Integrated research into the stress-strain state anomalies, formed and developed in the mass under conditions of high advance velocities of stope faces

This paper studies the ways of solving the resource-saving direction of the strategy for the mining industry development in Ukraine. The existing ideas about the patterns of changing stress-strain state (SSS) in the mass during the stope mining of minerals are analyzed. The problem of the host rock SSS formation and development is studied. The main directions of studying the relationship between the parameters of mass SSS anomalies in the area of stope operations and their technological parameters has been substantiated with the selection of a methodology for conducting multivariate computational experiments. A macromodel has been constructed to calculate the change in the distribution fields of the rock mass SSS components with subsequent substantiation of its idealizations. The principles of matching the macromodel and the subordinate models have been studied. A new methodical approach is proposed for taking into account the time technological parameters (average daily face advance velocity and the duration of its stoppage) through their relationship with the mechanical characteristics of the rocks. A test assessment of the adequacy of the performed calculations based on the spatial model SSS analysis for all stress components has been conducted. The degree of influence of the stope face advance velocity and the mass texture on the parameters of rock pressure anomalies has been studied, as well as the linking patterns in the area of conducting stope operations have been obtained: frontal and lateral bearing pressure zones and a zone of destressing behind the stope face. A base has been created for studying and predicting the rock pressure manifestations in critical areas in order to develop recommendations for choosing rational technological and design parameters for high-rate mining of coal seams.


