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Mining of Mineral Deposits
DNIPRO UNIVERSITY
of TECHNOLOGY
1899
ISSN 2415-3443 (Online) | ISSN 2415-3435 (Print)
Journal homepage http://mining.in.ua
Volume 12 (2018), Issue 4, pp. 9-19
UDC 622.834.2:622.862.3
National Mining
University
Founded in
1900
https://doi.org/10.15407/mining12.04.009
EXPERIMENTAL STUDIES OF THE SEAM OPENINGS
COMPETENCE IN DIFFERENT METHODS OF PROTECTION
UNDER PITCH AND STEEP COAL SEAMS DEVELOPMENT
Ya. Liashok1, I. Iordanov1, D. Chepiga1*, S. Podkopaiev1
1Donetsk National Technical University, Pokrovsk, Ukraine
*Corresponding author: e-mail daria.chepiha@donntu.edu.ua, tel. +380999815583
ABSTRACT
Purpose. Investigation of the seam openings competence in different methods of protection in complex mining and
geological conditions of pitch and steep coal seams development of Donbas.
Methods. To achieve this purpose, the research uses a complex approach, including analysis and generalization of
the openings protection experience, studying the static field of stress distribution in a coal-rock mass on cloudy crystal ball model, a mine experiment to study the haulage gate hardness and the experimental data.
Findings. When studying the wall-rock displacements on the haulage gate contour, it was recorded that in the case of
yieldable protective facilities usage for seam openings, the roof and foot convergence of the coal bed mining as the
productive workings advance is observed until the complete protective facilities compression, and in the zone of
steady rock pressure is damped. In the case of coal pillars usage for roadway protection, after the destruction their
hardness varies in a linear fashion, which contributes to a significant deterioration in the haulage gate stability behind
the face. The use of a goaf stowing for the seam opening protection, from the point of view of stresses distribution in
the coal-rock mass, ensures a gentle deflection of the wall-rocks behind the face by increasing the area of the subside
strata actual contact with the filling mass, when compared with the roadway protection with the coal pillars.
Originality. The effectiveness of the applied method for the seam openings protection is proposed to be evaluated
according to the change in the stability of the haulage gate, but taking into account the hardness of the protective
facilities. The hardness of protective facilities reflects their ability to resist deformation when the delaminated rock
strata is displaced and depends on the value of the external force, the time factor, and the geological conditions of the
developed coal seam.
Practical implications. The use of a goaf stowing, as a method for controlling the roof or for wide yielding seats
located above the roadway, will allow the haulage gates operational condition to be operational and increase the
safety of work while maintaining the workings.
Keywords: haulage gate, displacement, pillar, protective facilities, goaf stowing, delaminated rock strata
complete cave-in of the productive workings and openings. In other cases, these phenomena occur behind long
face and lead only to the caving of openings. In this case,
there is a loss of the roadway section regulated by the PR
(Preventive Regulations), which in turn contributes to an
increase in the level of injuries during the mine workings.
As it seems, as a result of the delaminated rock strata
shifting, in the vicinity of the shored up mine workings,
not only changes in the stress-deformed state of the wallrocks occur, as a result of which their competence may
deteriorate, but also the loss of the cross-sectional area of
the openings, specific measures aimed at maintaining the
haulage gates in the operational state, will meet the
requirements of safe mining.
1. INTRODUCTION
The efficiency of coal seams mining with increasing
depth of development and reliability of mining work to a
large extent depends on the state of mine opening. Their
unsatisfactory condition, especially when maintaining
seam roadways in difficult mining and geological conditions, increases the level of miners injuries. In the development of pitch and steep coal seams, due to the specific
features of the development associated with the angles of
incidence, there is a danger of sudden caving of the roof
rocks and the displacement of the bedrock. In some cases,
cavings of wall-rocks extend to the long face space, often
along its entire length and are accompanied by a partial or
________________________________
© 2018. Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. Published by the Dnipro University of Technology on behalf of Mining of Mineral Deposits.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/),
which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
9
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
characteristic shift zones takes place, the parameters of
which are significantly influenced by the way of roof
control in long face and roadways protection. It is known
(Zhukov, 2001; Viktorov, Iofis, & Goncharov, 2005) that
the most favorable for the wall-rocks condition, and,
consequently, for the mine workings, is provided by the
method of controlling the roof by goaf stowing.
The study of the process of wall-rock displacements
on the opening contour, the determination of the displacements magnitude, as well as the correct understanding of the geomechanical processes, will allow us to
justify the choice of a rational method for protecting
mine workings in specific mining and geological conditions. However, it is practically impossible to take into
account the variety of factors affecting the state of roadways, therefore it is proposed to maintain the maintenance conditions according to the size of contours rocks
convergence, changing the cross-sectional area, but
taking into account the hardness of the protective facilities and the stress-deformed state of the wall-rocks.
The purpose of the research is to study the features of
the rock pressure manifestation in seam openings and
changes of the stress-deformed state of the wall-rocks
under various methods of haulage gates protection in
complex mining and geological conditions.
In this regard, the study of rock pressure manifestations
in seam opening was accepted as the main object of research,
and for quantitative evaluation – the use of the amount of
rock displacement on the roadway contour and the change
in the hardness of protection structures, depending on the
method of protection and the distance from the face.
The study of the rock pressure manifestation features
in the excavations at great depth made it possible to establish that the nature of its dangerous manifestations is determined not only by the stress condition of the sedimentary rock massif and their physico-mechanical properties,
but also by the specific formation of the latter, which causes
inelastic deformation under volume compression, as well
as the ability to deform and collapse during unloading
(Nikolin, Podkopaev, Agafonov, & Maleev, 2005).
