APPLICATION OF THE GRAPHICAL METHOD TO THE STUDY OF VENTILATION SCHEMES IN KUZBASS MINES

A. F. KARATAEV

General Remarks

A ventilation scheme is usually understood as the representation on a plan of mine workings of a definite direction of air movement through underground mine workings. From this concept of a ventilation scheme it follows that it is determined by the arrangement of mine workings, depending on the adopted organization and procedure for conducting mining operations. Every ventilation scheme, as a definite order of air movement, has initial and terminal points of air movement. In the operation of a mine field, these points are the mouths of the downcast and ventilation shafts. The arrangement of the shafts of these mines in the mine field primarily determines the mine’s ventilation scheme.

Fig. 1. Relative arrangement of shafts under the central scheme of mine ventilation

Fig. 2. Relative arrangement of shafts under the flank (diagonal) scheme of mine ventilation

Depending on the arrangement of mine shafts, the following two principal ventilation schemes are distinguished: central and flank (diagonal).

Under the central scheme of mine ventilation, the shaft supplying air to the underground workings and the shaft discharging air from them are located in the center of the mine field (Fig. 1).

Under the flank (diagonal) ventilation scheme, one shaft is located in the center of the mine field, while the other, or others, are located on the flank or flanks (Fig. 2).

If in nongassy mines the main task of ventilation is to create the most hygienic working conditions for underground workers, then in gassy mines intensive ventilation is, in addition, the principal means of combating dangerous accumulations of mine gas—methane.

In the working of coal seams prone to spontaneous combustion, the success of combating fires depends to a considerable extent on the perfection of ventilation.

the occurrence of endogenous fires. Large air leaks through the worked-out area and to the surface, in seams with coals prone to spontaneous combustion, lead to the occurrence of endogenous fires.

Consequently, the importance of choosing a rational ventilation scheme for a mine increases with the increase in the gas-bearing capacity of the seams and their tendency toward spontaneous combustion. A rational mine ventilation scheme, when mining gas-bearing coal seams prone to spontaneous combustion, must ensure the smallest depression for moving the required quantity of air through the mine workings, in terms of gas-bearing capacity, and the least seepage of air through the worked-out area and to the surface.

We subject to investigation the principal mine ventilation schemes, i.e., central and flank ventilation, when one seam and a suite of seams are mined on the first and subsequent levels.

The mining of a single (isolated) seam is not characteristic of Kuzbass, but investigation of a single seam makes it possible to establish more easily the influence of individual elements of the ventilation scheme, under various conditions, on its rationality.

Essence of the graphical method for analyzing mine ventilation schemes and the technique for constructing the graph

For a visual judgment of the advantages and disadvantages of the projected mine ventilation schemes, and, consequently, for establishing the rationality of one or another ventilation scheme for various conditions of mining gas-bearing coal seams prone to spontaneous combustion, we have proposed a graphical method.

The essence of the graphical method is that, for the analysis of a ventilation scheme, a special graph of the ventilation regime conditioned by the adopted ventilation scheme is constructed from the data of the calculation of the total mine depression.

The task of investigating mine ventilation schemes is reduced to establishing, when designing the ventilation chiefly for newly laid-out mines:

1) the magnitude of the total mine depression conditioned by the ventilation scheme;

2) the distribution of depression among the workings;

3) the influence both of the total mine depression and of the depression of individual workings on the magnitude of leakage-intake through the worked-out area and to the surface, as well as on gas emission.

The application of the proposed graph to the investigation of ventilation schemes makes it possible:

1) to trace visually the change in the magnitude of the total mine depression under various ventilation schemes and its distribution among the workings that make up the ventilation scheme;

2) to facilitate the detection of places with high depression and maximum leakages;

3) to establish which workings affect leakages;

4) to detect errors made in the calculation of depression;

5) to establish how particular ventilation schemes affect the gas regime of the mine.

To provide greater clarity regarding the essence of the graphical method and the technique for constructing the graph of the ventilation regime conditioned by the adopted ventilation scheme, the simplest case is taken, when one seam is being mined and the shafts (hoisting and ventilation) are sunk directly to the drifts.

After calculating the total mine depression and compiling the form (Table 1), using the conventional ventilation layout of the mines, a graph of the ventilation regime is constructed. In the conventional (proposed by us) ventilation layout of a mine, all workings are transferred into one plane and are depicted as two parallel lines (Fig. 3). The lengths of the lines correspond to the lengths of the workings, i.e., they are drawn to a certain scale. In the conventional ventilation layout of a mine (Fig. 3), section 1—2 represents the hoisting shaft of the mine, 2—3 the main entry, 3—4 the longwall face (the mining system), 4—5 the ventilation entry, and 5—6 the ventilation shaft of the mine.

