On the Choice of a Method for Controlling Rock Pressure in the Mining of Steeply Dipping Medium-Thickness Seams of the Prokopyevsk–Kiselevsk Deposit

M. V. Kurlenya

(Presented by the scientific seminar of the departments of bedded-deposit mining, ore-deposit mining, mine construction, safety engineering, and mine ventilation)

The choice of a method for controlling rock pressure is one of the most important questions in the mining of hard-coal deposits. However, despite the long study of questions connected with the control of rock pressure, there still does not exist a fully definite methodology for choosing one or another method of controlling rock pressure as applied to specific mining-geological and production-technical conditions. To be sure, for the Central district of the Donbass, DONUGI [1] and N. A. Zaitsev [2] have developed classifications of side rocks from the standpoint of rock-pressure control. The authors do not take into account many factors—such as the tendency of coal to spontaneous combustion, swelling of floor rocks, gas content of the seam and of the enclosing rocks, the direction of seam extraction, and others—which have a direct or indirect bearing on the question. Moreover, these classifications of side rocks were created with consideration of the mining of seams exclusively by long pillars along the strike and by the continuous system. Consequently, the use of any other mining system on seams of medium thickness creates difficulty in the practical application of the methods of DONUGI and N. A. Zaitsev for establishing the most rational method of controlling rock pressure.

In mining steeply dipping seams of medium thickness in the Prokopyevsk–Kiselevsk district, the systems used mainly are long-pillar mining along the strike with caving and with stowing, and the shield system with caving of the side rocks. As is known, under the shield system of mining, in contrast to continuous mining and long pillars, the stoping face is located along the strike and moves down the dip of the seam. In this case the character of the caving of the side rocks becomes entirely different than in mining by systems in which the stoping face is located along the dip and its movement is carried out along the strike. According to investigations of the Siberian base station of VNIMI in the mines of the Prokopyevsk deposit, when seams are extracted down the dip, displacement of the rocks of the hanging wall normal to the bedding reduces the volume of the excavated space—

by 10–20%; the drawing-off of caved rock on the first and second levels ensures filling of the worked-out space, on average, by 65–80%, and only from 5 to 25% of the volume of the worked-out space is filled by rocks from the immediate roof [3].

Thus, the requirement in the classification of DonUGI and N. A. Zaitsev that the thickness of the immediate roof ensure self-stowing when working with complete caving—especially when mining seams down the dip under the conditions of the Prokopyevsk–Kiselevsk district, in the presence of the circumstances indicated above—is not obligatory.

Analyzing visual observations of the mining of steeply dipping seams of medium thickness and literary sources [1–16], we present in the table a list of the main (decisive) factors determining the necessity and possibility of applying methods of rock-pressure control by caving and by stowing. We have not considered the role of such factors as the cleavage of coal and of the side rocks, the length of the longwall face, etc., since they permit any method of rock-pressure control to be applied to an equal extent. In addition to the factors noted, such factors as the length of the extraction panel and the susceptibility of the seam to sudden outbursts of coal and gas have also been excluded from consideration, since the question of choosing a method of rock-pressure control with allowance for their influence has been little studied.

Complete stowing of the worked-out space ensures reliable control of rock pressure under the most varied mining and geological conditions and may be applied in all cases without exception where the mining of seams with caving is possible. However, in the table, only those factors under which rock-pressure control by complete caving is unacceptable or causes a number of difficulties have been assigned to the factors favoring the use of stowing.

It is evident from the table that, when the working face is arranged along the strike and moves down the dip, the range of application of the method of rock-pressure control by complete caving is expanded. If, in mining seams by long pillars along the strike and by the continuous system, such factors as the thickness of the immediate roof, the presence of a false roof and floor, heaving of the floor rocks, fracturing of the side rocks of the seam and of the enclosing rocks, etc., are decisive, then in mining seams by the shield system these factors have almost no influence at all. Thus, for example, when seams are mined by the shield system, exposure of the false roof and floor within the worked-out space almost does not occur, and if it does occur, the area of its exposure is insignificant. Consequently, the shield system permits the mining of seams with a false roof and floor with caving of the side rocks. Another example. In the case of mining seams with the working faces arranged along the strike and moving down the dip, with caving of the enclosing rocks, the caved space is located above the shield canopy and, naturally, the methane released from the freshly exposed roof and floor rocks or from the caved rocks migrates upward along the cracks to the ventilation level or to the surface. The main influx of methane into the face space comes from the coal massif. Consequently, when seams are mined by the shield system, the influence of the gas-bearing factor on the choice of a method of rock-pressure control does not have such decisive significance as in systems of mining by long pillars along the strike and in continuous systems, where the caved space, on the contrary, becomes a source of accumulation of harmful gases.

