The Influence of the Fault Zone
Width on the Activation of a Reverse
Fault
Wenquan Zhang
1.College of Mining and Safety Engineering, Shandong University of Science and
Technology, Qingdao 266590 China;
2. State Key Laboratory of Mining Disaster Prevention and Control, Qingdao
266590 China
Jiudang Yuan
1.College of Mining and Safety Engineering, Shandong University of Science and
Technology, Qingdao 266590 China;
2. State Key Laboratory of Mining Disaster Prevention and Control, Qingdao
266590 China;
Corresponding author, e-mail: [email protected]
Bo Li
1.College of Mining and Safety Engineering, Shandong University of Science and
Technology, Qingdao 266590 china;
2. State Key Laboratory of Mining Disaster Prevention and Control, Qingdao
266590 China
ABSTRACT
Taking the F5 fault of a mine as an example, using numerical simulation software, analyzes the reverse
fault footwall mining process with stress evolution rules and fault activation pattern, reveal the width
of fault zone of reverse fault activation pattern influence. Result of this study shows that when working
face of footwall fault advancing 140m (120m before the fault), with the working face advance, the
stress of the fault zone changed little. When the working face advancing to 210m(50m before the
fault), due to fault zone has a larger buffering capacity ,so the fault zone can absorb the secondary
stress and the stress cannot cross the fault zone into the front of the surrounding rock, stress peak area
is located between the coal wall of the working face and the boundary of the coal pillar failure zone of
the fault zone. The normal stress of the fault zone decreases slightly and then increases. The reverse
fault with large width of fault fracture zone is more easily activated, and the risk of water inrush is
greater.
KEYWORDS: Reverse fault; fracture zone width; fault activation
- 1647 -
Vol. 22 [2017], Bund. 06
1648
INTRODUCTION
In recent years, China's coal mining depth and mining intensity is increasing, the frequency of
coal mine water inrush accident significantly increased. Lots of reasons can cause mine water inrush
accident, research shows that 80% of coal mine water inrush accidents are related to fault (Miu XX
and Liu Wq, 2004). In the process of coal production, working face mining will cause the change of
fault displacement in the region, resulting in the fault slip instability (Li Zh, et al. 2011, Zuo Jp, et al.
2009, Li Zh, et al. 2010, Li Zh , et al.2008). At the same time, mining has also changed the fault in
the vicinity of the stress field distribution, leading to the fault activation (Yu ZM, et al.1998, Li K, et,
al. 2011, Zhang PS, et, al.2014, Huang CH, et, al.2013, Li QF, et, al.2010, Zhang PS, et, al. 2014, Lu
XL, et, al.2009, Zhang PS, et al.2016), and lead to mine disasters. The width of fault fracture zone is
one of the main causes of water inrush. Therefore, this paper studies the influence of the width of the
fault zone on the activation of the reverse fault and the water inrush, in order to further understand the
mechanism of the fault water inrush.
Analysis of the Engineering Geological Condition
A mine field is located in the northwest, Yanzhou coalfield, mainly containing coal strata of
Shanxi formation of Permian and Carboniferous Permian Taiyuan formation, the coal seam is stable.
The average thickness of the mining coal seam is 12.69m, and the coal bearing coefficient is 4.37%.
10605 working face is a single structure, the formation trend is NE~SW, and the tendency is SE, the
working surface elevation is -322.1m ~ -367.5m, 7 faults are exposed in the tunneling process, which
are reverse faults. F5 reverse fault runs through the entire 10605 working face, the fault trend is NE,
the tendency is SW. NO.10 mining area aquifer comprises Quaternary aquifer, the Carboniferous
Taiyuan group ten layers of limestone, Benxi Section 13, 14 layers of limestone, Ordovician
limestone, which direct water filling aquifer is 10 lower limestone of Taiyuan group. Under normal
circumstances, there is no hydraulic connection among aquifers, while there is a weak side water
supply in the working face, because of the influence of fault and mining, there are different ways of
hydraulic contact. 10605 working face layout plan as shown in Figure 1
Figure 1: 10605 working face2 The establishment of calculation model
Vol. 22 [2017], Bund. 06
1649
The advancing direction of the working surface of the calculation model is X axis, the tilt
direction of the working face is Y axis, the vertical direction of the model is the Z axis, the model size
is 720m * 30m * 120m. According to the research purpose, the grid of the fault zone is encrypted, the
model is divided into 13662 zones, 20360 grids, the specific grid is shown in figure 2. Around the
model were applied to the horizontal displacement constraint, the bottom boundary constraints are
imposed, the boundary is a boundary stress, the upper boundary of stress specific values for the
overlying strata of gravity (sigma gamma h) is determined by the overlying strata..
