Transition Method of Perpendicular Mining Districts in Surface Coal Mine Based on Combined Mining Technology Li Ma State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology, Xuzhou, 221116, China; e-mail: [email protected]

Kemin Li* State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology, Xuzhou, 221116, China; email:[email protected]

Xiaohua Ding State Key Laboratory of Coal Resources and Safe Mining, China University of Mining & Technology, Xuzhou, 221116, China

Zhiguo Chang Department of Mining, Xinjiang Institute of Engineering, Urumqi, 830023, China

ABSTRACT Mining districts transition method, an important issue, has to be faced with during the whole mining process of large horizontal surface coal mine, since the mine field is divided into several mining districts and the mined-out area is backfilled with overburden material. In order to ensure the first mining district turning into the second one smoothly in a right angle of Heidaigou surface coal mine, two transition methods are proposed, which contain fan advance of working face and gentle slope inner-dumping, and the gentle slope inner-dumping method is determined as the optimal transition mode for Heidaigou surface coal mine with considering the adaptation of the combined mining technology to the two transition methods. The gentle slope inner-dumping constraint condition is determined and the optimizing model of uncovered end-wall height is established for mining area perpendicular transition on the basis of the principle that the average stripping ratio is not more than the economic stripping ratio, and the optimal uncovered end-wall height is 87.88m for gentle slope inner-dumping. The research conclusions have important reference and guidance significance for similar surface coal mine on researching transition method.

KEYWORDS: surface coal mine；combined mining technology；perpendicular mining area；transition method

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INTRODUCTION Surface mining is a broad term which refers to the removal of the soil and strata over a mineral or fuel deposit and the removal of the deposit itself, the stripped materials mined out is dumped into the designated location via transport equipments. The land occupation expense of external dump and stripping haulage cost account for about 2/5 of the cost in the view of cost structure of surface coal mine. To reduce the cost, the stripped materials are usually dumped into the mined-out area as the external dumping is replaced by the internal dumping, which can not only save the land acquisition costs and reduce the haulage distance as well. For the rich resource reserves and horizontally buried ore body, the open-pit is usually divided into several mining districts to reduce the haulage distance and capital construction volume, so that the initial production stripping ratio can be decreased and the internal dumping can be realized as soon as possible (JI, 2011). However, re-stripping and continuous production are the major problems when the previous mining district is close to the end of mining according to the particularity of the open pit mine shapes (SHANG, 2004). Simultaneously, the layout of in-pit development haulage system and rational utilization of dumping space will be subject to different impacts in the transition period (LIU, 2001; XU, 2006). The mining method of one coal field divided into several districts and achieving inner dumping has been adopted in large surface mines since 1980s, as the service life of first mining district is coming to the end, the surface mines are now facing the problems related to the steering from the first mining district to the second one. CAI Qingxiang et al. (1996) analyzed basic mining districts transition methods of Anjialing surface coal mine and confirmed that the gentle slope mining with uncovered end-wall in a right angle was the optimal scheme. ZHOU wei et al. (2009) analyzed the influence factors of innerdumping covering height under the parallel mining districts condition and gave the corresponding calculation method. SHANG Tao et al. (2005) analyzed the problems encountered during the transition period of Antaibao open-pit mine, and proposed the corresponding solution methods. GU Zhenghong et al. (1995) determined that inner-dumping with leaving ditch was superior to recutting ramp in mining districts steering from the point of technical economy. The researches above are all on the conditions of discontinuous mining system of single-bucket excavatorbucket, there are not any research based on the combined mining technology. The paper based on the background of the combined mining system adopting in Heidaigou surface mine, the first mining area is gradually reaching the limit and in order to ensure the normal production steady, it is significant to research and optimize the reasonable transition method from the first mining area turning to the second one in a right angle of Heidaigou surface coal mine.

