Preparatory Workings Research Articles

Assessing the stability of protective structures in preparatory mining workings under conditions of static load

The object of this study is the deformation processes in protective structures under the action of static load in the coal massif in order to preserve the integrity of the side rocks and the operational condition of mine workings. Under laboratory conditions, the deformation characteristics of rigid and flexible protective structures, as well as supports made of crushed rock, were studied on experimental samples. The samples were subjected to uniaxial compression. It was established that there is a functional relationship between the coefficient of transverse deformation ν and the relative change in the volume δV of protection structures, which makes it possible to estimate their bearing capacity. For rigid protection structures (coal pillars, cast strip, cement blocks, blocks of reinforced concrete bollards, bundles of wooden racks), the deformed state of the structures determines their behavior. This happens at values of ν=0.3–0.5 and δV£0.09. Their stability is fixed within the safe deformation resource. An increase in the deformation energy density of such structures beyond the safe deformation resource leads to their destruction due to a change in shape. For flexible protection structures (bundles of wooden racks, rolling bundles made of wooden sleepers), which have a transverse deformation coefficient ν=0.02, at a relative change in volume δV£0.3, the compaction of structures is observed. Increasing their stiffness allows limiting the convergence of side rocks. For a support made of crushed rock, at ν=0.25–0.32 and a relative volume change of 0.12£δV£0.32, its compaction and increase in resistance occur. Under such conditions, the convergence of side rocks is limited. In order to preserve the integrity of the lateral and operational condition of preparatory workings in the excavation areas of coal mines, it is advisable to use flexible protective structures made of wood or supports made of crushed rock

Methodical principles of experimental-analytical research into the influence of pre-drilled wells on the intensity of gas-dynamic phenomena manifestations

Purpose.The research aims to substantiate the general provisions on coordination of the experimental-analytical research results of the influence of pre-drilled wells on the intensity of gas-dynamic phenomena manifestations (using the example of the mining-geological conditions of the phenomena at the PJSC Mine Administration Pokrovske, Ukraine). Methods. The research uses an integrated methodology consisting of indirect experimental methods for studying the adjacent rock mass state and tendencies. Findings. It has been proven that indirect experimental indicators of the rock mass state around the tunneling face are related to the peculiarities of the distribution of its stress-strain state components. Based on this research, the well lengths of up to 10-15 m has been determined to effectively and safely de-stress the rock mass. The experimental research validity is confirmed by conducted computational experiments, in the course of which the dependence of the propagation parameters of the stress-strain state component concentrations on the degree of hardness of the lithotypes is revealed, and a geomechanical substantiation to the tendencies of propagation of rock pressure anomalies near stoping and tunneling faces is given. The new knowledge obtained is the basis for creating a method for calculating rational parameters for the location of de-stressing pre-drilled wells. Originality. An objective assessment of the degree of adequacy and reliability of the computational experiment results has been made under the condition of using a new geomechanical model with mine studies of seismic-acoustic signal parameters and the initial gas release velocity. The main tendencies of vertical σу, horizontal σх and σz, as well as stress intensity propagation have been identified. The obtained results of exploring the bottom-hole mass are aimed at substantiating the parameters of anti-outburst measures for all preparatory mine workings. Practical implications. The conducted research is implemented in creation of a calculation method and recommendations for the selection of rational parameters for the location of de-stressing pre-drilled wells for the purpose of weakening the rock mass, surrounding the tunneling face, and reducing the probability of gas-dynamic phenomena occurrence due to the controlled weakening of adjacent rocks.

Evaluating the Efficiency of the Mine Workings Supporting Technology Application to Increase Contour Stability

Maintaining the mine workings will also require significant costs to repair them both before and after they are introduced into production, especially in the zone of influence of the mining operations. Maintaining and increasing the volume of underground coal mining is only possible with a highly efficient technology for conducting and maintaining preparatory workings. The purpose of the study was to assess the parameters for controlling the stability of the contours of mine workings secured by anchor support to create a technology for intensive and safe conduct of mine workings based on the identified patterns of behavior of the adjacent rock masses. The idea of the approach is to use the anthropogenic stress-strain state to develop an effective technology for securing the contour rock massif. The mechanism of rock deformation, shear and collapse in a structurally disturbed heterogeneous rock massif is studied to assess the state of the rock massif around mine workings. Technological prerequisites for anchoring the marginal soil rocks, taking into account the state of the rock mass around the excavation, are developed and the parameters of anchor support operation in mines to secure the rods in excavations to ensure the safety of mining operations are determined.

