Academic Journal of Science and Technology 
ISSN: 2771-3032 | Vol. 13, No. 1, 2024 

 

106 

Explore	the	Impact	of	Coal	Mining	on	the	Safety	of	the	
Upper	Reservoir	Based	on	FLAC3D	
Xinya Li1, *, Jiangfeng Wang2 

1College of North China University of Water Resources and Electric Power, Zhengzhou, China 
2College of North China University of Water Resources and Electric Power, Zhengzhou, China 
*Corresponding Author: Xinya Li 

 

Abstract: With the increasing scarcity of land resources, the rational utilization of coal mine goaf areas has become particularly 
important. To study the impact of coal mining on the safety of the upper reservoir and dam, numerical simulation software 
FLAC3D was used to model existing and future goaf areas created by coal mining. By analyzing the maximum and minimum 
principal stress clouds, vertical displacement clouds, and the distribution of surface plastic zones for two selected profiles, it was 
found that under current conditions, coal mining causes a maximum surface subsidence of nearly 2.0m, with the dam area located 
at the edge of the subsidence basin. The southern area is closest to the goaf, with a maximum subsidence of about 0.5m, and 
obvious tensile and shear plastic zones are produced; in the future, after the planned mining workface is completed, the reservoir 
dam area will experience cumulative subsidence of 2800mm, tilt of 5mm/m, curvature of 5×10^-3/m, horizontal movement of 
800mm, and horizontal deformation of 6mm/m, which could potentially cause severe deformation and damage to the reservoir 
dam. 

Keywords: Numerical Simulation; Coal Mine Goaf; Reservoir Dam; Aafety Assessment. 
 

1. Introduction 
With the continuous advancement of urbanization in China, 

the rational utilization of mining land is increasingly 
mentioned. Under the load of the upper structures, the stress 
of the overlying rock strata of the goaf is redistributed, the 
rock strata collapse, move, and gradually affect the surface, 
causing ground subsidence and other disasters, thereby 
causing immeasurable losses to the nation and the people's 
lives and property. Currently, a coal mine working face 
extends under the surface reservoir, and its goaf may undergo 
severe deformation or even instability collapse under the 
action of the reservoir dam site and water pressure, with the 
deformation characteristics of the near-surface goaf being 
more pronounced, affecting the safe and stable operation of 
the surface dam site area. Therefore, based on the current 
mining situation of the coal mine, future mining plans, and 
the engineering geological characteristics within the research 
scope, this paper uses FLAC3D technology to simulate the 
impact of coal mine daily production activities on the safety 
of the upper reservoir, guiding scientific mining activities and 
ensuring the safe operation of the reservoir. 

FLAC3D can assess the stability of the goaf by simulating 
the stress redistribution, displacement changes, and 
development of plastic zones during the mining process. At 
the same time, based on FLAC3D simulation, the concept of 
goaf failure probability can be introduced to quantitatively 
assess the overall stability of the goaf. By statistically 
analyzing the calculation results of FLAC3D grid cells, 
probability statistical methods (such as Excel's risk analysis 
add-in @Risk) can be used to calculate the failure probability 
of the goaf, thus achieving a quantitative evaluation of the 
stability of the goaf. [1] 
FLAC3D can adopt various methods when dealing with goaf 
areas, such as direct excavation method and stope softening 
method. The direct excavation method forms the goaf by 
directly excavating the coal seam part of the model and 

simulating it; the stope softening method simulates the 
collapse and destruction process of the rock strata after coal 
mining through softening treatment. [2] 

Existing research on goaf areas mainly focuses on two 
aspects: the surface stability of the goaf and the impact of 
surface engineering construction on the stability of the goaf. 
There are also many methods for evaluating the stability of 
goaf areas. Mainly based on the characteristics of the 
engineering construction object, the impact of the additional 
load brought by the engineering construction on the stability 
of the goaf is assessed, and finally, a comprehensive 
evaluation of the suitability of engineering construction on the 
goaf is made. [3-10] 