The technique for constructing graphs of the ventilation regime, determined by the adopted ventilation scheme, is as follows.

Fig. 3. Graph of the distribution of depression by sections of the central ventilation scheme under forced ventilation

1. Near the lines of the conventional ventilation layout of the mine that represent the walls of the working, we show, by conventional signs, the condition of the rocks forming the walls of the working, i.e., whether they constitute solid rock or collapsed rock.

2. After depicting on the graph the condition of the rocks surrounding the working, we proceed to construct the graph of the distribution of depression, determined by the adopted mine ventilation scheme, along the length of the workings. For this purpose, on one of the lines representing the wall of the working, at its ends we erect perpendiculars whose lengths, to scale, are equal to the magnitudes of the depression at the given points (sections of the working), and obtain the points \(a'\) and \(b'\) (Fig. 3a). We connect these points \(a'\) and \(b'\) with a straight line. The area \(abb'a'\), enclosed between the straight line \(a'b'\) and the plane of the working, will characterize the change in depression along the length of the working under the existing ventilation regime in this working.

From the point \(b'\), of lower depression of the working, we draw a line parallel to the plane of the working. As a result we obtain the quadrilateral \(abb'a'_1\) and the right triangle \(a'_1 b' a'\). The right triangle indicates the character of the losses of depression along the length of the working, depending—

...of resistance of the working to the movement of air through it. The angle of inclination of the line \(a'b'\) to the horizontal \(a'_1b'\) clearly characterizes the degree of ease or difficulty of ventilating the working. The greater the angle of inclination, the more difficult the given working is to ventilate.

Let us take sections of equal length, \(100\ \text{m}\), from the end of the workings, and from the points \(A'\), \(B'\), \(V'\), lying on the legs of right triangles, let us erect perpendiculars. The lengths of these perpendiculars \(AA'\), \(BB'\), and \(VV'\) determine the loss of depression in the workings per \(100\ \text{m}\) of their length. The segment \(AA' < BB'\) and \(VV'\); consequently, ventilation of the main drift is the easiest; of the ventilation drift, more difficult, since \(VV' > AA'\); and still more difficult is ventilation of the extraction section (longwall), since the segment \(BB' > VV'\). The ordinates \(aa'_1\) and \(bb'\) of the quadrilateral indicate the magnitude of the depression that will be expended in overcoming the resistance to air movement of all subsequent or preceding workings up to the end of the ventilation stream.

A graphical representation of the distribution of depression among the workings and of the condition of the rock surrounding the working (Fig. 3) gives a visual idea of the locations and relative magnitudes of possible leakages; therefore, when designing new mines, it is easier to establish the conditions in which the mine workings are located, and thereby also the places of maximum leakages through the goaf, through pillars, and to the surface. Since the combination of a large depression with the presence of cracks leads to large air leakages, and this creates favorable conditions for the occurrence of endogenous fires, it is therefore possible, from these data, to judge the fire hazard at the given point. In addition, this diagram makes it possible to establish the effect, on leakages in a given working, of the workings preceding and following this working.

This is clearly shown by the ordinates \(aa'_1\) and \(bb'\) of the quadrilateral, which indicate the magnitude of the depression expended in overcoming the resistance of workings preceding or following the working under study. The smaller the depressions expended in overcoming the resistance to air movement of subsequent and preceding workings, the smaller the ordinates \(aa'_1\) and \(bb'\), and, consequently, the smaller will be the influence of subsequent and preceding workings on leakages in the working under study.

The gas regime of a mine, i.e., the nature of gas accumulation in the workings, is in a definite dependence on the quantity of air entering the working. The quantity of air entering the working is determined by the depression of the working and by the presence of cracks through which leakages may pass. The proposed diagram gives a visual representation of these factors; consequently, it also makes it possible to judge the gas regime of the mine being designed, as determined by the mine ventilation scheme.

The dependence of the depression of a working on its length is expressed by a linear law. Therefore, workings of different lengths but of identical resistance have the same angle of inclination of the line \(a'b'\) to the horizontal \(a'_1b'\) (Fig. 3a).

If the depression of the indicated workings is calculated incorrectly, the inclination of the line \(a'b'\) will be different, and this will indicate an error made in calculating the depression.

Analysis of Ventilation Schemes of the First Horizon

Having adopted certain conditions, we calculate the magnitudes of the total depressions of mines as a function of the ventilation scheme and the number of panels in the mine field.

On the basis of the calculation data we construct diagrams (by the method indicated above), and with the aid of these diagrams we carry out an analysis of mine ventilation schemes.