In the coal-rock mass, containing workings, delamination is always preceded collapses and landslides associated
with the detachment of a certain volume of rocks from the
rest of the massif. In relation to this, the cleavage foliation
of a coal-rock mass should be considered as a factor that
weakens the rock, on which the roof competence of the
coal bed mining and seam openings state depends.
In this connection, in real conditions of coal seams
development, in various ways of protecting mine
workings, in practice one has to meet with a special kind
of wall-rocks loading depending on mining and geological conditions.
In most cases, as a parametric support for geomechanical calculations of wall-rocks and mine workings
competence, the situations determined by the static
method of applying the load are used. However, a number of events, to which sudden roof caving or delaminated rock strata collapse should be attributed, are characterized by the application of dynamic loads. The latter
should be considered as impact phenomena, which
adversely affect wall-rocks.
It is known (Shakirzyanov & Shakirzyanov, 2005;
Lawson, Tesarik, Larson, & Abraham, 2017; Iordanov et
al., 2018; Wang, Zhang, Zhao, Liao, & Zhang, 2018) that
in the dynamic structures behavior a huge role is played
the presence of a yielding base, the damping ability of
which leads to smoothing of stresses upon impact. The
use of a yielding base is one of the ways to protect structures based on the prevention or localization of a dynamic effect, or lowering the intensity of a static load
(Zhang et al., 2006; Kumpyak & Mescheulov, 2017).
In the case of the horizon coal seams mining, as a result of productive workings advance, layers are gradually
separated from the overlying strata and they are bent along
the normal to bedding, like a plate with a bi-directional
backfill (Shashenko, Pustovoytenko, & Sdvizhkova,
2016). With the increase in the angle of incidence of the
layer, the delaminated and destroyed layers of the underfilled layer, under the influence of their own weight, tend
to descend downward, promoting the manifestation of
various kinds of loads on the wall-rocks (Zhukov, 2001).
In the conditions of pitch occurrence of coal seams
and on dip at high angles, it is possible to take pressure
on the barring of the haulage gate as an action of the
socle beam, which underwent a fracture in the coal massif (Shashenko, Pustovoytenko, & Sdvizhkova, 2016). In
addition, the condition of the openings is determined by
wall-rock shifts in the long face, resulting in the formation of barring load (Zhukov, 2001; Hoek, 2002; Tajduś, Cała, & Tajduś, 2012).
As the study of wall-rocks shifting and deformation
process (Viktorov, Iofis, & Goncharov, 2005) shows,
when coal is extracted in the faulty strata, formation of
2. METHODOLOGY
At the first stage of the research, in order to study the
periodic character of the rock pressure manifestations in
seam openings and determining the magnitude of the
wall-rocks displacement on their contour, with various
methods of protection, experimental investigations of the
haulage gates competence were carried out in the conditions of the state enterprise “Torez-Vuhol” at the “Toretska” and “Centralna” mines1).
When carrying out experimental observations in the
haulage gate, at specially equipped gauge stations, the
value of the control points shift was established, for the
time interval between the measurements. The scheme of
the experimental section is shown in Figure 1. At a specially equipped gauge station, using the VNIMI tape measure,
the amount of the wall rocks displacement on the haulage
gate contour was determined when the bench marks convergence to each other was determined, according to the
most characteristic directions for pitch and steep-coal
seams. The measurement error did not exceed ±2 mm. The
scheme of the gauge stations is shown in Figure 2.
The investigations were carried out in the haulage
gate driven on layer l3 “Mazurka” horizon of 810 m level
of “Toretska” mine, on a section length l = 70 m, when
the roadway was protected with hardwood chock, and on
a section length l = 100 m, while protecting this roadway
with the pillars of coal.
1
PhD Student A.V. Polozhyi (DonNTU) and engineer A.V. Korol (DTEK)
were involved in the research
10
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
(a)
(a)
vpf
3S
3
L =100 m
Hardwood chock
Crib
(b)
0.4 m
α = 29 o
vr
1
2
4
(b)
vpf
1
hp
3S
L= 100 m
3
lp
Pillars h =8m, l= 5m
2
Figure 1. Scheme of experimental stretches for determination
of wall-rocks displacements on the haulage gate
contour, driven on the seam l3 “Mazurka”, with
protection (a) by hardwood chocks or cribs, (b) coal
pillars: 3S – location of the gauge station; hp, lp –
respectively, the height and width of the pillar, (m)
0.6 m
α=
4
59 o
vr
The cross-sectional area of the roadway, at the moment of the pursuance of the research, was S = 8.2 m2,
the distance between arch timbering frames AP-3 with a
wooden lagging of 0.8 m. The roadway was carried out
with the help of drilling and blasting operations (DBO).
The roadway advance is vr = 10 m/month, productive
workings advance is vpw = 7 m/month. Longwall face was
with a flat back stope. The way to control the roof in
longwall face was to hold on the chocks. The protection
of the roadway was carried out with hardwood chocks,
and after a while, due to the deterioration of the mining
and geological conditions, with the coal pillars, whose
size was h = 8 m, lp = 5 m, where h was the height of the
pillar, m; lp was the width of the pillar, m.
The thickness of a coal seam l3 in the “Toretska” mine
conditions was m = 1.32 m, the angle of incidence of the
seam was α = 29º. In the adjacent strata there was irregular
metal, of medium competence, up to m = 4 m thickness, the
main roof was represented with metal stone, up to m = 10 m
thickness. In the adjacent strata of the coal seam there was
irregular metal, of medium competence, up to m = 1.5 m,
in the main one – irregular metal, up to m = 4.1 m thickness. The advance of the roadway, at the moment of carring out full-scale investigations, was L = 100 m.
