Analysis of the Influence of Underground Coal Mining on the
Environment
H Nan and S Wang*
School of Energy Science and Engineer, Henan Polytechnic University, Jiaozuo
Henan ,China,454000
Corresponding author and e-mail: S Wang 1583316450@qq.com
Abstract The use of coal is an indispensable part of China's industrialization process. China
is a big coal country and the consumption of coal has been above 60%. The interaction of
various factors makes the underground mining of coal more and more serious. At the same
time, the depth of mining is increasing. The lack of appropriate management measures after
the mining of coal seams has resulted in the collapse of the overlying rock formations in most
of the goafs and the formation of fissures and gullies on the surface. The movement of the
overlying strata also destroys the aquifers in the strata, causing the groundwater to be lost and
the coal mining water to be discharged without treatment, so that harmful impurities penetrate
into the groundwater. Not only does it have a great impact on the environment, it also causes
irreparable damage to human daily life. In the previous studies, this article gives a more
succinct description of the influence of underground coal mining on surface, groundwater,
atmosphere and biology. Use the analytic hierarchy process to identify the most serious
environmental impacts. In addition, the causes of the impacts and the ways of summing up
are explained in light of their own majors.
1. Introduction
China is one of the countries with the most abundant coal content in the world. It is a country with
large coal resources and has a complete coal category. This explains the percentage of total national
resources consumed from the perspective of the side. The use of coal has always been very high. By
the end of 2014, the State Council promulgated The “Energy Development Strategic Action Plan
2014-2020” pointed out that China’s path to optimize energy structure is to reduce the proportion of
coal consumption, increase the proportion of natural gas consumption, vigorously develop renewable
energy such as wind power, solar energy, and geothermal energy, and develop nuclear power safely.
By 2020, non-fossil energy will account for 15% of primary energy consumption; natural gas will
account for more than 10%; coal consumption will be controlled within 62%; and oil will account for
the remaining 13% [1]. Moreover, China has used coal for thousands of years and is one of the
earliest countries in the world to discover and use coal. In the first century BC, coal was used for iron
smelting and copper smelting. Although China's industrialization of coal mining started relatively
late, but in just a few decades the country's development in all aspects are at full speed, including the
industrialization of coal mining. Coal mining technology, theory, equipment and a series of aspects
are now at the forefront of coal mining in the world. With the need of China's economic development
Nan, H. and Wang, S.
Analysis of the Influence of Underground Coal Mining on the Environment.
In Proceedings of the International Workshop on Environmental Management, Science and Engineering (IWEMSE 2018), pages 55-61
ISBN: 978-989-758-344-5
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
55
and the dependence of industrialization on coal resources, the annual output of coal is also a
long-standing one.
In the golden decade of the coal industry, the annual coal output is nearly 4 billion tons [1].
Therefore, coal seams that are shallow and deep underground in China are gradually mined. The coal
mine has been deepened from a depth of 200 to a depth of 500 meters, a depth of 1,000 meters, and
so on. The rapid economic development will certainly also cause damage to the environment. In
China, there is a long history of coal mining and use. As the industry's leading energy source, its
production, transportation, and utilization have an important role in promoting industrial economic
development. In the early stages of reform and development, China’s emphasis on economic
development also caused damage to the ecological environment. Because a variety of natural
resources coexist in the coal mining area, they together constitute the "organic environment of the
coal mine area" as an organic whole [2]. Therefore, due to the impact of coal mining damage, all
kinds of resources and environmental elements that are isomeric to coal resources are subject to
disturbances in terms of quality and quantity. While promoting social development, it also leads to a
variety of environmental pollution problems, which are manifested in the following three aspects: 1
During the process of coal mining, coal preparation, coal washing, transportation, and combustion,
some harmful gases harmful to the environment will be released. Into the air; 2 underground mining
of coal mines is used to extract coal seams that are underground, and underground goafs are formed.
