PRINCIPAL DIRECTIONS FOR IMPROVING METHODS OF MINING THICK COAL SEAMS

T. F. GORBACHEV

The scale of growth in the technical equipment of our enterprises is enormous. The result of technical growth is the steady increase in labor productivity observed in numerous branches of our socialist industry.

The coal industry is one of the leading branches of heavy industry, determining the economic power of our country. However, in terms of the growth of labor productivity it lags behind not only other branches of industry in our country, but also the coal industry of the USA. Despite the rise in the level of mechanization of work, the richest hard-coal basin of our country—Kuzbass, 40% of whose reserves are concentrated in thick seams—has for almost two decades already shown virtually no growth in labor productivity.

Labor productivity is the principal indicator characterizing the level of production technology.

In analyzing the main components of the latter, it is not difficult to note that over the past decade it has changed little. As before, in the technology of coal extraction in working faces, the process of erecting timber supports predominates; this consumes a large share of working time. An enormous quantity of first-grade timber is expended on supporting working faces, and the delivery of this timber is also associated with considerable labor costs.

The main reason for the weak growth of labor productivity in working faces is that timber supports and the manual method of erecting them have completely exhausted their usefulness and in no way meet the requirements of our time, when the question has been raised of the complete mechanization and automation of production processes.

Only by eliminating from the entire complex of coal-extraction operations the labor-intensive operation of supporting the working face will we be able to ensure a significant increase in labor productivity. The solution of this question must be carried out in the direction of creating self-advancing supports which, once assembled, would ensure reliable enclosure of the working space and eliminate the need for the constant erection of supports in the working face.

In choosing directions for the mining of thick seams in Kuzbass, it is first of all necessary to proceed from the specific mining-and-geological conditions, which are distinguished by extraordinary diversity. The Prokopyevsk-Kiselevsk district of Kuzbass represents a depos-

...deposit, whose interior consists chiefly of suites of thick steeply dipping coal seams gathered into synclinal and anticlinal folds. The seams are close together and, for the most part, are mutually undermined; they are complicated by frequent additional dislocations with rupture of continuity, are gas-bearing, dangerous with respect to dust, and prone to spontaneous combustion. The Novy Tom-Usinsk region is characterized by a deposit of thick gently dipping seams. The strength of the coal and the stability of the enclosing rocks vary within fairly wide limits. The thickness of individual seams normally reaches 16 m, and in various folds up to 30 m and more. Such diversity in the mining-and-geological conditions of occurrence of coal seams rules out the possibility of effectively applying in Kuzbass any single system of working. From this point of view it would be the grossest error to orient our technical policy toward any one method of working thick seams: toward working only without division into slices, or only with division into slices; toward working only with stowing of the worked-out space, or toward working only with caving. The correct position must be recognized as one in which we shall have at our disposal various means, equipment, and methods of work that we can apply most effectively in one or another specific situation.

Systems of working without division into slices

Steep dip

Of the large number of systems of working and the various variants of individual systems used in Kuzbass for working thick steeply dipping seams, the shield system of working has undergone the greatest development. This system is based on the principle of using, to fence off the working space, a shield that moves along the dip behind the clearing face. In this case, operations connected with supporting the clearing face are completely excluded from the technology of extraction work, and almost all working time (93%) is spent on the direct extraction of coal, owing to which the shield system of working ensures high labor productivity and high technical indicators. Many years of experience with shields in Kuzbass make it possible to give certain recommendations regarding the application of shield canopies.

1. For working seams 2.5–6.0 m thick, non-sectional shields should be used; they provide better indicators in comparison with sectional shields (Fig. 1). At present in Kuzbass non-sectional shields are being successfully used for extracting steeply dipping seams 2.2–2.5 m thick (the Ziminka mine and the Kalinin mine of the Prokopyevskugol trust). At the same time, the KVKP support-and-extraction unit merits attention; its design should be refined in order to make it inexpensive to manufacture while significantly simplifying assembly and disassembly operations.