ДОСЛІДЖЕННЯ ДЕФОРМАЦІЙНИХ ВЛАСТИВОСТЕЙ ОХОРОННИХ СПОРУД ІЗ ПОДРІБНЕНОЇ ПОРОДИ В УМОВАХ СТАТИЧНОГО НАВАНТАЖЕННЯ

Purpose. Investigate the deformation properties of structures made of ground rock under static load conditions to preserve the integrity of the side rocks in the produced space of the coal massif and the operational state of the preparatory mine workings along the length of the excavation site. Methodology. In laboratory conditions, experimental samples of protective structures made of ground rock of heterogeneous granulometric composition were subjected to static loading under conditions of uniaxial and compression compression. Results. It was experimentally established that under the conditions of uniaxial compression of protective structures made of ground rock with the possibility of its lateral expansion, the effect of forming the bearing capacity is manifested in the relative change of the volume of the embedded material in the range of values , when, after increasing the relative deformation, the resistance reaches the maximum compaction of the rock . In such conditions, it is necessary to ensure the stability of the bearing pillar of the embedded material. During compressive compression of crushed rock, such an effect is achieved in conditions where the relative change in the volume of the embedded material is . After maximum compaction , the resistance of protective structures increases. Scientific novelty. The type of functional dependence between the relative deformation is established protective structures made of crushed rock and relative volume of the embedded material under static load under uniaxial and compressive compression, which allows to evaluate the bearing capacity of flexible supports. Practical significance. In order to assess the stability of protective structures made of crushed rock, which are in different compression conditions during the unloading of coal massif, it is necessary to take into account the compaction coefficient of the original material and the longitudinal deformation of the support under load. Keywords: coal massif, guard building, ground rock, uniaxial compression, compressive compression.

Схемы бурения газодренажных скважин в выявленные зоны нарушения сплошности горного массива

. In order to find out the nature of the distribution of the stress state in the bottom-hole part of the massif and its effect on the development of cracks ahead of the face, the volume-stress state ahead of the faces of the preparatory workings was determined, and the nature of the zones of crack development (destruction) ahead of the face of the preparatory workings was determined, taking into account the cleavage of cracks in the array. As a result of the analysis of the zones of explosive destruction in the bottom-hole zone of the mine, it was revealed that the zones of crack development (destruction) in front of the mine face have an ambiguous character both in the height of the face and along each of the layers. This should be taken into account both when laying gas drainage wells and when drilling them. The development was carried out by the GPC tunneling combine from top to bottom. According to the regulatory documents, when carrying out the conveyor bremsberg, the current forecast of the emission hazard for the initial gas release rate and the output of the drill pin, as well as the forecast for the amplitude-frequency characteristics of the acoustic signal, is applied. To compare the effectiveness of methods for reducing the natural gas content of the D6 formation, comparisons were made of the results of the operation of reservoir degassing wells. The conducted studies allow us to identify a number of advantages of intensive degassing of the coal massif, directed along the course of production, in comparison with degassing by wells with drilling of the contour of future production.

Theoretical model of random freight flow distribution in the conveyor transport line of the coal mine

