Engineering, 2010, 2, 201-204
doi:10.4236/eng.2010.23029 lished Online March 2010 (http://www.SciRP.org/journal/eng/)
Pub
Study on the Law of the Movement and Damage to Slope
with the Combination of Underground Mining and
Open-Pit Mining
Gaofeng Ren, Xingkui Fang
School of Resource and Environment Engineering, Wuhan University Of Technology, Wuhan, China
Received October 10, 2009; revised November 21, 2009; accepted November 26, 2009
Abstract
Under circumstances in which both underground mining and open-pit mining are employed, the mining ef-
fects of two approaches will be superposed and the mining slope will receive several induced stress fields,
which makes the sliding mechanism and deformation law of slope rock mass more complicated. This paper,
targeting at the east slope of Antaibao Mine with the joint employment of underground mining and open-pit
mining, aims to study the moving law of the slope rock mass and the damage mechanism to the overburden
of the goaf by numerical simulation. It is supposed that models of possible damage to the slope could be ex-
plored for guidance to safety-production of the mine.
Keywords: Combination of Underground and Open-Pit Mining, Mining Damage, Deformation Mechanism,
Numerical Simulation
1. Introduction
Underground mining will damage the balance of the
ground stress and cause the surface movement of rock
mass, leading to mining damage in these areas. However,
in cases where both underground mining and open-pit
mining are employed, the mining slope will receive inte-
grated superposition according to the corresponding rela-
tion of the extraction level and the superposition process
of mining effect. It exhibits as a kind of mining effect
which interferes or acts to another balanced system,
making two types of excavation body arouse and inter-
fere mutually, and constitute a complex dynamic system.
Many domestic and abroad scholars have participated in
the study of Strata Movement and Mining Subsidence,
one of the bases in mining, and made many valuable re-
search results. Some coal-producing countries in Europe
carried out a systematic research on Strata and surface
movement in 1930s. Ever since the 1950s, studies on
Strata and surface movement have been developed vig-
orously. The methods of entire filling stoping, segmental
mining, concerted mining and strengthening building are
used in Germany, Poland, Russia and the United King-
dom, which have overcome the hazards of mining effect
and thus succeeded in coal mining under buildings and
railways, with the establishment of a series of rock and
ground movement theory [1].
The number of mines in foreign countries switching to
underground mining from open-pit mining approxi-
mately doubles every 20 years. Owing to their abundance
of natural resources in the United States, Canada, Aus-
tralia, there is less necessity for underground mining in
their mines. Therefore, the main researches focus on
when the switch happens. While many domestic large
and medium-sized mines have of the need for deep min-
ing, China is facing the problems associated with the
process of switching as well as joint exploitation of sur-
face and underground extraction. Yet, joint exploitation
hasn’t drawn enough attention in mining-developed
western country [2].
Based on the investigation about the east slope of An-
taibao Mine with the combination of underground mining
and open-pit mining, the article mainly studies the mov-
ing law of the slope rock mass and the damage mecha-
nism to the overburden of the goaf during different stage,
with the expectation of systematically exploring models
of possible damage to slope and offering scientific guid-
ance to safety-production of the mine.
2. Project Summary
Pingshuo Coal Industry Corporation is a large modern-
ized coal production base constructed in 1985. The Cor-

G. F. Ren ET AL. 202
poration built Antaibao and Anjialing open-pit mine suc-
cession. Joint employment of underground mining and
open-pit mining was approved by original State Devel-
opment Planning Commission in November 2002. An-
jialing mine included two shafts in the mining field ac-
cording to the document of approval and practical situa-
tion: Shangyao and Antaibao Mine, which are developed
respectively. In the second quarter of 2003, the two
shafts were constructed and started test extraction. Dur-
ing the course of test extraction, the impacts of under-
ground mining on surface appeared as surface deforma-
tion, cracking and subsidence that would affect safety-
production of the mine. Especially for the initial extrac-
tion area in Antaibao Mine, of which north and west is
slope of open-pit, mining effect is considerably compli-
cated. It is imperative to determine the law of displace-
ment, and possible manners of destruction and subsi-
dence aroused by mining. Integrant prevention and con-
trol measures should be done to make sure the safety of
surface and underground engineering at the same time.
