ROCK FRACTURING

C L A S S I F I C A T I O N OF K A R A G A N D A C O A L S

ON THE B A S I S OF THE B R E A K I N G S T R E N G T H

P. E. A n t o n o v , A. I . B e r o n , V. I . E f r e m o v , I . S. Z i l ' b e r t , a n d D. M. L y u b o s h c h i n s k i i

(UDC 622.233)

Our classification scale is based on ,~ in kg/cm, the index for determining the resistance of a coal to cutting

by DKS and SDM-1 equipment.

The system of coal classification proposed by Protod'yakonov [1], based on ~c does not help us to design min- ing machines and determine their range of application and expected output, because f does not allow for changes in the state of the virgin coal under the effect of rock pressure [2, 3]. Furthermore, it has been established [4, 5] that we cannot expect ro obtain unique relationships between f and the power expended on cutting.

Coal strength was taken as the basis for a more comprehensive classification by Giprouglemash [6], and is presently employed in the coal industry; its values are being determined for al l the main coalfields in the coumry.

However, this classification is based on a l imited number of dam and is not applicable to coals of some fields. Furthermore, the ranges and limits of the hardness classes do nor have an adequate scientific basis.

Table 1 gives the mean resistance of coals to cutting (and the sca t~r of these quantities) as measured with the DKS and SDM-1 apparatus; i t also gives a comparison of empir ica l and theoret ical series of determinations of the resistance, assessed by Pearson's tests for goodness of fit. For a l l the meas~ements • �9 • so we may infer that coal properties in a face follow a normal distribution.

Before assessing the difference between individual s=ength values of similar and dissimilar seams for different systems of mining-out the coal, we must assess the accuracy of ,~. The procedure for determining the acct~acy is as follows [7]. The error of the mean value of o x is

~ 9

" = • r

where o is the standard deviat ion of the sample, and n is the number of variants (experiments).

In determining the error we assume that o characterizes both the sample and the process as a whole.

The criterion of statist ical re l iabi l i ty is defined as

Al ~X

With n �9 30 variants (experiments) the mean characterist ic Ai is re l iable i f t H �9 3.

The index of accuracy of the mean is defined as

(2)

~X : _-=- 1 0 0 % .

Al

The resistance is found with a fair degree of confidence, and the index of accmacy of the mean, for the over- whelming majori ty of the seams, is below 5%, which is quite acceptable [8].

"Giprouglegormash." Karaganda. Tramlated from Fiziko-Tekhnichesk/e Problemy Razrabotki Poleznykh Iskopaemykh, No. 3, pp. 35-40, May-June, 1966. Original art icle submitted September 18. 1965.

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TABLE 1

Site of experiment (piL face)

Second Chmubai-Nminsk cross-hole

Second Chuzubai-Nurinsk cross-hole

47-49, 1 East, easterly d i - rection

70, 3-c West, westerly d i - rection

47-49, 5 East, westerly d i - rection

47-49, 1 East, easterly d i - rect ion

70, 3-c West, westerly d i - rection

70, 3 -a West, westerly d i - rection

38, 1 West, easterly direction 26, 21 West, easterly di-

rection 23, l - b i s East v / s , westerly

direction 31, 9 West, easterly d i -

rect ion Third S. M. Kirov, cross-hole

31, 8 Lower West, westerly direction

Seam

d,

ds

Middle K s

Middle Ks

Middl~ Ks

Lowermiddle K t

The same

Uppermiddle K4 New K m

Feliks KlO

The same

Six- foot KI= Upper Marl- anna KIZ

Four-foot K s

ImmLment used for the test

DKS

DKS

DKS

SDM-I

SDM-1

DKS

SDM-I

SDM-I

DKS

DKS

SDM-I

Strength X, kg/crn

79

84

154

120

163

164

178

171 174

2O8

220

DKS

DKS

DKS

223

230

266

TABLE 2

rn~ de-

viation o,

kg /cm

35

36

48

57

51

48

66

52 49

79

3O

51.0

57

59

Pearson test of goodness of fi t

exptl . Xe theoret. .XT

11.17 16.2'7

17.7 20.52

4.67 16.27

17.21 18.46

8.96 16.27

1.48 18.46

19.6 20.52

2.2 16.27 16.5 24.32

2.09 18.46

4.7 13.81

3.48 18.46

0.13 13.81

3.75 18.46

Seam

Ks

Kz

Kt0

Site of exper iment(pi t , face)

