10th Asian Regional Conference of IAEG (2015)

Slope Stability Analysis and Prevention Measures in D Area of South Part of
Baiyun’ebo Open-pit Iron MineZHANG Bin, YE Fujian, WANG Yang, LIN Weiru, ZHANG Zhongjian
School of Engineering and Technology, China University of Geosciences, Beijing 100083, China
Abstract
Landslide is one of the most common disasters of open-pit mine because of the characteristics ofhigh slope body, large gradient and frequent blasting vibration. This paper takes the main field of
Baiyun’ebo iron mine as an example. The engineering geological conditions and rock mass structure
characteristics and parameters were obtained by field investigation, and the rationality of rock and soil
strength parameters was verified by numerical inversion analysis. The 3D data of 2# slip mass was
obtained by three-dimensional laser scanning technique, then the numerical model of slip mass wasestablished based on the three-dimensional data. The current stability of slip mass was analyzed by
FLAC3D numerical calculation software. It is concluded that the slip mass is in the unstable state. In
order to ensure the mine mining construction and safety of personnel in the future, this paper intends tostudy the control measure of the slip mass which is cutting slope and reducing load, and analyses thestability of the slope with the control measure. It is concluded that the slope is in steady state after thethe control measure.
Key words: three-dimensional laser scanning, stability analysis, management

Introduction
One of the most common kind of geologicaldisasters in open-pit mine is a landslide which is
caused due to the height and gradient of theslope of open-pit mines coupled with the
influence of fracture zone, dikes and blastingvibrations. The sliding mass has physical andmechanical properties of a wide grading andhigh degree of loose, which makes the stabilityof the sliding mass poorer. As a result, thestability of the sliding mass should be analyzed,
and some reasonable measures should be put
forward to reduce the influence of safety
production of mine area.
Baiyun’ebo iron mine area is located in
150km north of Baotou, Inner Mongolia. The
main mine is nearly east-west distribution,
3.5km in length, 1.9km in width, covering 4.8
km2, it is shown in Figure 1.The horizontal layer
stripping method is adopted to improve themining in the main mine of Baiyun’ebo. Now it
is mining to 1556m elevation. There is a great
deal of difference between the ultimate goal ofmining main mine to 1230m elevation which isput forward by Anshan mining design andresearch institute in 1987 and current 1556m
elevation. As the exposed stope slope condition
shown, in the south of main mine, the lithology
and structure is complex. Fault fracture zones
and dikes are wide and large, and their strike issimilar to the strike of the slope, tend to bevertical or tilting. It is harmful to the stability ofthe slope, and the step close to boundary obvious
slide and collapse[1]. The 2# slope in D areastudied in this paper is located in the south part,as shown in Figure 2.The altitude of the area
where the slope located in is 100m, and the area
was divided into 5 working platform which is+1650,+1626.+1598,+1570.+1556, the generalslope angle is 41°- 44°. The landslide occurredin +1570-+1650 working platform, the typicalprofiles and photos of landslide mass wasrespectively shown in Figure 3,Figure4.
According to Baiyun’ebo main mine ultimate
design, the second installed ore crushing plant
will be built in the lower part of the sliding bodywithin the elevation of 1480-1514m. Therefore itis necessary to study the stability analysis andcontrol measure of the slip mass.

Figure 1 Baiyun’ebo iron main mine, mirror
image 50°1

10th Asian Regional Conference of IAEG (2015)

fault. Baiyun’ebo group is a set of low
greenschist facies volcanic and terrigenous
sedimentary rock. It is mainly composed ofmetamorphic glutenite, feldspar quartz sandstone,
slate and crystalline limestone. According to theInner Mongolia regional geology data[2],Baiyun’ebo group is divided into six
formation-complexes, as shown in fihure 5.

1626

1598

A
1570
M

1626

B

E

2# sliding mass
C

D

1598

1626

1650

Figure 2 Baiyun’ebo iron main mine stope
partition map

elevation（m）

1650

1625

Figure 5 geologic map of Baiyun’ebo mine area

1600

1575

1550
0

20

40

60

80

100

120

140 m

form line before sliding
form line of sliding mass

Figure 3 Profile of 2# slope in D area of mainmine

1-Early
Proterozoic
basement
complex
2-Baiyun’ebo
group
H2
quartzsand
conglomerate 3- Baiyun’ebo group H2 White
quartzite 4-Baiyun’ebo group H3 dark slate
5-Baiyun’ebo group H4 dark quartzite
6-Baiyun’ebo
group
H5
dark
slate
7-Baiyun’ebo
group
H8
domolite
8-Baiyun’ebo group H9 feldspar slate
9-REE-Nb-Fe ore body 10-Hercynian granite
11-alkaline dikes 12-basic dikes 13-Tertiary
sedimentary rock
14-main fault
15-theexposure point of igneous carbonates dikes
16-sampling location of carbonatite dyke;
17-sampling location of sodium hornblende rock
2. Landslide stability analysis
In this paper, Fast Lagrangian Analysis ofContinua software FLAC3D was used to analyze
stability of the slope before landslide, current
slip body and slope under governance measures.
2.1 Building modelWith the constant expansion of application of
FLAC3D in the geotechnical engineering,people realized that the accuracy of the model
will affect the results of numerical simulation[3].
The reason of inaccuracy modeling of FLAC3D
includes: 1. Pretreatment of FLAC3D haveproblem of big work load, complicated process
and low degree of visual. As a result, the model
had to be simplified to reduce the workload ofmodeling.
2.
Geotechnicalengineering
geological survey information is the original