Purpose. Increasing the efficiency of the conveyor transport system of the mine due to the application of rational parameters, which are calculated objectively on the basis of the reliable output data of random freight flow in the conveyor transport line, taking into account the velocity of minerals transportation, including a perfect theoretical model application of the freight flow distribution. Methodology. Complex research: - statistical studies on the actual distribution of random freight flow in the highly productive stages of the PSU Mine “n.a Heroiv Kosmosu” PJSC “DTEK Pavlohradvuhillia”; - description of histograms of the distribution of random freight flow by various indicative algebraic functions, normal and gamma distribution of a random variable and a specially constructed function with separately defined parameters of its branches; - analysis of research results regarding the correctness of the theoretical model of the distribution of random freight flow according to various criteria of genuineness, a center of grouping, amplitude, velocity of rise and fall, and deviation. Findings. A perfect theoretical model was built in the form of an indicative algebraic function, whose branches are described by the normal distribution law of a random variable with separately determined parameters. It describes well the distribution of random freight flow in the conveyor transport line of the mine and ensures the determination of its parameters by the methods of probability theory. Originality. A theoretical model of the distribution of random freight flow in the conveyor transport line of the mine has been obtained for the first time, which describes well various cases of its distribution, including symmetric and asymmetric ones, and provides the determination of the freight flow parameters by the methods of probability theory. Practical value. The actual value of the coefficient of nonuniformity of the freight flow in the conveyor transport line of the mine, which was determined by a perfect theoretical model, exceeds, by almost a quarter, the value inherent in the model accepted in practice, the normal law of the distribution of a random variable. The coefficient of nonuniformity of the freight flow in the highly productive longwalls of only the specified mine reaches a value of 2.012, which already exceeds the normative value limit for conveyor transport lines along horizontal and inclined preparatory workings of mining areas (2.0). Reliable initial data on the variation of the random freight flow in the conveyor transport line of the mine, which is substantiated by a perfect theoretical model of its distribution, have a positive effect on the calculation of its parameters and contribute to increasing the efficiency and reliability of the functioning of the conveyor transport system.

THE MOST EFFECTIVE DEGASING METHODS WHEN CARRYING OUT PREPARATORY COAL MININGS

The article presents the most effective degassing methods when carrying out preparatory workings for coal, provides an analysis of the effectiveness of each degassing method, the conditions for their use to reduce the gas content of the formation, increase the pace of preparatory workings and the safety of mining operations. To reduce the gas content of workings carried out in a coal seam, preliminary degassing of the seam can be used, carried out before the working, or degassing of the coal mass during the working period. The most effective way to reduce methane emission into development workings is preliminary degassing of the coal mass with a period of gas capture before the start of tunneling work in the prepared area of at least 12 months.

Technological conditions for ensuring the stability of the array of enclosing rocks during the fastening of mine workings

Ensuring the stability of the array of enclosing rocks during the fastening of mine workings is possible only if there is a highly efficient technology for conducting and maintaining workings. For fixing the mining, taking into account the technological stratification of coal-bearing massifs, a method using anchor fastening technology is recommended. The effect of the proposed method of fastening workings is that high reliability of fastening is ensured, and the volume of labor-intensive processes to combat the collapse and stratification of rocks is reduced. The stability of the contours of preparatory workings, taking into account their stress-strain state, depending on mining, geological, and technological factors of factors using the finite element method, is investigated. The boundaries of the area of inelastic deformations are determined by the method of successive loadings. The parameters of deformation of the lateral rocks of the mine workings from the angle of incidence of the formation and the depth of anchoring are considered.

DEFORMATION FEATURES OF EMBEDDED MATERIALS UNDER COMPRESSION CONDITIONS

Purpose. The purpose of the article is t o study the deformation characteristics of the backfill materials made of crushed rock of different granulometric composition under compression conditions to assess the stability of the side rocks in a coal massif with preparatory workings when selecting the parameters of protective structures. Methods. Compression tests were carried out in the laboratory to model the behaviour of crushed rock fill materials under load. Cylindrical specimens were subjected to axial static compression without the possibility of lateral expansion. The results. It has been experimentally established that the maximum value of the compaction coefficient of the crushed rock kс=1.57 is achieved under conditions of compression, when the relative change in the volume of the source material is 35-36% and the relative void is 5-6%. Under such conditions, the ultimate compressibility of the deformable body is achieved at its relative deformation λ = 0.36 and the presence of particles of different sizes (diameters) in the total volume of the rock layer (before compression). At the minimum value of the compaction coefficient kс=1.14, which corresponds to the small fraction of the crushed rock, the relative change of the void is 1.5%. For a large fraction of crushed rock at kс=1.43, the relative change in voids is 6.2%. This situation is associated with the destruction of rock particles and the reduction of voids between them. Compliance with certain requirements for backfill materials made of crushed rock, taking into account its particle size distribution, increases the efficiency of using the backfill of the excavated space. It is advisable to evaluate the bearing capacity of backfill materials by the value of the compaction coefficient of crushed rock. Scientific novelty. A functional relationship between the change in the specific potential strain energy and the relative deformation of the rock layer has been established, which allows us to estimate the degree of compaction of crushed rock under compression. Practical significance. To ensure maximum compaction of the crushed rock when using partial or complete backfilling of the worked-out space used for the protection of mine workings, it is advisable to use a heterogeneous (in terms of particle size) source material. Keywords: crushed rock, backfill material, stiffness, particle size distribution, compaction, deformation, compression.