Introduction
At present, the strategy for the development of the Ukrainian coal industry should be aimed at ensuring high-rate mining and, consequently, the use of high-performance stope equipment.In this regard, the problem of effective supporting of mine workings in the zone of stope operations influence, as well as their reuse, becomes relevant.A comprehensive solution to this issue provides a resource-saving focus on mining operations.
The patterns of changes in the coal-bearing mass state as the stope face approaches and retreats have been studied for many decades.Thus, certain ideas [1][2][3][4][5] about the parameters of 1254 (2023) 012062 IOP Publishing doi:10.1088/1755-1315/1254/1/012062 2 SSS anomalies depending on the mining-geological and mining-technical conditions for mining coal seams have been developed by now.There is no doubt that there are three main zones of the anomalous state of the coal-bearing mass around the stope workings and associated with them extraction drifts: • frontal bearing pressure zone ahead of the face, where the vertical stress σ y concentration is several times higher than the initial state of the undisturbed rock mass σ y = γH (here σ y -vertical stresses; H -mining depth; γ -weight-average unit specific gravity of coaloverlaying formation); • zone of lateral bearing pressure that occurs in the side of the extraction drifts from the side of undisturbed rock mass; here, also, the vertical stress σ y concentration is several times higher than the initial undisturbed rock mass state; • destressing zone behind the stope face, which occurs when a cavity is formed after coal mining, into which the roof rock layers are lowered and then collapse; in this zone, vertical stresses can almost completely disappear (σ y = 0) near the stope face, and as it retreats, the collapsed rocks are compacted and the rock pressure increases with stabilization at a certain distance at the level of the initial undisturbed rock mass state.
The parameters of the specified SSS rock mass anomalies usually include two interrelated indicators: the value of vertical stress concentrations K y = γH and the distance of their propagation in the plane of coal seam bedding.Index "i" denotes a family of concentrations K y (y is the vertical coordinate of the mass) of different values, which quite naturally propagate to different distances l y .
The noted parameters depend on the mining-geological indicators of mining the coal seams, as indicated by numerous studies, for example, [6][7][8][9][10][11][12][13][14] in different periods of the coal mining industry development both in Ukraine and in other countries.Among the influencing mininggeological factors (in addition to the mining depth) are, first of all, the mass texture, taking into account the existing discontinuity and the mechanical characteristics of the rock layers at a distance of at least 20 m to the roof and bottom from the seam [15].One of the main patterns of formation of anomalous SSS zones is considered to be determined, the essence of which is as follows: • the occurrence in the roof of more thick (from 3 -5 m and more) and increased hardness (hardness coefficient according to Protodyakonov scale is f ≥ 5-6) rock layers increases the propagation l y i of frontal and lateral bearing pressure zones with a simultaneous increase in vertical stress concentrations K y near stope faces and in the side of the extraction drift from the side of the undisturbed rock mass; • the same parameters of lithotypes occurring in the seam roof contribute to a deeper destressing of the mass above the stope face and behind it -the distance l y i of almost complete destressing (σ y = 0) increases, as well as the length of the rock pressure stabilization area at the level of the undisturbed rock mass initial state; • various types of discontinuity in the roof rocks (fracturing, small-amplitude breaks) act in the opposite direction of influence: the zones of frontal and lateral bearing pressure reduce their propagation in the bedding plane, and the vertical stress concentrations decrease; in the destressing zone, the length of areas of minimum rock pressure propagation, as well as the length of areas of rock pressure stabilization are reduced; • more thin-bedded and less strong rock layers of the roof cause tendencies similar to the action of various types of their discontinuity.
The noted tendencies for the same region or even the mine field flank are clearly manifested when measuring in the extraction drifts such indirect indicators as the convergence value of the roof and the bottom rocks in the mine working, as well as in its sides.As an example, figure 1 shows graphs (constructed based on the results of measurements) of changes in the drift contour displacements as the stope face advances for two roof rock textures: predominantly thick-bedded and medium-bedded; predominantly thin-bedded and medium-bedded.Moreover, the measurements were carried out in the same driven entry of the seam C 6 , Stepova Mine of PJSC DTEK Pavlohradvuhillya, where both types of roof rock textures are present in the length of the extraction site.As it can be seen from the graphs, with a thick-bedded texture, the frontal bearing pressure zone extends ahead of the stope face up to a 1 = -73 m in terms of the convergence of roof and bottom rocks U R,B and up to C 12 = -73 m in terms of the convergence of the drift sides U s .In the area of predominantly thin-bedded and medium-bedded texture of the roof rocks, the length of the frontal bearing pressure zone is significantly reduced: a 2 = -33 m (by 2.21 times) C 2 = -47 m (by 1.55 times).A similar situation is behind the stope face with regard to the stabilization distance of rock pressure manifestations.Thus, with a predominantly thick-bedded and medium-bedded texture of the roof rocks, the length of the area in terms of the parameter U R,B is 104 m, in terms of the parameter U s , the distance increases to d 1 = 124 m.In the area (in length of the mine working) with a predominantly thin-bedded and medium-bedded texture, these indicators are reduced: b 1 = 36 m (by 2.89 times); d 1 = 72 (by 1.72 times).
These patterns are typical for various mining-geological conditions and Donbass regions [16][17][18][19][20][21]; therefore, they should be considered as sufficiently objective and taken into account in further studies.Among the variety of technological factors, two are distinguished [22][23][24][25][26], which combine a significant influence, on the one hand, and, on the other hand, are amenable to regulation in the process of stope operations: the average daily velocity V d of the stope face advance and the duration t of its stoppage.
Thus, the presence of a significant influence of technological parameters (the velocity V d of the stope face advance and the duration t of its stoppage) of mining the coal seam on the formation of the load on the powered support sections of the stope complex has been experimentally confirmed.The load itself is inextricably linked with the parameters of the SSS anomalies around the stope face, and for this reason, it can be concluded that there is interrelation between the distribution curves of the stress components in the vicinity of the stope face and the specified technological parameters of the coal seam mining.Determining the linking patterns in a numerical form is quite a difficult task due to the influence of many different factors.But, the relevance of studying this problem is undeniable: after all, the experimental results in the Western Donbass convincingly prove a decrease in the rock pressure manifestations by 23 -47 per cent only due to a change in the velocity of the stope face advance, and this decrease increases the safety of mining operations and equipment life, thereby reducing the probability of accidents.
To date, two main ways have been formed to study the interrelation between the parameters of mass SSS anomalies in the area of stope operations and their technological parameters: • full-scale experiments for measuring indirect rock pressure indicators and their analysis in order to determine the linking patterns; • analytical research with the predominant use of numerical methods is the so-called computational experiment.
In this regard, many researchers use a combination of the above methods, for example, [27][28][29] which is justified by the desire to obtain more reliable results.Undoubtedly, the parameters of SSS anomalies and indicators of rock pressure manifestations are interrelated, and the nature of these relationships is revealed by a set of ideas about the mechanism of a coal-bearing mass displacement in the area of mining operations.
Thus, it seems the most appropriate way to solve the problem of studying the formation and development of SSS anomalies in the mass, which is substantiated by a three-stage structurallogical scheme: mine instrumental observations of the rock pressure manifestations in stope faces and extraction drifts; computational experiments to calculate the surrounding mass SSS and a linking element -the mechanism of rock displacements in the coal-overlaying formation, revealing the influence of the stope face advance velocity and the duration of its stoppage.