2. Seams 6.0–8.0–10.0 m thick are at present, in most cases, worked with single sectional shields, with the use of which Kuzbass has accumulated fairly extensive experience. However, in view of the significant advantage of non-sectional shields over sectional ones, the former should be preferred when working seams of any thickness.

From this point of view, a positive assessment is deserved by the new design of a non-sectional shield made of paired beams, developed by the staff of the laboratory of mining-system development of the mining-and-geological...

Fig. 1. Extra-wall external vibrating poker.

Fig. 2. Elastic wedge-less gate made of laminated beams

Visible labels in the drawing:

• View from above
• View from below
• Side gate posts
• 700
• 32
• 13
• \(w\ell\)
• \(I\)
• \(II\)
• \(1\)
• \(2\)
• \(3\)
• \(4\)
• \(5\)
• \(m0\,17\text{–}II\) [[unclear: dimension note]]

Fig. 3. Sectionless elastic panel made of reinforced-concrete beams

Visible labels in the figure:

• formwork
• thermoactive formwork
• channel No. 20
• tie bolt
• strip 150×10
• formwork
• reinforced-concrete beams
• 23.0
• formwork
• 4.5
• angle section No. 5
• channel No. 20

Fig. 4. Self-propelled concrete-placing shield on pile beams.

of the Institute of the West Siberian Branch of the Academy of Sciences of the USSR (Fig. 2) in 1956. With shields of this design, at mine 3 of the Kiselevskugol trust, in a seam 8 m thick, an extraction panel about 200 m long along the strike was mined. This problem is solved more fully by using elastic shields made of reinforced-concrete beams, whose strength, with considerable length, can be selected as desired.

In October–November 1956, in the Kuzbass, at the Ziminka mine of the Prokopievskugol trust, under the direction of engineer A. A. Surilachev, operational tests were carried out of a design, also proposed by him, of a reinforced-concrete shield in the Gorely seam, 5–7 m thick and with a dip angle of 68–70° (Fig. 3).

The tests showed the complete serviceability and high operating qualities of a sectionless shield made of reinforced-concrete beams.

1. In mining seams more than 10 m thick, one should be guided by paired sectionless shields (made of paired beams), the design of which successfully passed industrial tests at the Maneikha mine of the Prokopievskugol trust, where in December 1956, with the aid of this shield, a section of a seam 11–12 m thick was mined (Fig. 4).

2. In mining seams 15–16 m thick and more, and at dip angles greater than 70°, layer-by-layer extraction should be used, in which a thick seam is divided into two layers, each of which is mined by means of shields analogously to an individual seam (Fig. 5).

Fig. 5. System of layer-by-layer extraction of a thick coal seam by shields

The shield system of mining must be improved:

a) In the direction of reducing the level of coal losses and increasing its fire safety by extracting inter-shield pillars and replacing them with stowing strips, and by creating designs of extensible shields that make it possible to mine seams of variable thickness. At present, experimental testing under production conditions is being carried out on a wooden extensible shield of frame construction, developed by staff members of the Mining-Geological Institute of the West Siberian Branch of the Academy of Sciences of the USSR. The first results of the experimental work have confirmed the serviceability of shields of this design (Fig. 6).

b) In the direction of mechanizing the transport of coal under the shield, with the aim of reducing the number of coal chutes in the shield pillar. From this point of view, it makes sense to test the possibility of hydraulic breaking of coal under the shield.

c) Toward the creation of a shield system with complete stowing of the mined-out space, which would make it possible to carry out shield extraction beneath fire-hazardous areas and on lower horizons.

Inclined Seams

The positive solution of the problem of mining thick inclined seams by means of shield canopies, verified by experimental work under production conditions, already makes it possible at the present time to recommend, for the mining of seams up to 8 m thick: at dip angles

Fig. 6. Movable unsupported shield

from 35 to 55°, shields on rollers (Fig. 7); from 25 to 35°—shields with forced feed of the MZL shield type, designed by “Giprouglema—

Fig. 7. Shield on rollers for mining inclined seams

… (Fig. 8), thereby extending the use of shields to conditions of inclined bedding.