Working single (isolated) seams

Let us first consider a single-wing mine with a mine field length of 770 m, working one steeply dipping seam of thickness \(m = 1.45\) m, gas-bearing \((Q_{\text{om}} = 25.8\ \text{m}^3\) per 1 t of daily output) and prone to spontaneous combustion. The inclined height of the level is \(h = 100\) m. The seam-mining system is long pillars along the strike, variant: longwall–level. The annual advance of the longwall is \(a = 360\) m. The number of working days per year is \(n = 300\). The bulk density of coal is \(\gamma = 1.3\ \text{t}/\text{m}^3\).

The daily productivity of the mine is determined by the formula:

\[ A = \frac{h m a \gamma}{n} = \frac{100 \cdot 1.45 \cdot 360 \cdot 1.3}{300} = 226\ \text{t}. \]

The quantity of air to be supplied to the mine will be:

\[ Q = q\,\frac{A}{60} = \frac{2.58 \cdot 226}{60} = 9.75\ \text{m}^3/\text{sec}, \]

where \(q\) is the air standard per 1 t of daily output, in \(\text{m}^3/\text{min}\),

\[ q = 0.1 \cdot Q_{\text{om}} = 0.1 \cdot 25.8 = 2.58\ \text{m}^3/\text{min}. \]

Taking the clear cross-sectional area of the shafts as \(S = 6.0\ \text{m}^2\), the depth of the hoisting shaft as \(L = 120\) m, that of the ventilation shaft as \(L = 20\) m, the clear cross-sectional area of the main drift as \(S = 6.0\ \text{m}^2\), and that of the ventilation drift as \(S = 4.5\ \text{m}^2\), and neglecting leakages, we determine the total depression of the mine under a central ventilation scheme as a series connection, which will be equal to the sum of the depressions of the individual sections.

Depression of the hoisting shaft:

\[ h_{1-2} = \alpha \frac{L P}{S^3} Q^2 = 0.002 \frac{120 \cdot 10}{6^3}\, 9.75^2 = 1.05\ \text{mm water column}. \]

Depression of the main drift:

\[ h_{2-3} = \alpha \frac{L P}{S^3} Q^2 = 0.0018 \frac{770 \cdot 10.2}{6^3}\, 9.75^2 = 6.22\ \text{mm water column}. \]

Depression of the longwall:

\[ h_{3-4} = \alpha \frac{L P}{S^3} Q^2 = 0.0025 \frac{100 \cdot 6.9}{2.9^3}\, 9.75^2 = 6.73\ \text{mm water column}. \]

Depression of the ventilation drift:

\[ h_{4-5} = \alpha \frac{L P}{S^3} Q^2 = 0.00175 \frac{770 \cdot 8.8}{4.5^3}\, 9.75^2 = 12.4\ \text{mm water column}. \]

Depression of the ventilation shaft:

\[ h_{5-6} = \alpha \frac{L P}{S^3} Q^2 = 0.002 \frac{20 \cdot 10}{6^3}\, 9.75^2 = 0.18\ \text{mm water column}. \]

In an analogous manner we carry out the calculation of the total depression of the mine for the case when the mine is two-wing, and also for a single-wing and two-wing mine with a flank (diagonal) ventilation scheme.

When considering the influence of ventilation schemes on fire hazard, it is of essential importance to establish the magnitude of the maximum possible depressions caused by the ventilation schemes, since air leakages that cause the occurrence of endogenous fires are located ...

are in a definite dependence on the magnitudes of the depressions in the mine workings. Therefore we calculate the maximum possible magnitudes of the depressions caused by the ventilation schemes, and summarize the results in Table 1.

Table 1

From Table 1 and Fig. 3, for the specific conditions it is evident that if the mine is made two-wing, then in section 2–5 a parallel connection of ventilation workings will be obtained. With the former depression of this section, twice as much air will pass through it. The dimensions of the mine field in extent and the mine output increase twofold, while the total depression of the mine also increases, but only by 13%. This emphasizes the advantages of a two-wing mine field and of the parallel connection of workings, and indicates real ways of reducing depression when developing seams with coals prone to spontaneous combustion.

The transition from the central ventilation scheme to the flank (diagonal) scheme makes it possible to reduce the maximum possible depression—

¹ In the denominator are given the percentages of the maximum possible depression under the central ventilation scheme.

to be reduced by 23.6% (Table 1), but this does not mean that the flank ventilation scheme is more economical than the central ventilation scheme (Coal No. 12, 1946, V. V. Vladimirskii, “Choice of the Location of the Shaft in Diagonal Ventilation”). A reduction in the maximum possible depression reduces leakage and, consequently, under certain conditions may reduce the fire hazard in the mining of coal seams prone to spontaneous combustion.

A reduction in the maximum possible depression can be achieved by using forced-exhaust ventilation, when one part of the mine workings is ventilated by forcing air in and the other by exhausting it.

