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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.

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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.)

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.

The dip angle of coal seam is one of the important factors that cause the complexity and particularity of the mining dynamic behavior of the large dip angle stope and induce many disasters and accidents. In order to reveal the influence law of the dip angle of coal seam on the control of surrounding rock and the characteristics of mine pressure in the large dip angle stope, the research method of physical similarity simulation and numerical calculation is adopted. Based on a comprehensive analysis of the features of roof crack and gangue sliding and rolling filling in steeply dipping working faces, a finite element discrete element (FLAC2D-PFC2D) coupling algorithm is used to establish a coupled numerical model of high angle mining areas with different inclinations. The stress distribution of surrounding rock and the inclination effect of gangue filling features in steeply dipping mining areas are studied. The results show the following points. ① Under the action of mining, the stress distribution of the surrounding rock in the roof and floor of the high angle mining area is asymmetric arched. As the dip angle of the coal seam increases, the range of the arched vertical stress release zone and the degree of upward displacement gradually increase. But the range and force value of the horizontal stress release zone gradually decrease. Both vertical and horizontal stresses are prone to stress concentration at the top and bottom of the working face. But the maximum concentrated stress value will decrease with the increase of coal seam inclination angle. The stress magnitude and transmission direction inside the roof and floor of the steeply dipping working face exhibit asymmetric features. As the coal seam dip angle increases, the stress arch height of the working face roof and floor gradually decreases. The transmission direction of surrounding rock stress is mainly towards the mining space, and gradually deviates from the initial approximate vertical direction towards the vertical direction of the working face. ② The roof crack of the working face and the sliding and filling of gangue exhibit temporal and regional evolution features, and exhibit a certain dip angle effect with the change of coal seam dip angle. As the inclination angle of the coal seam increases, the initial breaking position of the direct roof will gradually shift towards the upper area of the working face. At the same time, due to the increased force of gravity along the inclination direction of the working face, the filling degree of the gangue along the inclination direction will be more dense. But the filling length will decrease. As the inclination angle of the coal seam increases, the degree of crack and the range of voids in the high-level rock layers in the upper and middle areas of the working face will also increase. ③ The mechanism of the action of gangue on the surrounding rock in the goaf is mainly reflected in providing lateral stress and vertical support, and is greatly affected by the gravity of gangue, which will show a strong inclination effect with the change of coal seam inclination angle.

The structure and stress environment of the surrounding rock at the longwall mining area in the steeply dipping coal seam are alienated, and the composition factors and disaster modes of the ”support and surrounding rock” system in the working face are affected. This leads to some frequent safety accidents in the working face, low coal extraction rate, and high roadway excavation rate. This paper analyzes the mining mechanics behavior of surrounding rock of in the steeply dipping coal seam and proposes a technological concept of partial backfill non-pillar mining in the longwall faces of steeply dipping coal seam. During the process of advancing the working face, partial backfill is carried out along the inclined direction in the lower part of the goaf. The filling body not only forms a gob-side roadway with the support effect of the roadway side, but also eliminates the protection coal pillar, achieving a non-pillar mining. At the same time, the length of the filling and compaction area at the lower dip of the working face is increased, enhancing the stability of the ”support and surrounding rock” system of the working face. Based on the characteristics of the longwall mining area in the steeply dipping coal seam, the partial backfill process of the steeply dipping coal seam paste was optimized and determined. And the partial backfill recovery system and mining and filling process in the steeply dipping coal seam were designed. By using a combination of theoretical analysis, simulation experiments, and numerical calculations, the regulatory mechanism of partial backfill on the mechanical behavior of surrounding rock at the longwall mining area in the steeply dipping coal seam was analyzed. The results show that the filling body affects the deformation and failure of the main roof rock beam, as well as the bearing characteristics of the coal and rock mass on the lower side of the mining area. The deformation of the main roof and the roof of the head entry, as well as the constraints on the coal and rock mass on the lower side of the head entry, all decrease with the increase of filling length. In order to prevent the hanging roof disaster in the unfilled area of the goaf, the filling length should not exceed 1/3 of the working face length. The partial backfill body restricts the fracture of the roof in the lower area of the working face, reduces the formation layer of the critical zone of the overlying rock, forms a stable roadway, and reduces the deformation of the surrounding rock gob-side roadway retained. At the same time, the length of the filling area at the lower part of the working face increases, and the length of the unstable area of the middle and upper surrounding rock structures decreases, improving the stability of the ”support and surrounding rock” system. The filling body changes the stress transmission path of the surrounding rock in the mining area, bearing part of the overlying rock load. The side abutment pressure on the lower side of the working face and the front advanced pressure both decrease with the increase of filling length, and the front support pressure in the lower filling area of the working face has the greatest decrease. The stress state of the gob-side roadway and the working face is improved. Technology of partial backfill non-pillar mining in the longwall faces of steeply dipping coal seam has the advantages of effectively improving resource recovery rate, reducing the roadway drivage ratio, alleviating the tension of mining and replacement, and strengthening the stability of the ”support and surrounding rock” system in the working face. It is of great scientific significance for guiding the green, safe, and efficient mining in the steeply dipping coal seam.