Substantiating the methodology for conducting multivariate computational experiments
To date, rich experience has been accumulated in measuring the indicators of rock pressure manifestations in various mining-geological conditions [30][31][32].
The main attention is paid to the substantiation of the methodology for modeling different velocities V d of the stope face advance as the primary stage; further, the results of the mass SSS calculations are analyzed in conjunction with the parameter V d and the patterns of its influence on the indicators of rock pressure anomalies in the vicinity of the stope face are determined.
When substantiating the methodology for conducting a computational experiment, we had to face a number of factors, the objective reflection of which in geomechanical models is conditioned by significant difficulties.
Firstly, the model of a stratified rock mass with two conjugated mine workings located in it (stope face and an extraction drift) is characterized, in addition to its extensive dimensions in space (figure 2), by a combination of significant heterogeneity of the geometric, mechanical and strength parameters of the elements that constitute this model.Thus, only the model of one rock mass includes a sufficiently large number of rock layers of the roof and bottom in the coal seam, differing from each other in mechanical properties.The strength characteristics of contacts of adjacent lithotypes for the Western Donbass conditions [33][34][35], as a rule, are very low, or there is no adhesion along the bedding planes at all.In addition, the research object is located in the zone of active influence of stope operations, where, along with significant vertical displacements of the coal-bearing mass, significant movements occur in the horizontal direction of the rock layers relative to each other.The noted facts make it possible to predict the destruction of contacts between adjacent rock layers, and this leads to a significant change in the distribution fields of the rock mass SSS components [36].In addition to these factors, it is also necessary to take into account the processes of weakening the rock layers (occurrence of tension cracks, partitioning into blocks and their partial caving into the mined-out space).More intense fracturing [37] and the occurrence of the so-called thrust-block systems in the roof increases their deformation capacity for more significant displacements, and rocks caved into the mined-out space radically change their mechanical characteristics [38][39][40].These factors have been sufficiently tested using modern methodologies for modeling geomechanical processes [41,42].
Secondly, it is necessary to more adequately and reliably represent the real mining-technical conditions of mining operations and to model in detail the objects for supporting mine workings (support of a stope face and extraction working, security structure, etc.) in accordance with their design and technological peculiarities.Each of these objects includes a set of elements with complex geometry, significant heterogeneity of mechanical properties and strength parameters.In this case, one of the main difficulties is the ratio of the scales of object elements and the rock mass texture parameters (the difference reaches two or three orders of magnitude), which is a serious obstacle to the stable conduct of a computational experiment.
Similar problems of the available degree of modeling idealization relate to the mechanized hydroficated support of a stope face.Undoubtedly, from the point of view of the reliability and adequacy of the research, it will be positive to reflect the actual design of the powered roof support used in a particular calculation, in accordance with its technical characteristics.However, when developing such a detailed model, it is necessary to overcome (for a long period of time) serious difficulties when reflecting the real operation modes of hydraulic prop stays and hydraulic cylinders, as well as hinged joints of the section elements.At the same time, a significant computing resource is required to calculate the SSS of only one powered roof support section, and in the stope plow set, for example, there are 196 such sections.
Thirdly, when taking into account the time factor (the stope face advance velocity and the duration of its stoppage), it is necessary to use an appropriate physical model (for example, viscoplastic) of the rock mass behavior (primarily) in combination with special technological methods (for example, regular changes in the parameters of the final element mesh) of a computational experiment [43,44].This formulation of the problem is not only time-consuming, but also requires significant computing resources in the absence of guaranteed calculation process stability.
As a result of the analysis of three groups of factors influencing the computational experiment reliability, an opinion has been formed on the need to introduce a number of idealizations and simplifications into the geomechanical model, which would have a minimal effect on the adequacy and accuracy of the final SSS calculation results, but at the same time significantly save the computing resource.
The approach described above is associated, first of all, with the consistent implementation of interrelated studies, the essence of which is the division of tasks and their consistent solution by constructing a common macromodel and more detailed development of subordinate models.The methodology for performing phased studies is as follows.
The macromodel dimensions are indicated on the scheme and determined based on: previous experience in modeling geomechanical processes in similar mining-geological conditions; experimental studies of rock pressure manifestations in the extraction drifts of the Western Donbass mines; normative guidance documents.
Thus, the methodological approach in terms of the phased and continuity of research provides a reasonable construction of two groups of subordinate models with a high degree of detailing the fastening and security elements of extraction workings.The adequacy of the reflection implies modeling of real parameters: frame support of the TSYS series; roof-bolting system combined of resin-grouted rockbolts and rope bolts; security structure (behind the stope face); the central and side prop stays of the strengthening support.
When constructing subordinate models at the second stage of research, the following methodological approach has been developed.
Firstly, to ensure the stability of the SSS calculation, it has been decided to switch to flat models that reflect the section in the plane Y Z, that is, the cross-section of the extraction working.The accumulated experience of calculating such models proves the high reliability of conducting the computational experiment.
Secondly, in the absence of a real possibility of a detailed reflection of the scheme elements for supporting an extraction working (in a spatial model) of considerable length, the two most critical areas of the drift has been selected, for each of which its own group of flat models is constructed: • the first area is a zone of frontal bearing pressure at a distance of 3 -5 m from the stope face, where the maximum concentrations of vertical and other stress components act, provoking an active increase in the load on the fastening structure; • the second area is the zone of stabilization of rock pressure manifestations behind the stope face, where the main part of the drift contour displacements has already been realized (figure 1), that is, the load approaching the maximum has been formed.
Thirdly, instead of the geomechanical system spatial construction in the critical areas of the drift, a set of flat models is proposed, each of which reflects the extraction working section (with a model thickness equal to a step of frame setting) with different supporting elements.The above is explained in figure 3 and figure 4, where one of the most effective schemes implemented in the Western Donbass mines is used as an example.The scheme for fastening and supporting extraction workings includes: • in the area of frontal bearing pressure zone: a frame support made of special profile SCP-27 of the TSYS series, set with a step of 0.8 m; resin-grouted rockbolts placed symmetrically in each side of the mine working in the middle of the inter-frame space with a step of 0.8 m; rope bolts, set in a checkerboard pattern in length of the mine working in the middle of the inter-frame space with a step of 3.2 m (every four frames) according to the scheme in figure 3; central and side wooden prop stays of strengthening support, placed with a step of 0.8 m; • additional fastening elements are set behind the stope face to support the drift for its reuse: side wooden prop stays of strengthening support are set continuously along the mine working and include two rows; there is one breaker-prop row on the drift berm.
The construction of three drift sections in each of the selected areas makes it possible to track changes in the SSS along the mine working in order to determine the degree of loading of fastening elements and identify their most dangerous sections.
Fourthly, in order to bring the loading conditions of flat models into conformity with the coal-bearing mass state, determined during the calculation of the macromodel, the following actions are performed.For the area with the maximum frontal bearing pressure (3 -5 m ahead of the stope face plane), three flat models are constructed (figure 3), in which the dimensions (in the plane Y Z), structure and boundary conditions completely coincide with those for the macromodel.The results of calculating the vertical stress σ y distribution curve for a flat model and a macromodel are compared.As an object of comparison, the contact plane of the immediate and main roof of the seam are chosen, which is conditioned by the greatest influence of the rocks in this area (immediate roof and one or two layers of the main roof) on the state of the extraction working fastening elements.Next, an external load (geostatic pressure) is selected at the flat model upper boundary, at which the distribution curves σ y have a minimum difference from each other, which contributes to a more adequate reflection (within the framework of a flat model) of the coal-bearing mass behavior in real three-dimensional measurement (macromodel).Similar actions are performed for flat models in the zone of stabilization of the coal-overlaying formation displacements.
Thus, the two-stage research makes it possible to determine two groups of patterns of the influence of the stope face advance velocity on the parameters of rock pressure anomalies near the stope face and the SSS of fastening elements of modern schemes for supporting extraction workings intended for repeated use.The analysis of these patterns is of significant practical value in the conditions of highly loaded stope faces.
To conduct a series of computational experiments for studying the influence of the stope face advance velocity V d , an interval of 5 m/day ≤ V d ≤ 15 m/day is chosen, which most fully reflects both the mine conditions of coal mining using the previous generation of stope equipment, and the modern performance achieved using the equipment of latest generation.Three discrete values of the average daily velocity of the stope face advance (V d = 5 m/day, 10 m/day and 15 m/day) are selected, for each of which a separate computational experiment is performed.Within the framework of the second idealization, a methodology has been developed for "linking" all three values of V d to the deformation modulus of each of the lithotypes included in the macromodel.
In modern computer programs, in particular ANSYS, the development of creep deformations creep is usually represented in the form where C 1 , C 2 , C 3 -approximation coefficients of experimental creep diagrams in the coordinates "deformation ε -loading time t"; σ -stress intensity; t -time of loading the rock samples.Equation ( 1), along with a sufficient simplicity of written form, most objectively reflects the rheological process of the creep deformation development, since it uses the results of experimental  studies accumulated to date.In this regard, one of the tasks is to match the parameters of the experimental diagrams "deformation -loading time" as reliably and adequately as possible with the parameters and coefficients included in equation (1).