For a visual representation of the ventilation regime resulting from the adoption of central or flank ventilation schemes, with forced or exhaust ventilation, and with forward or reverse mining, using the data of Table 1 we construct graphs of the distribution of the total mine depression over the workings constituting the mine ventilation scheme (Figs. 3–8). Consideration of reverse mining under the central scheme is necessary chiefly in order to substantiate the mandatory adoption, in extraction districts of seams with self-igniting coals, of reverse mining.

The graphs are constructed by the method described above.

Endogenous fires arise where there is crushed or fissured coal and where a large seepage of air is observed. The combination of a large depression, causing a large pressure difference between the space under study and the surface, with poor isolation of the mined-out space, gives the greatest seepage of air. Consequently, the magnitude of leakage both through the mined-out space and to the surface depends on the presence of cracks and their size, as well as on the pressure difference between the space under study and the surface. Therefore the influence on fire hazard of all the ventilation schemes analyzed is determined by the combination of the presence of crushed coal and the magnitude of leakage.

Under the central ventilation scheme with forced ventilation and reverse mining (Fig. 3b), air leakage through the mined-out space and to the surface is small in comparison with other ventilation schemes (Figs. 3–6), although the maximum possible depression of the mine, determined by segment \(1—1'\) or \(6—6'\) (Figs. 3–6), is greatest under this ventilation scheme. Air seepage through the mined-out space is insignificant, depends on the depression of the extraction district (longwall), and is determined by segment \(\kappa—\kappa'\) (Fig. 3b). Air seepage through cracks formed as a result of settlement of the rocks during caving depends on the magnitude of the depression of the outgoing current (the ventilation drift and the shaft), determined by segment \(4—4'\) (Fig. 3b), and will be small. As the stoping operations approach the shafts, the depression of the outgoing current decreases, which leads to a reduction in leakage and, consequently, to a reduction in the fire hazard of the ventilation scheme.

Reverse mining makes it possible to carry out preventive silting during stoping operations and, in addition, provides more rapid and better isolation of a fire seat that has arisen. After the isolation of the fire seat has been completed and the cutting furnace has passed through, it is possible to continue the stoping operations. Therefore this ventilation scheme (Fig. 3b) is the safest from the standpoint of fire.

Under the central ventilation scheme, exhaust ventilation, and reverse mining (Fig. 4b), there is somewhat greater intake of air from the surface and slight seepage through the mined-out space. The intake from the surface through cracks above the mined-out space is acted upon by the depression of the incoming current: the hoisting shaft, the main drift, and the extraction district (longwall). Segment \(4—4'\) (Fig. 4b)

greater than segment \(4\text{--}4'\) (Fig. 3b). If the ventilation drift is insufficiently stable under exhaust ventilation, considerable intake of air through cracks may occur along the entire length of the ventilation drift. This intake depends on the total depression of the mine. This ventilation scheme is less favorable than the preceding one (Fig. 3b).

Fig. 4. Diagram of the distribution of depression over the sections of the central ventilation scheme under exhaust ventilation

The greatest air leakages (intake) both to the surface and through the worked-out space occur with the central ventilation scheme and a direct course, irrespective of the method of ventilation, i.e., blowing or exhaust (Figs. 3a and 4a). In both cases, leakages to the surface or intake from the surface depend on the depression of the entire mine ventilation scheme; but under exhaust ventilation the conditions for intake from the surface are more favorable, and the depression acting on these leakages is greater by the amount of the depression of the upcast shaft. Segment \(6\text{--}6'\) (Fig. 4a) is greater than segment \(a\text{--}a'\) (Fig. 3a). Leakages through the worked-out space under blowing ventilation depend on the depression of the entire ventilation scheme (Fig. 3a), except for the depression of the upcast shaft and some part of the main drift, if one takes into account that compaction of the caved rocks will occur in a certain part of the worked-out space away from the shaft. Under exhaust ventilation, leakage through the worked-out space depends also on the depression of the entire ventilation scheme (Fig. 4a), except for the depression of the ventilation shaft and part of the ventilation drift, but the conditions for leakage are less favorable than from the surface.

From Table 1, and also from comparison of the diagrams (Figs. 3–4 and Figs. 5–6), it is evident that with a flank (diagonal) ventilation scheme the maximum possible depression of the mine is 23.6% less than with the central scheme. It would seem that air leakage would likewise be less. In reality this is not quite so.

With a flank ventilation scheme, blowing ventilation, and extraction of the level by direct course (Fig. 5a), leakages through the worked-out space depend on the depression of the working section and the outgoing air stream.

of the ventilation drift, and also the part of the main drift where the caved rocks have not yet compacted, to the surface through the freshly caved rocks, mainly from the depression of the ventilation drift. The depression of the extraction section (longwall) remains constant as it moves along the strike, while the depression of the ventilation drift decreases. Therefore, leakage through the freshly caved rocks at the boundary of the mine field will be minimal, and during work near the mine—maximal. In retreat mining of the panel (Fig. 5b), leakage through the gob depends on the depression of the extraction section (longwall), and leakage to the surface depends on the depression of the ventilation drift. The depression of the extraction section (longwall)

Fig. 5. Graph of the distribution of depression over the sections of a flank (diagonal) ventilation scheme with forcing ventilation

remains constant, while the depression of the ventilation drift increases. Therefore, during work at the boundary of the mine field, leakage will be minimal, and at the mine—maximal.

