STATE AND DEVELOPMENT PATHS OF BACKFILLING OPERATIONS IN THE PROKOPYEVSK DISTRICT OF KUZBASS

K. A. ANTONOV
Postgraduate student

Brief Characterization of the Prokopyevsk District of Kuzbass

The Prokopyevsk district of the Kuznetsk coal basin is distinguished by exceptionally high coal saturation and by coals of high quality. This coal deposit is represented by a suite of frequently closely spaced seams, gathered into sharp folds. The average dip of the seams in the district is taken as \(59^\circ\). The thickness of many seams is characterized by values from 5 to 15 m (seams III, IV Internal, Gorely, Moshchny, and others). The distance between seams is on average 25–50 m, but there are quite a few seams that are still more closely spaced. For most folds it is characteristic that the overlying seams of the suites are thick and especially thick seams¹, and this in turn complicates the parallel working of a group of seams simultaneously, limiting the rates of retreat along seams of medium thickness. The coals of the district are self-igniting. All the above-listed conditions of seam occurrence place the Prokopyevsk district among districts difficult to operate.

Until 1938, exploitation of the Prokopyevsk deposit was characterized by the predominance, on the upper levels, of mining systems with caving; however, their application on thick seams led to systematic losses, reaching in some systems up to 40–60% and more of the coal reserves, to the outbreak of fires, and to the creation of difficulties in the prospects for developing the lower levels.

Now, when in the district extraction operations are being transferred to the second and third levels, the question has arisen of changing from systems of mining with caving on thick seams to systems employing backfilling of the worked-out space, as more fully corresponding to the technology of the present period and providing a number of technical and economic advantages in operation.

The Prokopyevsk district of Kuzbass, by its natural-geological conditions, in its search for the best mining systems for thick steeply dipping and closely spaced seams and for methods of filling the worked-out space with waste rock, cannot make use of experience from elsewhere and is faced with the necessity of resolving these questions independently.

The State of Backfilling Operations in Prokopyevsk

The necessity of mining thick seams with backfilling of the worked-out space is urgently dictated by considerations of safety and economy in the production of extraction operations. The advantages and disad—

the shortcomings of backfilling operations are generally known. Operations with complete backfilling are an expensive measure, since a new shop is brought to life at the mines—the backfilling shop. In evaluating the entire complex of coal-mining operations, the application of backfilling under the conditions of the Prokopyevsk district is a necessity. The solution of the problem of backfilling the mined-out space in the operation of the Prokopyevsk deposit has become, for everyone, an obvious prerequisite for the further and successful development of the district—technically advanced and economically advantageous. Operational work over the period from 1937 to 1940 has established that the poorly organized service of the district’s backfilling shops does not make it possible to obtain high technical-and-economic indicators from the new systems of mining with backfilling and to determine conclusively their production capabilities, merits, and shortcomings. Coal losses are still high, amounting in operations with complete backfilling to from 22 to 30% (in particular, when systems of inclined and diagonal slices are used). The cost of backfilling materials, free at the mouth of the backfilling furnaces, averages by backfilling shops of the district within the range of 4 to 12 rubles per m³ of backfill in the loosened state. This, in turn, increases the cost of coal; furthermore, with a sharp growth in the volume of backfilling operations, it cannot be tolerated. In mining systems with backfilling, the accident rate is still high, which is explained by the lagging of backfilling operations. An analysis of the condition of the district’s backfilling shops, carried out by us during the second half of 1939 and the beginning of 1940, shows that the service of the mines’ backfilling shops is organized in a clearly irrational manner; it does not meet the requirements for fulfilling expanded coal-production plans and is becoming a brake in this matter. The practice of work in the preceding period shows that the questions of filling the mined-out space must in no way be separated from the fulfillment of coal-mining tasks; that the more backfill is lowered, the more coal will be issued. The problem of backfilling requires urgent solution; work experience shows that this is a very serious matter, and the attention of the technical community must be mobilized for it.

Features of Operations in Mines Using Backfilling

For the production of backfilling operations, in terms of weight, as much rock is required as coal is produced, if the coefficient of rock loosening is taken as \(k = 1.5\), the specific gravity of the native backfill rock as \(\gamma_{\mathrm{p}} = 2.5\), the coefficient of filling of the mined-out space as \(m = 0.8\), and the specific gravity of coal as \(\gamma_{\mathrm{u}} = 1.3\).

Taking into account the circumstance that about 60% of all reserves of the Prokopyevsk deposit are contained in thick and especially thick seams requiring mining with backfilling, and also the comparative complexity of the technological-process scheme for advancing backfilling material from the place of its extraction to the places of placement in the mined-out space, the full volume of work for producing backfill of the mined-out space becomes clear.

The production of backfilling operations is divided into the following stages:

1. Surface quarries: a) preparatory work—stripping of overburden, laying of tracks; b) blasting operations—charging of mine chambers, shotholes, and boreholes; the actual blasting; c) excavation of the rock of the blasted mass.

2. Surface transport of backfilling materials from the quarry to the crushing plant: a) in large-capacity cars of the Dumkar type, or b) in small-capacity cars of the Western type, by steam locomotives or motor locomotives.

1. Crushing plants: a) screening, b) crushing, c) sorting and blending, d) binning of the crushed material.

2. Surface transport from the crushing plants to district or central backfilling furnaces—raises: a) in large-capacity cars of the Dumkar type, or b) in small-capacity cars of the Western type. Train consists are hauled by narrow- and standard-gauge steam locomotives or by motor locomotives.

3. Lowering of backfilling material to the lower levels. Lowering to the lower levels may be carried out by gravity through furnaces, raises, pipes, or by forced means in small cars and cages, skips, and elevators.