Substantiation and studying the stress-strain state of "mass -support" geomechanical models
For a complete and adequate study of the process of formed rock pressure anomalies, the mass spatial model has dimensions (x = 255 m, z = 55 m, y = 50 m), which completely exclude the influence of boundary conditions and "edge" effects on its faces.
Based on the existing information provided by the geological surveys of the Western Donbass mines (stratified mass of weak rocks), the most common textural variants of the coal-bearing stratum are summarized and two types of its texture are formed: predominantly thin-bedded and medium-bedded; predominantly thick-bedded and medium-bedded.These two textural types are shown in figure 5 and accepted for research in order to determine patterns of influence on the parameters of rock pressure anomalies.The data of geological surveys of mines, studies of M.S. Polyakov Institute of Geotechnical Mechanics NAS of Ukraine and a number of studies [18,19], on the mechanical properties of the coal-bearing stratum; average characteristics for each lithotype are introduced into the geomechanical model.
The orientation in space of the stope face and the extraction working associated with it is fully reflected, taking into account the formation of bearing pressure and destressing zones.
The real parameters of the latest technology for supporting extraction workings have been modeled.
The developed algorithm of methodical methods makes it possible to assess the influence of the stope face advance velocity on the stress-strain state of the coal-bearing mass, the fastening and security structures of the extraction workings.

