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Purpose: To determine the parameters of detached rock packs with compensating voids. Methodology: Analysis of technologies for the protection of development workings, based on the management of the stress-strain state of rocks around the workings, physical modeling using equivalent materials, numerical modeling by the finite element method, and methods of structural mechanics. Results: In the conditions of soft soil rocks the expediency of application of protection means based on management of a stress-strain condition in a surrounding massif and redirection of extrusion forces from a working has been substantiated. On the basis of analysis of the existing protection measures of the workings behind faces the prospects of use of protection technologies by means of construction of detached rock packs with limiting surfaces between which there are compensatory voids left, have been proved. To determine the parameters of such packs and voids between them in the conditions of soft soil rocks, a set of laboratory and numerical studies has been performed. According to their results, it has been established that to ensure the redirection of extrusion forces from the working it is necessary to build rock packs with limiting surfaces in the form of rectangular parallelepipeds with orientation of their greater side perpendicular to the longitudinal axis of production and trapezoidal prisms with their narrower orientation towards the working. Recommendations on the parameters of these structures and compensatory voids between them in the conditions of soft soil rocks have been formulated. Scientific novelty: On the basis of numerical modeling the regularities of stress distribution in rocks under detached rock packs of different shapes have been investigated, which allowed substantiating the parameters of the last and compensatory voids between them to ensure the stability of workings in the soft soil rocks. Practical significance: The expediency of application of technologies of protection of preparatory workings behind faces in the conditions of soft soil rocks by means of rock packs with limiting surfaces between which there are compensatory voids has been proved, and their parameters have been defined.

The necessity of development and improvement of methods and means for the protection of preparatory roadways, in particular, protective structures, was proved on the basis of ordinary rock with binding surfaces. Analysis of the results of the study on the use of protective structures of ordinary rock and bounding surfaces was performed. It has shown the feasibility of reinforcing rock structures to ensure operational conditions for the protected roadways. Such structures include rubble strips reinforced with partitions made of metal mesh. To determine their efficiency and reinforcement parameters, studies were performed using provisions of structural mechanics, soil mechanics, and bulk media, as well as physical modeling using natural materials. According to the results obtained in the performed studies, the efficiency of reinforcement of rubble strips with a metal grid was proved and a procedure for calculation of reinforcement parameters that need to be considered in designing the above structures was developed. Such parameters include width and height of the strip, class of reinforcement, its diameter and tensile strength, size of the grid cells, angle of internal friction of rocks, and diameter of maximum rock pieces in the strip. It was established that reinforcement of the rubble strip by partitions made of metal meshes can reduce the width of the strip and volume of the rock fill by 1.33…2.66 times without losing the structure rigidity. To do this, the condition of reinforcement strength in grids must be met. It consists of comparing its tensile strength with maximum stresses in the partition. These stresses are determined by the magnitude of the load on the rubble strip from the roof rocks, the diameter of the reinforcement, and the maximum rock pieces, as well as relative extensional strain in reinforcement.

The conditions of coal seam mining in the mines of Ukraine have been considered. The problem of conducting coal mining by longwalls in the conditions of soft adjoining rocks, which concerns the protection of mine roadways located near the face, has been revealed. In such conditions, the existing protective constructions are ineffective due to the fact that they yield and get pressed into the soft rocks of the footwall. This indicated the need for research into the geomechanical state of soft rocks of the footwall. According to the results of known studies on the mechanism of rock mass failure around roadways and the data of physical and mechanical properties of the coal mass, which is represented by soft rocks, the correlation dependence has been obtained, the use of which allowed for the determination of the parameters of the rock deformation diagram and the establishment of the stability criterion of footwall rocks under the protection means and stability conditions of the geotechnical system “protective construction – adjoining rocks.” They are the basis of a new approach to ensure the stability of the roadways, which are supported behind the faces, by controlling the stress state in the system “protective construction – adjoining rocks.” This may be the basis for the development of new methods of protecting roadways in conditions of soft adjoining rocks., Razmatrani su uvjeti kod otkopavanja ugljena u rudnicima Ukrajine. Problem je otkopavanje ugljena metodom širokoga čela kada su stijene male tvrdoće („mekane”), je je time otežana zaštita rudničkih prostorija i cesta smještenih u blizini radilišta. U takvim slučajevima zaštitne konstrukcije postaju beskorisne jer se utiskuju u podinske stijene na radilištu. U radu su uspoređeni rezultati studija koje su ispitivale uvjete loma stijena ispod rudničkih prostorija (potkopa) te fizička i mehanička svojstva ugljena i okolnih stijena male tvrdoće. Iz toga je bilo moguće izračunati varijable stijenske deformacije te odrediti kriterije stabilnosti podinskih stijena. Zatim su utvrđeni uvjeti stabilnosti za geotehnički sustav „zaštitne konstrukcije – okolne stijene”. On je temelj za novi pristup u održavanju rudničkih prostorija, poglavito u prostoru iza čela radilišta, a uz kontrolu pritiska na i u stijenskome sustavu. Tako se mogu kontrolirati i uvjeti u rudničkim prostorijama, posebno onima koje služe za odvoz sirovine, a okružene su stijenama male tvrdoće.

