticaldisplacement continues to increase.
2, Experimental data statistics showed themore uniform the particles were, the wider the slope
angle of sand slope destruction becomes; and themore uneven the particles were, the smaller the slope
angle of sand slope destruction becomes; the slope
angle of the same parts sand slope constant ups anddowns during the slope accumulation process.
3, During the accumulation process of particles,
the most unstable particles in the slope controls thecritical angle, therefore, the poor stability of thisregion is due to the particles of this part has reached acritical state; in addition, the area that has not yet
reached the critical state of proportion also affects theoverall stability of the slope, the overall stability ofthe slope body is composed of the sum of the partial
ones.
4, Experimental observation shows that the fineparticles gradually reduce from top slope to bottom
slope while the coarse particles increasing.
Fractal dimension decreases from top to bottom,
indicating that the slope evolved through process of
spontaneous self-organization, embodying theself-organized criticality. Particle composition of theTable 4 The fractal dimension and unevencoefficient of each part of the slope
Numberfractal dimension

coefficientup

middlelowup

middlelow

12.34412.31182.30490.9476

0.96150.96442

2.30842.31752.29330.971

0.9556

0.96363

2.36662.38742.35090.88220.92040.935642.33412.31792.3306

0.95450.95890.930552.35762.38832.36830.93350.89360.930862.35972.32742.33530.93710.96030.954272.40172.38242.34490.89430.92610.93328

2.36772.40592.26570.92490.96090.973

92.40822.30832.38870.89080.95910.920110

2.421

2.40252.36

0.87380.89840.9359112.40042.37612.35440.88590.93290.9356122.4009

2.394

2.44

0.861

0.91580.822413

2.34732.369

2.23770.9446

0.92330.9623

middlelower

Fractaldimensi on

upper
2.5
2.45
2.4
2.35
2.3
2.25
2.2
2.15
2.1
1

2

3

4

5

6

7 8 9 10 11 12 13
The serial number

Figure 8 Granular fractal characteristics of theparticles in the slope‘s each part during theaccumulation process610th Asian Regional Conference of IAEG (2015)

slope deposits can be characterized by the fractal
dimension value of size, the larger the dimension
points indicates more accumulation of fine particles
in composition and smaller the ratio of the length ofthe particles shaft, whereas the smaller the fractal
dimension is, the smaller the fine grains is and thebigger the ratio of the length of the particles shaft
becomes.
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