4. Transport of backfilling materials on the backfilling level up to the moment of unloading into the district bunker: a) in ore cars with a capacity of 1.5–2.0 m³, of the Sanford-Day type, or by belt and scraper conveyors.

5. Transport of the backfill within the extraction field. Under the usual scheme of operations with gravity or mechanical backfilling, the flow of backfilling materials from the intermediate crosscut is distributed along the wings by means of belt conveyors. In pneumatic backfilling by the Torkret and Beien machines, or in wet backfilling, transport of the backfill within the extraction field is carried out through pipelines.

6. Placement of the backfill in the worked-out space in longwall faces. This operation is performed, depending on the adopted method of backfilling, by gravity, by water, or by machines of various kinds.

From the preceding scheme it is evident that, on the surface and on the upper levels of mines where backfilling operations are used, there appears, as it were, a second mine for the extraction and transport of backfilling materials. The indicated volume of work, and the considerable strength and specific gravity of the rocks used for backfilling purposes, predetermine the need for broad and comprehensive mechanization of all links in the work of the backfilling departments. Work with backfilling has led to the extraction of backfilling materials in open pits; excavators have appeared, as well as surface transport with a large number of access tracks, with a fleet of locomotives and rolling stock, and crushing plants. Transport of backfill along the upper levels underground has required the presence of a substantial fleet of electric locomotives and rolling stock, while the ventilation level has acquired additional essential functions in transferring the entire mass of backfilling material, timber, equipment, people, and air. This has led to the necessity of having ventilation levels solidly equipped (construction of permanent haulage tracks, maintenance of workings of considerable cross-section, etc.). The circumstance that complicates the productivity of the backfilling level is, above all, the presence of an upgrade in the direction of movement of the flow of backfilling materials, and also the fact that the backfilling level is at the same time also a ventilation level. Under the conditions of mines with a dust-and-gas regime, only battery electric locomotives are used here for transport; their tractive force on the upgrade is sharply limited, and their sensitivity to overloads is increased. This leads to a limitation of the size of the train consist to 4–5 cars with a capacity of 1.5–2 m³ and, consequently, to an increase in the number of operating electric locomotives and in the intensity of their movement, which has a particularly painful effect on operation in the frequent cases where only a single-track line is present. Mines that do not have a backfilling level are forced to create one, in particular in the form of driving a backfilling adit at Mine 3—3-bis of the Stalinugol trust, or to take the path of decentralized supply of individual districts via surface access tracks; however, implementation of the latter variant is associated with earthworks of considerable volume and with complication

surface transportation in wintertime (with its low temperatures and snowdrifts).

Thus, we see that at mines working with backfilling of the worked-out space, an independent and fairly complex, in terms of operations, backfilling shop has taken shape; the uninterrupted operation of this shop places coal extraction from thick seams in great dependence on it and often determines its scale. Servicing the work of backfilling shops from the quarry to the face required a considerable number of workers; in the general mine complexes there have been significant shifts toward an increase in the number of workers servicing the main production process—coal extraction. The mechanization of the district’s backfilling shops, and its obvious disproportion in individual links, do not correspond to the fulfillment of the tasks of expanded coal production and as yet do not contribute to reducing the cost of a unit of output. The technology of the process of moving backfill should not, in its perfection, lag behind the technology of the process of moving coal from the place of its extraction to loading into railway cars; on the contrary, it should outstrip it—this will spur coal production. The reserves of mine backfilling shops must be more substantial and flexible, since reserves in the work of backfilling shops must become, above all, reserves for coal production.

Brief review of existing methods for erecting backfill and the prospects for applying each of them under the conditions of working the Prokopyevsk deposit

Of the various methods of filling the worked-out space with barren rock, the following methods have found application under the conditions of the Prokopyevsk mine: 1) gravity backfilling, 2) mechanical backfilling, and 3) pneumatic backfilling.

A brief characterization of them and the prospects for applying each of them will be considered below.

1. Gravity backfilling. Under the conditions of the Prokopyevsk mine, gravity backfilling has become predominantly widespread. The average dip angle of the seams in the district is 59°; thus, we see that the natural conditions of the district are clearly favorable to the use of gravity backfilling here. The process of erecting the backfill in this case is as follows: the backfilling material, delivered to the upper outlet of the longwall of the slice, is unloaded from the conveyor and, under the action of gravity, moves downward along the inclined plane. The length of a longwall of a slice usually amounts to up to 30–45 m; thus it is evident that the path of movement of the backfilling material, as the worked-out space is filled, changes from 30–45 m to 0 m. This, in turn, affects the density of the erected backfill, which decreases in the direction from the bottom of the longwall to its top. The upper part of the worked-out space is not filled by gravity, and this operation requires the expenditure of a considerable amount of manual labor; to this day this operation, repeated in large volumes, remains unmechanized. At the top of the slices, with gravity backfilling, its density is much less than at the bottom of the slices, and the backfill here gives significant settlement. The support in slice systems, with an ascending order of slice extraction, rests on the backfill and weakens as it settles. The support of the side of the longwall, of the slices—that is, of the most critical part itself—becomes unreliable, and for these reasons collapses of the sides of longwalls and slices occur not infrequently.

The field of application of gravity backfilling extends to seams with a dip angle from 40 to 90°. However, it proceeds normally at angles

dips greater than 50°. Therefore, in systems with an artificially created angle of inclination of the beds to the horizontal (in the system of diagonal beds), the dip angle of the beds must be taken as no less than 50°.