The total leakage in retreat working will be less than in advance working, since, with equal leakage to the surface, leakage through the gob is smaller.

With a flank ventilation scheme, exhaust ventilation, and advance mining of the panel (Fig. 6a), leakage through the gob and to the surface depends on the depression of the intake stream of the hoisting shaft, the haulage drift, and the extraction section (longwall). The depressions of the shaft and the extraction section are constant, while that of the haulage drift increases. Therefore, maximum leakage will occur during work at the boundary of the mine field, and minimum leakage at the shaft. In retreat mining of the panel (Fig. 6b), analogous phenomena are observed, but the ventilation drift is located in the gob, which increases leakage.

It follows from the foregoing that, with a flank ventilation scheme and advance mining, exhaust ventilation is more favorable, while with retreat mining, forcing ventilation is more favorable.

The central ventilation scheme with forcing ventilation and retreat mining of the panel (Fig. 3b) gives the least leakage in comparison with the other eight considered variants of ventilation schemes (Figs. 3–6).

If the surface of the mine field is not hilly and makes it possible to connect the underground workings with the surface through pits, then

the indicated variant of the central ventilation scheme (Fig. 3b) can be significantly improved by driving raises ahead of the stoping operations (Figs. 7, 8). Driving advance raises eliminates the need for premature driving and, especially, maintenance of the ventilation drift along the entire length of the mine field. The maximum possible mine depression is thereby reduced the more, the longer the mine field and the more frequently the raises are laid out.

Fig. 6. Diagram of the distribution of depression by sections of a flank (diagonal) ventilation scheme with exhaust ventilation

In our case, the maximum possible depression of the central ventilation scheme of the mine, when advance raises are driven every 40 m, will be reduced by the amount of the depression of a ventilation drift 730 m long (Fig. 7). The central ventilation scheme is transformed into a variant of the flank ventilation scheme. The maximum possible depression of a mine with advance raises will be: \(h = 26.56 - 11.75 = 14.81\) mm water column.

Fig. 7. Diagram of the distribution of depression by sections of the ventilation scheme when the ventilating air current exits through an advance raise. Pressure ventilation

This amounts to

\[ \frac{14.81}{26.56} 100 = 55.8\% \]

of the maximum possible depression of the mine under the central ventilation scheme; that is, the maximum possible depression of the mine will decrease by 44.2%, which confirms

advantages of this ventilation scheme over the central ventilation scheme.

With direct advance, the flank ventilation scheme with the ventilation jet issuing through the face shafts under forcing ventilation (Fig. 7a), and operation on the first horizon, has greater advantages than any other mine ventilation scheme with direct advance. From Figs. 7a and 8a it is evident that the distribution of the mine’s total depression, equal in magnitude, is more favorable under forcing ventilation. With this ventilation scheme (Fig. 7a), regardless of the location of the extraction area (longwall) along the strike, the greatest—

Fig. 8. Graph of the distribution of depression over the sections of the ventilation scheme when the ventilation jet issues through a face shaft. Exhaust ventilation

—depression will always be at the beginning of the main drift. When a horizon is mined by direct advance, the depression in the main drift will initially be small, and air leakage will likewise be small. When working at the boundary of the mine field, the depression at the beginning of the main drift will be greatest and equal to the maximum depression of the entire mine, except for the depression of the hoisting shaft; but by that time the greatest compaction of the caved rock will have occurred, which will reduce leakage through the worked-out space and to the surface. The depression in the section of freshly caved rock depends on the depression of the shaft, the ventilation drift, the extraction area (longwall), and part of the main drift, and remains almost constant regardless of the location of the extraction area (longwall). All this helps reduce leakage.

Under exhaust ventilation (Fig. 8a), the maximum depression will at all times be at the shaft, in the place of freshly caved rock, increasing as the boundary of the mine field is approached. This leads to considerable suction of air from the surface and through the worked-out space.

When developing a suite of seams, the shortcomings of this ventilation scheme under exhaust ventilation increase. It is necessary to install an independent fan on each seam, which leads to the joint operation of several fans.

Consequently, when developing a single seam on the first horizon by direct advance, the flank ventilation scheme with the ventilation jet issuing through face shafts under forcing ventilation is the most rational.