Experiments in the “Centralna” mine were carried out
in the haulage gate of seam l3 of 1146 m level in a section length l = 55 m while protecting the roadway with
cribs and in a section that length was l = 78 m when the
roadway was protected with coal pillars.
Figure 2. Schemes of gauge stations for wall-rock displacements determination on the contour of the haulage
gate, driven on seam l3: (a) at 810 m level of the
“Toretska” mine; (b) at the 1146 m level of the
“Centralna” mine; 1,2,3,4 – bench marks; 1 – 3,
1 – 4, 1 – 2, 2 – 3, 2 – 4 – convergence of 1, 2 bench
marks in the direction to 3, 4 bench marks
The cross-sectional area of the roadway was
S = 8.5 m2, the distance between the AP-3 timbering
frames with the wooden lagging is 0.8 m. The roadway
was carried out with the help of the DBO. The roadway
advance was vr = 18 m/month, productive workings advance vpw = 12 m/month. The roadway was protected
with cribs for some time, and then by coal pillars, the
size of which corresponded to h = 8 m, lp = 5 m.
The thickness of coal seam l3 in the “Centralna” mine
conditions was m = 1.17 m, angle of incidence was α = 59º. In
the adjacent strata of the coal seam there was irregular metal,
up to m = 4 m thickness, in the main room was metal stone,
up to m = 7 m thickness. In the ground there was irregular
metal, up to m = 15 m thickness. The advance of the roadway,
at the moment of carring out investigations, was L = 100 m.
When conducting full-scale investigations on experimental stretches, the main attention was paid to the rocks
displacement on the contour of openings under various
protective methods, depending on the distance to the
productive workings, the depth of mining operations and
taking into account the geological conditions.
11
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
pose, measurements of the seam opening width b, (m)
and height h, (m) behind longwall face were made.
Hence, in Figure 4, graphs of the roadway cross-sectional
area change S, (m2) along its length, are given for various
ways of protection, taking into account the face advance.
3. RESULTS AND DISCUSSION
Based on the results of the experimental data processing, the graphs of the rocks displacement on haulage
gate contour of the l3 Mazurka of 810 m level of the
“Toretska” mine were plotted, while it was protected for
l = 70 m with hardwood chocks (Fig. 3a) and l = 100 m
with the coal pillars (Fig. 3b).
2
S, m
(a)
0
0
10
20
30
8.0
40
50
60
2
l, m
1
6.0
100
2-3
200
1-3
1-2
4.0
1-4
2.0
300
400
2.0
U, mm
0
100
200
300
400
500
10 20
30 40
50 60 70
20
40
60
80
100
l, m
Figure 4. Change in the cross-sectional area S, (m2) of the
haulage gate of l3 seam along the length l, (m) on
810 m level of the “Toretska” mine during protection with: 1 – hardwood chocks; 2 – coal pillars
(b)
0
0
80 90 l, m
2-3
It can be seen from the presented dependences that
when the roadway was protected with hardwood chocks,
its section S, (m2) changed from S = 8.2 m2 to S = 6.0 m2
at a distance l = 65 m behind the longwall face, i.е. the
reduction was up to 25%. Subsequently, beyond this
mark, the wall-rocks convergence was not observed
(Fig. 4, 1 dependence).
With the use of coal pillars for protecting the roadway, the cross-section of the roadway S (m2) over the
distance l = 100 m has changed from S = 8.5 m2 to
S = 3.6 m2 (Fig. 4, 2 dependence). In this case, the reduction was up to 60%.
Data from experimental data processing obtained
under the “Centralna” mine conditions, when the haulage
gate, driven on seam l3 of 1146 m level, was protected
with cribs in a section with length l = 55 m and coal
pillars at l = 75 m, are presented in the form of the dependencies depicted in Figure 5.
According to the experimental studies results of bench
marks convergence measurements in the opening, it was
established that the maximum displacements during the
protection of the roadway with cribs were marked at a distance l = 55 m behind the longwall face, in directions 1 – 4
and 1 – 3, when U1 – 4 = 350 mm, U1-3 = 290 mm (Fig. 5a).
When changing the protection method to coal pillars,
bench marks convergence in these directions was, respectively, U1 – 4 = 440 mm, U1-3 = 320 mm, at a distance
l = 75 m behind the face (Fig. 5b).
Analyzing the roadway cross-sectional area change S,
(m2) along the entire length, as the productive workings
advance, it was found that when the seam opening was
protected with cribs, its cross-section decreased from
S = 8.5 m2 to S = 6.8 m2 at the distance l = 55 m behind
the face (Fig. 6, 1 dependence).
1-3
1-2
1-4
U, mm
Figure 3. Rocks displacement U, (mm) on the haulage gate
contour of l3 seam along the length l, (m) at the
810 m level of the “Toretska” mine: (a) when protecting with hardwood chock; (b) when protecting
with the coal pillars
As a result of the full-scale investigations and
mea-surements in the haulage gate of the l3 mine of the
“Toretska” mine, it was established that the maximum
displacement values on the opening contour, when protecting with hardwood chocks, were marked at a distance
l = 70 m behind the face, in directions 1 – 4 and 1 – 2.
At this point, the bench marks convergence value in
these directions was, respectively, U1 – 4 = 340 mm,
U1 – 2 = 250 mm (Fig. 3a).
When protecting the roadway with coal pillars, the
maximum displacements were recorded at a distance
l = 100 m behind the longwall face, in directions
1 – 4 and 1 – 2. In quantitative terms, the displacement in
the direction of the bench marks 1 – 4 was
U1 – 4 = 440 mm, in the direction of the bench marks 1 – 2
was U1 – 2 = 300 mm (Fig. 3b).