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.

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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.)

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department 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.)

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. [ABSTRACT FROM AUTHOR]

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.

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology 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.)

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.

The stability of the coal pillar is the basis of safe and efficient mining in the longwall working face of steeply dipping coal seams. Based on a systematic analysis of the deformation and instability of the surrounding rock in the quarry of a steeply dipping coal seam, the structural model of coal pillar for multi-section mining of steeply dipping coal seams is established. The stress distribution of an inclined coal pillar considering the action of shear stress is studied, and a generalized Mohr circle characterizing the stress state of the inclined coal pillar is provided. According to the planar geometric relationship between the stress circle and strength envelope, the calculation equation of strength with an implied inclination angle is proposed, which can help solve the coal pillar safety factor. The influence of coal seam inclination angle, lateral pressure coefficient, width-to-height ratio and other factors on the strength of inclined coal pillar is discussed. The reliability of the theoretical analysis has been tested using on-site engineering examples. The difficulties in controlling the surrounding rocks of the section return airway for inclined coal seam mining are analyzed by using the engineering case in Pansidong coal mine as an example, and the asymmetric surrounding rock coupling support is proven to be a successful support strengthening technology. The research results can provide a reference for the coal pillar strength estimation in steeply dipping coal seams and the control design of surrounding rocks in similar working faces. [ABSTRACT FROM AUTHOR]

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]

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. [ABSTRACT FROM AUTHOR]

The migration process of rockfall has certain complexity and randomness in steeply dipping coal seams (SDCS). The three-dimensional random migration of rockfall with random parameters cannot be accurately simulated. Taking the transport process of arbitrarily shaped rockfall formed by roof leakage in steep seam working face as the research object, a method for generating rockfall with the random shape of irregular polyhedrons based on the ellipsoid equation is provided. And based on the geographic information system data, such as the contour line of the bottom floor of the working face, the 3D grid model of the bottom floor is established. The random transport process of rockfall in three-dimensional mining space was simulated using Monte Carlo random simulation technology combined with the energy tracking method (ETM) to compile the program, considering the randomness of collision recovery coefficient and friction coefficient between rockfall and working face floor. The influence of randomness of parameters on the migration velocity, angular velocity and energy of rockfall is analyzed. With the increase of the coefficient of variation of parameters, the influence of the randomness of the parameters on the transport characteristics of rockfall becomes greater. The impact of the collision recovery coefficient on the migration process of rockfall is much more significant than that of the friction coefficient. The offset ratio of rockfall increases with the increase of the variation coefficient. The method presented in this paper can be used to simulate the motion of rockfall more accurately, and a theoretical basis is provided for predicting and protecting rockfall hazards.