The rationality of this ventilation scheme under direct advance, in comparison with other schemes, increases with an increase in the tendency of the rocks to caving, and even with an increase in seam thickness and dip angle.

When mining coal seams prone to spontaneous combustion, the possibility of ensuring good isolation of the worked-out space and preventive stowing is of substantial importance in combating endogenous fires. In this case, the flank ventilation scheme with discharge of the ventilating current through the advance boreholes, under forced ventilation and retreat extraction of the panel from the boundaries (Fig. 7b), retains all the advantages in combating endogenous fires that are inherent in the central ventilation scheme when extracting the panel by retreat.

Consequently, when mining coal seams prone to spontaneous combustion, on the first horizon, under the ventilation conditions, the best is the flank ventilation scheme with discharge of the ventilating current through the advance boreholes, under forced ventilation and retreat extraction of the panel (Fig. 7b). This mine ventilation scheme provides the least total depression, the smallest leakages through the worked-out space and to the surface, and successful control of the occurrence and extinguishing of endogenous fires.

A major disadvantage of this mine ventilation scheme is the long period required to prepare a panel for operation, which increases greatly when the mine field is long. In our case, for production work under direct advance it is necessary to drive only a crosscut furnace of length \(l = 100\) m. At a driving rate \(v = 90\) m per month, the time for preparing the panel will be:

\[ T = \frac{l}{v} = \frac{100}{90} = 1.1 \text{ months}. \]

Under retreat, before production work begins it is necessary to drive a main entry of length \(l = 770\) m and a crosscut furnace of length \(l = 100\) m. The time for preparing the panel will be:

\[ T = \frac{l}{v} = \frac{870}{90} = 9.68 \text{ months}. \]

Under retreat, 8.8 times more time is required for preparing the panel. With mine fields that are long along the strike, this difference may be still more significant, which indicates the great importance of mechanization and the application of the newest high-speed methods for driving workings when preparing the panel. High-speed methods of driving development workings can have a significant influence on the broader use of retreat.

The principal factor determining whether direct or retreat extraction of a panel is used is the date when the new mine enters the number of operating mines. The main advantage of direct extraction of a panel lies in the rapid preparation of a horizon for operation. Therefore, in mining the first horizon, direct extraction of the panel is used, and retreat extraction only in special cases. When direct extraction of a panel is used, it is necessary to take into account the disadvantages inherent in it:

1. The difficulty of maintaining entries under these conditions, especially the ventilation entry under the central ventilation scheme, and the need to leave large near-entry pillars.

2. Large losses of coal in these near-entry pillars.

3. The difficulty of maintaining in serviceable condition a large number of stoppings in the furnaces cutting through the near-entry pillars.

1. In seams with coals prone to spontaneous combustion, there is a great danger of endogenous fires arising as a result of the crushing of pillars left near the drift and the seepage of air through cracks forming in the pillars and through damaged stoppings in the furnaces.

The indicated shortcomings increase greatly with an increase in seam thickness, instability of the surrounding rocks, and angle of dip. With rocks that compact rapidly, the situation improves. In direct extraction of a panel and a seam dip greater than 40–45°, maintaining the ventilation drift is very difficult, and with great thicknesses of coal seams under Kuzbass conditions it is almost impossible.

When working seams with spontaneously combustible coals, extraction of a panel by the direct method is inadmissible. To preserve all the advantages of the retreating method when working by the direct method, it is necessary to drive a field drift. Driving a field drift makes it possible, when extracting a panel by the direct method, to maintain on the extraction district a flank ventilation scheme, with the ventilation current leaving through the forward staple shafts under forcing ventilation. Air leakage through the worked-out area and to the surface will be negligible and almost constant throughout the entire period of panel extraction. Coal losses in pillars near the drift are small.

Working a Series of Seams

Coal deposits of Kuzbass are usually represented by series of seams. The seams in a series are often closely spaced. The great thickness of the seams, their proximity, gas content, tendency to spontaneous combustion, and the predominance of steep dip lead to the necessity of extracting the seams in a series in descending order. This is also confirmed by the practice of mining operations in Kuzbass mines. In analyzing mine ventilation schemes, we assume a descending order of extraction of the seams of a series.

When working a series of seams, it is necessary to take into account the possibility of undermining the ventilation drift not only by stoping operations on the underlying seam, but also by stoping operations of the overlying seam. The probability of undermining ventilation drifts depends on the thickness of the seam, the distance between seams, the properties of the surrounding rocks, the angle of dip, the height of the panel, and extraction with caving or with stowing.

Under Kuzbass conditions, especially in thick seams of steep dip, with a vertical panel height of 100 m and a small distance between the seams in the series, undermining of the ventilation drift by stoping operations on the underlying seam is inevitable. Consequently, the seams, in order to avoid undermining the ventilation drift, may and should be extracted only by the retreating method, with stoping operations on the overlying seam kept ahead. But, as established above, the retreating method has major shortcomings—lengthy preparation of a panel for stoping extraction; therefore, on the first horizon, when working a series of seams, it cannot be adopted.