2. Overview of the Study Area 
The study area reservoir (a certain coal mine) belongs to 

the north temperate continental monsoon climate zone, 
characterized by spring drought and windy, summer heat and 
rainy, autumn cool and humid, winter cold and less snow; 
belonging to the Yellow River basin's Yi Luo River water 
system, the water storage source is mainly composed of 
atmospheric precipitation, and the water storage volume 
varies greatly with the seasons; the majority of the landform 
belongs to the loess tableland landform, only the eastern 
boundary of the mining area is in the bedrock mountainous 
area. The overall terrain is lower in the south and higher in the 
north, lower in the east and higher in the west. The northern 
mountains, extending in the east-west direction, are mainly 
composed of loess, with relatively flat ridge surfaces, gentle 
northern slopes, and steep southern slopes, with many gullies 
cutting through. The southern part is composed of middle and 
low mountains formed by the Cambrian and Precambrian 
strata, with its front being the hilly area formed by the 
Carboniferous and Permian coal-bearing strata, with ground 
elevations ranging from 200 to 500m. The central part is a 
plain area formed by the accumulation of the Neogene and 
Quaternary, with ground elevations ranging from 100 to 



 

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200m. The western part has locally exposed Permian bedrock, 
with relatively large terrain undulations and gullies developed, 
which is conducive to the runoff and discharge of atmospheric 
precipitation, with gullies generally being "V" shaped and 
deeply cut. The eastern half is basically covered with loess, 
with relatively small terrain undulations. The surface is 
covered with the upper Pleistocene loess layer. The reservoir 
area is about 300 to 500m wide, about 500m long, with a 
ground elevation of about 320m, and the river valley at the 
dam site is about 30m wide, with a riverbed elevation of about 
285m. 

The coal mine is located in the central-eastern part of the 
Yanlong coalfield, in the Songji area of the southern margin 
of the North China stratigraphic region. The regional strata 
include the Archean Dengfeng Group (Ardn), the 
Mesoproterozoic Jixian System (Pt2j), the Upper Proterozoic 

Sinian System (Pt3z), the Lower Paleozoic Cambrian System 
(∈) and the Middle Ordovician (O2), the Upper Paleozoic 
Carboniferous Upper Series (C2) and Permian (P), the 
Mesozoic Triassic (T), and the Cenozoic Paleogene (E), 
Neogene (N), and Quaternary (Q). The Quaternary strata 
mainly consist of low-liquid-limit clay (Q3

al, Q4
al) and poorly 

graded gravel (Q4
al); the coal-bearing strata include the Upper 

Carboniferous Taiyuan Formation, the Lower Permian 
Shanxi Formation and Lower Shihezi Formation, and the 
Upper Shihezi Formation, with a total thickness of the coal-
bearing strata of 602.54m, divided into eight coal sections 
from bottom to top. The fully mined area is the II1 coal seam, 
with the roof lithology mainly being mudstone and sandy 
mudstone; the floor lithology mainly being siltstone and 
mudstone. 

 

 
Figure 1. Geological Profile Map 

 

3. Numerical Simulation Analysis 

3.1. Division of Rock Groups and Model 
Establishment 

This study takes the goaf area under the coal mine in the 
study area as the research object. According to the 
topographic map of the study area, a numerical simulation 
surface model is established. Referencing the comprehensive 
stratigraphic column of the mining area, the stratigraphic 
column near the dam, and the stratigraphic structure, the 
overlying rock mass is divided into 13 model materials based 
on the similarity of engineering geological characteristics, 
from bottom to top, they are: limestone of the first coal section, 
floor sandstone, coal seam, roof sandstone of the second coal 
section, mudstone of the third coal section, sandstone of the 
fourth coal section, sandy mudstone of the fifth coal section, 
mudstone and sandstone interbedded of the sixth coal section, 

interbedded sandstone and mudstone of the seventh coal 
section, mudstone of the eighth coal section, sandstone of the 
Shi Qianfeng Formation, Quaternary soil layer, and dam 
concrete panel. 