Figure 4 picture of 2# slope，mirror image 300°
1. The engineering geological conditions
The tectonic structure of Baiyun’ebo region
belongs to the cohesive zone of northern marginof north China platform and Inner Mongolia-thegreater hinggan mountain fold system. It isbelong to the northern margin of north China
landmass range as a whole. There are two nearly
east-west trending big fault in this area:
Wulanbogeli fault and Baiyun’ebo-Baiyijiaolake

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10th Asian Regional Conference of IAEG (2015)

data of building model. Its accuracy directly
affects the accuracy of the model. To improve
the inadequateness of FLAC3D pretreatment, thedomestic and foreign experts have tried a lot of
explorations: such as developing FLAC3D
pretreatment
programbyprogrammingstatements, using the function of pretreatment ofThree-dimensional modeling software or finite
element software(such as MIDAS , ANASY) inmodeling complex terrain[4-6].But there are few
studies about how to improve the accuracy of thegeological survey data which is used to establish
numerical
model.
In
this
paper,
three-dimensional laser scanning technology was
used
to
solve
the
problem.
Three-dimensionallaser scanner is shown in
Figure 6. Three-dimensionallaser data can becollected from object fast through thistechnology.
Every
one
of
Three-dimensionallaser data in the laser point
cloud is real data which are directly collected
form target. It makes the post-processing of data
completely reliable. This technology havecharacteristics of non-contact measurement, highdata sampling rate, active emission of scanninglight source, high resolution, high precision, thedigital acquisition, good compatibility, etc.[7]Figure 7 3D model of 2# slope of Baiyun’ebo
2.2 Parameter selection
Joint fissures and large faults are developedin Baiyuebo main mine slope. The slope rockmass are eluvial layer or fully weathered rockstratum, with structure of bulk solid andfragmentation. Considering the factor of
unloading rebound and blasting vibration during
excavation of the mine, about 30m cover layer ofthe slope surface are identified as dolomite
fracture zone in the stability analysis(i.e.,weathered zone). Mechanical parameters ofweathered zone decrease comparing withdolomite bedrock. Rock physics index values
can be seen as rock mass physical index standard
values; Internal friction angle of rock mass
standard values can be determined by Internal
friction angle of rock multiply by reduction
factor 0.80-0.95 according to the integrity ofrock mass; cohesion standard values of rockmass are determined by cohesion standard
values of rock multiply by reduction factor
0.20-0.30[8]. Combined with investigation reportof Study of over 1598m slope stability andcomprehensive management measures in
Baogang Baiyuebo main iron mine, parameters
are selected as Table 1.

Figure 6 three dimensional laser scanner

Table 1 The sliding body material parameters
material

volume-weightcohesion（C/MPa）

3γ（kN/m ）Internal friction Angleφ

Weathered dolomite

28.0

0.07

29.0

Fresh dolomite

29.0

0.435

38.0

Slip accumulation body

26.0

0.01

15.0

of this slope can be modeled (Fig. 8). The 3D
size
of
this
calculation
model
is
188m×240m×118m. This paper uses solid
elements and mixed meshes (include four-node
tetrahedron units, five-node pyramid units,
6-node triangular prism units and 8-node
hexahedron units) to simulating the rock soil
mass. The calculation model has 91171 units and56738 nodes in all. Its computational accuracy is
1×10-5.

2.3 Stability Analysis
2.3.1 Stability Analysis of the Slope before
Sliding
In order to verify the parameters given byForm 1, this paper calculates the stability of theslope before sliding. According to the Slope
design information which is provided by the
Final Boundary Map of the Main Orebody of
Baiyun’ebo, the three-dimensional (3D) model3

10th Asian Regional Conference of IAEG (2015)

actually happened phenomenon of the side slope
slippage (2# landslide). It means that theparameters of the slip mass are accordant withthe real situation.
2.3.2 Stability Analysis of Slip Mass
By analyzing the stability of the slip mass,
the possibility of its continued sliding can be
judged. The calculation model is shown by
Figure 7. The 3D size of this calculation modelis 188m×300m×118m. This paper uses solid
elements and mixed meshes (include four-node
tetrahedron units, five-node pyramid units,
6-node triangular prism units and 8-node
hexahedron units) to simulating the rock soil
mass. The calculation model has 91448 units and47852 nodes in all. Its computational accuracy is
1×10-5.

