10th Asian Regional Conference of IAEG (2015)

Investigation on the Overburden Deformation and Failure under the Influence of Thrust
Faults: A case study in the Yima Mining Area
Wanghua SUI(1), Yanwei GAO(2)(1) China University of Mining and Technology, China
E-mail: suiwanghua@cumt.edu.cn(2) Beijing Aerospace Geotechnical Engineering Institute Co., Ltd
Abstract
This paper presents an experimental and numerical simulation of the overburden
deformation and failure due to coal mining under the influence of a regional thrust fault,
namely F16, in the Yima mining area, Henan province, China. The failure heights of cavingzones and water flowing fractured zones after mining each coal seam were gained in thecondition with and without setting up fault coal-pillars, respectively. The results show thatthe fault has the “barrier” effect on overburden failure and deformation, the caving zone,
water flow fractured zone developed in the footwall would hardly extend to hanging wall.
The heights of overburden failure were finally determined by considering the results fromscale simulations, numerical simulations and calculations according to the code. The results
put forth an engineering geological basis for safety assessment of coalmining in the area
influenced by thrust faults.
Keywords: thrust fault, overburden failure, caving zone, water flow fractured zone, groundmovement.
1.

Introduction

2.

As important discontinuities in rock mass, faults
damage the integrity of the rock mass seriously, andalso dramatically change its mechanical strengths(Kurlenya and Seryakov, 1996). Faults are prone tobe activated by mining activities and then influence
the roof stability of coal seams. In the panels withfaults, the overburden failure will be affected
obviously and should be taken into consideration.
The hard roof and thick gravel stone strata are themain geological characteristics of the Yima mining
area, Henan, China, the influence on the overburden
failure of the complex shape of the fault are safety
geological problems during coal mining.
The F16 thrust fault is located in the southern partof the Yima mining area, it is a group of compressive
shear thrust faults with a strike of nearly east-west.
The fault and its influenced zone have a complex
geological conditions, with a thick overlying gravelstone strata and an obvious stress accumulation.
Therefore, in order to evaluate coal mine safety
production near the fault, the investigation on the
overburden deformation and failure during coalmining under the influence of thrust faults should bestudied systematically.

Geological Conditions

The Yima mining area is located in the west ofHenan province, China. It is the only huge thickMesozoic coal field in Henan province. The northern
and western boundaries of the Yima mining area are
the outcrops of coal Seam 2-3; its eastern boundary is
the Jurassic strata, and its southern boundary is theF16 thrust fault. The main body of mining area isgeologically located in the northern wing of a
syncline, and its whole shape is a southward
monocline, generally striking in East-West with a dip
in the middle of the coal field of less than 16º, and alarger one about 35º in the eastern part of the mining
area. Figure 1 shows the geological structure outlineof the Yima mining area.
J1-2

J1-2
Yangcun

J1-K

Gengcun

Qia n

qiu

J1-2
Yue

j in

profile Line 45
LegendFault

Boundary of Plotting
coal field scale
1:15000

NNorth
open-pitmineChangcun

T1

T
T1

Fig. 1 Geological structure outline of the Yimamining area1

10th Asian Regional Conference of IAEG (2015)

The regional major geological tectonic unit is the
Mianchi-Yima syncline, which presents a asymmetricsyncline with a length of 50 km and a width of 20 km,
approximately. Its axial direction is near the northeast,
dipping to the southwest. The faults in the Yimamining area are mainly divided into two types; tensile
shear faults and compressive shear ones. The
compressive shear faults are step thrust fault. They
were mainly formed in late Yanshanian Period.
3.

deformation and failure during mining, relevant
overburden movement, mining influencing scope, andinfluence on F16 thrust fault when mining in the
footwall. Figure 1 also shows the location of the
profile Line 45.
The geometric similarity scale for the modelb =0.07, weight scale
b=1/200, time scale a 
Cr is determined 1. Then, the strength scale CR=1/200.
The geometric size of the model is 3 m × 1.6 m ×
0.33 m (Length × wide × height). Two coal seams
would be extracted in the model; the upper is coal
Seam 1-2 (a productive coal seam with a thickness of
2.4 m) with a thickness of 1.2cm in model, the lower
is coal Seam 2-3 (a productive coal seam with athickness of 14.2 m) with a thickness of is 7.1cm inmodel. Figure 2 shows the engineering geologicalmodel of profile Line 45.
Rock physical and mechanical parameters of
profile Line 45 were measured and satiated according
to experimental results and geological data. The
proportion of each material to simulate rocks in the
profile Line 45 was determined by trial and error
method.
Grid calibration points were used to monitor the
overburden deformation and failure during mining.