Fig. 8. Shield with hydraulic feed by MZL for working seams of inclined bedding

Gentle bedding

If, in steep and inclined seam bedding, extraction to the full thickness by means of supports moving along the dip presents no particular difficulty, then the working of thick, gently dipping seams is associated not only with the difficulty of creating a mobile support for work under these conditions, but also with the difficulty of controlling the roof rocks of the seams. In this case, work with caving in any form is possible only where the roof rocks are weak and unstable. If, however, the latter are of considerable stability, extraction of the seam to its full thickness will be associated with the need either to carry out complete stowing of the mined-out space or to carry out artificial caving in order periodically to relieve stresses in the mass of overlying rocks, thereby reducing the pressure on the movable face support. Obviously, in this case one should be guided by short faces having a high rate of advance.

With regard to the design of mobile supports, one can only say that they must be walking supports, or, more precisely, must have sectional movement of the elements, so as to exclude cases of exposure of roof rocks over a considerable area, which is very important when working under conditions of gentle and horizontal occurrence.

It must be admitted that the question of working thick gently dipping seams to their full thickness is still problematic, unless one considers the room-and-pillar system, the use of which should not be abandoned when working seams whose thickness does not exceed 5 m, with stable roof rocks permitting considerable exposures and the possibility of extracting the inter-room pillars.

Confirmation of this can be provided by the experience of the mines of the Polish People's Republic, where gently dipping seams up to 6 m thick are being successfully worked by a room-and-pillar system with hydraulic stowing.

A proven system in the working of thick gently dipping seams is the system of working by inclined slices, both with caving and with stowing of the mined-out space.

The system of working with division into slices

Despite the expansion of the field of application of the shield system, which is proceeding at the expense of reducing the field of application of slice systems, the latter should not be classed as having no prospects. Taking into account that slice systems at the present time are still the only systems, tested under production conditions, for the working of thick seams in which complete stowing of the mined-out space is carried out, a positive solution to the question of stowing under the shield system of mining does not exclude the use of slice systems, in view of the existence in the Kuzbass of such mining-and-geological conditions under which only they are suitable. The question of improving slice systems of mining not only should not be removed from consideration; on the contrary, a large number of scientific and production workers must be enlisted for its solution.

The system of working by horizontal slices is still indispensable in the working of reserves concentrated in the trough-like parts of a deposit, in areas of local swellings, in disturbed sections with coal that is crumpled and broken by cracks, in sections of seams with weak side rocks, and in seams of variable thickness, where the application of any other mining system is impossible.

In connection with the low efficiency of this system, the need has long since arisen here for the implementation of comprehensive mechanization of the operations connected with coal extraction, both in work with stowing and with caving, by creating powered support-and-winning hydraulically actuated units of the type of the “Kuzbass” unit. From this point of view, a positive assessment should be given to the KuzNIIUI mobile hydraulically actuated support, which is a movable beam canopy controlled by hydraulic jacks. It should be noted that, with sectional advancing of support elements of this type, they can be used with equal success for work under the conditions of almost all slice systems with the descending order of extraction of slices, which better corresponds to the conditions for carrying out comprehensive mechanization of operations. The weak link in the implementation of the latter in slice systems is the process of erecting preliminary support, which is difficult to mechanize. Therefore, alongside measures for improving the methods of erecting preliminary support, research should be carried out toward the creation of advance supports that make it possible to dispense entirely with the need to erect preliminary support in slice mining systems. In this, one should orient oneself toward advance supports of active action (self-advancing supports).

