Mining of Coal Seams Under the Main Haulage Level

Abstract

The question of mining under the main haulage level as a way by which in some cases coal reserves can be effectively extracted is still discussed. The paper introduces advantages and disadvantages of this method. It presents examples of the bedding of a seam in a limited depth under level, for example 50 m, when the opening by the under level mining method is obviously more advantageous. Special attention is given to risks of ventilation short circuit which are higher in this method compared to classical opening. The paper also gives a brief economical reflection allowing to determine the efficiency of under level mining.

Full text

DOI: 10.2478/v10205-011-0002-6 23
GeoScience Engineering Volume LVII (2011), No.2
http://gse.vsb.cz p. 23-32, ISSN 1802-5420
MINING OF COAL SEAMS UNDER THE MAIN HAULAGE
LEVEL
PODPATROVÉ DOBÝVÁNÍ UHELNÝCH SLOJÍ
Josef CHOVANEC1, Petr URBAN2 , Ivo PĚGŘÍMEK3, Vitězslav KOŠNOVSKÝ4
1 Ing. PhD. Institute of Mining Engineering and Safety, Faculty of Mining and Geology,
VSB-TU Ostrava, 17. listopadu 15, Ostrava-Poruba, 708 33, (+420) 596995544
e-mail:josef.chovanec@vsb.cz
2 Ing. Ph.D. Institute of Mining Engineering and Safety, Faculty of Mining and Geology,
VSB-TU Ostrava, 17. listopadu 15, Ostrava-Poruba, 708 33, (+420) 596993357
e-mail: petr.urban@vsb.cz
3 Ing. Czech Mining Authority, Kozi 4, Praha 1-Staré Město, 110 01, (+420) 221775311
e-mail: pegrimek@cbusbs.cz
4 Ing. OKR, Paskov Mine, Staříč 528, 73943, (+420) 558493222
e-mail: vitezslav.kosnovsky@okd.cz
Abstract
The question of mining under the main haulage level as a way by which in some cases coal reserves can
be effectively extracted is still discussed. The paper introduces advantages and disadvantages of this method. It
presents examples of the bedding of a seam in a limited depth under level, for example 50 m, when the opening
by the under level mining method is obviously more advantageous. Special attention is given to risks of
ventilation short circuit which are higher in this method compared to classical opening. The paper also gives a
brief economical reflection allowing to determine the efficiency of under level mining.
Abstrakt
Otázka podpatrového dobývání, jako způsobu, kterým lze v určitých případech efektivně vytěžit uhelné
zásoby, je stále diskutována. V uvedeném příspěvku se uvádějí výhody i nevýhody této metody. Jsou uvedeny
příklady uložení slojí do omezené hloubky pod patrem, například 50 m, kdy je příprava sloje podpatrovým
dobýváním zřejmě výhodnější. Upozorňuje se také na rizika větrního zkratu, které je u této metody, oproti
klasické otvírce, vyšší. V práci je také uvedena stručná ekonomická úvaha, podle které lze určit efektivnost
podpatrového dobývání.
Key words: Gas, methane, seam, under the main haulage level, costs of coal mining.
1 INTRODUCTION
The presented work starts from findings, as published in [3], and supplement them by certain facts which
were not given in [3] for various reasons, especially the possibility of scope of the article. We draw attention
especially to the danger of a ventilation short circuit, which may cause serious complications when working
under the main haulage level, and suggest some opportunities for its improvement. We dealt with the
comparison, when working under the main haulage level is effective from an economic point of view. We give
an example, when it seems preferable to use a typical way by deepening pits for opening a deposit.
2 UNDER LEVEL MINING DEPENDING ON SEAM BEDDING
Figure 1 and 2 show fairly frequent cases of mining a seam under the main haulage level on different
conditions of its bedding. These are the situations of individual seams (or a seam), whose typical opening would
require a relatively high costs. In the literature [1] this method is described as "occasional, random".
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Fig. 1 Possible ways of under level mining depending on seam bedding. (Case "a")
In the case "a" as in Figure 1 it is a group of coal seams, which is directed to the boundary of the mining
field. The development of these coal seams would require driving out a long cross-cut plus a staple pit from the
bottom at the level of 595 m. Therefore, the under level mining method is more preferable.
Fig. 2 Possible ways of under level mining depending on seam bedding. (Cases "b, c")
The case "b" in Figure 2 represents a flat syncline, whose greatest depth is close to the upper level at 485
m, thus it is in a long distance from the bottom level of 595 m.
The case "c" represents the throwing of the seam (thrust fault), also in a small depth below the top level at
485 meters.