Methodology

3.1 Scale Model
Scale model simulation is a model experiment
technology based on the similarity theory (Bai et al.,
2001; Cui, 1990). The experiment in this paper ismainly based on geological conditions of F16 thrustfault and its affected zone in Yima mining area, fromthe coal geological drilling data and seismic
exploration results. The section at profile Line 45
across the F16 thrust fault was selected to be
prototype for scale modeling. Two mining situations
were simulated: one is with setting up fault coal-pillar(a coal-pillar left for safety purpose when mining
adjacent to a fault), another without. The overburden

Table 1 Types of rocks and its material ratios of profile Line 45
No.

Chronostratigraphy

Lithology

1
2
3
4
5
6
7

J2m
J2m
J2m
J2y
J2y
J2y
J2y

8

J2y

9

T3

10

T3

11

T3

sandy mudstone
fine sandstone
conglomeratemudstone
1-2 coal seammudstone
2-3coal seaminterbedded mudstone
and fine sandstone
mudstonemedium sandstoneintercalated by
mudstoneinterbedded medium
sandstone andmudstone
Fault zone

12

Weight proportion (%)

Thickness
(m)

UCS
(MPa)

Density(g/cm3)

Sand

CalciumcarbonateGypsum22.04
159.56
3.15
15.44
2.35
24.03
14.24

21.75
47.2
29.76
11.57
8.45
30.1
8.65

2.51
2.52
2.50
2.451
1.36
2.45
1.36

87.5
80
85.7
85.7
90.9
85.7
90.9

6.25
6
4.3
4.3
6.4
4.3
6.4

6.25
14
10
10
2.7
10
2.7

12.01

17.3

2.39

83.3

11.6

5.1

16.18

30.1

2.45

90.9

5.5

3.6

50.9

19.3

2.50

87.5

6.25

6.25

63.3

15.9

2.52

85.7

10

4.3

0.58

1.90

87.5

6.25

6.25

2

10th Asian Regional Conference of IAEG (2015)

300
ZK4504 50m 50m
1

∠6

+200

T3

34
6 5 7
8
9

°

+100

0
0-7

160

J2m

37
4 8 10

J2m

F16

2

2

11

J 2y

+300

for Seam 1-2 is 150 cm, and for Seam 2-3 is 150 cm.
Figure 4 shows the overburden deformation andfailure situations at each stage during the mining
process of the model. Along with the mining of Seam
1-2, separation began and then roof caved. The
caving zone and water flow fractured zone developed
continuously. Throughout the mining process, theimmediate roof periodically caved and the main roof
remained stable. After mining Seam 1-2, 24 hours
was needed to make sure the complete subsidence.
Along with the mining of Seam 2-3, at early stage themain roof remained stable, but after Seam 2-3 mining
60 cm, the caving zones of the Seam 2-3 and Seam
1-2 superimposed together, the caving zone and waterflowing fractured zone grow quickly.

T3+336.6 179°

J2y

+16.6

Fig. 2 Engineering geological model of profile
Line.45
3.2 Numerical Simulation
UDEC has been widely used in mining, tunnelingand other geotechnical engineering (Zhang and Yu
2004).
Numerical simulation model in this paper isestablished by using UDEC 4.0 to simulate
overburden deformation and failure situation in theprocess of mining, which is under the influence ofF16 thrust fault. The main purpose is: by analyzing
the failure structure diagram, we can get the
overburden deformation and failure process while
coal seam mining.
Comparing to the scale model, a two-dimensional
calculation model with a length of 600m and a heightof 320 m was established by using UDEC 4.0. The
elevation of the top of +336.6 m and the bottom is+16.6 m. The ground elevation is +620 m, then, theoverburden above the model thickness is about 280m.
According to the calculation, A vertical load of
7.0MPa was applied on the top of model to simulate
the overburden weight. Figure 3 shows the distinct
element calculation model.