Alongside work on creating support-and-winning units, in order to economize timber, it is necessary to revise the technology of supporting longwall faces in slice systems when working both with caving and with stowing:

a) In the direction of using, alongside wooden props, metal props, which should be removed immediately before

with backfill, in some cases switching to metal supports made of extensible props and hinged caps. At the same time, a more advanced method must be developed for extracting them from the backfill mass of the overlying layer.

b) In the direction of transferring the principal loads from the side of the roof rock of the seam from the stope support to the backfill mass. From this point of view, it is necessary to proceed along the line of reducing the distance from the face to the backfill mass, i.e., along the line of reducing the value of the backfilling step, which will help to simplify the design of the stope and preliminary supports and to reduce the labor input of erecting them. At the same time, the practice of using metal mesh, thin concrete slabs, old ropes, or metal strips as materials for erecting preliminary support should be widely extended; their use in the mines of France gives positive results.

c) At the same time, the search should be continued for rational methods of cementing the backfill mass and obtaining inexpensive binders, oriented chiefly toward local materials: limestone, burnt shale, waste from metallurgical production, etc.

System of mining by transversely inclined layers

Compared with horizontal layers, this system has advantages consisting in the gravity flow of coal and backfill material along the face; as a result, from the overall complex of stoping operations those works are eliminated that are associated with the presence of a conveying mechanism in the stope, and the volume of work for shoveling coal is considerably reduced.

Where mining-geological conditions permit, this system can successfully replace the system of mining by horizontal layers in work both with backfilling and with caving. In work with backfilling, two variants of this system should be distinguished: with a descending order of extracting the layers and with an ascending order of extracting them.

The latter should be applied only in the case of working reserves of coal concentrated under large buildings, structures, bodies of water, fire areas, and other objects that cannot be undermined. In the remaining cases, preference should be given to the variant with a descending order of extracting the layers, bearing in mind that the latter better corresponds to the conditions for the comprehensive mechanization of operations.

The use of “Kuzbass” cutter-loader units under conditions of transversely inclined layers has the following advantages in comparison with the conditions of operation of these supports in horizontal layers:

1) the gravity flow of coal along the face eliminates the need for a conveying mechanism;

2) with an inclined position of the layers, the pneumatic method of backfilling ensures a higher density of the backfill mass and a higher degree of filling of the worked-out space;

3) the absence of coal prisms at the hanging and footwall sides of the seam, which in the case of horizontal layers are difficult to mechanize both in the part of extraction and in the part of support.

Brief description of the “Kuzbass” unit for extracting coal by transversely inclined layers

The “Kuzbass” unit can be used for extracting coal in thick steeply dipping seams by transversely inclined layers from top to bottom, both with backfilling and with caving. It can be appli-

...and for slice extraction of coal from the thick seams of the Tom-Usinsk deposit. With minor structural modifications to the end parts of the support sections, it appears possible to use it also for extracting coal from horizontal seams in descending order. The unit consists of the following assemblies (Fig. 9): cutting member 1, face conveyor 2, transfer conveyor 3, entry conveyor 4, guide rods 5, combine traction chain 6, block of odd-numbered hydraulic props 7, block of even-numbered hydraulic props 8, movable jacks, hydraulic pipeline with oil tank and control panel (not shown in the figure), stowing pipeline 12, rolls of metal mesh 13, extendable element of the guide rods for sumping the extraction combine into the coal mass 14, loading blade 15.

At the beginning of the unit’s operation, the extraction combine 1 is located opposite the conveyor entry 16. Its cutters seize a strip of coal 300 mm thick. The combine drive is switched on; the cutters, rotating about their own axis, with the aid of a guide describe a circle 2900 mm in diameter. Simultaneously, the combine drive sprocket is set in motion, rolling along calibrated chain 6 stretched along the block of even-numbered hydraulic props 8. Along guide rods 5 the combine moves upward toward the ventilation entry 17, cutting a strip of coal 300 mm thick and 2900 mm high. Most of the cut coal falls onto face conveyor 2; the remaining coal is loaded forcibly by means of blade 15. The return travel of the combine is idle. When the combine returns to its initial position, feed is switched on and the combine is sumped by means of the hydraulic feed of the extendable element of the guide rods 14. Then, by means of two horizontal jacks, the even-numbered block of hydraulic props is advanced by 300 mm, after which the odd-numbered hydraulic-prop block is drawn up. The cycle is completed.