It is obvious that, in the immediate future, the district will base itself on the use primarily of gravity backfilling. The operation of preparing the top of the beds in bedded systems must certainly be mechanized immediately.

2. Mechanical backfilling. In mechanical backfilling, the process of constructing it is carried out with the aid of stowing machines of various types. The main advantage of mechanical backfilling is the use of cheap electric power, common to all consumers of the mine, which is of substantial importance under our conditions with such a considerable volume of work. Mechanical backfilling can be applied in the same places as pneumatic backfilling, i.e., in the system of horizontal beds, on gently dipping seams, when preparing the “top”¹ of beds in bedded systems, and when working seams by inclined and diagonal beds. At present, although it is beginning to enter practice, it nevertheless suffers from a number of shortcomings, namely: a) the bulkiness of the installation of the stowing machine and the conveyor delivering the backfill material to it; b) the difficulty of maneuvering in the beds as backfilling proceeds (shortening the conveyor, moving the machine, etc.); c) the difficulty of transferring the equipment from bed to bed in the system of horizontal beds as they are worked out, and the presence of assembly work of considerable scope. The application of this method of constructing backfill has a number of major advantages and a firm prospect for broad use in the very near future. It is only necessary to improve and lighten the design of the machine and of the feeding conveyors.

3. Pneumatic backfilling. Filling the worked-out space with the aid of compressed air has not become widespread over the past five years, since there is no basis for this—an expanded compressor plant. Experience in world practice testifies to its high cost in operation and in the cost of the initial equipment.

It must be assumed that the district will not proceed along the path of preferential use of this method of backfilling, and that it may be applied in the system of horizontal beds, in sections under fires in the locking parts of seams, or as a supplement to the principal method—gravity backfilling—for preparing the top of the beds.

Backfilling Materials of the Prokopyevsk District and Their Quality

The basic requirements imposed on the quality of backfilling material under any method of carrying out backfilling operations amount to the following: a) low cost of extraction and crushing of the backfilling material must be ensured; b) the density of the mass of backfilling material in the worked-out space must be ensured; c) where possible, the specific weight should be low and large reserves should be available; and d) the backfilling material must be easily transported from the place of its extraction to its placement in the worked-out space.

Additional requirements for the backfilling material are formulated depending on the totality of the conditions of work involved in constructing the backfill, such as: the method of backfilling, mining systems, the season of the year, etc. Briefly, they may be expressed as follows: a) the abrasive properties should be low for pneumatic and hydraulic backfilling; b) the clay content in the mine should be within the limits of 10–15%; c) the size of the backfilling materials should be definite; and a number of other requirements.

The history of the search for backfilling materials that could be used for the needs of backfilling in the development of the Prokopyevsk deposit suggests that attention should be focused on the following among them:
a) granulated slags of the Kuznetsk Metallurgical Combine named after Comrade Stalin; b) river-channel deposits of the Tom River bed (in the area of the city of Stalinsk); c) sands of the Novosibirsk area; d) artificial production of ice and the making of ice backfill; e) the thick strata of clays and loams that are richly developed in the Prokopyevsk district; f) the burnt rocks of the local hills of the district; g) the bedrocks of the hills and barren areas of the district; h) the rocks of mine dumps and the rocks obtained in driving capital rock workings; and i) mixtures of the above-listed backfilling materials in various proportions.

Below we shall briefly consider all these materials.

The first three sources for obtaining backfilling materials have not been used, because their reserves are limited, or because of the remoteness of the distances and the inevitable difficulties arising in transport on the main lines of the NKPS.

As early as 1931, engineer P. A. Leonov proposed using ice for backfilling purposes, obtaining it on the surface or directly underground (see the journal Coal of the East, No. 15 for 1931). However, for a number of reasons, the most important of which are the seasonal nature of these operations and the known temporariness of the backfill, the proposal was not put into practice.

Post-Tertiary deposits of clays and loess-like loams are widespread throughout the district. Their reserves are very substantial, since the thickness of the alluvium varies from 0.6 m on watersheds to 35 m in low-lying places. In addition, secondary soils are easy to extract and do not require blasting operations. However, soils of this kind, during extraction and transport to the place of backfilling, entail a number of major operational difficulties and cannot be used in pure form for backfilling purposes. Under underground pressures these backfilling materials give considerable settlement. At present clays and loams are used as an admixture to bedrock and burnt rocks in amounts of 15–20%. At one time attempts were made to use these soils by means of preliminary firing, as a mixture with quicklime, by pressing them into balls, etc. But all these attempts were insufficiently sound; the experiments were short-lived and were not carried through to completion. Therefore it must be assumed that clay-loams may be used for backfilling purposes after their preliminary treatment (leaning) by means of heat treatment, chemical treatment, or backfilling with the aid of water. The specific gravity of the clay-loams of the district varies from 1.8 to 2.1. Their natural moisture content is 9–16%. According to analyses by the Prokopyevsk chemical laboratory, the predominant components in the soils are silty particles with particle diameters from 0.05 to 0.005 mm.

Under the conditions of the Prokopyevsk district, the local hills contain burnt (in the distant past) rocks, which at present are used for backfilling purposes. Because their reserves are limited and scattered, they cannot be regarded as the principal material for backfilling. Their strength varies sharply, from easily disintegrating to slagged varieties, which, during blasting operations, yield a large output of coarse blocks. In the near future, burnt rocks will be extracted only in temporary mine quarries until the central quarries are put into operation. The specific gravity of burnt rock is 2.3–2.4. Compressive strength is 500–1200 kg/cm² and more (for slagged burnt rock). The sharp fluctuation in the strength of burnt rock creates great difficulties in crushing it.

