Video logging probe

There are many places in the different countries of the world where working in the underground mines have been done below surface structures such as railway lines, roads, buildings, villages/residential colonies, pipelines, etc. The workings are generally old, abandoned and presently unapproachable. In some places, important delicate surface structures are installed above a portion of old abandoned underground workings. Safety of these important surface structures above old underground mine workings is a serious concern in many countries all over the world. Many times, it is difficult to move or divert these surface structures due to a number of reasons including technical problems, the involvement of huge expenditures and socio-economic issues. There is a need to assess the stability of these places and the procedure to stabilise the places if found unstable to make the structures safe. Hence, there is a need of proper stability assessment of the ground below these surface structures. The railway line is one of such important structures, where stability should be ensured for the safety of the passengers. In India, many underground workings are present below railway lines. Most of the workings are old and unapproachable and their stability status is in doubt. Dismantling or diverting of the important railway lines is a high-level policy matter and involves huge time and money besides complicated socio-political issues like the rehabilitation of the affected people. But the safety of the commuters using railways passing over the coal-bearing areas having mining activities cannot be compromised. Therefore, it is highly preferable to take protective measures instead of dismantling and diversion of lines, wherever possible. It is necessary to establish the position and dimension of the inaccessible underground workings below these types of important surface structures and carry out its stability analysis to take appropriate protective measures for the safety of the structures and commuters. This paper highlights the delineation procedure of the unapproachable underground roadways below surface structures with special reference to railway lines and its stability evaluation with case studies. Appropriate protective measures have also been suggested which are proved to be effective and validated the results of the study.

Purpose. Development of an adequate model of steel arch support for underground workings of deep coal mines to assess its stress-strain state. Methodology. The study of the deformation of steel arch supports in main workings of deep coal mines, comparing them with the results of analytical studies, considering the peculiarities of the time-dependent geomechanical processes in the rock mass near the face, and development a new mechanical model of the deformation of steel arch support during its loading based on this. The research employed methods of structural mechanics, field studies, and statistical processing of field measurement results. Results. Considering the development of geomechanical processes during the advance of the face, a new two-stage deformation model of steel arch support has been proposed, which operates in the first stage under a regime of specified deformations due to the movement of the contour of the workings, and in the second stage under a regime of specified loading after the loss of stability of the rock at the bottom, which will allow for a reasoned approach to the design of support, justification of its rational form, and ensuring the stability of underground workings in deep mines and quarries. Scientific novelty. Based on the patterns of deformation of steel support in capital workings, a new two-stage deformation model of steel arch support for capital underground workings in coal mines and quarries has been proposed, which corresponds to the conditions of its operation in real conditions. By analyzing the stress-strain state of the arch support, its possible forms have been justified, which have reduced material consumption and are adapted to specific mining and geological conditions. Practical significance. The new model of deformation of steel arch support in coal mines will allow for a reduction in the consumption of steel rolled special profiles used for support production, which is scarce under conditions where the main producers of special profiles – metallurgical plants named after Illich and Azovstal, both located in temporarily occupied Mariupol – have been destroyed. This will also reduce the cost of the extracted mineral resources and increase production efficiency.

Определение оптимальных параметров устойчивых камер и целиков для предотвращения обрушения горных пород и проникновения песчаноглинистых масс в подземные выработки на Соколовском подземном руднике является актуальной проблемой. Для ее решения использовалось многовариантное численное моделирование методом конечных элементов с помощью программного комплекса Rocscience RS2, который учитывает не только физикомеханические свойства пород и действующие в массиве напряжения, но и структурные характеристики массива, а также степень техногенного воздействия. В результате определено изменение напряженнодеформированного состояния массива, на основании чего вычислены коэффициент устойчивости окружающего массива, величины и направления его смещений, а также установлены зоны распределения вероятности разрушения массива в заданных интервалах граничных условий. Определены параметры камер и целиков, обеспечивающие общую устойчивость, минимизирующие возможность прорыва водогрязевых масс в выработки. The determination of the optimal parameters of stable stopes and pillars to prevent the rock collapse and penetration of sandclay masses into underground workings at Sokolovsky underground mine is an urgent problem. The way for resolving this problem has used the multivariate numerical simulation by finite element method using Rocscience RS2 software complex, which takes into account not only physical and mechanical properties of rocks and actual rock mass stresses, but also structural characteristics of the rock mass, as well as the degree of technogenic impact. As a result, the change in the stressdeformed state of the rock mass has been determined, on the basis of which the stability coefficient of the surrounding rock mass, the magnitude and direction of its displacements have been calculated, as well as zones for distributing the probability of rock mass fragmentation in specified intervals of boundary conditions have been determined. The paper determines the parameters of stopes and pillars providing the general stability and minimizing the possibility of breakthrough of water mud masses into the workings.