Simultaneously with coal extraction, the interbed roof is covered. The metal mesh in rolls is located in the rear part of the odd-numbered hydraulic-prop block and is unwound automatically. After the unit has moved 1500 mm, planks 60 mm thick and 2–2.5 m long are laid diagonally on the mesh. The combine operates on the principle of large-chip breaking, processing the entire height of the face in one pass; the thickness of the coal strip removed may vary from 200 to 400 mm. Since the height of the face is constant, coal extraction by the combine is not regulated by height.

In the initial position, the combine, being opposite the conveyor entry, can independently sump into the coal mass to the thickness of the coal layer being removed. Watering of the coal is required.

Approximate data for the extraction combine: combine capacity—150 t/hour, working-travel speed—1.5, idle-travel speed—5, and sumping speed—0.2 m/min.

The support is made in the form of two blocks: a block of odd-numbered hydraulic props and a block of even-numbered hydraulic props. Each support block consists of two-leg sections of the supporting type, connected by detachable tubular rods into rigid frames.

Thanks to this design, the length of the unit can be changed easily and quickly, and it can be dismantled and assembled. Movement of the support by means of only two horizontal jacks simplifies control of the unit in the plane of the seam. Control of the unit’s movement in the plane perpendicular to the seam is achieved by changing the position of the cutting member relative to the face by means of adjusting screws 20. Movement of the unit in contact with the floor, in order to avoid undercutting, is ensured by the fact that the conveyor has a front suppor-

Fig. 9. Design of the “Kuzbass” removable scraper for operation in narrow stope faces of various systems of transverse-inclined and steep workings.

... a wall of special shape, preventing the passage of the bar. The conveyor is hinged to the block of even-numbered sections, and therefore always follows directly along the floor.

The rectilinearity of movement of the hydraulic-support blocks is ensured by their spatial rigidity. The roof is prepared artificially—the ties are laid over a metal mesh. The strength of the roof, its quality, will depend on the thickness of the ties and the care with which they are laid. The side rocks are supported by side hydraulic jacks 21. The ability of the tubular trusses to be disassembled into individual rods, and the simplicity of the hydraulic system, make it possible to transfer the unit easily from one seam to another.

When mining a seam with one face in two shifts, taking into account operation of the unit during only 4 hours per shift, with uninterrupted delivery of stowing material the unit is capable of producing 1060 tons. When the seam is mined simultaneously by two faces, productivity doubles.

The unit revives seam systems on a new, more advanced technical basis and makes them effective. It facilitates the erection of stowing, without which the mining of deep horizons in the Kuzbass is inconceivable, and almost eliminates timber consumption. Faces equipped with the “Kuzbass” unit satisfy the requirements imposed on systems for mining coal deposits: fire safety and general safety of work, high labor productivity, minimal coal losses, and high productivity of the section.

From November 11, 1948, to February 22, 1949, in the Kuzbass, at the Kapitalnaya-1 mine of the Osinnikugol trust, industrial tests of the first prototype of the “Kuzbass” unit were carried out. The tests were conducted on seam “P₁,” whose thickness varied from 0.9–1.15 m, with a dip angle of 2°–13°. The length of the longwall face was 20 m. Despite a number of design shortcomings that were revealed in the course of the tests, and difficult mining conditions, satisfactory technical-and-economic indicators were achieved: in 137.5 hours of useful operation, the unit extracted more than 1000 tons of coal.

During the period of normal operation of the unit, high technical-and-economic indicators were achieved. Thus, on January 23, 1949, in one 8-hour shift the unit advanced 2.4 m along the strike. The labor productivity of a worker at the face achieved thereby was 3 times higher than the labor productivity existing under ordinary methods of work in analogous conditions.