Combining the actual situation of the coal seams 001 and 
002 mined in the study area, the average thickness of the coal 
seam is taken as 4m, the strike length of the calculation model 
is 1900m, the dip width is 1200m, the height is 700m, the 
bottom elevation is set at -380m, the vertical X-axis, vertical 
Y-axis, and Z-axis bottom interfaces are set as fixed 
displacement boundaries, the top interface is set as a free 
boundary, and the vertical interface and bottom interface are 
set as rolling interfaces. A three-dimensional numerical 
model is used for stress field numerical simulation calculation 
and Mohr-Coulomb yield criterion to determine rock mass 
failure, and plastic flow is not considered. The simulation 
plane schematic diagram and model diagram are shown in 
Figure 2 and Figure 3. 

 



 

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Figure 2. Simulation Plane Schematic Diagram 

 

 
Figure 3. Grid Model Diagram 

 

3.2. Parameter Selection and Simulation 
Scheme 

According to the production geological report and reserve 

verification report provided by the mine, as well as the 
corresponding calculation results, the parameters used for this 
simulation are determined as shown in Table 1. 

 
 
 
 



 

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Table 1. Geological Model Material Parameters 

Rock Group 
Unit-Weight 

(kN/m3) 
Bulk Modulus 

(MPa) 
Shear Modulus 

(MPa) 
Cohesion 

(MPa) 
Internal Friction 

Angle (°) 
Tensile Strength 

(MPa) 

Dam Concrete 25 18840.58 10236.22 2000 35 2 

Quaternary Soil Layer 18 7.65 2.93 0 18 0.01 

Shiqianfeng Group Sandstone 26 1415.87 691.47 2000 32 1.5 

Eight Coal Section Mudstone 26 938.46 590.32 1154 30 1.3 

Seven Coal Section Sandstone 
and Mudstone Mutual Layer 

26.5 925.64 582.26 1740 35 1.2 

Six Coal Section Mudstone 
Mixed with Sandstone 

26.5 925.64 582.26 1740 35 1.2 

Five Coal Section 
Sandy Mudstone 

26.5 925.64 582.26 1740 35 1.2 

Four Coal Section Sandstone 26 1415.87 691.47 3200 32 1.5 

Three Coal Section Mudstone 27 938.46 590.32 1154 30 1.3 

Second Sandstone Roof of the 
Coal Section 

26 1415.87 691.47 2000 32 1.5 

Coal Rake 13 910.00 470.00 1000 25 0.25 

Bottom Plate Sandstone 26 1415.87 691.47 2000 32 1.5 

One Coal Section Limestone 28 16000.00 9600.00 3000 38 2 
 

 
Figure 4. Vertical stress cloud map of the initial stress field 

 
This simulation is mainly conducted in the self-weight 

stress field. The impact of underground coal seam excavation 
on the surface dam is divided into current and future parts. 
Under the current situation, the simulation has been carried 
out for the 001 and 002 working faces, where the 001 working 
face is only simulated to the area that may affect the dam. 
According to the future mining plan provided by the mining 
company, four working faces are planned below and near the 
reservoir dam. This simulation is carried out in four stages 
according to the future mining time. The simulation results 
are evaluated for the impact of each stage of working face 

mining on the dam by analyzing the stress, deformation, and 
plastic zone distribution. 

3.3. Simulation of Current Coal Seam Mining 
Under the current situation, the working faces affecting the 

dam area are 001 and 002. This time, the two working faces 
are simulated in the order of mining time, and the impact of 
coal seam mining on the dam is analyzed through the A-A' 
section and B-B' working face. The simulation results are 
shown in Figures 5-14. 

 



 

110 

 
Figure 5. Cloud map of the surface settlement contour line under the current situation 

 

 
Figure 6. Cloud map of surface plastic area distribution 

 

 
Figure 7. Maximum principal stress cloud map of A-A' section under current conditions 

 



 

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Figure 8. Minimum principal stress cloud map of A-A' section under current conditions 

 

 
Figure 9. Vertical displacement of A-A' profile in current situation 

 

 
Figure 10. Plastic zone distribution map of A-A' section under current conditions 

 

 

Figure 11. Maximum principal stress cloud map of B-B' section under current conditions 



 

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Figure 12. Minimum principal stress cloud map of B-B' section under current conditions 

 

 
Figure 13. Vertical displacement of B-B' profile in current situation 

 

 
Figure 14. Plastic zone distribution map of B-B' section under current conditions 

 
 

According to Figure 5, the maximum surface subsidence 
caused by coal seam mining under the current situation is 
close to 2.0m. The dam area is located at the edge of the 
subsidence basin. The southern area of the dam is closest to 
the goaf, with a maximum subsidence of about 0.5m. 
Generally, the edge of the subsidence basin is prone to cause 
tensile and shear cracks. According to Figure 6, there are 
obvious tensile and shear plastic zones in the dam area, and 
the southern side is more severe than the northern side. The 
simulation results are basically consistent with the field 
investigation. 