The Prokopyevsk district has taken the path of using bedrock for backfilling needs; among these, sandstones, clay shales, and argillites are predominantly widespread. The specific gravity of these rocks varies from 2.45 to 2.7. The compressive breaking stress ranges from 500 to 1700 kg/cm². It is therefore evident that the extraction and preparation of backfilling materials from bedrock will require—as work practice also shows—up to 250–300 g/m³ of explosives and considerable expenditures of electric power for crushing to specified size classes.

Ten mines of the Prokopyevsk district still have rock dumps on the territory of their mine fields, which have formed over a number of years. These dumps occupy a considerable area in the mine yards, often create difficulties in surface planning, and in summer pollute everything around with dust. The rocks composing the dumps are, for the most part: clay shales, sandstones, argillites, carbonaceous shales, which were obtained during the driving of mine shafts, chambers of various kinds, etc. In addition, old timber and coal are found in the dumps. In terms of the size of the material, the dump rocks can predominantly be used for backfilling purposes without crushing. The substantial reserves of rock in the dumps throughout the district, which, as a first approximation, amount to no less than 1,000,000 m³, the ease of extraction, and the convenience of transport suggest to us the possibility of using them as backfilling material. Concerns on this question come down only to the possibility of their spontaneous combustion, since studies of the dump rocks of Mine 3—3-bis, carried out at our request in the Prokopyevsk chemical laboratory, show that the combustible content in these rocks is from 20 to 48%. Sampling was repeated, but with screening through a 13 mm sieve, and the combustible content decreased to 12–25%. It is therefore evident that the main mass of coal is in the fines. Thus, it is practically entirely possible to use dump rocks for backfilling needs by blending them with bedrock coming from quarries, especially since cases of coal ignition in rock dumps have not been recorded in the history of the district.

One of the principal requirements imposed on backfilling material is that it be cheap. Therefore it is necessary to consider the use of such backfilling materials whose extraction involves the least expenditure. In the district, as noted above, alluvial rocks are widely distributed, but in pure form they still cannot be used for backfilling. The use of mine-dump rocks in pure form is dangerous from the standpoint of possible spontaneous combustion; however, since these materials are readily accessible, cheap, and available in sufficient quantity, it is possible to proceed along the path of using them by blending them in a definite proportion with bedrock from quarries. Realization of these possibilities would make it possible significantly to reduce the cost of 1 m³ of backfilling material, increase the productivity of mine backfilling shops, and increase their reserves.

Of all the backfilling materials of the district listed above, bedrock has received predominant distribution. In the future as well, it will account for the greatest share. However, its extraction and preparation are associated with rather considerable expenditures; therefore, in parallel, it is necessary to strive to introduce other kinds of materials as well, such as: alluvial rocks and mine-dump rocks. The question of the possibility of using clays and loams as the principal kind of backfilling materials, through their preliminary treatment by thermal or chemical means, as well as in hydraulic backfilling, is of full relevance.

Operating Practice of Existing Open Pits in the Prokopyevsk District

Brief Characterization of the Open Pits

A characteristic feature of the present period is that open-pit operations in the Prokopyevsk district of Kuzbass are extremely decentralized. Thus, nine mines operating here with backfilling have 10 small open pits, each with a monthly output of from 3 to 15 thousand \(m^3\). Operating practice in these open pits shows that they are organized in a clearly irrational manner: the cost of \(1\ m^3\) of backfilling materials is excessively high; the machinery fleet is not fully utilized, the labor force is overstaffed, and productivity is low. The existing open pits have been laid out in spoil heaps nearest to the mines, where the quality of the rock often changes very sharply, since inclusions of slagged burnt rock occur in them; considerable alluvial deposits, when the first benches are worked, fall almost entirely into the charge of backfilling material, causing an admixture of clay of up to 40–50%. In winter, frozen alluvial deposits, during blasting operations, contain large blocks with a volume of up to \(3.5--4.0\ m^3\); they clutter the face and necessitate additional excavator work for rehandling them, leading to losses that in individual cases reach 30–40% of the rock in the blasted mass. The accumulation of these blocks in individual cases makes it impossible to continue work, and the open pit has to be abandoned; this was the case, for example, in the open pit of the Mars Vysokii spoil heap in February 1940. Inclusions of slagged burnt rocks in a rock mass of exceptionally high strength yield a considerable volume of blocks during blasting operations and require their secondary blasting by plaster charges; this, in turn, leads to an increased consumption of explosives, up to \(550\ g/m^3\). In addition, inclusions of burnt rock of great strength form projections in the faces of open pits and distort them, which leads to a narrowing of the excavator working front and to a reduction in the effectiveness of blasting operations. The most widespread form of open-pit face is the trench-type pit. This form is clearly disadvantageous. It is characterized by a narrow working front and low productivity; the effect of blasting operations in them is reduced.

Blasting Operations

In the practice of conducting blasting operations in the open pits of the Prokopyevsk district, the following methods have found application: a) mine chambers, b) mine shafts, and c) blast holes.

Mine chambers are usually driven at the foot of the bench, with a clear cross-section of \(1.1--1.3\ m^2\), into the depth of the rock mass perpendicular to the face line. The chamber usually consists of a main adit and side adits. Charges are placed at the ends of the side adits, and the adits are stemmed with rock obtained from their own driving.

Experience has shown that mine chambers are expedient to use in monolithic strong rocks without cracks or voids; these rocks form a slope angle close to \(90^\circ\). At present the driving of mine chambers is carried out manually. This results in the preparation of new reserves of blasted rock becoming a bottleneck. In addition, the simultaneous performance of rock excavation and adit driving in trench-type open pits is difficult. Therefore, in practice, blasting is often carried out by shafts, which are placed vertically. Shaft driving does not interfere with excavation work in the open pit. However, blasting by shafts gives an increased yield of large pieces in comparison with mine chambers. With small face-slope angles, blasting by…

preference should be given to shotholes. In practice, the cross section of shotholes in the clear is most often from 0.7 to 1.0 m².