Along with work to implement comprehensive mechanization in the stoping faces of cross-inclined seams, it is necessary to carry out measures analogous to those listed above, i.e., to expand the practice of using metal support consisting of portable props and caps both in work with stowing and with caving. In work with stowing, both in descending and ascending order of seam extraction, operations must be organized in such a way that the main load from the roof beds is borne by the stowed mass.

The system of mining by inclined seams has, until recently, been used in the Kuzbass mainly for mining thick seams of inclined and gentle dip, except in those cases where the need arises for work with stowing. In connection with the successful resolution of the question of mining thick seams by shields on rollers and shields with forced feed, the field of application of the system of mining by inclined seams with caving has been considerably reduced. Specifically, at the present time it is determined by gently dipping seams and inclined seams whose thickness ...

exceeds 8 m, i.e., those seams for which the question of developing them with powered shields has not yet been solved, and seams whose development with caving is impossible for one reason or another. Thus, despite the reduction, the field of application of this system remains quite significant, especially if one takes into account the Tom-Usinsk district of the Kuzbass, whose reserves are concentrated mainly in thick gently dipping seams.

The system of working inclined seams is used in the Kuzbass both in operations with caving and with stowing. If the technology of conducting operations with caving entails only a descending order of seam extraction, then in operations with stowing two variants of this system should be distinguished: with a descending order of seam extraction and with an ascending order of extraction, which until recently was the only one in the Kuzbass. Recently, however, new directions have appeared in the practice of applying this system. For some reason, most specialists of the Kuzbass had formed the opinion that, under conditions where there is no well-caking stowing material, the descending order of extraction of inclined seams is, from a technical point of view, unacceptable. This opinion proved to be incorrect and was refuted by the practice of work at Mine “3—3-bis” of the Stalinugol trust, where, on the initiative of its workers, a seam 14 m thick and dipping at an angle of 40° was worked with gravity stowing by inclined layers, extracted in descending order. This direction must be developed further, since it is associated with the advantages provided by the descending order of seam extraction. These advantages consist in:

a) the possibility of working seams whose thickness may be as great as desired;

b) greater reliability from the point of view of work safety;

c) significantly greater possibilities both from the point of view of carrying out comprehensive mechanization of the work and from the point of view of using metallic prop supports.

Fig. 10. System of working inclined seams with extraction of the seams by strips along the strike

The essence of the second direction consists in the emergence of a tendency to shift to the working of inclined seams with stowing by short faces, the so-called strips along the strike (Fig. 10).

A positive feature of this direction is that, with a limited number of miners (no more than two) sent into longwalls of inclined or steep dip, the degree of utilization of a unit length of the working face will be the greater the shorter the latter is. The same can be said with regard to safety and convenience in carrying out the work, since these are ensured, when work is performed in short faces, to a greater degree than when work is performed in long faces having, moreover, a considerable dip.

The practice of the Stalin mine in Kuzbass has shown that reducing the length of the working face to 10–12 m not only did not worsen the indicators for the system but, on the contrary, contributed to an increase in the productivity of the extraction field, since in this case it becomes possible to increase the number of working faces having the same considerable rate of advance.

These two directions should be combined, i.e., the practice of working inclined seams with short faces should be extended, with primary orientation toward the descending order of seam extraction, as being more suited to the conditions of application of movable supports. In order to save timber and increase labor productivity, it is necessary to convert the working faces of inclined seams from timber supports to metal supports consisting of portable props and hinged caps.

Recently, technical thinking in Kuzbass has been developing in the direction of using various kinds of flexible canopies for mining thick seams; these canopies perform the function of shielding the working space from caved rock. In most cases this direction has been developed in combined mining systems, in which the principles of mining with division into slices and without division into slices are combined. Moreover, the element of the slicing systems has an auxiliary character for installing the flexible canopy. Much work in this direction has been done by the staff of the Kuznetsk Coal Research Institute, which for about 5 years has been working on improving the design of the flexible canopy and the methods of extracting coal from beneath it. In the basic version, the mining systems with a flexible canopy represent a modification of the system of mining by inclined slices, in which a thick seam is divided into two slices. The slice adjacent to the roof of the seam is mined first. Its thickness is selected with such calculation as to ensure maximum convenience in the work of installing the flexible canopy, which is laid on the floor of the slice. The lower slice represents the remaining main thickness of the coal seam, which is worked under the protection of the flexible canopy by means of drilling-and-blasting operations or with the aid of hydraulic monitors (Fig. 11).