In all these cases it is so-called "outstanding" (incomplete) mining under the main haulage level. It is
characterized by the fact that fresh air is fed from a higher (mining) level (the level at 485 m in Figure 1 and
Figure 2).
In contrast, in so-called solved (full) mining under the main haulage level the intake air is fed from the
bottom level (the level at 595 m in Figure 1 and Figure 2).
The fresh intake in the cases shown in Figures 1, 2 is fed from the main mining level through a staple pit,
or dip working to the lowest point, the location of the seam, and from here then it progresses up through
appropriate mine workings. The exhaust air returns to the main mining level and must be diverted to the return
level through the shortest path. However, in this way the risk of a ventilation short circuit occurs. This must be
prevented by air doors, or other appropriate means.
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3 INCOMPLETE UNDER LEVEL MINING
Figure 3 shows according to [2] a simple air diagram of the method of incomplete under level mining.
Since this is primarily the representation of ventilation, it is rather simplified. For instance, there is no pass-by in
the outline, which should be built for the filling point at the intake level. (This is shown in Figure 9).
Intake shaft
Upcast shaft
Upcast level
Intake level
Fig. 3 Isometric diagram of incomplete under level mining
From Figure 3 we can deduce how the air from the intake level is drained through an incline to the bottom
road under the coal face. Thereout then it proceeds across the face through the upraise to the upcast level. So as
the air flows at the intake level through the incline under the face, an explosion control object must be installed
behind the incline - see Fig. 4.
And just the possibility of its opening represents the risk of volume flow rate depletion for the active
face. Another sensitive point is also a permanent stopping between the return airway of the face and the upcast
level.
4 PLANNED UNDER LEVEL MINING
Planned mining under the main haulage level lies in that the entire coal reserves under the mining level
will be mined out on this level upwardly. Usually, the interval for mining the bottom seam managed to increase
and thus the development of the seam could start later. But due to certain disadvantages of under level mining
and in the meantime achieved progress for mining out between seams, the planned under level mining is
generally not recommended. Especially chutes and drag conveyors from the new means have proved themselves
in mining out between seams.
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Fig. 4 The ventilation control object in a coal mine
5 ADVANTAGES AND DISADVANTAGES OF UNDER LEVEL MINING
The major advantage of mining under the main haulage level lies in savings of costs on development
work, but at least in saving of time to carry out extensive development work. Therefore, possible under level
mining, as an alternative, cannot be completely excluded for instance when transiting to a deeper level. When
even the development of the bottom level is in default and there are enough reserves for mining under the main
haulage level at the mining level, the planned under level mining is very desirable.
On the other hand, however, the under level mining have many disadvantages that cannot be neglected. In
addition to complex ventilation management, it is necessary to pay special attention to water regime. The costs
of capturing and pumping water is the larger, the more water is contained in the mountain range. Also the
remaining water in the abandoned mining area of the initial under level mining after completing the extraction
must be taken into account.
The affecting of the main mining level by undermining by the coal seam (seams) being mined is however
also very unpleasant. Especially the sites of filling stations, whose shifters and chain tracks are very sensitive to
dip changes, are quite critical. Also the transport by means of mining large-volume cars is getting difficult.
6 VERTICAL AND DIP WORKINGS IN UNDER LEVEL MINING
For developing a seam (or a group of seams) either vertical or dip workings are used.
For dip workings the method of transport and excavation, which will take place on them, must always be
considered. Figure 5 shows several possibilities.
Fig. 5 Vertical and dip workings in under level mining. (The cases „c, d“)
In the case "c" it concerns the development of seams under the main haulage level by a dip working
(incline) with a dip of 30°. Selecting a higher inclination means shortening the working, but it also requires a
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more intensive means of transport for the extraction. In this case, a special conveyor should be chosen. For
details, see [2].
When developing according to "d" when the incline has the dip of 13° to 15° a conveyor belt could be
used.
Fig. 6 Vertical and dip workings in under level mining. (Case „a, b“)
As a transport means on inclines (Fig. 6) according to "a" or "b" with a dip of 19° to 21° a plate conveyor
should be used.
The inclines "b" (Fig. 6), or "c" are led out over the mining level - 700 m and leads into the bin over the
filling station.
For the "complete" under level mining, fresh intake is led between blind pits from the bottom level at 820
m. The upper level at 700 m is also intake one, namely up to the ventilation gate at the cross-cut, through which
the under level mining is open under this level at 700 m.
A relatively large distance of about 400 m between the filling point and a blind air pit creates a space
large enough for empty cars, which come from one side, and on the other side of the blind pit a ventilation gate
can be installed, where long trains can be placed just as well.
7 DANGER OF VENTILATION SHORT CIRCUIT
One of the serious risks in under level mining is a possible short circuit when opening the ventilation
door. Today, most of doors, especially those through which traffic is intense, or due to which unclosing a
dangerous short circuit can occur, have implemented a function of automatic opening and closing.