General analysis of the SSS of spatial models
Then, the assessment of rock pressure anomalies is studied that occur in the rock mass in the area of stope operations from the point of view of the correspondence of the computational experiment results for a spatial geomechanical model to existing ideas about the processes of coal-bearing rock mass displacements.Thus, the term "general SSS analysis" refers to a certain test assessment of the adequacy of the performed calculations.
The spatial model SSS analysis is carried out for all stress components, and the most informative ones are distinguished to illustrate the distribution curves: vertical stresses σ y , horizontal stresses σ z (along the extraction site) and stress intensity σ.
For the test analysis, fragments of the SSS calculation of one of the computational experiments (predominantly thick-bedded and medium-bedded mass with a relatively moderate stope face advance velocity of 5 m/day) are selected, since the general tendencies are qualitatively the same for other computational experiments with other initial data.
An analysis of the vertical stress distribution in the spatial model (figure 6, b) presents the following results.
Firstly, on the one hand, the spatial model clearly reflects all the main rock pressure anomalies in the vicinity of the stope: frontal and lateral bearing pressure zones; destressing zone behind the stope face.On the other hand, the selected spatial model dimensions ensure that the influence of the so-called "edge effects" arising from the application of boundary conditions on the model faces is absent.This factor improves the adequacy and reliability of the results obtained for the calculation of the geomechanical model SSS.
Secondly, the determined parameters of the frontal bearing pressure zone are quite consistent with the data range obtained by most researchers.Thus, the frontal bearing pressure developed into the seam roof is observed up to 23 -25 m.More significant concentrations of the level 1.46 -1.56 extend up to a height of 11.0 m, and individual local areas appear at a distance of up to 16.2 m.The width of this zone (with an average concentration in the area of 1.5) is 5.2 -6.0 m, and the beginning of the stope face influence is manifested at a distance of 20 -25 m, which is quite consistent with the results of mine observations in the Western Donbass.
Thus, for all generally recognized zones of rock pressure anomalies, there is a quite satisfactory correspondence with existing ideas, experimental and analytical studies of the coal-bearing stratum behavior in the area of stope operations.