Simultaneously, with the recording of bench marks
convergence on the contour of the opening, as the
longwall face advanced, a change in the cross-sectional
area of the roadway S (m2) was recorded. For this pur12
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
the reduction in the cross-sectional area S, (m2) in the
first case was 20%, in the second case was about 35%.
As a result of the carried out studies, it was established that the largest displacements, taking into account
the protection methods of the haulage gates used in the
mines, were fixed by the bench marks, from the side of
the roof rocks. It is characteristic that the displacements
on the hanging side, in all cases, were represented by
ground lit-by-lit flexure. Irregular metal, lying in the
rocks of adjacent strata, under the influence of the bearing pressure, was broken by a series of fractures, as a
result of which, in some cases, there was rocks rush in
the roadway. It was noted that the roof-lowering can stop
at a different distance from the face in the direction of the
mined-out space. This is due to the type of protective
facilities, when protecting the openings with timber constructions, behind the mark l = 50 m behind the face, the
wall-rock displacements practically fade and stabilize. In
the case of protection openings with coal pillars, such a
pattern can not be in evidence. Nevertheless, the nature of
wall-rocks displacement on the opening contour, with the
removal from the face in the mined-out space direction,
has the same qualitative picture, but differs in intensity.
Depending on the face position, the cross section of
the roadway was reduced due to the delaminated rock
strata pressure on the barring. The most intensive rocks
pressure on the roadway barring occurs from the adjacent
strata in a direction close to the normal toward the formation. The opening barring was deformed specifically
from the hanging side, it is inherent in the roadway haulage level. From the foot wall side, i.e. ground of the developed coal seam, deformations are insignificant. However, in case of protection with coal pillars, the ground
displacement increased by 25 – 30%, in comparison with
the use of timber constructions as a protective facility.
Apparently, without rejecting the principal possibility
of improving the roadway condition by increasing the
load-bearing strength of the barring, still the main direction ensuring the safety of the workings in an operational
condition that meets the preventive regulations in difficult mining and geological conditions should be considered the search for more reliable and constructively
simple ways to protect the haulage gates.
Because of the complexity of mining and geological
conditions for the coal seams development, in a coal-rock
mass containing openings, mining operations, geomechanical situations having negative impact on the rocks
state occur. To ensure their continuity, as well as the
safety of mine workings, in practice, various methods of
protection are used, the effectiveness of which depends
on the competence of the physical and mechanical system “coal seam – side rocks – protective facilities”. To
minimize the negative rock pressure manifestations in the
vicinity of the supported haulage gate, it is recommended
the use of yieldable protective facilities (Iordanov et al.,
2018). In this case, in the presence of yieldable links in
the physical-mechanical system, protective facilities
designed to support wall-rocks behind the face must have
a hardness rate – the modulus of elasticity, as well as the
springs (Yakobi, 1987; Das et al., 2017).
Therefore, in the second stage of the research, we use
the displacement method and the method of forces (Ikrin,
(a)
0
0
10
20
30
40
50
60
70
l, m
2-4
100
2-3
200
300
1-3
1-4
400
500
U, mm
(b)
0
0
10
20
30
40
50
60
70
100
l, m
2-4
2-3
200
300
1-3
400
1-4
500
U, mm
Figure 5. Rocks displacement U, (mm) on the haulage gate
contour of l3 seam along the length l, (m) at 1146 m
level of the “Centralna” mine: (a) when protecting
with cribs; (b) when protecting with coal pillars
2
S, m
2
8.0
1
6.0
4.0
2.0
2.0
0
20
40
60
80
100
l, m
Figure 6. Change in the cross-sectional area S, (m2) of the
haulage gate of l3 seam along the length l, (m) at
1146 m level of the “Centralna” mine during protection with: 1 – cribs; 2 – coal pillars
When using coal pillars, the section of the roadway S,
(m2) has changed from S = 8.6 m2 to S = 5.5 m2 over
l = 75 m (Fig. 6, 2 dependence). It should be noted that
13
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
2004) to determine the hardness influence of the applied
protective facilities on the openings state and the analysis
of the geomechanical situation in the vicinity of the supported roadways. Applied to the problem being solved,
we consider the roof rocks displacement of the developed
coal seam to be the largest displacement, when the
movement of the 1 bench mark in the direction to the
4 bench mark was fixed on the haulage gate contour,
when it was protected with timber constructions
(hardwood chock, cribs) or coal pillars. Then the coupling equation in the system under consideration, taking
into account the fact that the applied unit force in the
direction of the largest displacements has the form:
С=
1
,
U1−4
(a)
6
5
1
C, N/ m
4
2
3
2
1
0
0
10
20
30
40
(1)
50 60
l, m
70
80
90 100
(b)
6
where:
U1 – 4 – convergence of the 1 bench mark in the direction to the 4 one, m.
According to (1), we can conclude that the hardness
C, (N/m) reflects the ability of protective facilities to
resist deformation under external influence and depends
on the static displacement, in the case under consideration, the displacement of the adjacent strata rocks along a
line perpendicular to the strata. Meanwhile, in calculating
the wall-rocks and mine workings competence, we can
introduce the assumption that the movement of the body
point at any time of the static loading is the same as under the action of a dynamic loading (Rusakov, 2003).
Deformation of protective facilities consists of elastic
and residual parts. Depending on the possible magnitude
of the latter, we can talk about the plasticity or brittlity of
the protective facility (Sokolovskiy, 1969).