Table

Influence of natural and production-engineering factors on the choice of a method for controlling rock pressure in the mining of steeply dipping medium-thickness seams of the Prokopyevsk-Kiselevsk district

Thus, in mining steeply dipping seams of medium thickness in the Prokopyevsk–Kiselevsk deposit, the choice of a method for controlling rock pressure must be made as shown in the table. When extracting seams with the longwall face advancing along the strike, caving of the side rocks should be used in all cases except when:

1) the thickness of the immediate roof does not ensure complete filling of the worked-out space, taking into account the displacement of the rocks and the release of the overlying caved rocks;

2) the side rocks are hard to cave and massive, or, conversely, the side rocks are weak and fractured;

3) there is a false roof and floor;

4) the immediate roof and the floor of the seam are disturbed;

5) the seam floor is prone to heaving;

6) closely spaced seams are worked in ascending order;

7) the coals are highly prone to spontaneous combustion;

8) the coal seams and enclosing rocks are highly gas-bearing.

Stowing of the worked-out space should be used in those cases when caving of the side rocks is impossible for the reasons indicated above.

When extracting seams with the longwall faces arranged along the strike and advancing down the dip, caving of the side rocks may be used in all cases except the working of closely spaced seams in ascending order and in the presence of coals highly prone to spontaneous combustion. The latter two circumstances require the use of stowing of the worked-out space.

The systematization presented here of mining-geological and organizational-technical factors will make it easier to choose a method of controlling rock pressure under the most varied natural and production conditions.

REFERENCES

1. Davidyants V. T. Roof Control on Steeply Dipping Seams of the Donets Basin, Ugletekhizdat, 1949.

2. Zaitsev N. A. On the question of controlling rock pressure on steeply dipping seams of Donbass, Ugol, No. 8, 1948.

3. Institute of Mining, Academy of Sciences of the USSR. Improvement of Methods for Mining Thick Seams of Kuzbass with Stowing, Ugletekhizdat, 1956.

4. Belenkov F. A. Properties of Rocks from the Standpoint of Roof Control, ONTI, NKTP USSR, 1936.

5. Mikheev G. F. The Role of Stowing Clay in Preventive Silting, Ugletekhizdat, 1951.

6. Proceedings of the Conference on Rock-Pressure Control, Academy of Sciences of the USSR, 1938.

7. Slesarev V. D. Control of Rock Pressure in the Mining of Coal Seams of the Donets Basin, Ugletekhizdat, 1952.

8. Stowing of the Worked-Out Space, Ugletekhizdat, 1954.

9. Nekrasovsky Ya. E., Kremenchutsky N. F. Mining of Steeply Dipping Seams of Donbass, Ugletekhizdat, 1954.

10. Proskurin V. V. Investigation of the Order and Methods of Mining Closely Spaced Steeply Dipping Coal Seams of the Kiselevsk Deposit in Kuzbass, dissertation for the degree of Candidate of Technical Sciences, 1951.

11. Mikheev G. F. Detection of Spontaneous Combustion of Coal at an Early Stage, Ugletekhizdat, 1951.

12. Gas Content of Coal Mines in the USSR, vol. 1, Academy of Sciences of the USSR, 1949.

13. Goikhman G. I. Analysis of Mining Systems for Coal Deposits of the Donets Basin, Ugletekhizdat, 1950.

14. Korzhikov M. I. Stowing Support, Ugletekhizdat, 1955.

15. Heidemann W. Möglichkeiten einer Rationalisierung im westeuropäischen Steinkohlenbergbau durch Umstellung auf Rückbau, seine Vorbereitung und Durchführung beim heutigen Stande der Technik. “Glückauf,” August, 1955.

16. Parusimov V. F., Novikov K. P. Systems for Mining Coal Seams of Kuzbass, Ugletekhizdat, 1950.