Search

In order to solve the problems of ignoring multi-dimensional load characteristics, cumbersome modeling process and long design cycle in the design process of hydraulic support in steeply dipping angle coal seam, combined with the load characteristics of hydraulic support in large dip angle pseudo-inclined working face, the design system of large dip angle hydraulic support is developed. Based on the comprehensive research methods of motion simulation, strength test and physical experiment, taking the design of ZY5000/15.5/38 hydraulic support for steeply dipping angle coal seam as an example, the mechanical model is established according to the multi-dimensional stress characteristics of hydraulic support in large dip angle pseudo-inclined stope. The spatial load characteristics of large dip angle hydraulic support are analyzed, and the mechanical linear matrix of top beam and shield beam of hydraulic support in pseudo-inclined working face is established. The design system of hydraulic support is built by using VB.NET as the development language combined with linear matrix and SOLIDWORKS secondary development modeling software, and a good human-computer interaction user interface is developed. The research and analysis show that the trajectory range of the front end of the top beam of the model hydraulic support generated by the system is about 48 mm, and the trajectory curve of the front end of the top beam of the support satisfies the characteristics of double torsion line. The maximum stress value of the model support is 146.7 MPa, which is far less than the equivalent stress value of the material yield, and the maximum deformation displacement is not more than 0.531 mm. The working resistance of the physical model hydraulic support with a similarity ratio of 1:5 is about 38 kN. The loading characteristics of the top beam and the shield beam of the support are tested under different conditions. The mechanical data of the model support in the experiment are basically consistent with the mechanical data generated by the system, and the experiment meets the motion requirements and bearing characteristics of the support in the stages of initial support, resistance increase, constant resistance and pressure relief. The research results reflect the good adaptability of the model hydraulic support under the design system, which has certain scientific and practical significance for enriching the design theory of hydraulic support in steeply dipping angle coal seam and guiding the design and production of hydraulic support.

Abstract In the process of fully mechanized top-coal caving mining, the top-coal is affected by mining-induced stress, and the stress varies along the strike direction of working face, so the boundary position of its entering the limit equilibrium state changes accordingly. The determination of the boundary along the strike direction of working face can provide scientific guidance for the stability control of support-surrounding rock in fully mechanized top-coal caving face. Using the research methods of theoretical analysis, physical similarity simulation experiment and numerical simulation experiment, the stress state analysis model of the boundary position of the top-coal limit equilibrium zone under macro-scale conditions was established, the stress state characterization method of the boundary of the top-coal limit equilibrium zone along the strike direction of working face was given, and the quantitative characterization of the boundary of the top-coal limit equilibrium zone along the strike direction of working face was realized by combining with the mining-induced stress path, and the distance relationship between the boundary of the top-coal limit equilibrium zone and the langwall face along the strike direction of working face was revealed. The results show that after critical mining in fully mechanized top-coal caving face, the distance between the boundary of top-coal limit equilibrium zone and the langwall face along the strike direction of working face presents a relationship of increasing from top to bottom. The distance between the top-coal upper boundary and the langwall face was 2.85 m and the distance between the top-coal lower boundary and the langwall face was 5.39 m. The boundary of top-coal limit equilibrium zone along the strike direction of working face was verified by the top-coal elastic–plastic zone boundary and the boundary of the peak position of front abutment pressure in different layers of top-coal. The results show that the quantitative characterization of the top-coal limit equilibrium zone boundary along the strike direction of working face was reasonable. In order to improve mine production efficiency, optimization measures were put forward for hard coal seam and soft coal seam respectively.