Blasting operations may also be carried out by placing mine boreholes. The borehole diameter is usually 170 mm. This method is sufficiently advanced, provides rapid preparation, and can be strongly recommended for introduction into the practice of backfilling shops. The practice of producing concentrated blasting under various methods of conducting blasting operations and in rocks of different strength shows that the consumption of explosives per 1 m³ of backfilling materials in the loosened state amounts to 230–305 g. The consumption is quite considerable and is explained by the unfavorable conditions under which the blasting operations are conducted.

In conclusion it should be noted that improvement in the conduct of blasting operations should proceed along the following lines: a) advance execution of work to uncover the overburden (it is better to do this in summer by mechanical or hydraulic means); b) creation of a long quarry face line and abandonment of trench-type faces; and c) mechanization of the driving of preparatory workings (mine chambers, shotholes).

Until recently, grisutine 12% and 29% and ammonite No. 2 were used in the quarries as explosives; at present, ammonite No. 2 is used predominantly. However, all these explosives are sufficiently expensive, and attention must be directed toward the use of cheaper explosives—oxyliquites.

Excavator Operations

Excavators are used for loading backfilling materials after the rock mass has been blasted. In the practice of quarry operations in the Prokopyevsk District, excavators of various types have found application, such as, for example, steam excavators of the Votkinsk and Kirov plants, excavators of the Orenstein & Koppel firm, of the Škoda plant, and others. Experience with their operation shows that, under the conditions of the Prokopyevsk District, crawler-mounted excavators justify themselves best, as they have greater maneuverability in comparison with wheeled excavators. In terms of bucket capacity, excavators with buckets of 1.5–2.0 m³ have proved the most convenient in operation. Smaller bucket capacities are undesirable.

As regards the type of engine, under Siberian conditions preference is given to electric excavators, since they have a number of indisputable advantages, namely: a) rapid preparation for work (there is no period for heating boilers); b) during idle periods the power is switched off; c) they are not afraid of low temperatures; and d) low operating costs and reliability in operation.

On the basis of the time-and-motion observations we have conducted, it should be noted that the excavator fleet is clearly insufficiently loaded. Thus, the proportion of main work in the structure of the working day is 28–35%, while auxiliary work is 25–37%; the remaining time the excavators stand idle waiting for empty cars or because repairs must be carried out, since poorly organized scheduled preventive maintenance leads to frequent breakdowns of individual parts and assemblies. According to repeated observations made by photographing the operation of excavators of the Kirov and Votkinsk plants with a bucket capacity of 1.5 m³, productivity per hour of net working time is from 74 to 113 m³, and per shift 170–215 m³. In practice it is entirely possible to bring the shift productivity of excavators with a bucket of 1.5–2.0 m³ up to 500–700 m³. To do this it is necessary to create long faces in the quarries and improve the operation of transport. At present, as a rule, an excavator is served by one motor locomotive, the duration of whose trip depends on the haulage distance,

...the needs of the crushing plant and the transport possibilities at the mine backfilling level. At the present time, it is characteristic that the district has taken the path of creating central quarries, of which the principal ones will be: the Usyatsky quarry in the area of Usyaty station and the Tyrgansky quarry on the Tyrgan upland.

Crushing of Backfilling Materials

In gravity backfilling, material with a lump size of up to 110 mm may be used. In blasting operations, however, lumps of 110 mm and larger are obtained at the outlet; therefore the material must be passed through crushers. The development of crushing facilities in Prokopyevsk is lagging behind. Thus, at present, for example, there are only 8 Blake No. 9 crushers, each with a capacity of 35–40 m³ per hour. The Prokopyevskugol trust does not have a single crusher. At present, single-stage crushing has been adopted; pieces no larger than 300 mm can enter the Blake No. 9 crusher; larger pieces are subjected to secondary blasting, or at crushing plants they are broken by hand on the bars of a stationary screen. All this entails the expenditure of considerable quantities of explosives, the use of manual labor that is unproductive in this case, and the underutilization of the throughput capacity of the crushing plants. It is therefore urgently necessary to recommend, along with the centralization of crushing facilities, a transition also to two-stage crushing, with crushing limits of 800—225—110 mm. This means that all material from the quarries can be passed directly through the crushers. The time observations we have carried out show that the productivity of a Blake No. 9 crusher per hour of net time is, at mines 3—3-bis and the Koksovaya mine named for Comrade Stalin of the Stalinugol trust, from 24 to 27 m³. The net operating time of the crushers per shift is 36–45%. Downtime and interruptions for various reasons amount to 38–48%, and the average shift output does not exceed 62.0–85.0 m³. Downtime and interruptions occur chiefly because of the absence of empty cars at the backfilling level or while waiting for trains from the quarry. Here, a substantially negative role is played by the operation of crushing plants without bunkering the crushed materials. The fact is that when large volumes of backfilling materials containing clay impurities of up to 20–30% are stored in bunkers, in the cold and damp season of the year, and even at natural moisture content, freezing or caking of the rock occurs, with plugs forming at the mouths of the hatches. Thus, for example, the bunkers of the crushing plant of Sopka Mars Nizky at the Koksovaya mine named for Comrade Stalin stood clogged from the autumn of 1939 until the spring of 1940, and the crushers operated directly, without bunkering. The existing form of bunkers of the well type (small cross-section and considerable depth) does not justify itself, since moist rocks in autumn or spring, and frozen rocks in winter, when passing through the premises of crushing plants, fall from a height of 6–8 m, are compacted, and unloading the bunkers through hatches with a cross-section of 0.4 m × 0.4 m becomes difficult. Interruptions of this kind in the operation of crushing plants point to the need for reconstructing the bunkers (abandoning well-type bunkers and increasing the cross-section of the discharge hatches to 1 m²). Heating should also be removed from the buildings of the crushing plants, so that the backfilling materials, when passing through them, do not thaw in winter. It is also highly desirable not to allow prolonged storage of backfilling materials in bunkers; their movement should be, as far as possible, continuous. The angle of natural repose of backfilling materials observed in practice, especially of fines, ranges from 45° to 70°; therefore the slope angles of bunkers must be made steeper, since