Most often the automatic opening function is provided by a pneumatic or hydraulic cylinder - see figure
7, which is activated by motion of a lever mechanism hung in front of the door. The lever mechanism and
opening cylinders are connected by pulleys and a cable. Closing the door is controlled by signalisation that
informs on closing at the control room.
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Fig.7 Control of ventilation and dam doors
The risk of a ventilation short circuit often threatens on air bases of coalfaces, where the intake and upcast
are separated by a wooden door. The ventilation door is still without mechanized closing. They are inclined to
close themselves after release. Today, only sensors indicating opening the door are implemented. The signals are
led out to the mine control room. But also this way of signalling represents a clear increase in security. The
dispatcher may warn the nearest staff or technical supervision on the signal of opening by a loud intercom.
8 DOOR DESIGN ACCORDING TO FOREIGN SOURCES
Due to the importance of ventilation doors in case of a possible short circuit in ventilation network, we
were also interested in possibilities occurring in the door design over the world.
According to [4] there are several companies in the USA specializing in the manufacture of doors for
mining operations.
For example, the U.S. company American Mine Door, [5] offers 2 types of doors: High-and low-pressure
ones. Figure 8 shows an example of the low-pressure doors design.
Fig. 8 The mine doors design of the company American Mine Door
The low-pressure doors, i.e. apparently a similar type that is in our mines used to control the air at less
frequented workings, are made of lighter materials, narrower wings and a smaller frame. Therefore, they are
lighter and cheaper.
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The doors, during their opening, use opposing wings and thus cancel the effect of static pressure. Also at
higher pressure in surroundings they are relatively easy to open, because the pressure against one wing is
abolished by the wing on the opposite side.
The same pressure helping in opening the doors helps also in their closing. The pressure created by the
ventilation system is evenly distributed. This feature is particularly preferable in building the doors in dip
workings. The doors can be used several times. If they lose their importance in the original working, they can be
disassembled and relocated.
The mining doors are mechanically controlled and their position is indicated by light and sound signals.
They have an internal lock, which ensures the door not to open when another door is open too. They have an
open-door sensor that secures any object not to be ajar; remote opening and closing, sound sensors.
9 INTERIM BALANCE TO ASSESS THE EFFECTIVENESS OF UNDER LEVEL
MINING
In order to assess, whether it is economically advantageous to choose the method of under level mining or
proceed to the typical development, it is possible to use an interim economic balance. As an example of its
implementation we used the following procedure.
In [3] there is given a rough overview of the investment costs of opening out workings required for the
development of the block for under level mining. That block is schematically depicted in Figure 9. The amount
of investment costs on opening out workings required for obtaining reserves under the level - 436 m is listed in
Table 1.
Legend:
Air control Intake air current Upcast air current Direction of mining Tectonics
Fig. 9 Schematic outline for assessing the balance of under level mining
1., 2. dip working for making the reserves under the level accessible
3. pass-by from cross-cut at the level of 436 m
4. upraise for leading the mining output into the bin
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Tab. 1 Costs of developing the coal seam for under level mining.
Name of working
Number
Profile
Length
Costs of erection
(CZK)
Pass-by from cross-
cut at -436m
"3"
K14-P28-0,5 m
1 m=81 735,-CZK
300m
24 520 500
Upcast crosscut
"4"
K 14-P28-0,5 m
1 m=81,735,-CZK
110m
8 990 850
Vertical binbetween
upcast cross-cut
2436/3 and pass-by
at -436 m
"4"
1 m
about CZK 180,000
10m
1 800 000
Incline
"1"
K12-P20-0,7 m
1 m=CZK 36,816,-
175m
6 442 800
Incline
"2"
K12-P20-0,7 m
1 m=CZK 36,816,-
90m
3 313 440
Total costs on developing the workings for under level mining
45 613 893
From the face 44,974 tons were extracted. From the bottom block under the face further 48,610 tons
were extracted (i.e. 93,684 tons in total), so the work required for developing the seam for under level mining in
the given area would burden a ton of coal by the sum 487,- CZK/t.
For our own consideration on the profitability of applying the method of under level mining, we chose
the solution of using the typical way for opening out and preparing a certain quantity of reserves. This means
deepening pits and driving out the cross-cut at a lower level. In order the consideration to be based on the same
level heights for obtaining reserves, as those showed in Fig. 9, we assume therefore deepening pits by 45 m.