Close-hole roof-cutting technology (CHRCT, also called “dense drilling”) has been widely applied in coal mines due to its economic and safety benefits. Inappropriate cutting parameters and support schemes can lead to dynamic pressure disturbances in self-forming roadways with thick and hard roofs. Moreover, fully characterizing the procedure and process of self-forming roadways using CHRCT in the field is difficult, resulting in unconvincing results. Therefore, this study aims to fill the gaps in theoretical knowledge and methodology. First, the dynamic pressure characteristics of the self-forming roadway using CHRCT were investigated, and the dynamic pressure types of the roadway were classified. There are three main types: roof cut off along the coal wall side of, severe deformation, and overhanging roof of a roadway after the second working face mining. The effects of different hole parameters (inclination angle, depth and spacing) on the roof cutting to form a roadway were also investigated. The optimal hole inclination, depth and spacing of 15°, 8 m, and 200 mm were determined through a series of experiments. Then, three support schemes embedded in the roadway were compared in terms of stress evolution, bolt and cable axial forces, roof displacement, and structure. Finally, this study proposes a dynamic pressure mitigation strategy through the optimization of parameters for close-hole roof-cutting and support schemes, monitoring and controlling ground pressure in roadways, and taking auxiliary measures for pressure relief. The results show that this strategy can effectively eliminate the dynamic pressure of the roadway and meet the stability requirements of the full mining cycle. This paper presents a methodology for analysing CHRCT via numerical simulation. Moreover, this approach is of great theoretical and practical importance for dynamic pressure control for self-forming roadways using CHRCT in thin coal seams with thick and hard roofs.

In this study, the No.S1201-II working face of a coal mine using self-formed roadway mining technology without coal pillars was used as the engineering background, and physical experiments, numerical simulations, and field measurements were employed to study the spatiotemporal evolution laws of overburden fracture and obtain the periodic breaking law of the overburden. The results revealed the following: (1) the working face length increased after roof cutting, which led to an increase in the roadway stress on the side away from the mined area. The roof displacement remained essentially unchanged when the roadway was in the digging and cutting stages. However, the roof displacement continued to increase during the sinking and forming stages. (2) The height of the fall zone before roof cutting was approximately 17.1–19.4 m, which was 4.3–4.8 times the mining height. The maximum heights of the fracture zone on both sides and in the middle of the working face were 103.6–106.4 m and 92.4–96.1 m, respectively, corresponding to 25.9–26.6 and 23.1–24.0 times the mining height, respectively. The height of the fall zone after roof cutting was approximately 18.1 m, which was 4.5 times the mining height. The maximum heights of the fracture zone on both sides and in the middle of the working face were 100.6–105.2 m and 91.3–95.2 m, respectively, corresponding to 25.1–26.3 and 22.8–23.8 times the mining height, respectively. (3) Combined with the ground pressure behaviors and overburden breakage monitored in the field, the fracture budding phase, fracture development phase, and fracture maturation phase were divided according to the characteristics of microseismic events. A criterion for overburden deformation damage based on microseismic energy was proposed. This study provides a reference for the establishment of a microseismic-monitoring system and the application of this technology.

Abstract To study the fracture instability characteristics and fracture mechanism of overlying strata in steeply dipping and large mining height stope, through the combination of physical simulation experiment, numerical calculation, theoretical analysis and field measurement, the correlation between the evolution of mining stress field and the fracture of overlying strata in large mining height stope under the effect of dip angle is analyzed, and the stress transfer path and the fracture mechanism of overlying strata are revealed. Finally, the influence mechanism of key strata on the evolution of the mining stress field of overlying strata is explained. The research shows that under the influence of gravity dip angle effect and mining height increase, the mining stress is non-equilibrium transferred and evolved in space, and the principal stress field presents the characteristics of partition evolution. The fracture trajectory of rock strata is multi-step and “八” shaped, and the inclined masonry structure and multi-step key strata form a cooperative bearing structure. The key layer of the ladder is the stress transmission structure between the caving zone and the stress arch, and the high stress in the overhanging area under the main roof is transmitted to the advanced roof. With the increase of dip angle, the height of the caving zone decreases, and the fracture range of ladder and principal stress arch decreases. The cracks in the middle and upper broken rock blocks increase, and the instability of the “high ladder rock layer” is easy to induce the simultaneous fracture of the “inclined masonry structure”, resulting in regional unbalanced instability and impact. The research results can provide some reference and guiding significance for the stability control of surrounding rock in longwall stope with steeply dipping.