(b)

(c)

(d)

(e)

(f)

(g)
(h)
Fig. 4 Overburden deformation and failure atdifferent stages(a) before mining; (b) Seam 1-2 mining 60cm; (c)Seam 1-2 mining 100cm; (d) Seam 1-2 mining 150cm;(e) Seam 2-3 mining 60cm; (f) Seam 2-3 mining
80cm; (g) Seam 2-3 mining 115cm, (h) Seam 2-3
mining 150cm.

Fig. 3 A distinct element calculation model for profile
Line 45
4.

(a)Figure 5 shows the roof subsidence contour map
after mining the Seams 1-2 and 2-3. After mining
Seam 1-2, the overburden deformation and failure is
not obvious, the whole overburden displacement
value is smaller, mining has no impact on the fault
virtually, hanging wall has no overburden
displacement. After mining Seam 2-3, the overburden
deformation and failure extend to the top of model,
the whole overburden displacement value is large.
However, the hanging wall has no overburden
displacement still. Setting up fault coal-pillars canResults and Analysis

4.1 With Setting up Fault Coal-pillars
A 100 cm wide coal pillar on the left side ofmodel was set up. On the right side of the model, a 45
cm wide fault coal pillar in Seam 1-2 was set up, anda 60cm wide fault coal-pillar in Seam 2-3was set up.
Coal seam was extracted from left to right with aspeed of 5cm per hour mine. The total mining length3

10th Asian Regional Conference of IAEG (2015)

prevent caving zone and water flow fractured zone
extend to hanging wall, F16 thrust fault has a barrier
effect, thus guarantee coal mine safety production.
0
4
1

0
-7
6
1
F

00
0
3

-3
-6 -1 0

0
0
2

0
5
1

0
0
1

0
5

0
0

-6

0
5

-7.5

0
5
2

0
5

00
0
3

6
1
F

0
5
2

0
0
2

0
5
1

0
0
1

0
5

0
0

(d)

0
0
1

0
0
1

0
5

0

0
5

(c)

-1

Fig. 7 Contour map of roof subsidence after mining
without setting up fault coal-pillars

4.2 Without Setting up Fault Coal-pillars
Figure 6 shows the process of mining the fault
coal-pillar. Along with the mining of Seam 1-2, when
the fault coal-pillar Seam 1-2 mining lest 30 cm, F16
thrust fault started to move. When Seam 1-2 mining
into fault, F16 thrust fault completely separated along
the fault plane. Along with mining the fault
coal-pillar of Seam 2-3, the caving zone and waterflow fractured zone developed quickly, reached to the
top of model at last. Therefore, setting up 30 cm wide
fault coal-pillar is reasonable by scale simulation.

(b)

-3 -6
-1
0 -5
-7.5
-7.5

Fig. 5 Contour map of roof subsidence after mining
when setting up fault coal-pillar

(a)

0
4
1

0
4
1

0
0
1

0
0
1

3
1
0
- 3
-5 2
2
- m
2a
e
1
S
4
6
m
5
a
e
2 3-6S
0
410

0
4
1

footwall overburden displacement value is larger thanhanging wall. It shows that without setting up fault
coal-pillar, the fault barrier effect reduced, coalmining may lead to the fault plane cracking andactivation.

4.3 Numerical Results and Analysis
Figure 8 shows the failure pattern of overlying
strata after mining seams in profile Line 45. From theperspective of overburden deformation and failure
process, when Seam 1-2 was extracted to 300m,
caving rock filling mined-out area, the fracturesappeared in both sides above the mined-out area. The
height of caving zone is 15.35m and height of waterflow fracture zone is 63.13m. When Seam 2-3 wasmined to 300m, both sides above the mined-out area
formed shorter cantilever. The rock stratum between
Seams 2-3and 1-2 caved completely. The water flow
fractured zone expanded and displacement value of
curve subsidence zone increased. The height ofcaving zone is 57.5 m, and water flow fracture zone
150.7 m.