Driving concentration or group drifts with district or intermediate crosscuts makes it possible to apply the direct method in working a panel while preserving all the advantages of the retreating method within each extraction district, and the best ventilation scheme when carrying out stoping operations on the first horizon—a flank ventilation scheme with the ventilation current leaving through the forward staple shafts under forcing ventilation (Fig. 76).

This is why the concentration drift is driven along the underlying seam of the series. If the series is large and the intermediate crosscuts are semi-

are of considerable length, in practice the suite is worked in groups, and in each group a group drift with district crosscuts is driven along the lower seam. This, at the same time, considerably simplifies the organization of transport and the ventilation scheme. The number of parallel streams is increased, which leads to a significant reduction in the total mine depression and facilitates the prevention and extinguishing of endogenous fires. On all seams in a group within a level, except the lower one, advance working is possible; on the lower seam—retreat working. The indicated order of mining the seams in a group is expedient if the face line of the stoping operations of the seams in the group ensures the planned output of the mine.

Retreat extraction of the lower seam in a suite group does not permit stoping operations to be carried out simultaneously in the lower groups of the suite. Replacing group drifts along the lower seams in groups by field drifts sometimes makes it possible to eliminate this shortcoming and, at the same time, with the corresponding advance on the lower seams, to conduct stoping operations in all groups of the suite in amounts ensuring the annual output of the mine. The driving of field drifts makes it possible, under certain conditions, to use them for ventilation and when transferring mining operations to the underlying horizon.

Analysis of Ventilation Schemes for the Second and Underlying Horizons

For a correct judgment as to the expediency of applying one or another ventilation scheme on the second and underlying horizons, it is necessary first of all to have a clear idea of the depth of penetration of open cracks from the surface. The depth of penetration of open cracks can be established precisely only by detecting such cracks during the development of mining operations at the corresponding depths. For each mine, depending on the geological conditions of occurrence of the seams and on mining-engineering factors, it will be different. Of great importance are the degree of looseness of the rocks and their tendency to caving, as well as the thickness of the deposits covering the bedrock. For the conditions of Kuzbass, the depth of penetration of open cracks may be taken, approximately, on the basis of literature data, as equal to 80–100 m, and in individual cases even down to a depth of 200 m. Consequently, if the second horizon may still have open cracks reaching the ground surface, then on the underlying, i.e., on the third and lower horizons, there should be none. Final confirmation of the above requires observations.

Development of Single (Isolated) Seams

The second horizon under the conditions of the Kuznetsk Basin is usually already gassy. The absence of open cracks reaching the surface and the presence of mine gas (methane) make only exhaust ventilation permissible. Exhaust ventilation in this case is most favorable both when the fan is operating and when it is stopped. When the fan is operating, exhaust ventilation causes continuous removal of gas from active workings and from the worked-out space. The absence of open cracks reaching the ground surface, when the fan is stopped, at the first moment, as a result of the increase in pressure, causes air to rush into the mine along the active workings, which pushes back the gases of the worked-out space. In the presence of open cracks reaching the ground surface, stopping the fan should cause, and does cause, the inflow of air into

the mine through these fissures and the saturation of the mine air in the active workings with gases issuing from the worked-out space.

If it is assumed that, during work on the second and lower horizons, open fissures emerging at the surface are absent, leakage can occur only through the worked-out space. Then, from consideration of the graphs of the distribution of depression along the workings (Figs. 3, 4, 5, 6), it follows that with exhaust ventilation and in the absence of fissures emerging at the surface, only leakage through the worked-out space remains. Therefore, the most expedient is a central ventilation scheme with exhaust ventilation and retreat extraction of the panel (Fig. 46), in which leakage through the worked-out space is small and depends only on the depression of the extraction district (longwall). To reduce this leakage, the depression of the extraction district (longwall) must be made as small as possible. This can be achieved by increasing the cross section of the workings of the extraction district, and also by preserving their cross section. Thus, the fire hazard of the mine ventilation scheme for the second and lower horizons, in the absence of open fissures emerging at the surface and when mining self-igniting coal seams, depends mainly on the depression of the extraction district, and not on the total depression of the mine.

For extraction of the second stage by the advancing or retreating method, the time for preparing the stage for extraction does not have such decisive significance as in the development of the first (upper) horizon. The time during which the first horizon is being mined is quite sufficient for preparing the second horizon for stoping by the retreating method, but the premature nature of capital expenditures remains. By driving a district gate road, it is possible to preserve all the advantages of retreating extraction also when mining the second horizon by the advancing method. The presence of a district gate road on the first horizon makes it possible to apply a flank ventilation scheme for the mine, while preserving the merits of the central ventilation scheme—the dependence of leakage only on the depression of the extraction district. The use of a flank ventilation scheme ensures a reduction in the maximum possible depression of the mine.