Способ контроля газодинамической активности в приконтурной части угольного пласта

This paper presents the results of the study aimed at solving issues of ensuring the safety of mining operations in the mine development workings in terms of forecasting and controlling gas-dynamic phenomena. The experiment described in the work creates a basis for developing a method to assess gas dynamic activity in the bottomhole part of the coal seam using an innovative device that allows assessing changes in the gas content of the seam along the line from the bottomhole to the geostatic stress zone during the development of preparatory workings. It is proposed to develop a method of current forecast of emission hazard, which will increase the face advance rates and ensure the safety of mining operations, based on assessing methane mobility in the mine working and the new approach of assessing the gas-dynamic hazard of the formation presented in the paper.

Assessment of geomechanical processes occurring in the rock mass during development preparatory workings, taking into account the technogenic state of the rock mass

Assessment of geomechanical processes occurring in the rock mass during development preparatory workings, taking into account the technogenic state of the rock mass

Моделирование и управление параметрами поточных технологий с локальным гидротранспортом и обезвоживанием угля на основе анализа структуры проходческого цикла

Introduction. The article discusses the issues of modeling various variants of flow line tunneling technologies based on an analysis of the structure of the tunneling cycle. Materials and methods. As research methods, the authors used: analysis of the structures of the tunneling cycle of continuous mining technologies, mathematical modeling of processes and operations, and industrial testing of options for implementing the proposed technological tunneling systems. Results. The results obtained during the implementation of the economic and mathematical model for the variant of the flow technology presented above showed that the following parameters of the technological scheme are optimal: technical productivity of the combine – 1.1 m3/min; process water consumption – 200 m3/h; number of drilling rigs – 2; the number of miner units is 6. The speed of development with these parameters of the flow technological scheme will be 880 m3/month, the labor productivity of miners is 14.8 m3/person during the work shift. Conclusion. The article summarizes the results of research on the development, justification of parameters and implementation of various options for in-line technologies for carrying out inclined workings with a hydraulic slope for various purposes for a wide range of conditions of their application. Resume. Implementation of the model proposed by the authors made it possible to determine the primary area of application of the considered version of the flow technology for carrying out preparatory workings in relation to the mining and geological conditions of the Kuzbass mines. Variants of the considered technological schemes for carrying out workings were implemented during the mining of reserves of the Anzherskaya-Yuzhnaya-3 mine, during the underground mining of reserves of the Listvyansky and Kedrovsky open-pit mines located in the Kemerovo region of the Russian Federation and the implementation of a project for the combined mining of a graphite deposit in middle Vietnam.Suggestions for practical application and direction for future research. The materials of the article may be useful for scientific and design organizations, coal mining enterprises in modeling and implementing precision mining technologies.

Determining the deformation properties of crushed rock under compressive compression conditions