In 1956, at mines No. 5 and named after V. V. Vakhrushev of the “Kiselevskugol” trust in Kuzbass, industrial tests were carried out of the mining system with a flexible canopy proposed by KuzNIUI. The main technical-and-economic indicators obtained in this work are presented in Table 1.

It is evident from Table 1 that this system has fairly good indicators and, in our opinion, is one of the promising systems for mining thick coal seams. This is also evidenced by the fact that mining systems using a flexible canopy were widely represented in the competition for the best design of effective systems for mining thick coal seams in the Kuznetsk Basin, held in 1955–1956.

Table 1

The improvement of development systems of this kind should be carried out in the following directions:

1. Simplifying and reducing the cost both of the design of the flexible covering and of the work involved in its installation.
2. Applying the hydraulic method of coal extraction. The use of roof-bolting should be recommended in short stope faces of the chamber type, both in work with caving and with stowing of the worked-out space.

In considering the question of developing thick seams in Kuzbass, we have no right to pass over such a question as the stowing of the worked-out space, since with the transfer of working horizons to great depths the gas content of coal seams increases substantially. If in 1940 there were 5 mines of category III and super-category out of 36, or 14%, then in 1957 there were already 23 mines of category III and super-category out of 72, or 32%. The gas content of individual mines is so high that, with intensive coal breaking by blasting or by combines, reducing the methane concentration to a safe level by means of active ventilation becomes impossible. Thus, in longwall No. 15 of seam E₆ at the Kapitalnaya-II mine of the Osinnikiugol trust, 15 minutes after blasting operations the methane content at the face reaches 60%. In addition, as mining operations deepen, rock pressure increases. This phenomenon is especially evident at the Stalin and Voroshilov mines in Prokopyevsk. At the adit horizon, in a number of cases workings could stand almost entirely without support, which was installed more for control. On the first horizon, coal chutes passed without support. On the second horizon, some of the chutes already had to be supported. At present, on the third horizon it has become impossible to work with unsupported coal chutes. Moreover, some of them have to be re-supported rather often. At the same time, manifestations of such threatening phenomena as sudden outbursts and rock bursts are becoming more frequent. In Kuzbass there have been more than 100 cases of outbursts, including several major ones; 14 coal seams have been classified as dangerous with respect to outbursts.

An increase in the quantity of air supplied to the mine when working with caving will also cause an increase in its leakage due to seepage through the worked-out space, which, given the incompleteness of coal extraction that occurs here, creates the danger of underground fires arising, with a significant complication of the work of extinguishing them by means of flooding.

Added to all this is a new danger—the inrushes of pulp and clay into mine workings that have occurred in Kuzbass, that is, from

Fig. 11. System of working with a retreating face under a flexible covering

Visible labels in the figure: section along I–I; section along II–II; 6; 5; 58; 60°.

with the increase in the depth of extraction of coal seams, the general danger dictating the necessity of carrying out stowing of the mined-out space increases. Stowing is also needed as a measure that makes it possible to mine coal reserves concentrated under large buildings, structures, bodies of water, fire areas, and other objects which, for one reason or another, cannot be undermined.

According to preliminary calculations by the Kuzbassugol combine, by 1965, of the entire volume of coal mined in Kuzbass, 12% must be mined with stowing of the mined-out space. In the Prokopyevsk–Kiselevsk district, about 25% of the district’s total output must be mined with stowing. Already in the sixth five-year plan, production with stowing must increase to 7.0 million tons, or 8.0% of the total output of Kuzbass, which urgently requires the creation of more rational mining systems with stowing and productive methods for erecting the stowing mass.