3. Three-Dimensional Finite Element Nu-
merical Model
Numerical simulation of finite element could simulate a
variety of project activities under circumstances of com-
plex structure, complex boundary and loading. It is a
simulation research method widely used in geotechnical
engineering, which allows for repeated simulation ex-
periments with low cost [3].
Finite element numerical simulation is used in the stu-
dy to analyze the law of rock slope movement and dam-
age to overburden of East slope of Antaibao in B901 in-
tegrative mining face where both underground mining
and open-pit mining are employed. B901 integrative min-
ing face is located 70-110 m beneath the mine slope, and
in the middle of the slope in spatial relations. Finite ele-
ment model is an orthogonal hexahedron. As is shown in
Figures 1 and 2, Y axis stands for the vertical direction,
X, Z axis for “East – West” direction and “South – North”
direction respectively, with the dimensions of three axis
Figure 1. Three-dimensional finite element model.
Figure 2. Finite element mesh map.
as 1785 m, 700 ~ 1000 m, 2500 m accordingly. Numeri-
cal simulation takes into account four different extraction
states: original state, B901 integrative mining face re-
treating mining 500 m, B901 integrative mining face re-
treating mining 1000 m, B901 integrative mining face
mining over. In the process of numerical simulation, the
mined ore body is removed in the numerical model ac-
cording to the speed of open-pit mining and underground
mining, while the surface dump is forced on the model as
external load. The model border restricts its horizontal
displacement and its rotation; the bottom boundary limits
vertical displacement in Y direction and its rotation. The
rock mechanics parameters used in the finite element
numerical model are selected according to field investiga-
tion and indoors rock mechanical experiments [4].
4. Numerical Simulation Results and Analysis
Finite element simulation calculates slope deformation
and stress changes in underground excavating as well as
open-pit mining under the four states. By comparing dam-
age degree of mining slope rock mass in different states,
we can directly determine the law of the movement and
damage to slope with the combination of under ground
mining and open-pit mining. Some of the finite element
calculation results are listed as follows:
Figure 3. X direction displacement in original state.

G. F. Ren ET AL. 203
Figure 4. X direction displacement when B901 face mining
was over.
Figure 5. Average principal stress contour in original state.
Figure 6. Average principal stress contour when B901 face
mining was over.
4.1. Displacement Deformation Analysis
The graph of horizontal displacement deformation shows
that in original state the east-west displacement will slide
down along the East Slope of Antaibao under the influ-
ence of rock slope self-weight stress. With both under-
ground mining and open-pit mining carried on, the min-
ing effects are superposed. The east-west displacement
mainly appears in the middle of the East Slope of Antai-
bao in two forms: surface rock mass sliding in the upper
and middle part of slope; horizontal displacement ac-
companied with mining subsidence of the overburden of
the goaf in the middle and lower part of slope. The hori-
zontal displacement region is in parallel with the B901
and exhibits as large-scale band distribution, while its
movement direction is opposite to that of rock mass
sliding. As the horizontal displacement is caused by sur-
face subsidence in underground mining, rock mass that
falls down will fill goaf and thus helps to increase the
rock slope stability of Antaibao. Therefore in the process
of B901 mining, more attention should be paid to the
local landslide damage in the middle and upper part of
the east slope of the Antaibao Mine.
The graph about vertical displacement deformation
shows that vertical displacement of rock slope mainly
exhibits as surface subsidence. The largest subsidence
region changes dynamically right over the goaf in under-
ground mining. The final decline basin is located right
over the goaf and is oval-shaped in horizontal surface. It
is identical to surface movement basin formed in the use
of long-wall caving.
While the mining work in B901 face is over, the maxi-
mum horizontal displacement (28.99 cm) is located in the
upper part of the east slope, while the maximum vertical
displacement (269.14 cm) is located right above the min-
ing area. The data is similar to the result monitored by
GPS in this region.