Figure 7a, b shows the dependences reflecting the
change in the hardness C, (N/m) of hardwood chocks (a)
and coal pillars (b), as the productive workings advance
under the conditions of the “Toretska” mine.
Analogous dependencies were obtained for the conditions of the “Centralna” mine, when cribs and coal pillars
were used for the haulage gate protection. The results of
the studies are shown in Figure 8a, b.
For yielding protective facilities, plastic deformation
is typical, with a smooth increase in their reaction to the
maximum value. In these cases, the angled graph arm,
depicted in Figures 7a and 8a, characterizes the convergence of the wall-rocks, when compression of protective
facilities occurs for a certain period of time. Having depleted its yielding and reached a certain amount of hardness, equal to C = 2.75 N/m (Fig. 7a) and C = 2.9 N/m
(Fig. 7b) at a distance l = 50 m behind the longwall face,
conditions are created when in the zone of steady-state
rock pressure, the convergence of the wall-rocks is not
observed, and the roof-lowering has reached a maximum
value (Fig. 7a, 8a).
It is known (Das et al., 2017) that the strength and deformation properties of the coal pillar are determined by
the presence of defects in it and their characteristics.
As a result of the experimental studies, it was established
that the magnitude of the coal pillar hardness under the conditions of the pitch coal seams occurrence (“Toretska”
mine) varies from C = 5.8 N/m at a distance l = 10 m behind
the face, to C = 3.0 N/m at a distance l = 70 m (Fig. 7b).
5
C, N/m
4
1
2
3
2
1
0
0 10 20 30 40 50 60 70 80 90 100 110 120 130
l, m
Figure 7. Changes in hardness C, (N/m) of protective facilities along the haulage gate length l, (m) behind
the longwall face in the “Toretska” mine under
protection: (a) hardwood chocks; (b) coal pillars;
1 – experimental data; 2 – dependencies after treatment 1 (R2 = 0.92)
In the conditions of dip at high angles of the strata
(“Centralna” mine), the change in the pillar hardness is
C = 10 N/m at l = 10 m, and C = 2.1 N/m at a distance
l = 70 m (Fig. 8b). In the first case, the reduction in hardness is about 50%, in the second one is about 75%. With
the further advance of the face, under the conditions of
the “Toretska” mine, the pillar hardness was reduced to
C = 2.15 N/m, at a distance l = 100 m (Fig. 7b), which
led to a decrease in the investigated value by 65%.
Taking this into account, Figure 9 shows the linear dependencies presenting the change in P, (%) of the coal
pillar hardness along the length l, (m) of the haulage gate.
Correlation of the experimental data presented in the
form of the dependencies depicted in Figure 9 allows
determining the change in the hardness of the brittle
protective facilities along the length of the haulage gate,
taking into account the external force. In the cases under
consideration, between the convergence of the wall-rocks
and the change in the pillars hardness, there is a linear
dependency; the nature of the change depends on the
mining and geological conditions of the coal seam development (Fig. 9).
In a rock-fracture zone, the pillar is in the limit stressdeformed state and its load-bearing strength is insufficient to support the underworked seams (Protosenya &
Verbilo, 2017). In such conditions, the protective coal
pillars are prone to destruction and eruption.
14
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
l = 50 – 60 m behind the longwall face, as well as a decrease in the cross-sectional area of the opening.
The experience of mines on layers with complex mining and geological conditions showed that in some
cases, where timber constructions (hardwood chock,
cribs) were laid to protect the haulage gate, still there
were roof collapses. Analysis of such situations made it
possible to establish that this was due not only to mining
and geological, but also to technical factors. The latter
should be attributed to the inconsistency of the methods
used to protect mine workings and roof management, the
particular exploitation conditions.
DonUGI and DonNTU studies previously found that
the filling mass prevents the development of intensive
fracturing in the vicinity of the mine workings and
creates zones of hard ground, in the worked out space,
behind the face. At the same time, for various reasons,
the method of complete goaf stowing is not currently
applied, although its implementation eliminated the collapse of the adjacent and caving of the main roof, as well
as the displacement of the bedrock.
In view of the foregoing, in order to study the negative manifestations of rock pressure in a coal-rock mass
containing workings, studies were conducted on cloudy
crystal ball models. The purpose of such studies was to
determine the initial qualitative picture of tangential
stresses distribution, at which comparatively smaller
negative manifestations of the rock pressure in the haulage gate should be expected when it is protected with
rock walls of different hardness or with the coal pillars.
Investigation of the stress-deformed state of the rock
massif in the vicinity of the haulage gate was carried out
using cloudy crystal ball model of igdantine using the
photoelastic method (Stepanova & Dolgih, 2017) in the
DonNTU rock pressure laboratory. The simulated depth
corresponded to H = 1200 m, the seam inclination was
α = 60°, the thickness of the coal seam was m = 1 m. The
thickness of the adjacent and main roof rocks corresponded to 5 m, where m is the thickness of the coal
seam, (m). The rocks of the adjacent roof and ground in
their properties corresponded to rocks such as irregular
metal of medium competence, rocks of the main roof and
ground corresponded to metal stone of medium competence. Three models were tested. The thickness of the
models was 40 mm. The scale of the simulation corresponded to M1:100. Simulation is performed in accordance with recommendations (Surendra & Simha, 2015;
Alsiya, Lekshmi, Priya, & Mehta, 2016). The physical
and mechanical properties of the coal pillar and the rock
wall in the model corresponded to the actual samples.