At mining and processing complexes, many parameters today are evaluated from the point of view of the total process from geology to the final product. Changes in certain mining parameters inevitable lead to the changes in the following downstream processes. In this article, the focus is on the ore fragmentation, which is one of the most important parameters in many mines as it affects the downstream ore preparation and processing efficiencies, productivities and costs. In most of the cases, the cheapest way to improve the fragmentation of the ore is by changing the drilling-and-blasting design parameters. It of course increases the mining costs, but at the same time decreases the costs of the following processes, which are normally significantly higher. Therefore, authors of this article propose a new way of optimization of the drilling-and-blasting process by introducing new blast design modifications. Based on the analysis, research of the scientific information and the mining practise, the authors discuss the way of creation of the preliminary stress in the block of the open pit and hence improving fragmentation. Physical experimental blasts in “Belaya Gorka” open pit were performed and shown positive results reflecting a potential for continuation of the research in this direction in the future.

Problems of maintaining of development the roadways in conditions of the soft adjoining rocks have been considered. The engineering solution for resistance of rigid protection means by building local reinforced zones under these constructions has been suggested. Combination of protection means and reinforced zones has reduced roof rock subsidence. The operation of protection means and reinforced zones as a holistic construction has been viewed on physical and numerical models. Based on simulation results, the efficiency of deepening of protective means below the footwall, the alternative to which can be creation of the reinforced zones in the footwall rocks, has been established. Factors that have to be taken into consideration when setting parameters of a local reinforced zone under the protective means have been identified.

Tests of rock supports for the possibility of constructing stable isolated structures have been carried out. It was established that the stability of these supports can be achieved by layer-by-layer laying of the ordinary rock and metal mesh of reinforcing steel, and the construction of these structures at the boundary between the production and the developed space allows to maintain the operational state of the production. It has been suggested that the use of supports with an ellipsoidal shape of the bases, their orientation with a larger axis perpendicular to the production axis and the leaving of the compensation cavities, will reduce the displacement of the underlying soil rocks into the cavity of development.

In order to develop effective measures to ensure the operational condition of the development workings behind the face in the conditions of soft footwall rocks, the construction of local reinforced zones under the protection means has been proposed. The presence of such zones allows transferring the current load deep into the massif and creating a stable foundation under the protective structure. The results of researches concerning establishment of rational parameters of local reinforced zones with application of the method of finite elements, the method of experiment planning and the method of statistical processing of these results have been presented. The empirical dependence of the subsidence of the local reinforced footwall under the protection means on their load, deformation characteristics of the local reinforced zone and host rocks, width of protection means, strength of soft underlying rocks and geometric dimensions of the zone has been determined. The relative indicator of efficiency of local strengthening of a footwall which is used for determining of rational parameters of a locally reinforced zone has been offered.

The prospective coal-bearing areas of Donbas in Ukraine have been identified. Their development will increase the energy security of Ukraine. It has been suggested that the development of these areas will involve mining the coal seams in a weak roof and floor environment, which are characterized by low compressive strength, lower density and a tendency to plastic deformations. The stability has been assessed of the rocks outcrop on the contour of mine roadways for mines operating in these areas. It has been determined that roof rocks in most of these mines belong to a range of groups from very unstable to moderately stable, and the bottom rocks are, in most cases, prone to swelling. This complicates the intensive prospective areas mining with the use of advanced technologies, as well as secondary support for retained goaf-side gateroads with limited yielding property. The mines have been determined, for which this issue is relevant when mining the seams with further increase in the depth. The mechanism of displacement in the secondary supports and has been exemplified and studied using the numerical method. The obtained results allowed us to substantiate the necessity of developing new technical solutions for the protection of gateroads under conditions of prospective Donbas areas.

An effective way of protecting development workings by integrated rock wall structures is considered. The necessity of improving this method and its experimental verification is substantiated. Integrated rock wall structures are experimentally tested under laboratory conditions. On the basis of the results of physical modeling, parameters of integrated structures have been specified in terms of impact factors; their yield strength is also specified. The condition for ensuring the stability of the integrated protective structure, which allows calculating appropriate rock wall width, is determined.