THE ENGINEERING BACKGROUND Heidaigou surface mine lies in the middle of Zhunge’er coal field with horizontal ore body, and it is divided into three mining districts. The first mining district started operation in the July of 1992 and was put into production in the October of 1999.The designed production capacity is 12Mt/a, and the coal production exceed 30Mt in 2012 after twice capacity expansion,Therefore, it has become the largest surface coal mine in production capacity with single pit. Combined mining technology is adopted in Heidaigou, in which the upper loess is stripped by continue system of bucket wheel excavator; The shovel-truck discontinued system is applied in central rock thickness of 45~75m, with the bench height of 15~20m; And casting blast-dragline stripping technology is adopted in bench height of 40~45m over the coal roof; The shovel-truck,

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Th e

fir

st

m

in

in g

di str ict

crusher and belt conveyer consist the semi-continued technology for coal exploiting. Figure 1 is the divided mining districts sketch map of Heidaigou surface coal mine, the perpendicular mining districts transition method is the problem to be solved under the condition of adopting the combined technology.

The

third

m in

The seco nd m

in g d

i n in

istri ct

g dis trict

Figure 1: The divided mining districts of Heidaigou surface coal mine

MINING DISTRICTS TRANSITION METHODS OF COMBINED TECHNOLOGY The basic mining districts transition methods According to the positional relation of the two adjacent perpendicular mining districts and formation characteristics of the new mining working face, the mining districts transition method can be classified as two basic modes, which are fan advance of working face and gentle slope inner-dumping (Cao, 2012).

(1) Fan advance of working face Before the first mining district reaching the pit limit, working face should be rotated around one side in the form of the fan advancing, until the new working face in the second mining district is formed, then the mining districts transition is completed. As shown in figure 2, the volume of stripping and excavating is stable and without the re-stripping phenomenon of covering end-wall during the whole fan advance transition period.

(2) Gentle slope inner-dumping When the first mining district is closed to the pit limit, the whole end-wall near the second mining district is not be covered with inner dumped materials and a ditch is left at the boundary of the mining district, then it can be used as the working slope of the new mining district, shown in figure 3. The method can reduce the re-stripping overburden volume of the second mining district, but it can also result in the inner-dump space reduction and the haulage system cannot be

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arranged at the end-wall, so that the bilateral transportation routes turns to the single one, which makes the transportation distance increased.

mining district Ⅰ

mining district Ⅰ

mining district Ⅱ

Figure 2: Fan advance of working face

mining district Ⅱ

Figure 3: Gentle mining inner-dumping

Adaptation of combined mining technology to transition methods Compared to gentle slope inner-dumping, the working face of fan advancing is inclined with the end-wall, and the mining width is not fixed along the working face, the enlarged working line length makes it more difficult of organization and management. For the gentle slope innerdumping, due to the reduction of the covering materials volume to the working slope of second mining district, the inner dump space in the first mining district reduced so that the external dumping volume and the haulage distance increased. Under the special conditions of adopting combined mining technology in Heidaigou surface coal mine, the shovel-truck discontinuous technology is characteristic of flexible and stronger adaption for the working face and suitable for various kinds of working face layout forms. Considering the particularity of dragline working and shifting of belt-conveyor, both of them have a higher requirement for the working face layout, so the mining technology of bucketwheel- excavator system and dragline are the key restrictive factors of influencing mining districts transition selection.

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Table 1: Different mining technology adaption to transition methods production technology

gentle slope inner-dumping

fan advance of working face

shovel-truck discontinuous technology

high

higher

higher

low

higher

low

high

high

bucket-wheel-excavator-belt conveyor continuous technology dragline stripping technology shovel-truck-crusher-belt conveyor semicontinuous

As shown in the table 1, BWE system and dragline technology have a higher adaption to gentle slope inner-dumping transition method. For the technology including truck of discontinuous and semi- continuous, the gentle slope inner-dumping method has a greater adaption to fan advance of working face. Hence, considering the restrictive requirement of BWE system and dragline technology, the gentle slope inner-dumping is selected as the applied transition method for Heidaigou surface mine’s turning.

OPTIMIZATION ON THE INNER-DUMPING COVERING HEIGHT The gentle slope inner-dumping constraint condition of mining area perpendicular transition Adopting the gentle slope inner-dumping method in mining area perpendicular transition, overburden material dumped in the terminal stage of the first mining area must be re-stripped when exploiting coal seams of the second mining area under the inner-dump.