In models, the filling material of the rock wall was
modeled with foam rubber. To impart hardness to such a
material, the foam for a while was placed in a paraffin
solution and held in it for t = 1 s and t = 3 s. The magnitude
of the rock wall yielding property was determined according to recommendations (Shakirzyanov & Shakirzyanov,
2005), using the method of photographic fixation (Obiralov, Limonov, & Gavrilova, 2004). The results of the
studies are presented in Table 1. The photoelastic method
makes it possible to establish an initial picture of stress
distribution in a place that is formed in the wall-rocks in
the first period of time after the coal is extracted.
(a)
6
5
1
C, N /m
4
2
3
2
1
0
0
10
20
30
l, m
40
50
60
(b)
12
10
C, N/ m
8
1
6
2
4
2
0
0
10
20
30
40
50
60
70
80
l, m
Figure 8. Changes in hardness C, (N/m) of protective facilities along the haulage gate length l, (m) behind the
longwall face in the conditions of the “Centralna”
mine during protection: (a) cribs; (b) coal pillars;
1 – experimental data; 2 – dependencies after
treatment 1 (R2 = 0.92)
100
C, N/m
80
1
60
2
40
20
0
0
10
20
30
40
l, m
50
60
70
80
Figure 9. Changes in the coal pillar hardness P (%) along the
length of haulage gate l (m): 1 – “Toretska” mine;
2 – “Centralna” mine; ▪, • – experimental values
(R2 = 0.91)
This leads to the formation of openings above the
roadway, a significant decrease in the pillar hardness
and, consequently, the loss of the cross-sectional area of
the formation haulage gate when it is maintained in the
mined-out space, i.e. behind the face.
This fact is confirmed by studies of the formation
haulage gate condition, protected by the coal pillars under the conditions of the “Centralna” mine, when a sharp
destruction of the pillar and the adjacent strata of the
developed coal seam was recorded behind the mark
15
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
Table 1. Data of laboratory studies of the rock wall hardness
determination
Time,
t, (s)
1s
3s
Simulation
variant
Yielding
capacity,
(m)
Hardness,
С, (N/m)
1
2
3
4
5
1
2
3
4
5
0,028
0,03
0,029
0,03
0,029
0,011
0,011
0,011
0,012
0,011
35
33
34
33
34
84
85
85
83
84
(a)
0.5
Average
value
of hardness
С, (N/m)
0.5
0
0.5
,
0.5
0.5
0.5
0.5
,
0.5
0.5
0
0,
0.5
0
00
34
0
0.5
0,5
0.5
0,
0.5
0,5
0,5
0.5
0,5
0.5
0,5
0.5
0,5
0.5
0,5
0.5
85
0,5
,0.5
0,5
0.5
0.5
0,5
0,5
0.5
0,5
0.5
0,5
0.5
(b)
The method is based on the transmission by a parallel
light beam of the model, when the lines of the greatest
tangential stress action are identified on the screen
(Surendra & Simha, 2015; Alsiya, Lekshmi, Priya, &
Mehta, 2016).
When using the photoelastic method in the problem
being solved, it is considered (Baklashov, 2004) that the
stress concentration leads to creepages, and in the course
of time, in the places of compressive and tensile stresses
concentration the destruction of the subside massif takes
place. This is confirmed by an earlier analysis of the
mechanical processes taking place in a coal-rock mass
with mining workings, when the stress state of the rocks,
as far as the distance from the development contour,
changes from a state close to the general extension and
displacement to a compression state in the depth of the
massif (Norel, 1983).
The simulation results are shown in Figure 10 and
11a, b. Analysis of the static field of tangential stresses
indicates that when protecting the roadway with the coal
pillars, we have the maximum concentration of stresses
in the roof rocks and ground, and also in the vicinity of
the haulage gate (Fig. 10).
0.5
, 0,
1.0
00
1.0
0.5
0.5
0,5
0.5
2.0
,
1.0
2.0
,
,
1.5
1.0
1.5
0,5
0.5
0,5
0.5
11.0
,0
1,0
1.0
1,0
1.0
1,5
1.5
11.5
,5
1,5
1.5
1.5
1,5
0,5
0.5
11.0
,0
0.5
0,50,5
0.5
0.5
0,5
1,,0
1.0
0,5
0.5
0,5
0.5
11.0
,0
11.0
,0
0,5
0.5
0,5
0.5
0,5
0.5
0,5
0.5
Figure. 11. Static field of tangential stresses in the vicinity of
the haulage gate in the method of the mining pressure controlling in face with goaf stowing: (a) with
the filling mass hardness C = 35 N/m; (b) the same,
C = 84 N/m
Coal pillar is a brittle body and is a classic object of
linear fracture mechanics. In the linear fracture mechanics, brittle failure is viewed from the standpoint of the
accumulation mechanism of damages and fractures
growth (Karkashadze, 2004).
While pillar loading is applied to the moment of displacement, the accumulation of loads in it occurs according to linear fashion, with relatively small deformations
(Khani, Baghbanan, Norouzi, & Hashemolhosseini, 2013;
Fekmistov & Golovin, 2015). Apparently, the greater the
load-bearing strength and hardness of the protective facilities, all other things being equal, the more destructive
efforts are exerted on the rocks of the adjacent strata at the
places of overstress that are formed due to the contact of
the nonyielding facility with the wall-rocks (Fig. 10).
The foregoing negative geomechanical features of
rocks performance are reduced to the minimum in the
method of roof control with goaf stowing. The modeling
data show that the use of a filling mass for roof rocks
maintenance, reduces the concentration of stresses in the
coal-rock mass. However, the hardness of the filling mass
has a significant influence on the stress level (Fig. 11a, b).