since when the two sides of the bunker meet in space, the coal arches over, and the backfilling materials are held up precisely in these corners, reducing the useful cross-section of the unloading area. At present, for the crushing plants of the Prokopyevsk mine it is characteristic that crushing is carried out without preliminary screening of the rock. This means that all the fines, in a volume of up to 40%, which could have been screened out and routed past the crushers, are passed through them. And since a large part of the clay admixture is present in these fines, the moistened clays envelop the pieces of native rock, and in the jaws of the crusher they slide, while with clay compaction occurs. Therefore the crushers have to be stopped and cleaned from time to time. At the crushing plant of the Mars Vysoky hill, preliminary screening is carried out, and the productivity of the crushers there, according to observations, is 45.4 m³/hour. From this it is evident that reserves exist in the crushing facilities in Prokopyevsk, and they consist in the use of preliminary screening. This will increase crusher productivity by 35–40% compared with the existing level. It should be noted, however, that the crushing operation is rather costly, and where possible one should aim to crush a smaller quantity of backfilling materials.

Transport of Backfilling Materials

The process of transporting backfilling materials from the place of their extraction to the place of placement in the stoping faces is divided into four stages: 1) transport from the quarry to the crushing plant and from the crushing plant to the backfilling furnaces—shafts; 2) lowering of the fill to the lower levels; 3) transport of backfilling materials on the backfilling level of the ventilation drift inside the mine; 4) transport within the extraction field and placement of the fill in the worked-out space.

Let us consider the distinctive features of the work at each of the indicated stages of transport.

1. Transport of backfilling materials from the quarry to the crushing plant is carried out in large-capacity Dumkar-type cars by locomotives on standard gauge, or in small-capacity Western-type cars. The capacity of the latter is usually 3.5 m³. For moving them, 0—4—0 No. 157 locomotives of the Kolomna Plant or motor locomotives are used. The excavator loads the cars directly from the bucket; therefore, as the face advances, the tracks in the quarry must be moved. One of the major shortcomings in the operation of surface transport is the poor condition of the tracks. In many cases the tracks were laid in winter, and their lining and leveling was insufficiently thorough. The terrain, abounding in sinkholes from caving operations, often greatly hinders the laying of tracks, and preparation of the route is associated with earthwork of considerable volume. The spring thaw weakens the sections. When the tracks are laid in winter, their profile changes sharply in spring, and this limits the train size to 3–4 cars. The low productivity of surface transport is also noted, since motor locomotives and steam locomotives have to wait a long time for the excavator to finish loading and for the cars to be unloaded at the crushing plant or at the mouths of the backfilling furnace-shafts.

2. Lowering the fill to the lower levels. At present, mining operations are moving to the 2nd and 3rd levels; therefore the backfilling materials must be lowered from the surface to a depth of 50–100 m. In the Prokopyevsk district, lowering the fill by gravity has become predominant, as a very simple

method. The practice of lowering backfill by gravity already to a depth of 60 m shows the obvious imperfection of this method. Thus, for example, when moist backfill is lowered in chutes, rock plugs form at the mouths of the backfilling chute-shafts. The chutes are more often arranged at an angle of 55–75°; their clear cross-section is 1.0–1.5 m². The lining of the chutes is often damaged, since large pieces, moving at high speed, quickly destroy it. Therefore the walls of the chute must be lined with old rails. Alongside the backfilling compartment a travel compartment is also arranged, from which observation windows are driven every 10 m along the dip for observing the advance of the backfill along the chute and for eliminating delays that occur. Work experience shows that the chutes remain under repair for a very long time; therefore, as a practical measure, it can be strongly recommended to install two mutually substituting chutes side by side, so that during the repair of one the other can receive backfill. When selecting the site for laying out backfilling chutes, one must also consider the possible inflow of water into the chute, since in water-bearing rocks the backfill quickly becomes wet, cakes, and in winter also freezes to the strength of concrete.

Bunkered backfill should not be kept in the chutes for more than one shift. It is noted that in winter, when the suction fans above the chutes are stopped, cold air from the surface descends to the working level and the backfill freezes at the mouths of the chutes. In general it should be said that lowering backfill by gravity is low in productivity and sensitive to seasonal changes; even at a depth of 50–100 m it does not justify itself, and it must be assumed that backfill to the lower levels should be lowered by a forced method.