Change in the SSS of spatial models at different stope face advance velocities
After substantiating the adequacy of the spatial models, six computational experiments is performed, the main task of which is to assess the degree of influence of the stope face advance velocity and the coal-bearing stratum texture on the parameters of rock pressure anomalies in  A comparative analysis of the SSS components of spatial models is conducted, where, for example, the minimum value of the average daily velocity V d = 5 m/day of the stope face advance is taken as the base.For it, the main parameters of rock pressure anomalies are determined in the form of concentrations of stress components (or the degree of their destressing) and the propagation distances of these concentrations into the mass.At two other values of V d (10 m/day and 15 m/day), the same order of research is set and the result is presented in relative units of change (increase, decrease) of certain parameters of rock pressure anomalies.
The obtained results in terms of the V d influence on the dimensions of the frontal bearing pressure zone are presented in the form of graphs (figure 7) for a more visual representation of the correlation degree between the studied parameters.The non-linearity of the growth in the relative dimensions of the frontal bearing pressure zone with an increase in the average daily velocity V d of the stope face advance is clearly observed.At the V c of 10 m/day, there is a decrease in the increase gradient P .It should be clarified that when constructing these graphs and subsequent ones, average values of P are taken in each range of vertical stress σ y concentration coefficients K y .The general conclusion on the frontal bearing pressure zone dimensions is such that the velocity V d has a very significant influence (in the range of V d = 5 -15 m/day), varying in the range from 132 percent to 281 percent.Similar patterns of the average daily velocity V d influence of the stope face advance are shown in figure 8 for the dimensions P (at different concentration coefficients K y ) of the lateral bearing pressure zone.The main difference is in the relatively lower degree of influence from 100 percent (no link between P and V d ) to 163 percent for most dimensions of this zone.The only exception is the propagation distance of the concentration K y = 1.25 -1.35 into the seam bottom.It is noteworthy that the concentration K y = 2.0, which is capable of weakening the border rocks, practically does not change its propagation with an increase in V d by 3 times (from 5 to 15 m/day).This means a sufficient constancy of the dimensions of weakened rocks from the side of the undisturbed rock mass and, at least, the absence of an increase in the mass displacements (in this direction), if the time factor of their development is not taken into account (limitation of displacements at high values of V d ).Lower concentrations σ y propagate to more remote areas at V d = 10 -15 m/day, but it is their moving away (up to 13-15 m along the strike) that makes it possible to predict the minimum impact from the undisturbed rock mass on the rock pressure manifestations in the extraction drift.
In the destressing zone behind the stope face, similar tendencies in the velocity V d influence on this rock pressure anomaly values are observed (figure 9).