The hydraulic support is the core of the stability of the ‘surrounding rock and equipm ent’ system in the pitching oblique working face of steeply dipping coal seam. The existing hydraulic support structure can not meet the requirements of spatial stability of pitching oblique mining, which seriously affects the safe and efficient mining of working face under such conditions. Taking the pitching oblique working face of steeply dipping coal seam as the research background, the comprehensive research methods of engineering analogy, structural kinematics analysis and numerical simulation are used to analyze the stability characteristics of ‘support-surrounding rock’ in the pitching oblique working face of steeply dipping coal seam. Based on ZY7000/22/45 hydraulic support, a new parallelogram hydraulic support is invented, the structural rationality design is carried out, and the kinematic response characteristics of key components are analyzed.The research shows that the non-uniform filling of the caving gangue and the crushing, pressing and pushing effect of the gangue on the support are the key factors affecting the stability of the support. The parallelogram top beam and the base are more suitable for the pitching oblique working face. The arrangement of the top beam, base and column of the parallelogram support is parallelogram. The special-shaped shield beam, the rear connecting rod, the oil cylinder connecting rod and the base constitute a flexible four-link structure. The column of the parallelogram support is the main bearing structure, and the cylinder connecting rod is the main motion mechanism. The main influencing factors of its motion characteristics are the distance between the upper and lower column sockets and the distance between the front and rear connecting rods and the hinged position of the shield beam. The shield beam and the rear connecting rod are the key to the position and posture control of the support, and there is no double torsion line during the movement of the support. The research results provide a type selection for the support of this kind of working face, which ensures the safe production of this kind of coal seam to a certain extent.

Abstract To solve the problem that the macroscopic deformation and failure of coal–rock medium under external loads are easy to be observed while the internal stress transfer mode and path are unclear. Based on the discrete element idea, the numerical models for pure coal or rock samples and coal–rock combination samples with different lithologies and combination methods under concentrated force are established by PFC2D software. Then the influence of coal or rock strength and combination methods on the internal stress transfer law and distribution evolution characteristics of coal–rock medium are discussed from the perspectives of macroscopic stress and mesoscopic force chain, respectively. The results showed that under concentrated load, the macroscopic stress transfer paths within pure coal or rock samples and coal–rock combination samples are primarily in the form of ‘point source radiation’. However, when transferring between coal–rock interfaces, there is a certain interface effect. For pure coal or rock samples, differences in lithology does not change the transfer rules and macro distribution patterns of internal stress, but it can cause changes in internal unit transfer stress value and local area transfer direction. For coal–rock combination samples, the greater the difference in lithology between the two sides of the interface, the more likely the interface effect will occur. In addition, the internal stress transfer is also influenced by the relative stratigraphic relationships of coal and rock. When the stress is transferred from a higher-strength rock to a lower-strength coal mass, the interface effect will be more significant. However, regardless of the combination pattern, the locations where significant stress surges occur are always within the higher strength rock mass near the interface. The findings are helpful to understand the mechanical properties and failure mechanism of mining coal and rock mass, and provide a theoretical basis for the study of the mining-induced mechanical behavior of the floor under the action of the coal pillar.

To solve the problem of stability control of coal pillar in steeply dipping coal seam (SDCS), based on the characteristics of surrounding rock structure and stress environment of the coal pillar, a special bearing structure of ‘roof-coal pillar’ combination is proposed through theoretical analysis. The mechanical model of inclined ‘roof-coal pillar’ structure is established, and the stress and strength characteristics of each element in the structure are deduced. Combining numerical calculations (PFC2D-FLAC2D coupling model) and physical similarity simulation, the stress evolution characteristics and failure mechanism of the ‘roof-coal pillar’ structure under the influence of mining were revealed. The results show that the coal pillar of SDCS is easy to form a ‘roof-coal pillar’ combined bearing structure with the roof strata. Under the influence of mining, the stress distribution and deformation evolution within the ‘roof-coal pillar’ structure show strong non-uniform and asymmetric characteristics. Among them, the stress distribution shows an ‘ellipse’ shape which is offset to the upper section, and the main deformation zone of the structure is a diagonal deformation distribution zone that runs through the coal and rock in the same direction as the stress offset. The failure of the ‘roof-coal pillar’ structural firstly occurs in the coal area near the coal-rock interface on the side of the lower section, and finally forms a diagonal failure crack running through the coal and roof, which is manifested as a diagonal shear failure mode. The findings can provide a theoretical basis for the stability control of coal pillars in multi-section mining of SDCSs and improve the safety production technology level of the working face.