70, 3 West, westerly direction

47-49, 5 East, westerly direction

47-49, 1 East, easterly direction

70, 3 West, westezly direction

26, 2 West, easmrly direction

23, 1-bis East, westerly direction

Mining method

LGD, individual supports

KM-97 aggregate

Donba=- l , individual supports

OMKT aggregate

Donba=- 6, individual supports

KM-100 aggregate

Strength

A, k g / c m

120

163

164

178

208

220

in comparison with individual supports, ~o

100

126.4

100

107.9

100

105.5

The data in Table 1 ahow that the breaking resistance of the coat varied among the seam= from 79 to 266 m. kg /c In t/Line succes ive determinations the resistance of the coal in Seam K z was found to be 120, 154, and

163 kg/cm. It must be noted that in the first case the longwall face was worked in a westerly direction, in the sec- ond case in an easterly direction, and the value 163 k g / c m was found in a IongwalZ face in which a KM-87 cutmr- loader was being used. I t is noteworthy that in ident ical seams the resistance was greater in those longwaH faces

266

TABLE 3

Seam

K3

K2

Klo

kg/cn

1~*

178"

220*

kg/cn

4,4 3,9

5.8 6

2.9 9,4

Dp

~ g / c r ~

43

14

12

5,9

8,35

9,8

7,3

1,7

1,2

* Worked by KM-87, OMKT, and KM-100 sys- tems, respectively.

TABLE 5

Limits of re= Class sist~nce, Seams

kg/c.rn

Ill IV V VI

VII VIII IX

Up tog0 90--120

120--150 150--180 180--210 210--240 240--270

d,, d5 Ka Ka

K=, K~, Kl, Kl~ K2, KI0

KLo, K~=, Kta Kit

TABLE 4

}Boundary |values o f re-

G r o u p s Islstance indl- O'xdiff tg ce= kg/cm ' f

I--II 84--120 II - - I l l 120--154

llI 154--178 I l l - - IV 178--208

IV 2O8--23O IV--V 230--266

5,7 8,2

19, 4

13,6 12,0

6,3 4,2 2,5 2,7 1,84 3,0

where mechanized supports were in use. This difference was greater in faces worked in a westerly direction than those worked in an easterly direction (Table 2).

The difference between the mean resistances for dif- ferent mining methods does not indicate the rel iabi l i ty of the difference between means. The rel iabi l i ty can be found by comparing the variat ional series by taking the differences between the means and the errors in the differences of these means. With this aim, we performed an analysis using the system in [7].

Let us find the difference between the means of the indices of resistance of the coal.

D = A I - A , = 154-- 120- '34 kg/cm. (3)

The error of the difference of these means is given by

ax d i f f = § "V ~ -- .r, + a2r, "-- ] ' / '7,3: + 3,9: - 8.2, (4)

where Oxl and Oxz are the errors of the mean value of corresponding resistance indices.

A rel iable difference between the means satisfies the inequality

D t g - - - - ~ 3 .

~x dtff (5)

Put D = 34 kg /cm and o x diff = 8.2:

3 4 4 , 2 ) 3 . tg = �9 8 ,2

We can thus assert that the difference between the mean values of the index of resistance A of longwall faces worked in easterly and westerly directions with individual supports is not random, bur stat ist ically significant.

By a similar method we found the difference between the mean indices ~ for the same seams for longwall faces with individual and powered supports. The results are given in Table 3.

Calculations show that in westerly faces technological factors have a marked influence; in easterly faces the difference may be random. However, i t is found that in a l l cases where powered supports are used there is some increase in the mean index of resistance. I t follows that in compil ing a coal classification we must take account of factors connected with the technological methods used. These data and the accumulated experimental mater ia l permit a provisional classification of the coals in the seams of the Karaganda field according to their indices of resistance.

The choice of the number of classes in the scale depends on the prac t ica l problem of determining the expected productivity of cutting machines and establishing their regions of usefulness. For this p~pose the number of resistance

267

TABLE 6

Seam

Specific output over total underground outpua U/o

5, k g/cm, when in- dividual mpports are used

d,

1.8

79

d.