Work on creating rational systems for mining thick seams with stowing has in recent years been carried out in several directions:

a) in the direction of a significant increase in the efficiency of slice mining systems with stowing, by carrying out complex mechanization of operations in the stoping faces of individual slices;

b) in the direction of creating highly productive systems of mining with stowing of the mined-out space when extracting a seam at once over its full thickness.

Among the systems belonging to the second category, the shield mining system with inter-shield concrete pillars and arches deserves attention.

Engineering logic suggests that such a system of mining thick seams will become widespread, in which the stowing will perform the function of supporting the stoping face, completely eliminating the consumption of support material.

In some cases one should not reject the possibility of working with partial stowing of the mined-out space. From this point of view, the combined system for mining thick steeply dipping seams (chamber-shield), proposed by a group of authors (Fig. 12), is of importance. The practical significance of this system lies in the fact that it makes it possible to use two highly effective systems for mining thick steeply dipping seams, well known in the practice of Kuzbass: the chamber system and the shield system, while eliminating their shortcomings.

In the combined system, the chamber system acquires entirely new content, since the latter provides for filling the chambers with stowing material and extracting the inter-chamber pillars by means of shield covers. At the same time, the system of extracting thick steeply dipping seams by chambers has the special feature that, when mining a seam at once to its full thickness, it makes it possible to control the side rocks by simply filling the worked-out sections of the chamber with stowing material, thus assigning the function of supporting the near-face space to the stowing without the additional use of any temporary supports, while making it possible to use the natural conditions of steep occurrence of coal seams for transporting coal and for transporting the stowing material to the place where it is to be placed.

However, one should proceed not only in the direction of creating highly efficient systems of mining with stowing, but also in the direction of improving methods of extraction, preparation, and transportation

Fig. 12. Combined system for mining thick steeply inclined seams
(chamber-and-shield)

Visible labels in the diagram: sections \(I\!-\!I\), \(II\!-\!II\), \(III\!-\!III\), \(IV\!-\!IV\); dimensions \(80\), \(300\), \(0.3\); item numbers \(1\), \(2\), \(3\), \(5\).

placing stowing material on the surface by carrying out complete mechanization and automation of these processes, thereby achieving a sharp reduction in the cost of stowing material. Given the present high level of development of our quarry equipment, this does not present any special difficulties. As stowing materials, one should first of all use rock from old mine dumps and dumps of concentrating plants, the reserves of which, at the mines of the “Stalinugol” and “Prokopyevskugol” trusts in Kuzbass alone, exceed 8 million m³. Such a volume of rock occupies an area of 41 ha, beneath which more than 3 million tons of coal reserves prepared for extraction have been immobilized. Part of the dumps has burned out. In unburned dumps the combustible content should be less than 30%. In some cases, in order to reduce the combustible content, rock from dumps should expediently be mixed with stowing material from a quarry.

To increase the resistance of stowing pipelines to wear, the practice of lining them with basalt should be widely introduced. In this case the pipes should preferably be made of strong manganese steels.

With regard to methods of extracting coal under all mining systems, one should orient oneself toward the mechanical method, as the one most consistent with the technical policy being pursued in our country. In creating extracting units, one should mainly be guided by narrow-web extraction.

One of the immediate tasks should be considered the conduct of experiments on the use of hydraulic mining in combination with movable supports, and first of all experiments should be undertaken on breaking and transporting coal in a shield system.

In conclusion, it is necessary to note that recently in England tests were successfully carried out of a movable hydraulic support of the “Kuzbass” type, the operability of which had been confirmed by experimental work conducted at the Kapitalnaya mine in Kuzbass as early as 1948. Nevertheless, its further improvement has been inexcusably delayed, although the question of creating movable supports is fundamental to the implementation of comprehensive mechanization of work connected with coal extraction.