A GRAPHOANALYTICAL METHOD F O R R E V E A L I N G SMALL FAULTS IN COAL SEAMS

G.

A.

Antinenko

UDC

622.12'14:551.24

The presence of faults in worked sectors of coal deposits c o m p l i c a t e s roadway drivage and maintenance, particularly if these faults are not r e v e a l e d by the survey. Measures taken to improve surveying (drilling continuous ~palisade" lines of boreholes, additional surveying of small faults during exploitation o f the mine, etc.) are not a l ways sufficiently effective [1]. In this connection the method of c o m b i n e d profiles [2, 3], which enables one to r e v e a l probable fault zones of horizontal and gently dipping c o a l seams, merits attention. In this method the seam surface, represented by points with coordinates x, y, and z, is investigated by a system o f v e r t i c a l plane cross sections, drawn on die same plan. If faults are present in the profiles, characteristic (binary or m u l t i p l e ) breaks are = a c e d ; from these, one m a y establish the boundaries of the probable fault zones. The use of this m e t h o d i n surveyed or partly surveyed areas of the Donbass r e v e a l e d that it is highly effective in the presence of flips of the order of 10 m or more. In certain cases even smaller faults were detected. However, in most cases slips of less than 10 m are not detected owing to errors in graph construction. The investigations showed that in many cases small faults m a y be r e v e a l e d if the a n a l y t i c a l principle is o b served [2, 3], but that v e r t i c a l cross sections represent n o t the seam profile, but the seam gradient i, which is c a l c u l a t e d by the formula

La - -

b ~

Z b -m ~ So-

Za

b

where z a . z b are the seam reference marks at adjacent points a and b of the profile line, and Sa_ b is the distance between these points in plan. The marks of the points of the seam surface on the profile lines are d e t e r m i n e d by linear interpolation [2], and the distance s is found graphically on the plan. T a b l e 1 gives all the calculations for each o f the profile lines. The values of the gradients i, increased by a factor of 10 or 100 for convenience, are plotted to scale upward (with i > 0) or downward (with i < 0) from the profile line. Then straight lines p a r a l l e l to the profile line I - I ' are drawn through the ends of the sectors in each interval (Fig. 1, curve 1). Figure 1 shows the graph of the gradients, constructed from data of T a b l e 1. For comparison, this figure shows the seam profile constructed from the absolute marks (graph 2). Graph 1 shows that the seam gradient changes between points 6 and '/; this shows that a fault m a y be present in this i n t e r v a l On the seam profile (graph 2) there is v i r tually no sign of a break in this interval; therefore a small 2 fault m a y r e m a i n undetected. Thus, the use of gradients enables one to reveal small anomalies in the shape of the | I I seam surface far more c l e a r l y than in the case of seam proI l I I I I I I I files. ]-.J, ~ ~_~ __~ 9 ~. ~~ J~-.z 4 1

2

J .~ 5

a

7

ag~o/~

~2

Fig. 1. 1) Graph of gradients i; 2) seam profile constructed from absolute marks.

Investigations of this method, using g e o m e g i c models, showed that the character of the change in gradients for different modes of occurrence of the seam: if the position of

Dnepropetrovsk Mining Institute. Translated from F i z i k o - T e k h n i c h e s k i e Problemy Razrabotki Poleznykh Iskopaemykh, No. 2, pp. 122-125, March-April, 1971. Original article submitted March 7, 1969. 9 Consultants Bureau, a d i v i s i o n of Plenum P u b l i s h i n g Corporation, 227 g'est 17th Street, New York, N. Y. 10011. A l l rights reserved. This article cannot be reproduced for any purpose w h a t s o e v e r without permission of the publisher. A copy o f this article is available from the p u b l i s h e r for $15.00.

240

TABLE

Point No.

I

Refer ence

marks in floor, m 92.8 94,2 95,3 96,0 96,8 98,5 104,5 1('6.0 1176,5 107,2 107 ,8 109,2

I

2 3 4 5 6 7 8 9 10 11

12

r

s, IT/

AZ, m

I = AZl0n s

1,4 1,1

135

1.04

115

0,7 0,8 1,7 6,0 1,5 0,5 0,7 0,6 1.4

70 85 145 192 120 5r 70 60 140

0.96 1 ,(O 0,94

.,

1,17

3.13 ! ,25 1,00

1,00 1 .(~0 1,00

m'

I

/.

-6

7

-o~,

I

-

~

/~

- 6L 8?

Fig. 2. Example of fault detection by the g r a p h o a n a l y t i c a l method: 1) borehole, its number, and absolute m a r k of seam floor; 2) profile point, its n u m ber, and absolute mark of seam floor at the given point. the bed is regular, the gradients, c a l c u l a t e d for all the intervals of the profile line, are approximately equal, but with synclinal or a n t i c l i n a l bedding the gradients regularly decrease or increase. If a fault is present along the profile line, the value of i in the region of the break differs m a r k e d l y from that in the other intervals. The efficiency of the method was verified by means of data of preliminary and detailed surveys of m i n e fields of the Donbass. The criterion of the assessment was a comparison of the remits of fault zone detection with the existing survey data or operational e x p e r i e n c e . For e x a m p l e , the m i n e workings of No. 2 c o l l i e r y (West Donbass) were found m have a fault (No. I fault) with a slip of 4 - 7 m at several points (Fig. 2). This fault was not r e v e a l e d on the hypsometrie plans or in the survey data. The remits of an analysis of the survey data (Table 2) show that

241

TABLE 2

Point No. on profile

i.10 2

0,30 0.30 2,60 --2.30 3.40 3,40

point No. on profile

8 9 10 11 12 13 14

1.102

I Point No. on profile

1,70 1.80 3.10 1,40 1,50 1.50

15 16 17 18 19 20

I !02 9

1,90 1,90 3,50 1,20 1,20

between points 3-5, 10-11, and 17-18 on the profiles, there are anomalous deviations of i, from which one may assume that a fault exists in these intervals. It will be seen from Fig. 2 that fault zone Z, detected analytically, coincides with the fault revealed by mining operations. The width of the fault zone in this case was, in fact, much greater, due to the relatively sparse network of boreholes drilled in this sector. Nevertheless, this concrete example confirms the relatively high sensitivity of the method, which enables us, under specific conditions, to reveal probable fault zones with slips of 3-5 m or more in sectors being surveyed. The efficiency of this method of revealing faults is undoubtedly due to the dense survey grid, to the general pattern of surface variation, and to the accuracy of determination of the coordinates of the points of contact of the survey workings with the seam. Note that for fault detection during surveying, the combined use of all existing methods (geometric, analytical, and geological) of processing geological information enables one to characterize more fully and more reliably the tectonic scheme of sectors being surveyed and to select on a sounder basis the sites of tectonic boreholes for finalizing the positions of faults.

LITERATURE It

2. 3.

242

CITED

G. I. Lugovoi and E. V. Terent'ev, Third Geological Conference on Solid Fuel Minerals Abstracts of Reports [in Russian], ONTI VIEMS, Moscow (1967). A. I. Osetskii, Ugol' Ul~ainy0 No. 7 (1968). A. I. Osetskii and G. A. Antinenho, Abstract Information on Completed Research by Higher Colleges of the Ukrainian SSR [in Russian], Izd. Ugol'noi i Gornorudnoi Promyshlennosti, Kiev (1968).