4.2. Analysis of Stress Change
While not being affected by underground mining, rock
mass in the original state mainly maintains a sliding
trend with small tenslie stress of about 0.83 MPa. In the
process of joint mining, stress in rock mass is redistrib-
uted, and induced stress constantly generates and super-
poses each other. When the mining work in B901 is over,
the average principal stress shows the appearance of high
accumulation of tensile stress ranging from 9 to 17 MPa
in goaf boundaries, the accumulation of compressive
stress ranging from 50 to 80 MPa in the top of non-min-
ing area, and tensile stress of about 1.32 MPa in the up-
per and lower part of slope. According to the physical
and mechanical indicators of mining rock, we can judge
that the goaf formed in underground mining will be
naturally caving and filling because of existence of
stretching destruction from rock mass of two sides, while
the slope above goaf will be destroyed by partial com-
pressive stress, which will not happened in most other
part of slope. If the goaf formed in underground mining
is not caving and filling in time, the sudden damage of
slope and refuse dump by high tensile stress may cause a
C opyright © 2010 SciRes. ENG

G. F. Ren ET AL. 204
large subsidence area in the whole slope as a basin. If
surface soil and rock mass effect mutually, it may lead to
the occurrence of large-scale landslide in Antaibao East
Slope. Therefore, we should make goaf overburden fall
and fill itself as much as possible.
5. Conclusions
We can obtain the following conclusions based on the
study about the four states of East Slope of Antaibao by
finite element numerical simulation.
1) Rock mass movement patterns of slope are complex
under the joint employment of underground mining and
open-pit mining. In fields bordered by the strike of un-
derground mining goaf, the sliding trend of rock mass in
uphill of goaf is more apparent, while rock mass in dip
head of goaf slides into goaf reversely. In the process of
combinational mining, safety monitoring to upper rock
mass of mining slope should be strengthened.
2) Mining damage caused by underground mining oc-
curs firstly, then the two sides of goaf and roof are de-
stroyed and the damage spreads upside to surface slope,
resulting in the formation of caving zone, fault zone and
bending zone. So slope movement in combinational
mining mainly exhibits as the deformation caused by
underground mining.
3) Stress balance in slope rock mass is a dynamic ad-
justment process in the condition of combinational min-
ing. The major damage region of slope rock mass is
mainly located in the overlapping areas affected by both
mining systems.
4) With the implementation of underground mining
and open-pit mining, the main damage region in the mine
slope approximately parallels to strike and dip of main
sectional plane in underground mining area. Thus, accu-
rate grasp of the spatial relationships between mining
area and mining slope enables the effective understand-
ing of the law of mining slope movement.
5) In order to prevent large-scale landslide from oc-
curring in mining slope as the result of mining effect, for
subsidence pit in slope surface, bulldozers should be
used to fill cracks punctually so as to avoid infiltration of
rainfall which may affect the stability of slope.
6) Backfilling the refuse in slope side is conducive to
slope stability. In the production processes, for Antaibao
slope, the section paralleling to B901 mining face in
strike is proposed to be given priority in terms of back-
filling.
6. References
[1] S. X. Zhang, “Solid mineral resources development pro-
jects,” Wuhan University of Technology Press, Wuhan,
2005.
[2] G. F. Ren, S. X. Zhang and T. Peng, “Numerical simula-
tion research on east open-pit mining into underground
mining in Daye Iron Mine,” Chemical Minerals and
Processing, No. 2, pp. 20-23, 2006.
[3] S. X. Zhang, T. Peng, F. S. Wang and J. H. Hu, “Study of
the stability of the principle of space in rock deep-pit
slope engineering,” Journal of Wuhan University of
Technology, Vol. 23, No. 11, pp. 75-79, 2001.
[4] J. P. Tang and Y. S. Pang, “Research on ANSYS used in
numerical simulation of coal mining,” Rock and Soil
Mechanics, Vol. 25, No. 11, pp. 329-332, 2004.