Coal gangue is widely used as a filling material in coal seam mining. During the gangue filling in steeply dipping coal seam, the loading rate, gangue gradation, and filling speed have an important impact on the deformation and failure of gangue, and further affect the bearing of gangue on overlying strata and the control of surrounding rock movement and deformation. Therefore, this article uses a self-made steel cylinder to conduct a gangue compression test on the HCT pressure testing machine. The research analyzes the influence of loading rate, gangue gradation, and filling rate on the deformation law of gangue in the compression process. After completing the test, the gangues with different particle size groups were rescreened, weighed, and recorded to analyze the crushing situation in the compression process. The results show that loading rate, gangue gradation, and filling speed have greatly influenced filling gangue's bearing capacity, deformation, and crushing rate. The larger the loading rate of gangue, the greater the bearing capacity and deformation of gangue, and the higher the crushing rate of gangue. The smaller the gangue gradation, the smaller the deformation, and the stronger the resistance to deformation. A more optimized gangue gradation ratio is obtained according to the distribution law of the mass proportion of gangue with different particle size groups after compression. The faster the filling speed of manual filling gangue, the greater the strength and deformation of the gangue body. Moreover, the faster filling speed can effectively improve when the strength reaches the peak and deformation tend to be stable. The results can provide theoretical guidance for the local filling of artificial gangue in the longwall working face of steeply dipping coal seam. [ABSTRACT FROM AUTHOR]

The gangue filling mining method is used to reduce the occurrence of dynamic disasters on the roof of a steeply dipping coal seam (SDCS) effectively and improve the stability of the overburden structure. To comprehensively study the movement law of the overburden under different filling quantities, the 3221 working face of the Lvshuidong coal mine was taken as the research site. The vertical displacement, vertical stress, and plastic zone of the overburden under different filling quantities were analyzed by using FLAC3D numerical simulation and physical similarity simulations. The results show that the maximum stress in the stress concentration zone decreased with the increase of filling size. The vertical stress range of the overburden and floor in the filling zone increased significantly. The affected zones of the vertical displacement of the roof and floor and the vertical displacement of the overburden were reduced to varying degrees. The overall plastic zone was shrinking. The movement of overburden was well-controlled as the proportion of the fillings increased. The results of this study can provide an important reference for the stability control of the roof of SDCS filling mining. [ABSTRACT FROM AUTHOR]

Many recent examples have shown that rockfalls can occur in underground steep coal mines. The stratigraphic circumstances, block formation mechanism, and cumulative damage effects of rockfalls in the longwalls of a steeply dipping coal seam (SDCS) make them detrimental to workplace safety. Therefore, this study examined an approach for mitigating rockfall hazards in SDCSs. A passive mesh system was installed to prevent the propagation of rockfalls, which decreased the number of collisions between the falling rocks and mining equipment. The interactions of the falling rocks and passive mesh were studied using a series of full-scale numerical impact tests. The following conclusions could be drawn. The displacement of the mesh increased with the rockfall kinetic energy, showing the characteristic of strain hardening. The peak stress appeared near the contact area between the rockfall and mesh, and it spread to the mesh edge in an X-shaped pattern. Stress concentrations were likely to occur in areas that were in direct contact with the mesh and mesh edges. The displacement of the mesh increased when the incidence angle increased, and the number of mesh cells entering the plastic state increased significantly. The internal energy ratio increased with an increase in the incidence angle, indicating that a greater incidence angle led to a larger amount of kinetic energy being transferred from the block into the internal energy of the passive mesh. Finally, the method was verified by comparing the numerical test with the on-site damaged equipment. The high replacement frequency of a passive mesh system and the annual fatality rate in the longwalls of SDCS were significantly improved. This study provided the design for a drapery mesh system for rockfall disaster prevention, particularly the mitigation of rockfall hazard risks in underground SDCSs.

In fully mechanized caving mining, the earlier the top coal enters the limit-equilibrium zone, the easier it is for leakage to be induced in front of the support. As the dip angle of the seam increases, the leakage of the top coal in front of the support drastically reduces the stability of the stope support–surrounding rock system. In this study, theoretical analysis, a physical simulation experiment, a numerical simulation, and field measurements were performed to consider the influence of the coal seam dip effect on the gradual deterioration of top coal for the first time, and quantitative characterization of the limit equilibrium boundary of top coal was realized based on analysis of the continuous damage medium mechanics. The results show that the two boundaries exhibit a consistent, asymmetric ‘double arch’ distribution along the incline. The top coal in the inclined upper-middle region of the working face is the first to enter the limit-equilibrium state, whereas the inclined upper and lower regions lag behind. The initial and final boundaries of the limit-equilibrium zone are distributed from 1.24 to 3.04 m and from 0.19 to −1.95 m in front of the coal wall, respectively. The distribution of the limit-equilibrium zone boundary was verified by the leakage times of the top coal in the working face. These results could provide reference information for evaluating stope support–surrounding rock systems in fully mechanized caving mining with steeply dipping coal seams.