3. Transportation on the backfilling (upper) level of the mines. At this stage, the transportation of backfilling materials is at present carried out from the bunkers of the crushing plant (mines 3–3-bis and Koksovaya named after Comrade Stalin) or from the mouths of the backfilling chute-shafts to the section bunkers by electric locomotives and, under dust-and-gas conditions, as a rule, by storage-battery locomotives in Sanford-Day side-dump cars with a capacity of 1.5–2.0 m³. Since more often the backfilling level in the mines is a former working level, the track has an up-grade in the direction of movement of the stream of backfilling materials; this sharply limits the size of the train and the productivity of transport on the backfilling level. The size of the train in this case ranges from 5 to 6 cars, i.e., 7.5–9.0 m³. The presence, in most cases, of only single-track lines creates congestion in the movement schedules on the backfilling level. In winter, part of the moist backfill freezes to the walls of the cars, reducing their useful capacity and increasing the dead weight. The productivity of electric locomotives on the backfilling level is very low; this is explained by the long idle times of the electric locomotives while awaiting loading at the bunkers of the crushing plants and unloading at the section bunkers.

4. Transportation of backfill within the extraction field is carried out by belt conveyors. Backfill from the section bunker enters the belt conveyor of the intermediate crosscut and from it onto the belt conveyor installed in the drift of the seam being worked with backfill. At the end of the conveyor the backfill is discharged by means of a blade (plow, set at an angle of 45° to the axis of the conveyor belt) and, falling into the bed under the action of its own weight, fills the worked-out space. With the system of mining most widespread in the Prokopyevsk district—by inclined slices, with two-sided extraction of them, in a seam 9 m thick, divided into 3 slices, and with an advance of 18–20 m of each wing per month, it will be necessary to fill

...to fill about 16 thousand m³ of worked-out space, and, in order to carry out the work of securing it, to deliver to the seam about 800 m³ of timber of various standards. Hence the large volume of transportation work within the extraction field and the sections becomes obvious. Here it is important to resolve questions concerning the division of the flow of stowing materials into two wings and the coordination in time of operations for transporting stowing materials and delivering timber.

Among the shortcomings in the work of transporting stowing within the extraction field of the sections, the following should be noted: a) insufficient supervision of the conveyors (distortions during installation due to improper driving of stowing crosscuts); b) poor organization of planned-preventive repair of conveyors, which leads to their frequent breakdowns; and c) the fact that the chutes of the sectional bunkers are primitively equipped; they are covered with plates; their throughput capacity is very small; delays are frequent; loading of the conveyors takes place extremely unevenly. Thus, according to our observations, the productivity of receiving stowing into the seam in the best shifts was 60–80 m³. Conveyor idle time occupies up to 60–70% of the working day.

Technical and Economic Indicators of the Work of the Stowing Shops of the Prokopyevsk District of Kuzbass

The reduction of the cost of coal in mining systems using stowing must first of all proceed along the path of reducing the cost of one cubic meter of stowing. Below we present data on the cost of 1 m³ of stowing in 1939, by month, at mines 3—3-bis and Koksovaya named after Comrade Stalin. From these data it is evident that the cost of 1 m³ of stowing in the loosened state varies by month of the year from 4 rub. 20 kop. to 18 rub. 50 kop.

Table 1

Cost of 1 cu. m of stowing by quarries of the Koksovaya Mine named after Comrade Stalin
(free-at-mouth of the stowing furnace on the surface)

From Tables 1 and 2 it is evident that the principal cost items are: a) wages with charges, b) materials, c) energy and fuel, d) depreciation, and e) other expenses. Further, a sharp and direct dependence is seen between the cost of 1 m³ of stowing and the productivity of the quarry.

Table 2

Cost of 1 cubic meter of backfill (in loosened state) at mine 3–3-bis
(free-at-mouth of the backfilling furnace from level 0 m to level 7 m) for 9 months of 1939

Note: In June and July, 2 operating sections did not receive backfill (since one of them had been worked out, and the second was under preparation); at that time, very considerable work was being carried out to prepare the route in a new quarry. This explains a certain deviation from the normal dependence, since at that time quarry output fell in July to 5931.0 m³, while the entire complement of workers was assigned to carrying out work in the quarry.

Thus, for example, with the productivity of the quarry of mine 3–3-bis in January 1939 at 3300 m³, the cost of one cubic meter was 18 rubles 50 kopecks, while in September of the same year, with output of 10706 m³, it was already 4 rubles 92 kopecks. Or at the Koksovaya mine, likewise, when productivity changed from 13950 m³ to 25910 m³, the cost of 1 m³ of backfill fell from 8 rubles 05 kopecks to 4 rubles 23 kopecks.

On the other hand, attention is drawn to the lower productivity of backfilling at the Koksovaya mine named after Comrade Stalin, where the quarry has higher productivity than the quarry of mine 3–3-bis. Hence the logical conclusion is that the quarry operations of the district must proceed along the path of centralization. This will improve the utilization of backfilling mechanisms, transport, and crushing plants, and will increase the maneuverability and reserves of the backfilling shops. The depreciation costs are impermissibly high, amounting per 1 m³ of backfill to from 0.63 to 1.98 rubles/m³.

Wages per 1 m³ range from 1 ruble 65 kopecks to 10 rubles 43 kopecks. Such sharp fluctuations are caused by a large number of worker stoppages for various reasons and by the low productivity of small quarries. The coefficient of filling the worked-out space on average for the year at mines 3–3-bis and Koksovaya named after Comrade Stalin is 0.56–0.63 of the full volume of the worked-out space for systems of diagonal and inclined seams. This indicates insufficient thoroughness in filling the worked-out space, which entails a significant number of accidents. This requires the introduction of strict mine-surveying control over the filling of the worked-out space.

General comments, findings, and conclusions

As a result of studying the condition and work of the backfilling shops of the Prokopyevsk district of Kuzbass, the following conclusions may at present be drawn:

1) In terms of the conditions under which its seams occur, the Prokopyevsk district has no analogues; therefore it cannot make use of the experience of other basins of the USSR or abroad, and, in resolving questions concerning the choice of mining systems and methods of backfilling the worked-out space, it is faced with the need to solve these questions comprehensively and independently. The successful solution of these tasks will make it possible to carry out the expansion of coal production in Prokopyevsk more rapidly.