AbstractWhen the working face of a steeply dipping coal seam crosses a fault, the dynamic disturbance caused by the mining load induces fault activation, causing large deformation and failure of the roadway. In this study, a physical similarity simulation and numerical calculation method were used to determine the main factors that the deformation and failure of fault zone roadway and reveal the underlying mechanisms. The results show that when crosses a fault, the high static load formed by the coupling of mining stress and fault pillar stress induces mining stress-type fault activation, which leads to large deformation and damage to the roadway in the fault zone. The main controlling factors are the fault location and mining load intensity. In terms of fault location, the vertical stress concentration away from the roadway side of the fault surface was high, the principal stress deflection angle was large, and the surface deformation of the fault on the roadway left side was the greatest. In terms of mining load intensity, the deflection angle of the principal stress of the surrounding rock initially increased and then decreased, and tensile failure easily occurred near the fault surface. These results provide a reference for roadway support.

The steeply dipping coal seam is one of the main forms of coal storage in China. It is widely and regionally distributed. According to incomplete statistics, twenty-six provinces, autonomous regions and municipalities directly under the central government are involved in the mining of such coal seams, with abundant reserves, large production and high production concentration in the central and western regions. It shows diversity and complexity in terms of the conditions of existence, with different regions having different coal formation periods and different tectonic control processes, forming diverse and complex mining conditions and giving rise to different mining technology requirements. The mining of steeply dipping coal seam is technically difficult. The asymmetry of the movement and damage of the peripheral rock in the mining area affected by the inclination angle of the coal seam is obvious, and the difficulty of the stability control of the support system and equipment, the matching and coordination of the “three machines”, the layout and support of the mining roadway, and the safety guarantee of the “human-machine” environment at the working face has increased significantly, which seriously restricts the safe and efficient mining of the mine. This has seriously restricted the improvement of safe and efficient mining. The regional economic demand for the mining of steeply dipping coal seam is strong. This kind of coal seams and the production of more concentrated areas are mostly seen in the coal industry-based resource cities, the economic structure is relatively single, the safe and efficient development and utilization of coal resources for the regional energy supply, people’s livelihood, economic stability has the role of the bottom of the pocket, the demand is urgent. For a long time, mining technologies for the steeply dipping coal seam changes focus on solving the “difficult” and “need” contradiction. In the coal mining methods and techniques, strata control theory and technology, complete sets of equipment development and application of the three aspects of continuous improvement, innovation, development, to achieve the transformation from non-mechanized to fully-mechanized mining, the level of safety and production efficiency has increased dramatically, the personnel labor intensity has decreased dramatically, and the operating environment has improved significantly. In the mid-1990s, Lvshuidong Coal Mine of Sichuan Coal Industry Group Limited Liability Company successfully realized longwall fully-mechanized mining in steeply dipping coal seam with medium mining height for the first time, breaking through the "forbidden zone" in this filed. Under this demonstration, the three pioneering engineering practices of longwall fully-mechanical mining of steeply dipping coal seam with thick mining height, steeply dipping coal seam with large mining height, and longwall fully-mechanical mining of steeply dipping coal seam with thin mining height in pseudo-inclination have been successful successively, which innovated the non-linear limiting arrangement of the working face and the way of adjusting the slanting, established a multi-dimensional interactive control mode of the system stability of the “bracket-surrounding rock”, and researched and developed the “support and stability and heavy weight, high-strength and light-weight, safe and reliable, and matching synergistic” complete set of equipment of the working face, which has achieved good results, and the scope of application of the comprehensive mechanized mining technology has further been widened. At the same time, there are still many key scientific problems and technical bottlenecks that need to be broken through in the mining of steeply dipping coal seams, resulting in a large gap between the intelligence level and that of the flat/gently inclined coal seams. Research on the mining dynamics of coal and rock bodies in inclined bedded coal beds, revealing their control mechanisms on the disaster of the surrounding rocks in the mining field, and realizing quantitative characterization need to be further strengthened. It is necessary to further clarify the multi-dimensional dynamic process and law between the system of “rock-bearing structure - mining equipment group”, improve the theoretical and technological basis of “multi-dimensional dynamic multi-objective synergistic control of equipment and surrounding rock”, and realize the transformation and application of the technology. On the basis of breakthroughs in scientific issues, we will carry out systematic technological innovation and research and development of coal mining methods, mining techniques, rock formation control, and complete sets of equipment, so as to crack the bottleneck of the constraints on the double enhancement of “safety and efficiency” in the mining of steeply dipping coal seams, and make the upper limit of the inclination of the steeply dipping coal seams for comprehensive mechanized mining extend upward under the prerequisite of reliable technological safeguards, so as to lay the foundation for the realization of automated and intelligent mining.