There will be no supporting overburden rock in the goafs, and then a series of Fall will form the
collapse of the surface. The collapse of the surface not only caused unevenness of the ground, but
also caused great harm to the people’s lives. At the same time, the location of the rock itself, where
the collapsed portion also changed, is the original position. For example, damage to the aquifer of the
subsidence area causes the loss of groundwater, etc.; 3 Coal gangue and other abandoned materials
produced during the mining process occupy a large amount of land. Yes, the farmer cultivates land
and reduces crop production. The spontaneous combustion characteristics of coal gangue have great
fire hazards. Fly ash causes loss of biodiversity and landscape damage to surrounding vegetation in
the mining area [3]. All these have resulted in the waste of resources in certain mining areas, the
declining economic development, the unbalanced ecological balance, and the intensified social
problems in towns and villages.
Reckless overexploitation has created an irreversible situation for the environment. Therefore,
domestic and foreign research scholars have gradually developed the study of subsidence of goaf.
The scope of the study is also relatively extensive and mainly includes related majors such as
geology, environment, and mining [4]. The study of the mechanism and theory of ground subsidence
caused by coal mining began in the 19th century. At that time, scholars at home and abroad proposed
some relatively shallow theories and understandings. For example: Oesterr's natural slope theory,
Fayol's circular arch theory, Jlcinsky's bisector theory, etc. These theories are relatively one-sided [5].
However, with the development of the era, the theory of surface subsidence has gradually formed a
relatively mature set of theoretical systems. China's research on it is relatively late relative to that of
foreign countries, beginning in the middle of the 20th century. Although the study started late, it has
independently developed and applied the most widely used probability integration method in China
by studying the combination of some foreign theoretical knowledge and our country's actual
development. The probability integration method is a computer method used to predict the landmark
settlement deformation curve. The overlying rock formations in the goafs not only caused the ground
surface to collapse, but also brought about a series of other reactions. For example, the pollution of
groundwater caused by coal mining, the destruction of underground aquifer by surface subsidence,
and the impact of water resources destruction and pollution on biological systems are inevitable.
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2. Impact on the surface
The general situation of coal mining in some areas of China is that underground mining causes the
roof of the coal bed to fall, causing the ground to descend and forming a collapse. As a geological
disaster, subsidence is the main way to destroy the ecological environment during the mining process
of major coal production bases. The subsidence area accounts for more than 75% of the total
underground coal mining area [5]. China is a developing country with coal as its main energy source.
The formation of ground subsidence during the mining process also has a great impact on human life.
After the coal seam is mined underground, a goaf is left underground. The collapse of overlying
strata under the joint action of stress and gravity on the overburden strata of the mined-out region
generally occurs in three zones: the fallow zone, the fissure zone and the curved subsidence zone, and
the fall zone: the rock mass after the fracture. Irregular and deranged, the arrangement is extremely
irregular, the loose coefficient is relatively large, generally 1.3-1.5, and can be reduced to 1.03 right
after re-compacting; fractured zone: the rock is still arranged neatly after fractured rock, the broken
expansion coefficient is smaller Bending sinking belt: The rock layer from the top of the cracked belt
to the ground surface is called the bending belt. Its characteristic is that the rock layer has continuity
and integrity in the moving process, and the subsidence between the upper and lower parts of the
vertical section is very small. A hard and hard key layer may appear away from the horizon. With the
exploitation of coal seams, the mined-out area gradually becomes larger, and overlying strata will
continue to fall under the action of gravity and other stress combinations, and the scope of surface
subsidence will not be expanded.
There are many types of surface subsidence, such as cracks, pits, landslides, landslides, etc. [6].
Surface subsidence has the most direct impact on the residents living above, and a series of surface
deformations caused by subsidence have a tremendous impact on human life, travel and personal
safety. Landslides, subsidences and deep pits not only caused irrecoverable damage to residents’
houses but also caused damage to the arable land of farmers. The destruction of arable land indirectly
caused the direct economic losses of farmers and affected the improvement of people’s living
standards. Cracks formed on the surface are also very influential to people's travel. They may go
home from work in the afternoon or be a good road. When they go to work the next day, they find
that the road sinks down and there are even large cracks. Therefore, the impact of surface subsidence
on people’s daily life is most directly reflected. Take Shanxi Province as an example. Shanxi
Province is a large coal producing province. Therefore, the area of goafs in Shanxi Province is also
very large. According to statistics, the area of goafs in Shanxi Province is nearly 30,000 square
kilometers, which is nearly the size of Taiwan Province. Therefore, there is no doubt that Shanxi is
called “the Hanging Temple”[7].