The Polkowice-Sieroszowice mine is one of three underground copper ore mines in Poland. These three mines belong to KGHM Polish Copper JSC, excavating one of the largest copper ore deposits in the world. The deposit is situated in the south-western part of Poland in the Lower Silesia province. Due to the specific and difficult geological-and-mining conditions in the three mines, seismic events occur which often result in an excavation serious damage defined as the rock-burst or elastic recovery. Such dynamic phenomena have been occurring since 1972 and have posed the most dangerous natural threats in underground workings. Therefore, the mining technology has to take the account of seismic hazard prevention. Numerous preventive measures adjusted to the conditions prevailing in the given operating field have to be applied so that the hazards can be mitigated, fought or limited. The appropriate choice of prevention activities must be preceded by measurements and observations, which constitute different methods for identifying, predicting and assessing the condition of the rock mass as well as for evaluating the protection effectiveness. In the Polkowice-Sieroszowice mine the rock-burst prevention involves: assessment of rock mass state and active, technological, and organizational-technical methods for combating the hazard. The active prevention consists in blasting works which provoke the rock mass to distress itself and thus to reduce its capability to accumulate elastic energy. The technological prevention embraces yielding the edges of the walls and pillars in the place of development, the extraction of the deposit with a wide opening of the front and the adjustment of the size of the technological pillar to the local geological and mining conditions. The organizational-technical measures introduce after-blasting waiting time and high hazard zones where the number of employees should be reduced. The influence of changes and improvements in the prevention activities on the seismic hazard was analysed and determined. The effectiveness of prevention methods was assessed in connection with their modifications, which concerned certain elements of active methods, the pillar size changes and alterations in the frequency of rock mass observations. Most of these modifications resulted from the operational progress and had a little impact on the seismic activity. Nevertheless, the effectiveness of such alterations was calculated. The research was carried out for one mining division in the Polkowice-Sieroszowice mine over the period of 2013-2015 years. The increase in the effectiveness of seismic/rock-burst prevention in most cases resulted in reduction of seismic activity.

The measurement method with the application of an extensometer for the detection of the manifestation of tectonic strain is presented in this paper. The instrument is operated in underground construction for engineering purposes, and the authors applied it in a deeply placed underground old mine gallery in the Bochnia Salt Mine, just at the tectonic boundary of the Outer Carpathians which is commonly considered to be a tectonically active zone. The presented study is characterized by two basic features. The first is the placement of the measurements deep in an old mine which is an environment free of atmospheric factors disturbing the detection of a tectonic signal. The second is a combination of routine measurements carried out for engineering purposes and research measurements enabling the extension of the observation of displacements in the space outside underground workings, inside the rock mass that has been penetrated by extensometer probes. The extensometric measurements have been made using three 7-meter long sections. The results showed the differentiation in the displacement rates of points placed in the side walls: in the southern profile, the annual displacements are approximately 1.5 mm and in the northern one – approximately 1 mm. The combined result corresponds to the amount of the annual convergence value which has been determined by the classical surveys in the excavation where extensometric measurements have been made. What is more, the ongoing displacements in the southern side wall involve the entire part of the rock mass which is penetrated by an extensometric probe, but the displacements in the northern side are only observed in the first 2 m of the penetrated part of the rock mass. This differentiation is interpreted by the authors as being the result of tectonic strain acting from the south exerted by the Carpathians.

There is currently a need for better understanding of backfill design requirements at depth or under highstress conditions, or in rock mass with poor quality. It is generally acknowledged that rock mass closure affects backfill performance but there is currently negligible practical guidance for a design engineer. Understanding how mining conditions induce closure onto backfill is essential, as is predicting the reaction of the backfill to passively supporting the rock mass. This paper introduces a new framework for backfill design incorporating closure conditions. Rock mass-backfill interaction is considered using parametric studies that consider the backfill’s ‘loading system’ as a combination of field stress, rock mass stiffness and the evolving geometry associated with ongoing mining. Parameterisation is used so that the extent of potential rock mass closure can be estimated for different mining conditions. Then, stiffness contrasts between backfill and the rock mass are considered. Load transfer from rock mass to backfill must be understood, neglecting initial closure occurring before the open stope is backfilled. The resulting analysis framework predicts the extent to which backfill distress may be an issue and enables assessment of the efficiency of increasing backfill strength and stiffness for a particular design scenario. A critical determination is that opportunities to engineer the backfill’s strength and stiffness to resist initial rock mass closure on the backfill when the adjacent stope is mined is limited to cases where stresses are relatively low and rock mass quality (evaluated using the geological strength index [GSI] or equivalent) is moderate to high. Conversely, in high-stress conditions the initial closure on the backfill may have negligible consequences if the rock mass quality is sufficiently high. These extremes are quantified for a particular mining method and geometry. However, the analysis approach is equally applicable to other mining methods and geometries, and the framework to tackle these different mining problems is provided.