The object of this study is the process that forms fill materials from crushed rock under load for managing the condition of side rocks in a coal-bearing massif with preparatory workings. Deformation properties of crushed rock under laboratory conditions were evaluated on the basis of a study of compressive compression of the fill material. It was registered that there is a quadratic functional dependence between the change in the bulk density of crushed rock of different granulometric composition and the specific potential energy of deformation. It was experimentally established that the specific potential energy of deformation reaches the limit values at the maximum compression of crushed rock when the fill material consists of parts of different sizes. For experimental samples with different thickness of the rock layer h0 (m), there was a linear relationship between their longitudinal deformation Dh (m) and the external load F (kN), which determined the behavior of the deforming body at critical levels. Under such conditions, with a relative change in the volume of the fill material dV=0.36, that is, with the same relative deformation at any values of the parameter h0 (m) and the compaction coefficient of the crushed rock kcon=1.57, the maximum stiffness of the rock supports was ensured. With a limited amount of external static load on the experimental samples, in the process of their deformation when the parameter h0 was reduced by 2 times before their compression, the compaction coefficient of the crushed rock increased from kcon=1.33 to kcon=1.57. At the same time, the specific potential energy of deformation increased by 40 %, which made it possible to ensure the maximum rigidity of the fill material at the minimum value of the longitudinal deformation Dh (m) of the experimental samples

Monitoring of the stress-strain state during preparatory workings

Maintaining and increasing the volume of underground coal mining is possible only if there is a highly efficient technology for conducting and maintaining preparatory workings. The purpose of the research was to assess the parameters of stability control of the contours of the mine workings, anchored with anchorage, to create a technology for intensive and safe excavation of mine workings based on the identified patterns of behavior of adjacent rock massifs. The idea of the approach is to use a man-made stress-strain state to develop an effective technology for fixing a contour rock mass. The mechanism of deformation, displacement, and collapse of rocks in a structurally disturbed inhomogeneous mountain range is investigated to assess the state of the rock mass around the mine workings. The technology of fastening contiguous soil rocks has been developed taking into account the state of the mountain massif around the workings and the parameters of the operation of the anchor supports in mines for fixing rods in workings in order to ensure the safety of mining operations in the mines of the Karaganda coal basin have been determined.

Evaluation of the effectiveness of secondary support of haulage drifts based on a comparative analysis of the deformation characteristics of protective structures

The object of this study is the processes of managing the state of lateral rocks in the coal rock array with preparatory workings. The influence of deformation characteristics of the protective structures of the preparatory workings on the stability of lateral rocks in the coal rock array has been established. The stable state of the above-the-drift pillars of coal is provided within the deformation resource, which corresponds to the critical level of the specific potential energy of the deformation. The limits of the deformation resource are the range of change in the relative deformation of coal pillars 0.1≤λ≤0.25. When the critical level of the specific potential energy of deformation is passed, at λ˃0.25, there is a relative change in the volume of pillars δλ˃0,1, as a result of which their durability decreases and the state changes. Under such conditions, the residual strength of coal pillars is not enough to limit the movement of lateral rocks, which provokes their collapse. For protective structures made of crushed rock, within the established deformation resource of 0.4≤λ≤0.7, with an increase in static load and cross-sectional area, the specific potential energy of deformation decreases, simultaneously with the relative change in the volume of the embedded material. This is due to the compaction of the crushed rock and an increase in its strength. Regularities of change in the specific potential energy of deformation of protective structures have been established, which, under conditions of uniaxial compression, make it possible to assess, within the deformation resource, their stability. To ensure the stability of lateral rocks in the coal rock array and to preserve the operational condition of the preparatory workings, it is advisable to use protective structures made of crushed rock. This method will limit the movement of the roof and sole in the produced space and avoid collapses.