According to rock mechanics test and engineering analogy, it can be known that Mohr-Coulomb
criterion (ZHOU JW, et al.2007,ZHU DR,1994) can better reflect the rock failure characteristics. So
this paper calculates the failure of the rock mass by selecting the Mohr-Coulomb criterion.
1 + sin ϕ
1 + sin ϕ
− 2c
s1 − s 3
fs =
1 − sin ϕ
1 − sin ϕ
(1)
where σ 1 is the maximum principal stress, σ 3 is the minimum principal stress, ϕ is the friction
angle, c is the bond strength. If f s >0, the material will produce shear failure. Under the general stress
state, the tensile strength of the rock mass is low, therefore, according to the tensile strength of rock
criterion we can judge whether tensile failure (WU LH,2004).
Based on the field geological survey and rock mechanics test, the physical and mechanical
parameters of the main rock strata are shown in Table 1 on the basis of considering the scale effect of
rock.
Figure 2: Mesh division of model
Vol. 22 [2017], Bund. 06
1650
Table 1: Physical and mechanical parameters of main rock strata
Lithology
Poisson ratio
Elastic modulus
/GPa
Compressive strength
/MPa
Bulk density
/g.cm-3
Internal friction angle /°
Medium sand
0.22
38
33
2.79
30
Fine sandstone
0.18
45
44
2.65
35
Silty sandstone
0.25
26
34
2.54
32
Coal
0.27
18
11
1.4
28
Mudstone
0.23
20
28
2.5
32
Limestone
0.23
66
35
2.66
30
Calculation Scheme
In view of the actual geological conditions of F5 reverse fault, we use numerical software
FLAC3D to study the activation law of mining induced reverse fault. On the basis of the existing
data, research and analysis of fault fracture zone width (width of the shattered zone respectively 4m,
6m, 8m and 12m) and footwall coal mining process in reverse fault characteristic of activation.
Simulation scheme for the footwall coal mining, working face advanced every 10m for the calculation
of a balance, in the fault zones and fault footwall are respectively arranged stress and displacement
monitoring points.
Simulation results analysis
The influence of the width of the broken zone on the stress of fault
Figure 3: Footwall mining different fault zone width of the fault zone stress distribution
Vol. 22 [2017], Bund. 06
1651
Figure 3 shows that when the fracture zone width is different, in the process of the footwall coal
seam, the fault stress curve. From Figure 3, we can see that footwall working face advancing 140m
(120m before the fault), with the working face advance the fault zone stress is changed little, working
face continue to advance, the fault stress increases gradually; when the working face is advancing the
same distance, the larger the width of the fault zone is, the greater the stress value of the fault zone is.
When the working face advancing to 210m, the fault normal stress showed a trend of first decreased
slightly and then increased. This is because when working face advancing to the fault zone , the fault
zone can absorb the secondary stress and the stress cannot cross the fault zone into the front of the
surrounding rock, stress peak area is located between the coal wall of the working face and the
boundary of the coal pillar failure zone of the fault zone, finally a higher stress peak appears.
The effect of the width of the broken belt on the slip of the fault zone
Figure 4: Relative slip of two plates with different fault zone width when footwall mining
From Figure 4 it can be seen, when footwall mining early, the working face is far from fault,
mining has little influence on fault, the relative slip of two wall of the fault is small, fault is not active,
with the working face continue to mining, when the working face advancing 100m (160m before
fault), two wall of the fault began to appear in the relative displacement and with the increased of the
advancing distance, the greater the width of the broken zone, the greater the relative slip of the two
wall of the fault.
Vol. 22 [2017], Bund. 06
1652
CONCLUSIONS
According to the reverse fault activation study by numerical simulation, it can be known that the
greater the width of the broken zone, the greater the normal stress and the relative slip of the two wall
of the fault.