Purpose. The research is aimed at developing the technology for chemical strengthening of mine workings using epoxy reagent to create a protective shield in unstable zones of rock masses, as well as at assessing the strength of the strengthened areas and improving the stability of mine workings. Methods. During the research, core samples extracted from the epoxy reagent-strengthened mass were tested to assess their strength and resistance to external influences. Numerical modeling was performed in ANSYS Mechanical 14.5 to analyze the stress-strain state of strengthened and non-strengthened areas. Findings. Tests of core samples taken from the Akbakai mine showed that failure mainly occurs in the zones of contact between the rock and the adhesive composition, with the share of new fractures not exceeding 15%. The adhesion strength was 0.15 MPa, which is three times higher than that of non-strengthened rock. The results of modeling confirmed the reduction of stresses and displacements in strengthened zones by 2-3 times compared to non-strengthened ones, which indicates the high efficiency of the proposed method to improve the stability of mine workings. Originality. For the first time, an innovative method of chemical strengthening of mine workings with the use of protective epoxy shield, which significantly increases the stability of the mass when conducting mine workings under the influence of mineral salts and external loads, has been substantiated. Practical implications. The developed technology of chemical strengthening of mine workings with the use of protective epoxy shield has a high practical significance for the mining industry. Its application will significantly improve the stability of rock masses, especially in unstable zones exposed to the influence of mineral salts, which contributes to improving the safety and durability of mine workings, reducing the risks of caving and cleavage, as well as increasing the efficiency of mining-tunneling operations.

The present study investigates the possibility of developing a novel method for reducing seismicity and rockbursts in deep underground mines based on modifying drilling and blasting patterns. The main goal was to develop and implement firing patterns for multi-face production blasting, which allow increasing the capability of inducing stress relief in the rock mass, manifested in the seismic event. This method may improve stability control in underground workings, and mitigate risks associated with the dynamic effects of rock mass pressure compared with currently used methods. Thus, the seismic energy may be released immediately after blasting in a controlled way. For this purpose, underground tests using modified blasting patterns and precise electronic detonators were carried out. Vibration data recorded from the multi-face blasting in the considered trial panels were assessed in the scope of amplitude distribution. Results of trials have proven that the method is promising and should be further developed to improve the effectiveness of rockburst prevention in deep hard rock mines.

1. For evaluating the stability of rocks in underground workings and predicting stability a differential consideration of the effect of geological factors and especially jointing is necessary. 2. It was established that the formation of falls in underground workings is due to the presence of a fall-hazardous model of joints. A rock block bounded by this model and located within the arch of the working is fall-hazardous. The shape and spatial arrangement of fall-hazardous blocks are predetermined by the joint systems developed in the rock mass. If the shape of the base of the fall-hazardous block is not isometric, then the orientation of the working influences the formation of the fall-hazardous model. 3. It was established that mineral filling of joints as a calcite coating does not have a strengthening effect on the rock. Falls are confined both to joints with and without calcite. The presence of a fall-hazardous model is determining. Joints with loose filling (clay gouge, rubble) not forming a fall-hazardous model do not participate in fall formation. In the absence of a fall-hazardous model the factor of the length and density of joints does not have an effect on fall formation. 4. A timely analysis of the rock mass around the tunnel by a geologist in the working under construction makes it possible to give recommendations on the use of temporary support and increases the safety and effectiveness of tunneling operations.

Coal mining disrupts the stress equilibrium of the surrounding rock mass, and the rock mass cracks as a result of the changes in the stress field, releasing strain energy and causing microseismic events. Monitoring seismicitiy during coal mining is critical for ensuring safe production and preventing geological disasters. In this study, we deployed 29 surface seismic nodes above an underground coal mine in the Yulin region of Shaanxi Province, China, to monitor the mining operation for 665 hours. A large number of microseismic events have been detected from continuous monitoring data, and analyzed using event clustering, source location, and mechanism estimate. The results show that (1) the frequency and intensity of microseismic events are related to underground mining working conditions; (2) the temporal and spatial locations of the microseismic sources may be utilized for real-time tracking the location of the underground coal mining face; and (3) three rupture mechanisms of tension rupture, implosion rupture, and shear rupture reflect the triggering mechanisms of the coal pillar failure, roof breakage and movement and fault slip. 