1.0
0.5
0.5
1.5
1.5
1.0
0
1.0
0.5
0.5
0,5
0.5
0,5
1.5
1.5
,
0,5
0.5
0,5
0.5
0,5
0.5
0.5
,
1.0
1,0
0,5
0.5
,
0.5
0.5
11.0
,0
0.5
0,5
0.5
,
0.5
0,5
0.5
,
1.0
1.0 1.0
0.5 1.0 0.5
Figure 10. Static field of tangential stresses in the vicinity of the
haulage gate during protection of the coal pillars
16
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
When comparing the original qualitative picture of the
tangential stresses distribution in a coal-rock mass containing workings, while protecting the haulage gate with
goaf stowing, we have less negative manifestations of
rock pressure than when it is protected with coal pillars.
Coal pillars are brittle protective facilities, the change
in hardness of which occurs according to a linear law,
taking into account the mining and geological conditions
of the developed coal seam. As a result of the effect on
these seats of external force, after the destruction their
hardness decreases, which contributes to a sharp deterioration in the competence of the haulage gate behind the
longwall face.
The hardness of the filling mass determines the level
of stress concentration in the wall-rocks. Reduction of
this value by 2.5 times leads to minimum values of
stresses in the coal-rock mass, when we have a gentle
deflection of the wall-rocks along the entire length of the
longwall face. At the same time, the area of actual contact of subside rocks with a rock walls does not change,
and only stresses redistribution at the boundary of contact between wall-rocks and the filling mass occurs. In all
cases, in the protection of seam opening with rock walls,
the barring in the haulage gate is uniformly deformed
(Fig. 11a, b). It follows that the most favorable for the
mining workings state located in a sedimentary rocks
massif, in terms of stress distribution, is influenced by
the method of roof control with goaf stowing.
In a coal-rock mass with mining workings, the underworked and delaminated seam roof rocks, which are a
block mass consisting of beams of different length, uncontrollably subside behind the productive workings, creating
an unfavorable geomechanical situation in the vicinity of
the shored up openings. Unexpected appearance of such
situations contributes to the negative dynamic loads manifestation and it is one of the seams development features
with yielding wall-rocks. In order to minimize rock pressure negative manifestations, it is necessary to ensure the
effective of the coal roof rocks maintenance.
Experimental studies of the flexural modes of the
simulated beam were conducted to study the competence
of the coal roof, which was represented in the form of a
socle beam, which was supported behind a filling mass
of various hardness, under the influence of instantaneous
loads in such conditions, in the form of sudden wallrocks collapses, in the DonNTU rock pressure laboratory
on models of equivalent materials (Iordanov et al., 2018).
As a result of the studies carried out, it was found that
the filling mass, whose cavitation is M ≤ 6% at the
maximum loose density, is a hard base for the delaminated roof rocks, and the latter, with the action of external
force, are more yieldable to destruction. It is evident, that
to ensure the operational status of seam openings, using a
filling mass of the mined-out space, certain requirements
must be imposed on the filling mass. In particular, for the
normal functioning of the system under consideration, it
is necessary that the filling mass consisted of a nonhomogeneous particles of the loosened rock or had a cavitation M = 7 – 20% with a decrease in the loose density.
When these conditions were fulfilled, the integrity of the
modeled strata beam was ensured when an external force
was applied to it.
Thus, in accordance with the results of the studies
performed, it can be stated that in order to ensure the
operational state of seam openings in difficult mining
and geological conditions, when the requirement to effective wall-rocks maintaining of the developed coal
seam behind the longwall face along the haulage gate
was be regarded, application of wide yielding seat or
goaf stowings as protective facilities would be reasonable. Protective facilities of this type provide sufficient
overpressure to the subside rocks of the hanging wall and
their gentle deflection behind the longwall face, in the
mined-out space.
4. CONCLUSIONS
As a result of carried out experimental studies on the
wall-rocks displacement nature on the contour of seam
openings under various methods of protection, the effectiveness of the latter was assessed by changing the condition of the roadway, taking into account the hardness of
the protective facilities. In order to ensure the operational
status of haulage gates, in difficult mining and geological
conditions, it is necessary to focus on the use of a goaf
stowing as a method of rock pressure or wide yielding
protective facilities control, which will make it possible
to maintain effectively and gentle deflection of the wallrocks behind the face, along the length of the openings.
ACKNOWLEDGEMENTS
The authors are grateful to the staff of the 10th VGSO
Minvuhleprom of Ukraine and the technical directorate
of SE “Torez-Vuhillia” for their assistance in conducting
experimental studies.
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ЕКСПЕРИМЕНТАЛЬНІ ДОСЛІДЖЕННЯ СТІЙКОСТІ
ПІДГОТОВЧИХ ВИРОБОК ПРИ РІЗНИХ СПОСОБАХ ОХОРОНИ
В УМОВАХ ПОХИЛИХ І КРУТИХ ВУГІЛЬНИХ ПЛАСТІВ
Я. Ляшок, І. Іорданов, Д. Чепіга, С. Подкопаєв
Мета. Дослідження стійкості пластових підготовчих виробок при різних способах охорони у складних гірничо-геологічних умовах розробки похилих і крутих вугільних пластів Донбасу.
Методика. Для досягнення поставленої мети в дослідженнях використовується комплексний підхід, що
включає аналіз і узагальнення досвіду охорони підготовчих виробок, вивчення статичного поля розподілу напружень у вуглепородному масиві на оптичних моделях, шахтний експеримент із вивчення стійкості відкаточних штреків та обробку експериментальних даних.