2) From the scheme adopted in the Prokopyevsk district for the technological process of moving backfill material from the place where it is extracted to its placement in the worked-out space, it is evident that on the surface and on the backfilling level there has appeared, as it were, a second mine for the extraction of backfilling materials. The complexity of this scheme and the volume of extraction-with-backfilling operations—up to 60% of total coal production—predetermine the need for broad and comprehensive mechanization of all links in this process.

3) It is obvious that in the near future the Prokopyevsk district will follow the path of predominant use of gravity backfilling, as the simplest method and one not requiring large capital expenditures. The operation of undercutting the roof of lava layers must now be mechanized. However, alongside gravity backfilling on steep dips, it should be thought that, under a system of horizontal slices, in closed-off and gently dipping parts of seams, as well as in areas under fires, the standard method of backfilling will become mechanical backfilling with the aid of throwing machines; these need only be further improved and better mastered. Pneumatic backfilling is unlikely to take a leading role and, in the immediate future, may serve as a supplement to other types of backfilling.

4) The practice of backfilling operations shows that the Prokopyevsk district has taken the path of using, as backfilling materials, chiefly native rock; but it was noted above that these rocks possess considerable specific gravity and strength; their extraction, preparation, and movement to the place of placement involve substantial expenditures of explosives, energy, and transport work. Therefore, alongside the use of native rock for backfilling purposes, consideration should also be given to the use of rocks from dumps and deposits of clayey loams.

5) From consideration of the question of quarry operations it is clearly evident that the existing temporary quarries are organized in an obviously irrational manner. Here it is necessary to proceed toward centralization of quarry operations, which is what the district is now doing, creating two large quarries: the Usyatsky and the Tyrgansky. This will lead to an increase in quarry productivity, full utilization of indebted mechanisms and crushing plants, and to a reduction in the cost of 1 m³ of backfill and, consequently, of coal as well. In the quarries it is necessary to create a long working front for excavators, to put blasting operations in order, to reduce their specific consumption, and to shift to the introduction of oxyliquites. Great attention must be paid to the conduct of overburden operations in the quarries.

6) In the practice of quarry operations in the district, up to six types of different excavators have found application. The conditions of their operation and the experience of previous work indicate that, under these conditions, single-bucket excavators with bucket capacities from 1.5 to 3.0 m³, crawler-mounted, electric or steam, may be recommended. Taking climatic conditions into account, preference should be given to electric excavators. The productivity of excavators at present, on average for the district, is about 200 m³/day. Here we see large unused possibilities. This is due to the existing decentralization of quarry operations.

7) On the question of crushing backfilling materials, it should be noted that this operation is expensive; therefore one must strive to pass

pass through the crushing plants in the smallest possible quantity. As an element of rationalization, here one may strongly recommend carrying out preliminary screening before crushing. This is a way to increase the productivity of crushing units by 35–40%. It is obvious that jaw crushers will continue to be used in the future, since they have already proved themselves sufficiently well in operation, even in crushing the strongest country rocks.

8) In assessing the condition of the bunker installations of backfilling shops, one must note the irrationality of their design. In the future, designers will have to abandon bunkers of the well type. The cross section of discharge hatches should be no less than 1.0–1.2 m², and the angles of inclination of the hatch walls 45–50°. It must be considered entirely impermissible for crushing plants to operate without bunkering of the crushed materials—in this one must see the general causes of the poor operation of the crushing plants and of transportation to the crushing plants and after them.

9) To improve the operation of surface transport, supervision over the laying of surface tracks and their operation should be strengthened. This is the first condition for increasing transport productivity. In addition, communications should be improved (by means of telephones) between the backfilling shops and the operating sections; this will help eliminate a mass of idle time of rolling stock and other mechanisms.

10) The questions of lowering backfill acquire exceptional importance, since mining operations are moving to lower horizons. Lowering backfill by gravity to a depth of 50–60 m has already revealed a number of major shortcomings, the chief of which are: its low productivity, uneven operation, and sensitivity to seasonal changes. Therefore it is necessary to consider the transition to lowering backfill by one of the forced methods. For the present moment, in order to ensure uninterrupted work in lowering backfill, one may recommend installing, in the backfilling furnaces, two backfilling compartments, which could be interchangeable.

11) In order to increase the productivity of transport on the backfilling horizon when moving up an incline, it is necessary to proceed along the path of increasing the tractive force of electric locomotives.

12) The questions of advancing backfilling materials within the limits of the mining fields of the sections are especially urgent. The sharply increased volume of work in transporting backfilling materials and timber materials along the ventilation drift requires resolving the question of simultaneously feeding, from the conveyor of the intermediate crosscut, two wings of the mining section, and of combining in time the operations for transferring backfill and timber materials. The predominance of manual work in preparing the top of layers in layer systems with gravity backfill makes the operation of conveyors intermittent and low-productivity. The conveyor is forced to stop very often, since the backfill is supplied in portions of 10–15 m³ and, after it has been manually raked apart, the conveyor is switched on again, and so on.

13) The area of technical standardization, accounting, and planning in the backfilling shops of mines remains, to this day, at a low level, and much work still needs to be done here.

In conclusion it must be said that the questions noted above require urgent resolution and the involvement, for this purpose, of broad circles of the technical community and workers of scientific-research institutions.

1. i.e., at the places where the bed joins the ventilation or bed entry. ↩↩