Taking the steeply dipping and large mining height working face of a mine as the engineering background, through the combination of physical simulation experiment, numerical calculation, theoretical analysis and field monitoring, based on a comprehensive analysis of the deformation and failure characteristics of the macrostructure of surrounding rock, the roof breaking mechanism and support instability characteristics of large mining height working face under the angle effect are studied. The research shows that due to the influence of the dip angle of the coal seam, the roof stress is asymmetrically deflected along the tendency, and the load of the overlying strata is transmitted to the upper and lower coal bodies with the stress-deflection boundary as the boundary, resulting in the deformation and failure of the roof and the filling showing obvious asymmetric characteristics. With the increase of dip angle, the asymmetric characteristics of roof stress transfer are enhanced, the stress release arch is reduced, the height of caving zone is reduced, the deformation and failure area is gradually moved up, and the regional characteristics of roof loading and deformation and failure are more obvious, which leads to the significant increase of unbalanced loading degree and instability probability of supports in different areas. Combined with the actual production, the prevention and control measures of hard roof caving and support crushing in fully mechanized mining face with steeply dipping seam and large mining height are put forward.

Coal wall of large mining height face in steeply dipping coal seam has large free height, wide free movement space and poor self-stabilization balance, coal wall is not an isolated body in the face, it can form a load-bearing structure with the surrounding rock, supports and other mediators, and the mining behavior is closely linked. The dip angle effect can easily promote the dissimilation of the coal wall bearing environment, complicate its response behavior, increase the difficulty of coal wall and surrounding rock stability control, and restrict the safe and efficient production of the face. In order to solve the problem of coal wall stability control of large mining height face in steeply dipping coal seam, theoretical analysis and numerical calculation are comprehensively used for research. The stress in the plastic zone of large mining height face in steeply dipping coal seam increases exponentially, there is an asymmetric arch residual stress influence zone in the vicinity of the coal wall, the plastic zone breadth is dissimilated in different regions, and the width from large to small is the upper, middle and lower part, and the distribution pattern is in the shape of stepped arch, coal in the plastic zone bears repeated pressure, and will be enhanced with the expansion of plastic zone. As the mining height increases, the residual abutment pressure near the coal wall decreases, the compressive strength, displacement value and disturbed range of the coal in front of the coal wall will increase. The stress and transport of the coal wall under the dip angle effect develop in a zonal manner, in which the stress distribution is lower> upper> middle, while for the displacement is middle> upper> lower. In addition, the working face inclination under the oblique angle will lead to the transformation of the coal wall instability mode, when the oblique angle is large, the dip angle of face is small, the compression component of abutment pressure is enhanced, and the external convex spalling mainly occurs. On the contrary, it’s the sliding instability under the coupling of mining stress and self weight. The comprehensive analysis shows that the coal wall mining behavior is regionally heterogeneous under the coupling effect of dip angle and mining height, and because the stress unloading and migration in the middle and upper part of the face are larger, therefore the two regions should be the key prevention and control areas for coal wall instability of large mining height face in steeply dipping panel.

AbstractIn this paper, taking a mine in Xinjiang as the engineering background, through the combination of physical simulation experiment, 3DEC numerical calculation, theoretical analysis and field monitoring, the fracture evolution characteristics of overlying strata and its influence on the stability of support under unbalanced loading conditions are systematically studied. The results show that under the action of gravity-dip effect, the non-uniform filling of gangue leads to the typical cross-layer migration characteristics of overburden caving shape and roof bearing arch. The unstable inclined masonry structure is formed in the middle and upper areas, which is prone to rotation and sliding instability, forming impact pressure. The mining stress of the overlying strata changes significantly due to the mining of the coal seam. The lower the overlying strata, the greater the peak stress, the smaller the stress value in the goaf, and the greater the stress change. The amplitude and instability probability of the support migration increase with the decrease of the working resistance of the support, the increase of the friction between the roof and the support, and the increase of the partial load of the support. Finally, the prevention and control measures of roof caving crushing support in steeply dipping and large mining height working face are put forward.