B

I

ΔH α C

res

J G

K

E

g pin p i tr

H

β F

h

Figure 4: The gentle slope inner-dumping transition model of perpendicular mining area As can be seen from figure 4, the sectional area of coal under the covered end-wall can be calculated as:

= S1 h ( 2 H − 2∆H + h ) cot α

（1）

where, S1 is the sectional area of coal exploited under the covered end-wall, m2 ; α is the entity end-slope angle, °; H is the distance of the coal seam to the surface, m; ∆H is the height of uncovered end-wall, m; h is the thickness of coal seam, m.

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Meanwhile, the sectional area of rock need to be removed can be expressed as:

= S2

1 2 [( H + h) 2 − ∆H 2 ] ⋅ (cot α + cot β ) + ( H − ∆H ) cot α 2

（2）

where, S 2 is the sectional area of rock to be removed, m2 ; β is slope angle of the inner dump, °. Consequently, the height of uncovered end-wall should meet the conditions as the formula (3) according to the principle of average stripping ratio being not more than the economic stripping ratio (GUO, 2010).

η

1 2 ( H − ∆H 2 )(cot α + cot β ) + ( H − ∆H − h) 2 cot α 2 ≤η j h(2 H − 2∆H + h) cot α

（3）

where η is the average stripping ratio; η j is the economic stripping ratio.

The uncovered end-wall height optimizing of gentle slope inner-dumping Due to the end-wall being not covered completely, there are two factors constituting the economic benefit of gentle slope inner-dumping in perpendicular transition, one is the increased haulage expense C1 and another is decreased re-stripping expense C2 , which can be expressed as:

Q ⋅ ∆L ⋅ γ ⋅ c 1000 C2 = Sg ⋅ l1 ⋅ a

C1 =

（4） （5）

where γ is average bulk density of overburden material, t/m3 ; c is ton-km freight of truck, RMB/t·km ; l1 is the length of the new mining area, m ; a is the secondary stripping unit expense, RMB/ m3 ; ∆L is the increased haulage distance, m; Q is the increased transportation volume, m3 ; S g is the sectional area of the covered end-wall, m2 . And there are relations as the follows:

∆L = l − (2 H − ∆H ) cot β

（6）

Q= l1 ⋅ [l − ( 2 H − ∆H ) cot β ] ⋅ ∆H / 2

（7）

S= ( H ∆H − ∆H 2 / 2) ⋅ (cot α + cot β ) g

（8）

Taking the time value of money into consideration, the total benefit J of the gentle slope inner-dumping in mining area perpendicular transition can be expressed as:

= J C2 (1 + ρ )

−

l1 d

-C1

（9）

where d is the advancing length per year, m/a; ρ is the annual interest rate, %. According to the formula (4) to formula (9), the relationship between the total benefit J and the uncovered end-wall height ∆H can be simplified as:

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（10）

l − l1rc ⋅ cot 2 β l1rc ⋅ (l − 2 H cot β ) cot β l1a (cot α + cot β ) d where= I1 = − ⋅ (1 + ρ ) , , I2 2000 1000 2

= I3

l − l1rc ⋅ (l − 2 H cot β ) 2 − l1aH (cot α + cot β ) ⋅ (1 + ρ ) d 2000

Then taking the derivative of the formula (10), the two extreme value can be obtained as:

-2I ± 4 I 22 − 12 I1 I 3 ∆H = 2 6I1

（11）

According to the actual situation of Heidaigou surface coal mine, the parameters for calculating the optimal uncovering end-wall height of gentle slope inner-dumping are listed in Table 2.

Table 2: The parameters for calculating the optimal uncovering end-wall height parameters