3. Impact on groundwater
The groundwater environment is a splendid link between geological environment and ecological
environment. It has extremely important ecological functions. Coal mining has an important
influence on water bodies, especially groundwater. In order to produce coal safely, the mine must
exclude a large amount of mine water, and the discharged mine water has the most serious pollution
to groundwater. In the early stage of coal mining, the coal seam is shallow, the stratum structure is
less, and the amount of spalling water is less, so it has less impact on the water environment.
However, with the deepening of the depth of coal mining and the deepening of the thickness of coal
mining, the impact on groundwater has become more and more serious.
First: Improve groundwater conditions in mining areas. Underground mining is the excavation of
coal seams buried hundreds of meters underground. This undoubtedly undermines the geological
composition of the entire primary rock formation, which results in the destruction of the distribution
and condition of the underground aquifers in the mining area, and destroys the hydrology of the
entire mining area. Happening. During the mining process, as the coal is mined, the overburden
Analysis of the Influence of Underground Coal Mining on the Environment
57
collapses and new compaction results in newly formed cracks in the rock formation. This causes the
water in the aquifer above the coal seam to be gradually “pulled out”, forming a funnel that forms a
descending aquifer of the underground aquifer in the goaf area, which causes the aquifer in the goaf
area to change from pressure bearing to pressureless. The flow direction of groundwater also changes
from horizontal flow to vertical flow, and the original groundwater conditions are destroyed [8].
Second: change the existing groundwater storage place. After the coal was mined, the overburden
collapsed. Therefore, with the formation of collapsed original rock formations above the goaf, the
original rock formations were misplaced. As a result, the original surface of the water-retaining layer
and the aquifer is destroyed, so that the water in the original aquifer is permeated through the fracture
to other rock layers until a new aquifer is formed in the undamaged aquitard. This resulted in a
reduction of the natural base flow of the original aquifer and a drop in the water level. Decreasing the
water level of the aquifer will reduce the corresponding surface water flow system and affect the
surface water flow.
Third: Coal mining causes water pollution. The consumption of water by coal mining is very large,
especially in the coal seams adjacent to the aquifer. The groundwater seeps into the mining area. To
prevent the occurrence of water damage, the water needs to be discharged, and most of the
discharged water is returned to the underground aquifer. As a result, the groundwater is doped with a
large amount of calcium and magnesium compounds to form hard water, resulting in a significant
decrease in water quality. These hard waters, which are upstream, flow into rivers and seas through
the water circulation and deteriorate their water quality. These contaminated currents not only have
an impact on the organisms therein, but also pose a great safety risk to the residents' water use and
livestock drinking water [9].
4. The optimal solution to the choice
The analytic hierarchy process, abbreviated as AHP, is a commonly used analytical method to solve
multi-objective decision making. It was proposed by Saaty, an American operational researcher, in
the 1970s. The basic idea of this method is to decompose complex multivariate problems into
multi-level multi-factors and then make comparative judgments based on the importance degree
between the two indicators, and establish relevant matrix judgment calculations to obtain the weights
of different programs. The choice plan provides the basis. The general steps for creating an AHP are
shown in Figure 1[10]:
Figure 1. Analytic hierarchy structure.
Logical tree result ->
reason
Structure hierarchy model
Construction judgment
matrix
Solving Weights
Calculate comprehensive weights and
sorting
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The basic idea of building a hierarchical model is to divide the results, causes, and solutions of
complex problems into upper-middle and lower-level relationships. The bottom layer is the solution
to the problem; the middle layer is the influencing factor to the result; the top layer is the most ideal
solution to the problem. The results of this paper are mainly to select the optimal measures to reduce
the impact of coal mining on the environment. According to the hierarchical relationship analysis of
the AHP, the top level is the optimal measure to reduce environmental impact; the middle level
indicates that the factors influencing the results mainly include surface subsidence, underground
book pollution, air pollution, and vegetation destruction. The lowest level is the solution, as shown in
Figure 2:
Figure 2. hierarchical analysis tree.