(a) Model initialization(e)(f)
Fig. 6 Overburden deformation and failure situations
at each stage(a) Seam 1-2 mining with 30 cm fault coal-pillar left;(b) Seam 1-2 mining to fault; (c) Seam 2-3 mining
with 45 cm fault coal-pillar left; (d) Seam 2-3 mining
with 25 cm fault coal-pillar left; (e) Seam 2-3 mining
with 10 cm fault coal-pillar left; (f) Seam 2-3 mining
into the fault.

(b) Seam 1-2 mining 300 m

Figure 7 shows the roof subsidence contour map
after mining the fault coal-pillars of Seams 1-2 and2-3. It is found that the maximum overburden
displacement value is located in the footwall, and the(c) Seam 2-3 mining 300 m

4

10th Asian Regional Conference of IAEG (2015)

5.

When setting up fault coal-pillar, the thrust fault
has a “barrier” effect on overburden deformation. Asa natural discontinuous structural plane, fault has an
obvious barrier effect, the fault zone, water flow
fractured zone and subsidence developed in the
footwall would hardly extend to the hanging wall.
However, when there is no fault coal-pillar, barrier
effect of the fault reduced, coal mining may lead tothe fault plane cracking and activation.
With setting up fault coal-pillar, mining in the
footwall will not leading to fault slide along the fault
plane, hanging wall has no obvious overburden
displacement. Without setting up fault coal-pillar, due
to the existence of fault zone, the rock mass broken
seriously in the fault zone and its influence scope,
specific performance for caving zone is high and roof
stability is poor. As the distance to the fault planedecreased, the fault influence on overburden
increased, the footwall overburden near fault plane
was most likely to cave.
Through comparative analysis of the calculations,scale model simulations and numerical simulations
results, the heights of overburden failure were finallydetermined.

(d) Seam 1-2 mining to the fault(e) Seam 2-3 mining to the fault
Fig. 8 Failure pattern of overlying strata aftermining along profile Line 45
The mining of the fault coal-pillar of Seam 1-2
shows that F16 thrust fault appeared its activity whenthe mining distance to the fault reached 65m. Alongwith the mining of Seam 2-3, in the footwall, cavingrocks filled the mined-out area and the water flow
fractured zone expanded to reach the top of model atlast. In the hanging wall, rock stratum slide along thestratum’s surface. Thus setting up 70m wide fault
coal-pillar is reasonable according to the results.

Acknowledgements
The work is financially supported by 973
Program under Grant No. 2013CB227903.

4.4 Comparison Analysis for Failure ofOverburden
According to the Code "Buildings, water bodies,railways and the main shaft’s coal pillar setting andpress coal seam mining regulations (National Coal
Industry Department, 2000)", the heights of cavingzone and water flow fractured zone can be calculated,
and then compared with the results from scale model
simulations and numerical simulations. Results areshown in table 2.

References
Bai Y., Bai S., Jin Z. and et al. (2001): Testing studyof similar material for layer-divided top coal cavingin specially thick coal seam, Chinese Journal ofRock Mechanics and Engineering, Vol. 20, No. 3,
pp. 365-369.
Cui G. (1990): The similarity theory and scale modelexperiment, China University of Mining
Technology Press, pp. 1-30.
Kurlenya., M.V. and Seryakov., V.M. (1996):
Deformation of a rock mass during mining of theprotective working in the vicinity of a fault, Journalof Mining Science, Vol. 32, No. 4, pp. 274-278.
National Coal Industry Department (2000): Buildings,
water bodies, railways and the main shaft’s coalpillar setting and press coal seam mining regulations,
Coal industry publishing house, pp. 225-233.
Zhang. J. and Yu. Y. (2004): Discrete element
method for rock movement analysis, Journal of
Hydrogeology and Engineering Geology, No. 4, pp.
9-13.

Table 2 Results and comparisonswater flowing
caving zone
fractured zone
height (m)height (m)Methods

Calculations
Scale
simulations
Numerical
simulations

Seam
1-2

Seam
2-3

Seam
1-2

Seam
2-3

13.91

24.80

58.00

87.80

4.10

55.50

22.20

146.00

15.35

57.50

63.13

150.70Conclusions

5