Paste composite filling mining is one of the effective ways to realize green mining. In order to study the movement and deformation characteristics of overlying stratum in paste composite filling stope, taking the test mine as the engineering background, a mechanical model of movement and deformation of roof rock beam in paste composite filling mining was established by combining theoretical analysis, physical simulation and numerical simulation. The movement and deformation laws of main roof, sub-key stratum and main key stratum in the process of working face advancing under the conditions of multiple factors (mining height, filling ratio and buried depth) were analyzed. The results show that the displacement contour of overlying stratum is inverted trapezoid in the process of advancing working face which is unfilling or filling 2/3. The subsidence of stratum near the coal seam is larger, and the subsidence of stratum with higher distance from the coal seam is smaller, and the maximum subsidence point of overlying rock appears near the side of the open-off cut. With the increase of mining height, the range of overlying rock caving zone becomes larger, and the maximum subsidence value gradually increases. When the paste filling ratio of the working face increases, the collapse range of the roof decreases, the overall compression of the collapsed rock decreases, and the effect of control on the movement and deformation of the overlying rock is obvious. The subsidence of overlying stratum increases with the increase of buried depth of working face, but it does not change much. The deflection value of the roof rock beam changes slowly at both ends of the propulsion due to the support of the coal wall. The closer to the middle, the greater the change. The results of this study can provide an important reference for the control of the roof stability and surface subsidence of the paste composite filling mining.

Revealing the space-time evolution characteristics of overlying strata deformation and failure is the key for safe and efficient mining of steeply dipping coal seam. In this paper, based on the physical similarity simulation experiment and field measurement method, the non-uniform filling characteristics of gangue in gob and the roof migration law are comprehensively determined, the evolution characteristics and distribution patterns of the abutment pressure in the upper and lower sections, the distribution characteristics of the working resistance of the support, and the regional strata behavior law in the mining process are analyzed, and the technical measures for the stability control of the support in steeply dipping coal seam are put forward. Results shown: With the advancing distance increases, the accumulation range of gangue increases, and the inverted triangle airspace begins to appear repeatedly in the gob behind the support. In the deep gob, the angle between the gangue pile and the horizontal plane decreases continuously from the lower part to the upper part along the inclined direction. Horizontal displacement, vertical displacement and combined displacement of roof show an evolutionary trend of ‘increase – stability’. The peak displacement position moves from the upper part to the middle part of the working face, which is located at the hinge point between the broken block and the failure envelope surface. The evolution of abutment pressure of headgate and tailgate T-junction shows a trend of ‘increase – stability’. The peak and concentration coefficient at headgate T-junction are greater than tailgate T-junction. The load imbalance characteristics of the support in working face are obvious, and the basic characteristics along the inclined direction are the largest in the middle area, the second in the upper and the smallest in the lower area. The initial force and working resistance of support should be improved, and the position of the support should be adjusted in time in practical engineering. The results provide reference and guidance for practical production.

The deformation and failure law of stope roofs is more complicated than horizontal coal seams affected by the angle of the coal seam during the mining process of steeply dipping coal seams. This study focused on and analysed the working face of a 2130 coal mine with steep dipping and large mining height. Through the use of numerical calculation, theoretical analysis, physical similar material simulation experiments, and field monitoring, the distribution characteristics of roof stress, as well as the threedimensional caving migration and filling law, in large mining height working faces under the dip angle effect was investigated. The influence mechanism of the dip angle change on the roof stability of large mining heights was investigated. The results revealed that the roof stress was asymmetrically distributed along the inclination under the action of the dip angle, which resulted in roof deformation asymmetry. With the increase in the dip angle, the rolling and sliding characteristics of roof-broken rock blocks were more obvious. The length of the gangue support area increased, the unbalanced constraint effect of the filling gangue on the roof along the dip and strike was enhanced, and the height of the caving zone decreased. The stability of the roof in the lower inclined area of the working face was enhanced, the failure range of the roof migrated upward, and the damage degree of the roof in the middle and upper areas increased. Furthermore, cross-layer, large-scale, and asymmetric spatial ladder rock structures formed easily. The broken main roof formed an anti-dip pile structure, and sliding and deformation instability occurred, which resulted in impact pressure. This phenomenon resulted in the dumping and sliding of the support. The 'support-surrounding rock' system was prone to dynamic instability and caused disasters in the surrounding rock. The field measurement results verified the report and provided critical theoretical support for field engineering in practice. [ABSTRACT FROM AUTHOR]

Copyright of Archives of Mining Sciences is the property of Polish Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)