Figure 8 3D model of Slope terrain before
sliding

Figure 9 Slope stress distribution nephogram
before sliding

Figure 12 Slope stress distribution nephogram
after sliding

Figure 10 Slope shear strain increment
nephogram before sliding

Figure 13 Slope shear strain increment
nephogram after sliding

Figure 11 Slope plastic zone map before sliding
The data of shear strain increment in Figure
10 show that the shear zone has a breakthroughpoint on the surface. At the same time, big
plastic zones can be found above the formation
region of the shear zone and all of them have ashear failure (Fig. 11). Considering the shear
zone and the plastic zones, this slope is most
likely to sliding along the connecting plastic
zone. This conclusion is in conformity with the

Figure 14

Slope plastic zone map after sliding

The data of shear strain increment in Figure
13 show that there is a connecting shear zone
around the slipping zone. So the slipping zone isin danger of continued sliding. The fully plastic

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10th Asian Regional Conference of IAEG (2015)

distribution appears in the slipping zone. The
failure of the most part of it is shear failure andthe small part of it belongs to tensile failure. (Fig.
14) Considering the shear zone and the plastic
zones, a conclusion is obtained: this slope ismost likely to sliding along the slipping zone.
Furthermore, there is a connecting shear zone at
the step of the right side (west side) of theslipping zone. There is a huge possibility that thecontinued sliding of the slipping zone would
drive the surrounding weathered zone sliding.
2.3.3 Stability Analysis of the Slope after

Figure 16 3D model of slope terrain after
cutting slope

Cutting
Now this slip mass is in a state of flux. It
might slip and become a landslide at any time.
The landslide will not only affect the safety ofmining and threat to the life safety of the staffs
who work in the mine area, but also directly
influence the construction of the second phase ofore crushing plant which is below the landslide.
Therefore, it is necessary to take effective
measures to prevent and control the side slope.
This paper proposes a control plan by cutting
slope and analyzes the stability of the slope after
cutting by using numerical simulation method.
The typical cross-sections of the slip mass before
and after governance are shown by Figure 15. As
can be seen from the cross-sections in Figure 15,
the overall slope angle is decreased roughly from
47° to 41° after slope cutting. The calculation
model of the side slope after cutting is shown by
Figure 16. Its 3D size is 188m×300m×118m andtotally has 154681 units and 98940 nodes. The
computational accuracy of the model is 1×10-5.

Figure 17 Slope stress distribution nephogram
after cutting slope

elevation（m）

1650

Figure 18 Slope shear strain increment
nephogram after cutting slope

1625

1600

1575

1550
0

20

40

60

80

100

120

140 m

form line after slope cutting
form line of sliding mass

Figure 19
slope

Figure 15 Typical profile before and after
treatment of landslide

Slope plastic zone map after cutting

The shear strain increment nephogram in
Figure 18 shows that there is no connecting
shear zone in this side slope. Even though there
are some shear zones, they do not link to eachothers. The distributions of plastic zones in
Figure 19 shows that most of them are located in5

10th Asian Regional Conference of IAEG (2015)

the bottom of the side slope. And all the failureof the plastic zones are shear failure. However,there is no obvious plastic zone appeared in the
cutting area. Considering the shear zone and theplastic zones, it can be said that the side slope ismore stable after cutting.

Nationalmajor
scientificinstruments
development project of National Natural Science
Foundation of China (61427802)and the Central
university funding basic scientific researchbusiness project(2-9-2015-071)for the researchwork.

3 Conclusion
After the 2# side slope of Baiyun’ebo Main
Orebody slipping, the representation of its
geological structure becomes more complex.
Using the traditional modeling method can notmeet the requirement of accuracy. This paper
uses 3D laser scan technology to get the 3D dataof geological representation structure, and then,establishes the calculation model by using
FLAC3D according to the 3D data. This method
possesses the advantages of fast modeling andreflecting the 3D topographic and geologic
shape accurately. In addition, the mathematical
calculate model can provide guarantee forgetting the more reliable result of numericalsimulation.
Using FLAC3D combined with 3D laser
scanning technology builds the calculation
model of the 2# slip mass of Baiyun’ebo Main
Orebody and does the simulate calculation.
Combined with the 3D laser scan technology,
the calculation model of the 2# slip mass of
Baiyun’ebo Main Orebody is built by FLAC3D
program. Doing the simulate calculation, theresult shows that this slip mass is in a state offlux and the relevant control measures need to betaken. This paper proposes a control plan by
cutting slope. Using numerical simulation
method to analyze the condition after taking thecontrol plan, it can be found that the stability ofthe slope is increased.

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Acknowledgement: Thanks to support

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