symbol

unit

value

working face length

l

m

2159

γ

kg/m3

1.49

overburden material haulage cost

c

Yuan /t·km

3.6

entity end-slope angle

α

°

38°

slope angle of the inner dump

β

°

26°

distance of the coal seam to the surface

H

m

170

coal seam thickness

h

m

average bulk density of overburden material

30 3

the secondary stripping expense

a

Yuan /m

14

advancing length per year

d

m

340

annual interest rate

ρ

%

5

Vol. 18 [2013], Bund. U

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440

375

375

375

375

375

375

375

375

375

375

375

375

440

7000

18500

19000

19500

20000

20500

21000

21500

22000

22500

23000

23500

24000

7000

北 440

440

6500

6500 1217.203

1208.319

1216.257

1235.9

1238.570

1204.4

1204.3

1200.6

1253.485 1255.089

1189.2

1229.2

1220.4

1238.392

1186.4

1215.261

1234.464

1210.799

1237.255 1216.449

1231.4

1226.370

1214.357

1242.7

1226.631

1237.116

1244.7

1199.431

1236.275

I

1212.480

1205.599

1219.418

1260.223

1245.373

1228.9 1239.525 1228.962

1276.916

1311.922

1239.2

1276.069

1203.7

1244.581

1277.574 1260.358

1244.130

1259.084

1251.387

1214.384

1218.182

1247.2

1248.082

1247.3

1287.800 1288.130 1287.200

440

1287.999

1241.520

440

1242.872

1259.000

1250.948

1274.982

6000

1248.505 1251.43

1231.0

1287.300

1286.339

1215.068

1251.230

1213.600 1251.980

1214.85

1249.630

1287.433

1279.146

6000

1287.052

1259.233

1289.159

1248.995

1250.247

1218.574

1242.080

1280.034 1212.301

1287.500 1289.164

1276.679

1276.821

1287.800

1246.702 1256.796

1217.556

1241.344

1276.856 1256.8

1256.808 1273.995

1243.097

1233.868

1278.296

1276.988 1273.757

1268.837

1277.900

1274.204

1260.065

1280

1260

1200

1220

1240

ter Ex

5500

1231.093

1257.7 1219.144

站

3#

1237.094

1277.018

1265.2

1249.9

1260.051

、

4#

破碎

440

1237.248 1217.770

5500

1226.397 1228.945 1252.3

1256.7 1239.810

1251.3

1265.4

1219.070

1277.2

1257.5

1276.321

1239.404

1245.4

1257.8

1219.891

1262.6

1270.3

1218.762

1286.5

1239.791

1266.7 1245.148 1249.0

1274.062

1275.2

1239.029

1279.3

1218.169

1260.860

1218.456 1218.169

1285.3

1238.810 1245.9

1273.5

1223.1

p m du

1260

1229.377

1235.113

1252.7

1241.2

l na 1260

5000

1233.786

1257.1 1256.7

1280

440

1230.974 1231.177

1260.1

440

1241.886 1232.050

1287.145

1252.1

1257.5

1291.212

1287.932

1287.8

1259.650

1260.505

1260

1239.404

1217.169

1286.439

440

5000

1259.050

1263.6

1217.982

1255.5

1254.4

1240.791 1245.417

1275.529

1259.116

1247.081 1240.029 1256.481 1216.236

1244.000

1238.846

1249.580 1216.133 1243.636

1253.033

1245.876

1200

1220

1240

1244.483

1243.894

1240

1249.537

1240.480 1212.104 1246.8 1266.88

12

1229.382

60

1241.199

1230.636

1215.948

1252.541

1239.218

440

440

1210.006

4500

1240

1233.0

站

1237.000

破碎

12

12

15

2#

1236.5

4500

1214.477

1241.664

1255.1 1253.950

In ter

1#

、

1251.2

1240.2

1220

1212.8

1220

12

80

126 0

1206.458

440

1213

1215 端帮路

4000

1240

11

1180

1160

70

1200

1241.483

1208.199 1238.472

1228.977

1240.051

1206.825 1261.529 1237.360

1224.997

na l

11

48

1148

1185.000

1179

1230.364

48

124

0

1260.742 1224.983

1239.600 440

4000

1260.425

du m p

1224.741

1240.000 1259.026

1224.824

1258.612 1258.771

1240.000

1204.031

1236.3 1259.045 1228.964 1259.304

1221.811

1241.914

1259.296 440

440

3500

11

3500

121

1245.759

3

22

11

1260.339 1230.903

63

117

9

0

1210 1195 1180

reg io

440

10

3000

120

10

1

1

62

117

117

1

11

121 3 122 3

en ch

1

co al be nc h

1216

113

7

1213

1219

1210 1216 1213

113

7

25

114

121 9 123 4

pe rc oa lb

bo tto m

1

11 37

16

0

11 11

up

120

n

11 11 25 40

114

ing

11 52

11 11 37 52

94

wo rk

11 64

11 11 49 64

120

94

ne

440

11 49

10

10

dra gli

11 72

3000

1245.500

11

02

1

114 8

1222 1219

440

440

2500 1222

27

1221

82

11

co al be nc h

1222 1222

10

1220

98

1222

11

58

idd le

11

m

2500

11

68