Due to the fault zone with large buffer capacity, so it can absorb the secondary stress and the
stress cannot cross the fault zone into the front of the surrounding rock, stress peak area is located
between the coal wall of the working face and the boundary of the coal pillar failure zone of the fault
zone, finally a higher stress peak appears. Thus, when the working face is pushed to a certain
position, the normal stress of the fault zone first slowly decreases and then increases slightly.
REFERENCES
Huang Cunhan, Huang Junjie, Li Zhenhua. Numerical simulation of Coal Seam Floor
concealed small fault water inrush [J]. coal mine safety, 2013,44 (10): 24-26.
Li Kai, Mao Xianbiao, Chen Long, et al. Mining on confined floor fault activation and risk
analysis of water inrush mechanics [J]. Chinese quarterly early of mechanics, 2011, 32
(2):261-268.
Li Qingfeng, Wang Weijun, Peng Wenqing, et al. Influence of activation fault after coal
extraction on coal mine Karst water-inrush [J]. Journal of rock mechanics and
engineering, 2010, 29 (S1):3417-3424.
Li Zhihua, dou Lingming, Mou Zong long, et al. Effect of faults on top of rock burst [J].
Mining & Safety Engineering Journal, 2008, 25 (2): 154-158..
Li Zhihua, Dou Linming, Lu Zhenyu, et al. Study on fault slip instability induced by mining
[J]. Journal of mining and safety engineering, 2010, 27 (4): 499-504.
Li Zhihua, Dou Lingming, Cao Anye, et al. Mechanism of fault slip induced rockburst during
mining [J]. Journal of China coal society, 2011, 36 (S1):68-73.
Lu Xingli, Liu Quansheng, Wu Changyong, etc., Hydro-mechanical coupling analysis of
mining effect around fault fractured zone [J]. Rock and soil mechanics, 2009, 30 (s):165168.
Miu Xiexing, Liu Weiqun, Chen Zhanqing. Rock mass seepage theory [M] Beijing: Science
Press, 2004
Wu Lihui. Empirical strength criterion of rock mass [D]. Xi'an: Chang'an University, 2004
Yu Guang Ming, Xie He Ping, Yang Lun, et al. Numerical simulation of fractal effect on post
fault activation of coal mining [J]. Journal of China coal society, 1998, 23 (4) :396-400.
Zhang Peisen, Yang Jian, Wang Minghui, et al. Experimental study on fault activation and
water inrush induced by mining under the solid -fluid coupling model [J]. coal mine
safety, 2014, 45 (3):24-27.
Zhang Peisen, Yang Jian, Wang Minghui, et al. Simulation study on the variation of
interfacial stress of fault induced by mining under solid-liquid coupling mode [J]. China
mining magazine, 2014, 23 (4):84-89.
Vol. 22 [2017], Bund. 06
1653
Zhang Peisen, Yan Wei, Zhang Wenquan, et al. Study on the mechanism of coal mining
induced floor damage and fault activation in the coal seam under the solid fluid coupling
model [J]. Journal of geotechnical engineering, 2016, 38 (5): 877-889.
Zhang Wenquan, Bo Li, and Jiudang Yuan: “Detection and Evaluation of Crack
Development Near a Fault Zone Under the Influence of Coal Mining” Electronic Journal
of Geotechnical Engineering, 2016 (21.23), pp 1-36. Available at ejge.com
Zhu Deren. Failure criterion of rock engineering [J].1994, 19 (1): 15-20.
Zuo Jianping, Chen Zhonghui, Wang Huaiwen, et al.: The law of fault activity induced by
mining in deep coal mine [J]. Journal of coal industry, 2009, 34 (3):305-309.
Zhou Jiawen, Xu Weiya, Shi Chong: Investigation on compression-shear fracture criterion of
rock based on failure criteria [J].2007, 26 (6): 1194-1201.
© 2017 ejge
Editor’s note.
This paper may be referred to, in other articles, as:
Wenquan Zhang, Jiudang Yuan, and Bo Li: “The Influence of the Fault Zone
Width on the Activation of a Reverse Fault” Electronic Journal of
Geotechnical Engineering, 2017 (22.06), pp 1647-1653. Available at
ejge.com.