Mining of groups of seams

Everything stated above concerning the order of extraction of seams in a group on the first horizon applies fully to the second horizon as well. As has already been established, when developing a single (isolated) seam of the second horizon, in the absence of open fissures emerging at the surface, the most expedient is a central ventilation scheme with exhaust ventilation of the mine and retreat extraction of the stage (Fig. 46). This proposition also remains valid when developing a group of seams of the second and lower horizons in the absence of open fissures emerging at the surface.

To preserve all the advantages of retreating extraction when mining a group of seams of the second and lower horizons by the advancing method, as in the development of a group of seams of the first horizon, it is expedient to drive concentration or group gate roads with intermediate or district crosscuts. If district gate roads are present on the first horizon and concentration gate roads are replaced by district gate roads on the second horizon, it is possible simultaneously, in a group or suite of seams, to mine all seams by the advancing method and to apply a flank ventilation scheme for the mine.

The transition to lower horizons under the conditions of the Kuznetsk Basin is associated with an increase in gas abundance. This causes a considerable increase in the quantity of air that must be supplied to the mine; therefore,

the cross-section of the workings and their length substantially affect the magnitude of the general mine depression. In order to reduce the magnitude of the general mine depression on lower horizons, it is advisable, when working a series of seams, to have a flank ventilation scheme for the mine. On the second horizon, when there is still the possibility of the appearance of open cracks reaching the surface, it is advisable to use pressure-and-exhaust ventilation. This makes it possible to reduce the absolute magnitude of the total depression of the mine and the pressure difference between the working and the surface, which will undoubtedly reduce leakage. In the Kuzbass it has already become widespread, but for its final confirmation special scientific research work is required.

Conclusions

From the foregoing it follows:

1. The application of the proposed graph in the study of ventilation schemes for Kuzbass mines provides:

a) a visual representation of changes in the magnitude of the general depression of a mine, depending on the adopted ventilation scheme, as well as its distribution among the workings comprising the ventilation scheme;

b) easy detection of places with high depression and maximum leakages, as well as determination of the relative magnitudes of possible leakages when designing the ventilation of newly laid-out mines;

c) determination of the influence of the depression of one working on the leakages of another;

d) detection of errors made in calculating depression.

1. On the basis of an analysis of the ventilation schemes of Kuzbass mines using the proposed graph, the following has been established.

a) The most rational ventilation scheme, under the conditions of ventilation when working self-igniting and gas-bearing coal seams in the Kuzbass, is the flank (diagonal) ventilation scheme. To move the required quantity of air for mine ventilation under this ventilation scheme, the maximum possible depression is 23.6% less than under the central ventilation scheme; leakages will also be smaller. The depression over the entire period of operation of a panel remains largely constant; this facilitates regulation and creates favorable conditions for the automation of ventilation installations; reduction of the depression and its constancy contribute to increasing the efficiency of the ventilation installation. In addition, the danger of the occurrence of “short-circuit” phenomena between the main and ventilation drifts disappears, which helps preserve normal atmospheric conditions in underground workings.

b) When working both a single (isolated) seam and a series of seams on the first horizon, the most rational is the flank (diagonal) ventilation scheme with forced ventilation and with the ventilation stream exiting through advanced shafts. To preserve all the advantages of direct and reverse extraction of a panel, when working a single seam it is necessary to drive a panel drift; when working a series of seams, the horizontal opening scheme should be carried out by group drifts in combination with intermediate crosscuts. With high mine capacity, group drifts should be replaced by panel drifts.

c) With an increase in gas emission and mine capacity, the advantages of the flank ventilation scheme increase, while the disadvantages (driving an extra shaft) decrease.

d) A correct solution to the problem of ventilating the second and lower horizons can be given only with a clear and precise understanding of the depth of penetration of open cracks and the nature of gas emission. Up to the depth ...

penetration of open fractures, forcing ventilation is rational, and below it—exhaust ventilation.

Exact data on the depth of penetration of open fractures under Kuzbass conditions are lacking. It is assumed that this depth ranges from 70 to 200 m; therefore, ventilation of the second horizon is more rationally carried out by means of forcing-and-exhaust ventilation.

For the final confirmation of the area (conditions) of application of forcing-and-exhaust ventilation, it is necessary to conduct special observations in Kuzbass mines in the sections where it is used.

REFERENCES USED

1. V. B. Komarov and D. F. Borisov—Mine Ventilation, 1938.
2. D. F. Borisov—“On the question of ventilating mines developing self-igniting coals,” Mining Journal, No. 12, 1936.