The deformation behavior of the rock and soil is a key problem in the construction of the underground pipe work, and will directly influence the time limit and difficulty of a project. Actually for the underground rock mass, the construction of pipe work is a stress release process which makes the deformation characteristic of the rock mass totally different with other conventional constructions, such as building construction, road and bridge construction. The reason is the stress paths of the two kinds of engineering are different; one is download stress path and the other is upload stress path, so the mechanical property and deformation characteristic of a kind of soft rock under both download and upload stress paths in the Three Gorges area were studied by using the elastoplastic modeling method. Through the experiments of lamellar marlstone of Badong formation, the manner of the interaction between plastic volume stain and shear strain, the direct effect of the plastic volume stain on shear resistance were investigated, and the conclusion that stress path is exactly the comprehensive performance form of the interaction between plastic volume stain and shear strain which has been proved by the trixal experiments of soft rock. Finally, the deformation behavior of marlstone was used to calculate the settlement in the numerical simulation of the underground pipe work's construction.

For the October deposit conditions extraction of the gently-sloping deposit of copper-nickel ores within the wings numerous faults intersecting the ore body is connected with increased danger of rock bursts and the requirement for carrying out a considerable amount of labor-consuming driving of dead ends. Mining is carried out in a continuous sequence by layers and chambers with stowing of the worked-out space with consolidating mixtures. Previously by driving and filling parallel cross drifts over the upper contact of the deposit a continuous concrete layer is built. The workings are orientated almost along the strike of tectonics fractures [1]. In seeking the possibility of reducing the volume of driving in zones of tectonic faults industrial experiments were carried out in two areas of the deposit intersected by faults. In contrast to the traditional scheme for constructing a protective slice there was simultaneous erection of sections of a protective slice within the wings of a fault before approaching the extraction front of the main reserves towards the tectonic fault zone. It was assumed that presence of an additional front of a protective slice leads to mutual shifting of the wings of a tectonic fault with loosening of the ore mass. As a result of this treatment of the reserves in the wings of the fault was accomplished without creating a protective slice beneath part of the ore bounded by the overlaying strata. The set of instrument and full-scale observations confirmed this assumption. In test areas both in stopes created beneath the protective slice and in the overworked part of the ore body no signs of increased mine pressure were noted [2]. However, industrial experiments were limited by the specific mining and geological conditions. Observations and measurements made in the test areas give information about the mechanical state of the rock mass at a limited number of points. Transfer of the technology to other conditions and depths requires additional substantiation and studies connected with considerable expenditure and organizational difficulties. In this situation it is possible most simply by means of mathematical modelling to reveal the most common features of stress field formation within the vicinity of a fault. Calculations of the stress-strain state for a rock mass were performed by the finite element method. In the mathematical describing material deformation the rock mass outside the plane of a tectonic fault was represented by elastic materials with corresponding mechanical properties. This assumption is correct in view of the fact that the rocks comprising the rock mass have high elasticity constants and the theological properties appear to an insignificant extent. The deformation of a tectonic fault was described by an elastoplastic material reflecting the main features of fault behavior under load [3, 4]. The original stressed state for the ore and surrounding rock masses is characterized by the presence of tectonic forces. Horizontal compressive stresses are 0.6-1.7"rH, and vertical stresses are 0.6-1.43,H (H is working depth). The most clearly expressed regions of disturbance of the original stressed state are confined to large amplitude faults. According to measured data in them both horizontal and vertical stresses may predominate which may lead to a marked difference in the mechanism of rock mass deformation within the vicinity of a fault on introducing mine working. In the present work the case is considered when within the vicinity of a tectonic fault horizontal stresses predominate. The original stress field in all of the calculations discussed below is adopted as follows: Cry = 3'H, a x = 1.53,H, rxy = 0. Corresponding to this at the outer boundary of the calculation region normal and tangential force components were prescribed. The stress -strained state of the rock mass was determined for the plane strain condition which is fulfilled here due to the considerable extent of a tectonic fault, and stoping and preparatory workings in direction perpendicular to the section in question. Values of mechanical properties for the ore body, the surrounding rocks, and stowing material were taken as typical for the October deposit conditions [5]. The corresponding values of Young's modulus were 5" 104, 8- 104 and 3.104 MPa, and for Poisson's ratio they were 0.25, 0.2, and 0.4. The ore body thickness was 25 m.