25

1217

1202

大 成 线 公 路

11

11

40

11 11 49 64

00 306.69

11 11 37 11 52 37

11 11 25 40

11 11 13 28

440

2000

60

2000

1215

11

440

1200 2012

1165

0

11

0

0

121 0

0

122

121

49

120

52

0

120

119

11

0

0

123

122

440

440

1500

1500

375

375

375

375

375

375

375

375

375

375

375

375

18500

19000

19500

20000

20500

21000

21500

22000

22500

23000

23500

24000

Figure 5: The planed project position of Heidaigou surface coal mine in the end of 2013 The reasonable range of the uncovered end-wall height is less than 157.7m according to the formula (3), and the height determined by formula (11) is 87.88m, which is the optimum value since within the reasonable range. At present, Heidaigou surface coal mine is being in transition gradually to the second mining district, the bottom of uncovered end-wall locates on the 30m above the casting blast bench and the uncovered height is around 80m. Figure 5 shows the planed project position of Heidaigou surface coal mine in the end of 2013, the bucket wheel excavator system has been working in the second mining district for loess stripping, and the other technology system are still working in the first mining district.

CONCLUSIONS (1) Two kinds of transition methods of fan advance and gentle slope were determined for the transition of the adjacent perpendicular mining districts in consideration of the formation characteristics of the new working face. (2) It was analyzed that the adaptation requirement of the different mining technology to the transition modes, and both the BWE system and dragline technology are the key factors, therefore, the gentle slope inner-dumping method was confirmed as the transition way for Heidaigou turning into the second mining district. (3) The gentle slope inner-dumping constraint condition of mining area perpendicular transition was confirmed on the basis of the principle that the average stripping ratio is not more than the economic stripping ratio, the optimizing uncovered end-wall height was confirmed as 87.88m in terms of the optimization model.

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ACKNOWLEDGEMENT The authors acknowledge the support of the National Natural Science Foundation of China (51034005)

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JI, C.S (2011) “Study on Turning Method Between Neighboring Mining Panels in Surface Mine” Coal Engineering, No. 12, pp 1-3,7.

2.

SHANG, T., Q. X. CAI, and Y. LIU (2004) “Optimal Selection of Pit Haulage System in Transition Period for Mining-in-Areas,” Journal of China University of Mining & Technology, Vol. 33, No.4, pp 412-416.

3.

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4.

XU, Z. Y., Q. X. CAI, and X. Q. LIU (2006) “Some Problems and Countermeasures of Mining Area Turning for Antaibao Surface Coal Mine,” Coal Engineering, No. 12, pp 9-12.

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CAI, Q. X., and C. S. JI (1996) “Transition Method from One Mining Area to the Next in Large Surface Coal Mines,” Journal of China University of Mining & Technology, Vol. 25, No. 4, pp 45-49.

6.

ZHOU, W., Q. X. CAI, and Y. P. LI (2009) “Study on Inner Dumping Covering Height in Large Near Horizontal Surface Mine,” Coal Science and Technology, Vol. 37, No. 1, pp 53-55.

7.

SHANG, T.,Q. X. CAI, and Y.D. ZHANG (2005) “Analysis of Some Technological Problems for Large Surface Coal Mines in China,”. Journal of China University of Mining & Technology, Vol. 34, No. 2, pp 138-142.

8.

GU, Z. H., and S. G. LI (1995) “Study of Remained-Slope Mining In Surface Mines with a Flat-Buried Deposit,” Journal of China University of Mining & Technology, vol. 24, No. 2, pp 59-63.

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CAO, B. (2012) “The Optimization Research and Application of Surface Mine Transition Alternative Mode of Mining Area and Transportation Dumping Engineering under Complicated Geological Conditions,” China University of Mining & Technology (Beijing).

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