Influence of the coal-bearing mass texture on the stress-strain state of spatial models
The studies accumulated to date on the stratified coal-bearing mass stress-strain state, including the Western Donbass weak rocks, convincingly prove the presence of the influence of its texture on the parameters of distributing stress components in the area of stope operations.Therefore, this factor is subjected to a detailed study in combination with a variable velocity of the stope face advance.The studies are illustrated by the example of spatial curves of the three stress components distribution: vertical σ y , horizontal σ z (in the plane of the cross-section of extraction workings) and stress intensity σ.
First of all, the peculiarities of vertical stress distribution are studied, the curve of which is shown in figure 10 for the minimum (V d = 5 m/day) and maximum (V d = 15 m/day) stope face advance velocities in the studied range of their change.Since the analysis of the distribution parameters σ y for a predominantly thick-bedded and medium-bedded structure has already been presented, the results of comparison with the peculiarities of the curve σ y for a predominantly thin-bedded and medium-bedded structure are presented below.At the minimum stope face advance velocity (V d = 5 m/day), the following differences in the distribution curve σ y for predominantly thin-bedded and medium-bedded texture of the coal-bearing stratum have been revealed.
In the frontal bearing pressure zone, the change in the mass texture has caused a number of transformations in the vertical stress σ y distribution.Thus, the minimum influence of the approaching stope face (K y = 1.05 -1.25) is noted at a distance of 13 -15 m to the rise of the seam.This is by 35 -40 percent closer to the stope face than with predominantly thick-bedded and medium-bedded texture.This is quite consistent with the results of mine observations of rock pressure manifestations and is explained as follows: less thick rock layers that are not capable of developing a high repulse reaction to vertical rock pressure weaken and break into blocks with a small length of a stable cantilever, which deform the underlying layers at a greater distance (to the rise) from the stope face.
The minimum concentration of K y = 1.05 -1.25 propagates into the seam roof up to 23 -24 m, which practically coincides with the results of the predominantly thick-bedded and mediumbedded texture variant.Into the seam bottom, the minimum concentrations are distributed to an equivalent depth and go beyond the boundaries of the spatial model.
More significant concentrations of the K y = 1.46 -1.56 level reach 2.5 -4.6 m to the rise from the stope face plane, that is, they reduce their impact by 23 -52 percent.This concentration in the roof reaches 6.7 m (decrease by 39 percent), and in the bottom -18.6 m, which is by 2.04 times higher than in the predominantly thick-bedded and medium-bedded texture.
The most dangerous concentrations of K y = 2.0 level are located near the stope face and are characterized by the following dimensions: to the rise of the seam -2.1 -2.6 m (81 -87 percent); throughout the height into the roof -up to 4.6 m (by 1.19 times greater); in depth of the bottom -up to 11 m (by 2.29 times greater).
Summing up the above data, one should pay attention to the tendencies of reducing the propagation of concentrations σ y to the rise of the seam and mainly the growth of their dimensions into the roof and bottom of the seam.
The obtained tendencies in terms of the development of rock pressure manifestations in the extraction workings make it possible to predict the following: • reduction not only of the distance (ahead of the stope face) of the coal-bearing mass displacement intensity into the cavity of mine workings, but also the value of their displacements; • directly near the junction of the stope face with the drift, an increase in the displacement velocity of the rocks in the roof and the bottom of the seam.
In general, according to the results of the performed studies on the stress-strain state of spatial models, a number of influence patterns of the coal-bearing mass texture type and the average daily velocity of the stope face advance on the parameters of the three main rock pressure anomalies in the area of conducting stope operations have been determined: frontal and lateral bearing pressure zones, as well as destressing zone behind the stope face.
These studies are used in the development of recommendations for the selection of rational design parameters for high-rate mining of coal seams in the Western Donbass conditions.
Based on the performed research, the state of modern fastening and security structures has been studied, which provides the possibility of reusing the mine working at high velocities of stope face advance in order to improve the schemes for maintaining extraction workings.
The state of the fastening and security structures is studied in terms of three main stress components.The SSS analysis is performed sequentially for each of the studied areas of the mine working maintenance.
For example, a curve of the vertical stress σ y components is studied (figure 11).
The conducted comparative analysis of the vertical stress distribution in all fastening structure elements proves the significance of the influence of the stope face advance velocity and the mass texture.The identified tendencies should be taken into account when substantiating the fastening parameters.The patterns determined during the performance of multivariate computational observations have been confirmed in the course of instrumental observations in the mine workings of the Western Donbass mines (figure 12).The decrease in the material consumption of fastening and security structures at high velocities of advancing stope faces has been substantiated and confirmed by calculations.It is recommended to fasten with the lightweight SCP-22 profile and with an increase in the step of setting the frame support and resin-grouted rockbolts up to 1.0 m, the rope bolts are placed in a checkerboard pattern with a step of 4.0 m, the permissible diameter and the number of rows of side prop stays of the strengthening support and the breaker-prop row are reduced.The use of such a highly efficient scheme for maintaining extraction workings provides a reduction in the time and cost spent on end operations.Thus, this creates an opportunity for the full operation of modern high-performance stope equipment and, as a result, the intensification of mining operations in difficult mining-geological conditions.