According to Figures 7-8 and Figures 11-12, the stress 
simulation results of A-A' and B-B' show that coal seam 
mining causes the overburden stress to redistribute. Stress 
concentration occurs at both ends of the working face, and the 
roof forms a tensile stress arch. At the same time, due to the 
full mining of the working face, the stress effect extends to 

the surface, and some areas on the surface form a tensile stress 
zone. The minimum principal stress in the dam area is tensile 
stress, and the tensile stress value on the south side of the dam 
is larger. Under the action of tensile stress, tensile failure is 
prone to occur. 

According to Figures 9-10 and Figures 13-14, the 
displacement and plastic zone simulation results of A-A' and 
B-B' also show that the dam area is located at the edge of the 
basin, and plastic failure has occurred in the dam area. 

3.4. Simulation of Future Coal Seam Mining 
According to the future mining plan provided by the mine, 

after the mining of 003,004,005 and 006 in the future, 
multiple working faces may lead to the formation of large 
goaf, resulting in secondary collapse and the expansion of 
surface deformation range. See Table 2 for the specific 
prediction results in surface movement deformation. 

 



 

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Table 2. Calculation results of surface movement and deformation in the reservoir dam 

Time Settlement (mm) 
Tilt 

(mm/m) 
Curvature 
(×10-3/m) 

Horizontal Scroll 
(mm) 

Horizontal Distortion 
(mm/m) 

In 2035, 300-2300 1-9 0.01-0.10 10-650 0.1-7 
In 2040, 900-2500 0.1-7 0.01-0.10 10-700 0.1-7 
In 2043, 1000-2500 0.1-7 0.01-0.09 10-700 0.1-7 
In 2047, 2200-2800 0.1-5 0.01-0.07 100-800 0.1-6 

 
According to the calculation results, the future mining of 

the mining area may cause significant damage to the surface 
facilities such as the reservoir dam and spillway. This time, 
based on the mining time of the working face, the results of 
the minimum principal stress, vertical displacement, and 

plastic zone of the A-A' section are analyzed for the impact of 
future mining in 2030, 2035, and 2040. The impact in 2043 is 
only shown through the range of the entire surface plastic 
failure area. The simulation results are shown in Figures 15-
24. 

 

 
Figure 15. Minimum principal stress cloud map of A-A' section (2030) 

 

 
Figure 16. Vertical displacement cloud map of A-A' section (2030) 

 

 
Figure 17. Plastic zone distribution map of A-A' section (2030) 

 



 

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Figure 18. Minimum principal stress cloud map of A-A' section (2035) 

 

 
Figure 19. Vertical displacement cloud map of A-A' section (2035) 

 

 
Figure 20. Plastic zone distribution map of A-A' section (2035) 

 

 
Figure 21. Minimum principal stress cloud map of A-A' section (2040) 



 

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Figure 22. Vertical displacement cloud map of A-A' section (2040) 

 

 
Figure 23. Plastic zone distribution map of A-A' section (2040) 

 

 
Figure 24. Future mining surface plastic zone distribution change map 

 

Through the analysis of this simulation process, it can be 
found that when the simulation is excavated to the planned 
face in 2040, the numerical calculation process becomes non-

convergent, and the overburden and surface have a large area 
of plastic failure; According to the minimum principal stress 
cloud map, vertical displacement map, and plastic zone 



 

116 

distribution map of the three stages, due to the interval mining 
of the future planned face, there is still coal pillar support 
between the mining faces in 2035, and the tensile stress 
distribution of the overburden does not extend to the surface. 
The surface deformation basin further expands, and the 
plastic failure of the dam area is also further aggravated 
compared to the current situation. By 2040, all the working 
faces on the south side of the dam have been mined, and the 
simulation calculation becomes non-convergent. The tensile 
stress area of the entire overburden extends to the entire 
surface, and the dam and the surrounding area of the dam have 
a large area of plastic failure. Therefore, future mining may 
cause serious damage to the dam. 