Study of gas hazard pattern in underground workings after blasting

Determining the sources of hazardous and toxic substances released into mine air, their gas composition, as well as providing each such source of pollution with the required amount of fresh air are important issues in terms of ensuring normal healthy and safe working conditions for miners. This paper studies blasting as one of the most dangerous sources of mine air pollution. The study was carried out for a long dead-end exploration working, and a development (preparatory) working of a copper-nickel mine. In accordance with the federal rules and regulations (FNiP), a number of requirements, including monitoring of gas hazard at a face, is applied to blasting operations.The study examined the behavior of gas-air mixture in dead-end mine workings after blasting. The findings are based on the experimental data obtained in the conditions of two dead-end workings at an operating coppernickel mine. A technique for the experimental studies of gas release after blasting in a dead-end working was developed. The main technical characteristics of the instruments involved in the in-situ measurements are given. Time dependences of the concentrations of toxic gases after blasting at the blasted working mouth, at the return ventilation current, and near a booster were established. In order to assess the reliability of the data obtained, the volume of released carbon oxides was calculated based on the data of gas analyzers and chemical reactions of explosives decomposition during detonation, depending on the types and weights of the explosives. A model of gas-air mixture transfer was described, constructed, and calibrated allowing for longitudinal dispersion. The Voronin model was used to simulate the gradual removal of toxic gases from the working face and solving the problem of boundary conditions. Based on experimental data, the coefficients of longitudinal dispersion, ventilation efficiency, and volume concentration of the considered gas admixture in the mixing zone at initial time were determined for a long dead-end mine working.The constructed gas-dynamic model and longitudinal dispersion coefficients obtained as a result of the analysis enabled the time required for long dead-end mine workings ventilation to be analysed and estimated. Based on the model, the algorithm for calculating the velocity of spreading the combustion products in a mine ventilation network in emergency situations is being improved. The value of longitudinal dispersion coefficient for different operating conditions is also being refined.Based on the gas distribution simulation within the interval of 1,500 m from a working face, the time required for the ventilation of a dead-end mine working was determined.

Ensuring a safe geomechanical state of the rock mass surrounding the mine workings in the Karaganda coal basin, Kazakhstan

Purpose. The research purpose is to determine the instability zones in the host rocks and the dynamics of propagation of active fracturing zones to ensure the stability of the rock mass surrounding the mine workings. Methods. The research uses a set of analytical and experimental studies to determine the dynamics of the deformation process development in the coal-rock mass surrounding the mine workings. Mathematical modeling of the stress-strain state of the rock mass surrounding the active extraction workings is performed using the numerical method of finite elements in modern AN-SYS, Mergel and KMS-III software products. Findings. The influence has been studied of the mine working section shape and the coal seam dip angle on the value of the maximum stresses that arise in the rock mass when the mine working is fastened with the roof-bolt support. The instability zones in the host rocks and the dynamics of propagation of active fracturing zones have been determined both ahead of the front of the conducted mine working and on its sides for rocks of different strength. Originality. For the conditions of the Karaganda coal basin, the dependence of a change in the development of conventional inelastic deformation zones (CIDZ) on the host rock strength has been revealed. The influence of the coal seam dip angle on the dynamics of stratifications around preparatory working has also been substantiated. In addition, new data have been obtained on the influence of the roof rock strength on the stratification of the rock mass surrounding the mine working. Practical implications. By determining instability zones in the host rocks and the dynamics of propagation of active fracturing zones, it is possible to control geomechanical processes in the border rock mass of a mine working and influence it in order to prevent the occurrence of negative rock pressure manifestations. The data obtained are the basis for the development of recommendations on the use of roof-bolting technology for fastening extraction workings to ensure their stability and reduce the cost of their operation.

Analysis of the use of composite materials for further application in the support of mine workings

Purpose. To analyze composite materials and prospects of their use for roof support in coal mines. Research methodology. To achieve this purpose, we used analytical data on the market of composite materials, the volume of their production capacity, and cost indicators. Data on the physical and mechanical properties of composite materials and their quantitative indicators were used. Research results. The areas of application of composite materials in industry are analyzed and summarized. The analysis shows that composite materials are used in many areas of industry: medicine, construction, defense, etc. A comparative analysis of the physical and mechanical properties of carbon fiber-reinforced plasticand steel shows that this composite material has identical (and sometimes even better) properties than metal materials. The study concluded that it is better to use carbon fiber as a support material for mine workings in coal mines. The advantages and disadvantages of carbon fiber-reinforced plasticas a roofing material for coal mine workings are evaluated. It is clarified that the current limiting factor is the cost of carbon fiber-reinforced plastic, but over time, their price will decrease and their demand will increase. It is concluded that the use of this composite material in the elements of mine support can increase the pace of their implementation, reduce the labor intensity of the work performed and improve the working conditions of miners while lightening the structure. Scientific novelty. The physical and mechanical properties of composite materials have been analytically determined and it has been substantiated that carbon fiber-reinforced plasticsupports can be used in the support of preparatory workings in coal mines. Practical value. The obtained results prove that the support made of carbon fiber-reinforced plasticwill facilitate the design of the support, which, together with the acceleration of the shift operation, will contribute to the development of underground coal mining.