Conclusions
Generalization of the research results makes it possible to formulate the following conclusions.
The analysis of existing analytical studies and experimental measurements of the rock pressure manifestation parameters has convincingly proved the significance of the influence of technological parameters of coal seam mining on the formation of SSS anomalies (frontal and lateral bearing pressure, destressing zone behind the stope face) in the coal-bearing mass adjacent to stope operations.For indicated three main SSS anomalies, a set of parameters has been substantiated that completely characterize this research object.On the other hand, two technological parameters have been distinguished that not only significantly influence on the formation and development of SSS anomalies, but are also inextricably linked with the intensification of mining the coal seams: the average daily velocity V d of the stope face advance and the duration of its stoppage t.
Based on the analysis of existing scientific-practical developments, the most expedient three-stage structure for performing research has been substantiated, where mine instrumental observations and multivariate computational experiments are combined and complement each other through a linking element -the mechanism for coal-bearing mass displacement in terms of the impact of the selected technological parameters for conducting stope operations.
A new methodological approach has been developed in the technology of conducting computational experiments, which ensures the research continuity when separating and sequentially solving two groups of problems on a common macromodel and subordinate models with a more detailed reflection of real conditions.Such a two-stage research structure makes it possible to more adequately and reliably determine two groups of patterns of the influence of technological parameters on the indicators of rock pressure anomalies and stress-strain state of fastening, security elements in the latest schemes for resource-saving maintenance of extraction workings in the conditions of highly stressed stope faces.
Six main peculiarities of the substantiation and construction of geomechanical models have been formulated and systematized, with account of which it is possible to ensure a sufficient degree of adequacy and reliability of the results of computational experiments for studying the correlation between the rock pressure anomaly parameters and mining-geological, technological factors of highly-productive mining of coal seams.
It has been proved that the results of calculating the SSS of spatial geomechanical models correspond to the prevailing ideas about the mechanism and nature of the coal-bearing stratum displacement process in the zone of stope operations.The consistency of the results and their objectivity has been determined based on the analysis of the parameters of rock pressure anomalies.
A very significant influence of the average daily velocity V d of the stope face advance (in the range of changing V d = 5 -15 m/day) on the dimensions P of the frontal bearing pressure zone has been determined.The link between P and V d is non-linear with some damping of the growth gradient of the zone dimensions at V c = 10 m/day.The average values of increasing P at V d = 15 m/day are from 132 percent (to the rise of the seam at K y = 1.05 -1.25) to 281 percent (in depth of the bottom at K y = 1.46 -1.56).The revealed patterns should be taken into account when choosing the mode for conducting stope operations and, especially, when substantiating the parameters of the fastening structures and the means of their strengthening (ahead of the stope face) for the extraction drifts.
A reduced influence of V d on the dimensions P of the lateral bearing pressure zone has been revealed.Moreover, the distribution of "destructive" vertical stress σ y concentrations practically does not change in the range of 5 m/day V c 15 m/day.On the other hand, reduced concentrations σ y that are influenced by V d cannot significantly affect the rock pressure manifestations in the extraction drift due to their remoteness.This brings to the fore the pattern for limiting the adjacent mass displacement at high velocities of the stope face advance.
A tendency to reduce the influence of the stope face advance velocity on the dimensions of the frontal bearing pressure zone with a more thin-bedded mass texture compared to a thick-bedded texture has been revealed.This is conditioned by the reduced stability of less thick lithotypes, which, during their bending, "react" to a lesser extent to limiting the period of acting bending loads at increased stope face movement velocities.At the same time, in the zone of lateral bearing pressure (in the area of the drift ahead of the stope face, where the maximum frontal bearing pressure acts), the opposite tendency has been determined -an almost universal increase in the degree of V d influence on the dimensions of the zone under conditions of a more thin-bedded mass texture.In the destressing zone, there is a decrease in the degree of V d influence, similar to the tendencies in the frontal bearing pressure zone.
The results of research in various mining-geological conditions are experimentally confirmed, as well as recommendations for the implementation of resource-saving fastening and security systems are presented.

Figure 1 .
Figure 1.Dependences of the convergence development in the roof and bottom rocks sides of the drift with predominantly thick-bedded and medium-bedded (1), with predominantly thinbedded and medium-bedded (2) texture of the roof rocks.

Figure 2 .
Figure 2. Macromodel for studying rock pressure anomalies in the area of stope operations.

Figure 3 .
Figure 3. Scheme for fastening the extraction working in the frontal bearing pressure zone.

Figure 4 .
Figure 4. Scheme for supporting the extraction working in the displacement stabilization zone of the coal-overlaying formation behind the stope face.

Figure 6 .
Figure 6.Curves of vertical stresses σ y in a spatial model of a predominantly thick-bedded and medium-bedded mass at an increased (a) and decreased (b) stope face advance velocity.

Figure 7 .
Figure 7. Patterns of the average daily velocity V d influence of the stope face advance on the growth of the relative dimensions P of the frontal bearing pressure zone at concentration coefficients σ y .

Figure 8 . 15 Figure 9 .
Figure 8. Patterns of the average daily velocity V d influence of the stope face advance on the growth of the relative dimensions P of the destressing zone at concentration coefficients σ y .

Figure 10 .
Figure 10.Curves of vertical stresses σ y in a spatial model of a predominantly thin-bedded and medium-bedded mass at an increased (a) and decreased (b) stope face advance velocity.

Figure 11 .
Figure 11.Curves of vertical stresses σ y iin the fastening structure of the extraction drift in the frontal bearing pressure zone at the stope face advance velocities V d : (a) V d = 15 m/day; (b) V d = 5 m/day.

Figure 12 .
Figure 12.The state of mine working at the experimental site.