Followed by the construction of the judgment matrix. For the five factors in the middle tier, the
impact of the pairwise comparison on the topmost target tier, the judgment matrix is:
A=
(1)
After the judgment matrix is established, it is also necessary to check the consistency. First, the
maximum eigenvalue of the matrix A and its maximum eigenvector are calculated, and the
consistency index CI=(λ
max
-n)/(n-1) is calculated, if the consistency ratio CR= When CI/RI<0.10, the
matrix A has consistency. The consistency reference values are shown in Table 1.
Table 1. Reference values of the consistency index RI.
n
1
2
3
4
5
6
RI
0
0
0.58
0.90
1.12
1.24
Analysis of the Influence of Underground Coal Mining on the Environment
59
According to the meaning of Saaty's mid-1 to 9 scales and the meaning of the reciprocal.
Comparing the above five conditions, we can see that 1 means that two elements are equally
important; 3, 5, 7 and 9 indicate that one element is slightly more important, obviously more
important, more strongly important, and absolutely more important than the other element; 2,4, 6,8
represents the median of two adjacent odd-numbered scales [11]. According to the above-mentioned
coal mine safety evaluation index system, the first-level indicators obtained after the comparison of
the two pairs are the following:
A
5*5
=
(2)
The weight vector calculation method of the analytic hierarchy process includes: a geometric
average method, an arithmetic average method, a feature vector method, a least squares method, and
the like. Each calculation method has its own algorithm. This paper uses the geometric average
feature, arithmetic average feature and eigenvector of matrix A to solve. Calculation formula:
(3)
(4)
(5)
=S*W=
*W (6)
(7)
(8)
n represents the number of influencing factors in the middle layer. a
ij
is the ith row and jth
column elements in matrix A. W is the weight vector; m
i
is the geometric mean of each row of matrix
A. ω
i1
represents the geometric weight. ω
i2
is the arithmetic weight vector. ω
i3
Representing feature
vector weights. λ
max
is the matrix maximum eigenvalue [12].
According to the above calculation scheme, the surface subsidence has the greatest influence on
the optimal measure selection, followed by groundwater pollution, atmospheric pollution, vegetation
destruction and ecological environment damage.
Of course, there are many successful examples of coal mine ecological governance. For example,
the Xinan Coal Mine of the Yimei Coal Group is an example of successful coal mine ecological
environment governance. Xin'an Coal Mine follows the working concept of “eco-nature,
afforestation economy, Jiangnan style, and low-carbon habitability”. Efforts have been made to build
a modern coal mining that integrates "ecological mining areas and tourism-oriented mines". The
perfect combination of "production development, affluent life, and good ecology" has been achieved.
The success of the environmental management of the Xin'an coal mining demonstrated the results of
different coal production and environmental protection before our eyes. So that we can feel a
different mining environment. It's refreshing.
5. Conclusions
The above calculations show that the main impact of underground mining on the environment is the
formation of goafs from underground mining, which causes the collapse of overlying rock formations
and the collapse of the surface. The surface collapse causes a series of re-breaks and forms the
greatest damage to the environment. Therefore, in order to better reduce the destruction of
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60
underground mining and better protect the environment, coal mining underground mining design
should adhere to scientific mining, improve the original lighting policy and design using more
environmentally friendly mining methods. Fully consider the overburden of the overlying strata and
establish a scientific, rational, safe, and environmenta lly friendly mining mechanism. Such as filling
mining, mining coal mining and other mining methods and so on. Fill mining is the use of waste
generated during coal mining as a fill to fill gobs. This not only solves the problem of waste disposal
but also has a good preventive effect on surface subsidence. At the same time, the destruction of
surface cracks, collapses, etc. shall be filled or built in time to improve the building structure of
residents' houses and increase the anti-deformation characteristics of the houses in the collapsed areas.
For the detection of overburden and aquifer conditions during mining, the principle of reuse of mine
water is applied, and the excess mine water is softened and discharged.
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