ASSESSMENT OF THE RISK OF LOSS OF STABILITY OF A SLOPE DRIFT IN THE DEVELOPMENT OF STEEP COAL SEAMS

Purpose. The purpose of the article is to assess the risk of loss of stability of the preparatory mine workings in order to adjust measures to prevent hazards and their consequences in the excavation areas of a coal mine with steep seams.. Method. An integrated approach was used, including: analysis and synthesis of known studies, expert evaluation, application of the basic principles of probability theory, processing, analysis and interpretation of the results. Results. During the examination of 7 objects (excavation sites), the a priori ranking identified significant factors that affect the loss of stability of preparatory mine workings. Accidental events were considered: the collapse of the roof, the slippage of the sole in the produced space of the coal massif, and the failure of fastening in the roll-back stretch. The ranking results are confirmed by the concordance coefficient (0,9). The analysis of accidents related to the loss of stability of the preparatory workings with different methods of protection allowed establishing the frequency of roof collapses and ground slides in the coal massif at the excavation site. To statistically evaluate the failures of the arch support ω in the working face, field studies were carried out. It was found that in the area of influence of the cleaning operations when protecting the heading with coal blocks, the failure rate of the arch support is ω=0.24, bushes from the racks ω=0,27, and wooden fires ω=0,16. Taking into account the combination of the identified significant factors, the a posteriori probability of loss of stability of the heading in the area of influence of the longwall face in the area of 10 ≤ l ≤ 45 m is 0,036-0,055 m when using coal blocks, 0,044-0,078 bushes from the risers and 0,0176-0,036 wooden fires. The probability of arch support failure is approximately 0,6. On the basis of research, a quantitative assessment of the component risks wa established, which leads to the loss of stability of the rollback stretch. The maximum risk assessment R = 576 corresponds to the conditions when the production is protected by bushes made of wooden risers. Scientific novelty Assessment of the risk of loss of stability of the preparatory mine workings is a set of research and analytical measures aimed at reducing the manifestation of hazards in the coal massif at the excavation sections of a coal mine. Practical significance. To obtain qualitative and quantitative estimates of the risk of loss of stability of the preparatory mine workings along the length of the excavation section, a model of formation of a possible dangerous situation was proposed. Key words: coal mine, preparatory workings, cave-in, side rocks, simulation modelling, miners’ safety.

ДОСЛІДЖЕННЯ ПРОЦЕСІВ ДЕФОРМУВАННЯ ОХОРОННИХ СПОРУД ПІДГОТОВЧИХ ГІРНИЧИХ ВИРОБОК

Purpose. Research of deformation processes of protective structures of preparatory mine workings to ensure the stability of side rocks in the coal massif and preparatory workings in excavation areas in a coal mine. Methodology. To simulate the behavior of security structures under static load in laboratory conditions, experimental samples have been tested under conditions of uniaxial compression. Results. Rigid security structures (coal targets, BZBT bollards, cement blocks and cast strip) and flexible security structures (wooden bonfires and rolling bonfires made of wooden sleepers) have been considered. It has been established that under conditions of uniaxial compression of flexible security structures under the action of a static load, when the ratio of the potential energy of the change in shape Uф to the change in volume Uо is Uф/U0 ≤2.12, compaction of wooden structures (without loss of stability) and an increase in their bearing capacity, which makes it possible to limit the convergence of lateral rocks. For rigid protective structures, when Uф/U0 ≤4.1-6.5, there is a loss of stability of the supporting structures, a decrease in their bearing capacity, which eventually leads to the collapse of side rocks. The assessment of security structures in terms of stability, rigidity and bearing capacity should be based on the properties of the material of the supporting structures. Scientific novelty. Under the conditions of uniaxial compression, the functional dependence of the change in the specific potential energy of deformation of protective structures of preparatory mine workings on the coefficient of their transverse deformation has been established. Practical significance. To ensure the stability of side rocks in the coal massif during its unloading, it is advisable to use flexible protective structures.