4. Conclusions and Suggestions 
Through the numerical simulation analysis of the current 

situation of coal mining, it is believed that the cracking and 
settlement of some areas of the reservoir dam and spillway 
are related to the mining of the 001 and 002 working faces; 
The surface movement and deformation caused by the current 
mining has entered a slow residual deformation period, and 
the surface movement and deformation have stabilized. Under 
the condition that there is no new mining impact, it is suitable 
to carry out the dam risk mitigation and reinforcement work. 

(2) Through the numerical simulation analysis of future 
coal mining, according to the future mining plan provided by 
the mining company, it is believed that the surface facilities 
such as the reservoir and dam, spillway located in the goaf 
collapse basin may be affected by the future planned working 
face mining, which may cause serious mining-induced 
deformation and damage to the reservoir dam and spillway 
(including the planned risk mitigation and reinforcement 
project), which may lead to the reservoir unable to operate 
normally. 

(3) It is recommended to carry out special demonstration 
work before mining the 003, 004, 005, and 006 working faces, 
fully understand the possible impact on the ground facilities 
after mining, and minimize economic losses as much as 
possible. 

(4) During the future mining period, the reservoir 
management should strengthen the patrol and fixed inspection 
of the reservoir dam structure, continuously carry out the 
settlement and horizontal monitoring of the dam and the 

nearby surface, and the monitoring range should not be less 
than the reservoir dam. The monitoring frequency should be 
no less than once every quarter; During the future planned 
mining period, increase the maintenance and protection 
measures for the reservoir dam. 

Reference Documentation 
[1] Shang Zhenhua, Tang Shaohui, Jiao Wenyu, et al. Scale goaf 

failure probability study based on FLAC ~ (3D) simulation (J]. 
Rock-soil mechanics, 2014,35(10):3000-
3006.DOI:10.16285/j.rsm. 2014. 10.028. 

[2] Zhang Lei. Discussion on the treatment method of the goaf in 
FLAC ~ (3D) [J]. Shanxi Coking Coal Technology, 2017,41 
(11): 26-30. 

[3] Liu Bin. Study on the comprehensive evaluation and treatment 
scheme of the goaf stability of a copper polymetallic mine [J]. 
Mining Technology, 2023,23(06):88-
93.DOI:10.13828/j.cnki.ckjs. 2023.06.032. 

[4] Wang He, Zhang Chi. Refined stability analysis based on 3 D 
laser scanning empty area [J]. Non-ferrous metals (mine part), 
2023,75 (05): 70-75. 

[5] Ma Mingkang, Lu Yongjun, Guo Xu, et al. Study on the slope 
stability of Maogou open pit mine under the influence of goaf 
[J]. Open-pit mining technology, and 2022,37(01):69-
71+75.DOI:10.13235/j.cnki.ltcm. 2022.01.019. 

[6] Xue Guoqiang, Pan Dongming, Yu Jing Estate. Overview of 
geophysical exploration applications in goaf in coal mines [J]. 
Progress in Geophysics, 2018,33 (05): 2187-2192. 

[7] Li Shu-Mingzhi. Research and application of key technologies 
of urban construction in coal mining subsidence area [J]. Coal 
mining, 2016,21 (02): 73-77. 

[8] Teng Yonghai, Tang Zhixin. Research and application of 
ground building technology in the old goaf [J]. Coal Science 
and Technology, 2016,44 (01): 183-186. 

[9] Liu Yixin, Zhang Junying, Jia Xinguo. Assessment of 
foundation stability in goaf of photovoltaic power station built 
in coal mining subsidence area [J]. Coal Science and 
Technology, 2016, S2:189-192. 

[10] Guo Keyi, Yi Sihai, Teng Yonghai. Construction and 
protection technology of wind farm project in mining mining 
area [J]. Metal Mines, 2015, (04): 150-153.