1,9

84

3,3

164

3,0

137

2,5

152

Km

I0,I

208

Kn

21 ,~

230

Kts

I1

223

K~,

9,8

Kta

8,I

174

I1,6

90*

* Provisional by analo~ with machines working in seams d 4 and d s.

classes should be determined from a comparison of the resistance indices of individual seams, and also within a single

seam (allowing for mchnical factors) where there is a statistically significant difference. Analysis of [he data in

Table 1 shows that the seams can be divided into groups according to resistance. Consequently, we can judge the appropriateness of such a division if we know the difference between the boundary values of the resistance indices of

adjacent groups and the limis of each group. Table 4 gives the results of calculatious performed by the method de- scribed above.

From the table we see that there is a statistically significant difference between groups I andII, II and HI, and

IV and V; we can assume that there is aLso a difference between groups Ill and IV. Within Groups HI and IV there is no significant difference. Thus, our analysis of the data on breaking resistance of coals of the Karagands field en-

ables us to propose a division of these coals into seven classes (Table 5), compatible with the ge~ral coal classifi- cation of the USSR [2].

To preserve continuity and determin~ the position of the Karaganda coals in the general classification, the

number of classes was taken in conformity with the classification sug~smd by the Skochlnskii Mining InstRute [2] for all goals of the USSR.

Naturally, this classification can be augrnensed for the design of machinery. For the Karaganda coals some

changes are possible in the limlt~ and number of the classes if additional material can be accumulated on the re- sistances of the coals.

Knowing how each seam contributes to underground output and knowing the resistance of each seam, we can make a preliminary estimate of the weighted-mean resistance for the Karagnnda coalfield as a whole on the as- sumption that coal is exlzacsed from the longwall faces by normal methods (cut~er-loads, individual supporm) or by combined equipment. We must mention that in determining the weighted-mean resistance, the different values found in identical seams are averaged out. owing to differences in mining methods. Table 6 gives the necessary data.

The weighmd-mean resistance is found from the expression

XD , Aw.me• ' '

l

where D and Ai represent the percentage contribution of the seam to underground output and the seam's resistance, respectively.

From these calcula t iom it was found that the weighted-mean index of resistance for normal mln~ng systems in the field is 195 kg/cm. When combined syssems are used t l~ resistance must be increased on average by 12.5 (see Table 4). When the Dollusk seam series mal~es an increased contribution to the r~tal underground output we can expect that the weighted-mean index of resistance for the field will decream.

Io 2.

L I T E R A T U R E C I T E D

M. M. Protod'yakonov, Determining the hardness of coa l in a mine, ugor, No. 9 (1950). A. I. Beron, A. S. Kazanskii, B. M. Leibov, and E. Z. Pozin, Coal Cutting, Moscow, C-osgorsekhizdat (1962).

268

3. P.E. Antonov, I. S. ZiFber t , and D. M. Lyuboshchinskii, Cutting Resistance of Coals of ~he Karaganda Field. In symposium, "Cutting Resistance of Rocks in Mining," Moscow, Izd. AN SSSR (1962).

4. B.M. Leibov, Investigation of Mechanical Process of Coal Cutting, Moscow, Ugletekhizdat (1950). 5. P.P. Inozemtsev, F. M. Polozhii, M. I. Shnaidman, F. B. Cherkasskii, D. M. Lyuboshchinskii, and E. Z. Pozin,

Mechanization of Coal Loading in Pits of the Karaganda Coalfield, Moscow, Ugletekhizdat (1956). 6. N.A. Lapovenko, B. N. Lyubimov, and A. M. Terpigor 'ev, Cutting Resistance of Coal dining the Operation

of Mining Machines, Moscow, Uglemkhizdat (1958). 7. A. L Fedorov, Methods of Mathematical Statistics in Biology and Experimental Work, Alma-Ata ,

Kaz gost~khizdat (195"/). 8. A . M . Dlin, Mathematical Statistics in Indus~y, Moscow, Izd. "Sovetskaya Nauka" (1958).

All abbreviations of periodicals in the above bibliography are letter-by-letter translitera- tions of the abbreviations as given in the original Russian journal. Some or all o f th i s peri- odical literab.zre may wel l be ava i lab l e in E n g l i s h t rans la t ion . A complete l ist of the cover-to- cover English translations appears at the back of the first issue of this year.

269