In recent years, there has been a spate of quite unexpected major failures within surface and underground mines that have significantly compromised mine stability and resulted in sustained loss of production. In the majority of these cases, evidence suggests that incipient, weak, generally incoherent structural fabric within the rock mass played a significant role in influencing the failure development. With the trend towards underground mines going ever deeper, and many of the large open pits transitioning to block cave operations, more focus is needed on gaining better structural geological understanding of incipient rock mass fabric within and outside the mining block so that such failure risks can be minimised. Current trends towards mine scale quantification of rock mass characteristics and development of local and regional scale discrete fracture network simulations, as basis for generation of synthetic rock mass models based on rigorous quantification of geological fabric assessments, is allowing better appreciation of the variability within a rock mass. However, comprehensive understanding of key elements of the geological fabric is often missing. This can lead, in worst case scenarios, to situations when the resulting models cannot be expected to capture the controlling mechanisms. This paper presents several structural geology techniques that are not widely known, or even commonly applied, either for large deep open pit design studies or for deep high stress underground mining. These techniques have merit for aiding risk minimisation for deep excavation through improved insight. Guidelines are provided for using fault striae data and applying stress inversion, slip tendency and critical stress evaluation approaches for advancing understanding of past and present day stress states — both key factors important to establishing the current stability state of major geologic structures transecting or bounding large surface or underground mining extraction blocks. Some techniques for estimating likely risk for inducing adverse slip on incipient geologic structures, potentially affected by mining, are also explored in the final sections of the paper.

Purpose. Predicting the formation of a stress-strain state (SSS) in the rock mass within the boundaries of influence of stope operations on the horizon -480 m in axes 2028 at the 10th Anniversary of Kazakhstans Independence (DNK) Mine. Methodology. An engineering-geological data on the host rocks properties are analyzed based on the international ISRM standard. Numerical modelling of the rock mass stress-strain state and the calculation of the load-bearing capacity of the compound support (roof-bolt+shotcrete+mesh) and arch support used at the mine are performed with the help of the RS2 software. This program, based on the Finite Element Method in a two-dimensional formulation, makes it possible to take into account a significant number of factors influencing the rock mass state. Findings. The calculations performed indicate that the support resistance is incommensurably low in comparison with the values of the initial stress field components in the rock mass. In such conditions, it may be more effective to strengthen the mass in the vicinity of mine working than setting more frames or using more massive support profiles. Originality. The paper presents the results of mathematical modeling and calculation of the stress-strain state of the underground supporting aquifer rock mass structures developed for complex mining-and-geological and geomechanical conditions of driving, supporting and operating mine workings on deep horizons of the mines at Donskoy Ore Mining and Processing Plant. Based on the performed research, the preliminary (advanced) strengthening of the border rock mass in the zone of inelastic (destructive) deformations has been substantiated, as a priority method to control the stability of mine workings. Practical value. The research results can be used when creating a geomechanical model of the field and designing stable parameters of mine working support.

This research aims to develop a methodology of selecting and validating support system designs for different purpose roadways by means of synthesizing the rock mass quality index Q and the stability categories which are in application in mines in Russia. The existing approaches to rock mass quality evaluation based on different combinations of complementary classification criteria are reviewed and generalized. It is found that the stability categories in use in Russian mines comply with the Q-index, which enables their flexible adaptation to specific features of a deposit and allows revealing of average mining conditions for different mines. The multi-factor rock mass quality rating and classification made it possible to justify mine designs per different categories. On this basis, the safe shapes and cross-section sizes are determined for the face entries for the prevalent geological conditions of ore mining under equicomponent (hydrostatic) stress state. The analysis and generalization of actual data from operating mines in the ore provinces in Yakutia, Russian Far East, Krasnoyarsk Krai and Eastern Kazakhstan allowed correlating the maximum permissible widths and cross-section shapes of roadways, as well as the roadway purpose and the rock mass quality by the Q-system by Barton. The revealed patterns of rock mass stability effect on the roadway roof span size made it possible to define rockbolting design variables for the face entries of operating mines in rock masses characterized by the widely ranging Q-index. The implementation of the integrated approach to rock mass stability estimation can improve reliability of the pre-project and project design solutions aimed to enhance safety and efficiency of roadways in different geological and geomechanical conditions of mineral mining.