If the investment costs of deepening a pit by 1 m are CZK 500,000, then the required total investment
for both the pits will reach CZK 45 million. We also assumed that for making the reserves accessible up to the
development stage (when only the workings in the seam will be open out), it will be necessary to open a 200m
cross-cut. When the costs per 1 m of the cross-cut are CZK 85,000,-, it would be CZK 17 million in total.
Thus the development phase, in case we theoretically make the reserves accessible by deepening the pits,
will require the costs of deepening the pits and opening out the workings CZK 62 million.
From this very simple consideration the costs of opening out by the method of under level mining
(which amount to CZK 45.6 million, see Table 1) are more preferable.
However, if in opening out using the method of deepening the pits and crosscutting also the reserves at
the deepened level are made available, which is very likely, then the consideration of economic efficiency would
be changed. In order the way of developing by deepening the pits to achieve the same amount of costs per 1 ton
of reserves, as in opening by the under level mining method, it should achieve according to the equation (1) at
least

 (1)
I n investment costs of deepening the pits and crosscutting (CZK)
T weight of open reserves (t),
which results in T = 127,310 t.
This very simplified consideration implies that if the manner of developing resting on deepening the pits
opens the reserves, whose weight exceeds 127,310 tons, this way would be more preferable compared to under
level opening.
The consideration, though simplified, as neglects e.g. the costs required for mining equipment (plate
conveyors, etc.), may be very appropriate for an indicative decision. For the given hypothetical example a graph
can be compiled that would express how the costs of opening by deepening the pits burdens the costs per 1 ton of
open reserves. (Fig. 10).
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Burdening costs by deepening pits
(CZK/t)
Open reserves (t)
Costs of development vs. tons
Costs of development (Czk/t)
Fig. 10. The dependence of the total costs per 1 t of open reserves in the given situation according to Fig.
9 on the costs per one ton of the reserves opened by deepening pits and crosscutting
For the situation according to Figure 9 and Table 1, on the curve left from the red line there is the weight
of reserves when opened by deepening the pits, the typical development would burden the costs per one ton of
the open reserves less than the system of under level opening.
10 CONCLUSION
The presented article shows the possibilities of mining coal reserves by means of mining under the main
haulage level. From extensive problems associated with this method of opening reserves only basic systems of
development have been selected.
Furthermore, we pointed out the danger of an air short circuit, which is in under level mining specially
significant, and indicated opportunities to improve its handling. The brief economic balance should indicate the
procedure allowing evaluating the way of under level mining in comparison with the typical development by
deepening pits.
REFERENCES
[1] FRITZSCHE C. G.: Bergbaukunde. Springer Verlag Berlin, Göttingen, Heidelberg 1958.
[2] WALTER BISCHOFF, HEINZ BRAMANN,:Westfälische Berggewerkschaftskasse Bochum: Das kleine
Bergbaulexikon. 7. Auflage, Verlag Glückauf GmbH, Essen, 1988, ISBN 3-7739-0501-7.
[3] URBAN, P.: Řešení větrání a bezpečnosti u podpatrového dobývání v oblasti 112sloje na Dole
Staříč,OKR - ČR. [Solution of ventilation and safety in under level mining in the area of the 112 seam of
the Staříč Mine, OKR - CR.] Sborník mezinárodní konference [Proceedings of the International
Conference] “Systemy wspomagania w zarzadzaniu środowiskia“ Politechniky Ślaske, Harrachov 2009.
[4] http://www.google.com (mining door).
[5] info@minedoor.com.
This paper has been elaborated upon solving the GACR grant project No. 105/09/0275 under the support
of the Grant agency of the Czech Republic.
80000
100000
120000
140000
160000
300 400 500 600 700
otevřené zásoby (t)
náklady otvírky (Kč/t)
Zatížení nákladů prohloubením jam
(Kč/t)
náklady otvírky vrs.
tuny
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RESUMÉ
Současné poznatky a vědomosti o podpatrovém dobývání se jeví pro uhelné hornictví ne- zcela
dostačující.
Vznikají nesrovnalosti v definování podpatrového dobývání uhlí a v odborné hornické veřejnosti bývá
tento termín vykládán s mírnými odlišnostmi.
Část báňských odborníků považuje za podpatrové dobývání pouze hornickou činnost dobývání pod
posledním patrem z přístupněným vtažnou jámou, jiná část pak i dobývání pod jakýmkoliv patrem, pokud se
porub dostane pod výškovou úroveň těžního patra.
Z porovnání výhod a nevýhod podpatrového a nadpatrového dobývání vyplývá kromě jiného zřejmá
nevýhoda a nebezpečnost podpatrového dobývání.Představuje problém především v oblasti větrání a havarijních
stavů, zejména protipožární prevenci.
Na tyto problematiky je z části zaměřen presentovaný článek “Podpatrové dobývání uhelných slojí”.
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