Результати. При вивченні зсувів бічних порід на контурі відкаточного штреку зафіксовано, що в разі використання для охорони пластових підготовчих виробок піддатливих охоронних споруд, конвергенція покрівлі й
підошви вугільного пласта, який розробляється, в міру посування очисного забою спостерігається до повного
стиснення охоронної споруди, а в зоні сталого гірського тиску практично згасає. У разі використання для охорони штреків ціликів вугілля після руйнування їх жорсткість змінюється за лінійним законом, що сприяє значному погіршенню стійкості відкаточного штреку позаду очисного вибою. Застосування закладання виробленого
простору для охорони пластових підготовчих виробок, з точки зору розподілу напружень у вуглепородному масиві, забезпечує плавний прогин бічних порід позаду очисного вибою за рахунок збільшення площі фактичного
притискання товщі, що опускається, до закладного масиву, при порівнянні з охороною штреків ціликами вугілля.
Наукова новизна. Ефективність застосовуваного способу охорони пластових підготовчих виробок пропонується оцінювати за зміною стійкості відкаточного штреку, але з урахуванням жорсткості охоронних споруд.
Жорсткість охоронних споруд відображає їх здатність чинити опір деформації при зрушенні розшарованної
породної товщі й залежить від значення зовнішньої сили, фактору часу та гірничо-геологічних умов розроблюваного вугільного пласта.
Практична значимість. Застосування закладання виробленого простору, як способу управління покрівлею
або широких піддатливих опор, розташованих над штреком, дозволить забезпечити експлуатаційний стан відкаточних штреків і підвищити безпеку робіт при підтриманні підготовчих виробок.
Ключові слова: відкаточний штрек, зміщення, цілик, охоронні споруди, закладання виробленого простору,
розшарування бічних порід
18
Ya. Liashok, I. Iordanov, D. Chepiga, S. Podkopaiev. (2018). Mining of Mineral Deposits, 12(4), 9-19
ЭКСПЕРИМЕНТАЛЬНЫЕ ИССЛЕДОВАНИЯ УСТОЙЧИВОСТИ
ПОДГОТОВИТЕЛЬНЫХ ВЫРАБОТОК ПРИ РАЗЛИЧНЫХ СПОСОБАХ
ОХРАНЫ В УСЛОВИЯХ НАКЛОННЫХ И КРУТЫХ УГОЛЬНЫХ ПЛАСТОВ
Я. Ляшок, И. Иорданов, Д. Чепига, С. Подкопаев
Цель. Исследование устойчивости пластовых подготовительных выработок при различных способах охраны в сложных горно-геологических условиях разработки наклонных и крутых угольных пластов Донбасса.
Методика. Для достижения поставленной цели в исследованиях используется комплексный подход, включающий анализ и обобщение опыта охраны подготовительных выработок, изучение статического поля распределения напряжений в углепородном массиве на оптических моделях, шахтный эксперимент по изучению
устойчивости откаточных штреков и обработку экспериментальных данных.
Результаты. При изучении смещений боковых пород на контуре откаточного штрека зафиксировано, что в
случае использования для охраны пластовых подготовительных выработок податливых охранных сооружений,
конвергенция кровли и почвы разрабатываемого угольного пласта по мере подвигания очистного забоя наблюдается до полного сжатия охранного сооружения, а в зоне установившегося горного давления практически затухает. В случае использования для охраны штреков целиков угля после разрушения их жесткость изменяется
по линейному закону, что способствует значительному ухудшению устойчивости откаточного штрека позади
очистного забоя. Применение закладки выработанного пространства для охраны пластовых подготовительных
выработок, с точки зрения распределения напряжений в углепородном массиве, обеспечивает плавный прогиб
боковых пород позади очистного забоя за счет увеличения площади фактического касания опускающейся толщи с закладочным массивом, при сравнении с охраной штреков целиками угля.
Научная новизна. Эффективность применяемого способа охраны пластовых подготовительных выработок
предлагается оценивать по изменению устойчивости откаточного штрека, но с учетом жесткости охранных
сооружений. Жесткость охранных сооружений отражает их способность сопротивляться деформации при
сдвижении расслоившейся породной толщи и зависит от значения внешней силы, фактора времени и горногеологических условий разрабатываемого угольного пласта.
Практическая значимость. Применение закладки выработанного пространства, как способа управления
кровлей или широких податливых опор, расположенных над штреком, позволит обеспечить эксплуатационное
состояние откаточных штреков и повысить безопасность работ при поддержании подготовительных выработок.
Ключевые слова: откаточный штрек, смещения, целик, охранные сооружения, закладка выработанного
пространства, расслоение боковых пород
ARTICLE INFO
Received: 3 May 2018
Accepted: 2 October 2018
Available online: 12 October 2018
ABOUT AUTHORS
Yaroslav Liashok, Doctor of Economic Sciences, Rector of the Donetsk National Technical University, 2 Shybankova Ave.,
85300, Pokrovsk, Ukraine. E-mail: iaroslav.liashok@donntu.edu.ua
Ihor Iordanov, Candidate of Technical Sciences, Associate Professor of the Department of Mineral Deposits, Donetsk
National Technical University, 2 Shybankova Ave., 85300, Pokrovsk, Ukraine. E-mail: gendir@eme.kiev.ua
Daria Chepiga, PhD Student of the Department of Mineral Deposits, Donetsk National Technical University,
2 Shybankova Ave., 85300, Pokrovsk, Ukraine. E-mail: daria.chepiha@donntu.edu.ua
Serhii Podkopaiev, Doctor of Technical Sciences, Professor of the Department of Mineral Deposits, Donetsk National
Technical University, 2 Shybankova Ave., 85300, Pokrovsk, Ukraine. E-mail: serhii.podkopaiev@donntu.edu.ua
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