The breaking features and stress distribution of overlying strata in a steeply dipping coal seam (SDCS) differ significantly from those in a near-horizontal one. In this study, the laws governing the evolution of vertical stress release and shear stress concentration in the overlying strata of coal seams with different dip angles are derived via numerical simulation, rock mechanics tests, acoustic emissions, and field measurements. Thus, the stress-driven dynamic evolution of the overlying strata structure, in which a shear stress arch forms, is determined. Upon breaking the lower part of the overlying strata, the shear stress transfers rapidly to the upper part of the working face. The damaged zone of the overlying strata migrates upward along the dip direction of the working face. The gangue in the lower part of the working face is compacted, leading to an increase in vertical stress. As the dip angle of the coal seam increases, the overlying strata fail suddenly under the action of shear stresses. Finally, the behavioral response of the overlying strata driven by shear stresses in the longwall working face of an SDCS is identified and analyzed in detail. The present research findings reveal the laws governing the behavior of mine pressure in the working face of an SDCS, which in turn can be used to establish the respective on-site guidance. [ABSTRACT FROM AUTHOR]

The gangue filling mining method is used to reduce the occurrence of dynamic disasters on the roof of a steeply dipping coal seam (SDCS) effectively and improve the stability of the overburden structure. To comprehensively study the movement law of the overburden under different filling quantities, the 3221 working face of the Lvshuidong coal mine was taken as the research site. The vertical displacement, vertical stress, and plastic zone of the overburden under different filling quantities were analyzed by using FLAC3D numerical simulation and physical similarity simulations. The results show that the maximum stress in the stress concentration zone decreased with the increase of filling size. The vertical stress range of the overburden and floor in the filling zone increased significantly. The affected zones of the vertical displacement of the roof and floor and the vertical displacement of the overburden were reduced to varying degrees. The overall plastic zone was shrinking. The movement of overburden was well-controlled as the proportion of the fillings increased. The results of this study can provide an important reference for the stability control of the roof of SDCS filling mining.

Roof regeneration in coal mining occurs when the remaining bottom slice of thick coal is re-mined. In view of the challenges of roof fall and instability support of a regenerative roof in the mining of steeply dipping coal seams, combined with the geological and engineering conditions of the working face in the Panbei Coal Mine, the mechanism of the instability of the regenerative roof and support is studied, and control countermeasures are proposed. Based on the comprehensive combination of the measurement of the roof structure, physical simulation, numerical simulation, and theoretical analysis, the cementation and compaction degree of the regenerated roof were described. The caving and sliding law of the regenerated roof after bottom slice mining was explored, and the model of support dumping and sliding instability under the roof fall state was established. The results obtained yielded three main findings. Firstly, the compaction degree of the regenerative roof is higher than that of the middle part of the working face, and the compaction degree of the upper part of the working face is the smallest. Secondly, the overburden structure instability of the bottom slice underwent six stages. The fracture of the cantilever beam and the slippage of gangue are the reasons for the enhancement of the acoustic signal at each stage. Finally, the upper part of the stope was identified as the crucial zone in the prevention and control of the support instability. A moving method of metal mesh with pressure and roof scraping was developed, and the support anti-overturning and anti-skid jack was set up to effectively control the stability of the support and roof fall, for safe and efficient mining of a steeply dipping coal seam under a regenerative roof. [ABSTRACT FROM AUTHOR]

Flying gangue has the characteristics of dynamic migration and enormous detriment. Reasonably con-trolling its damage is one of the prerequisites for the safe mining of steeply dipping coal seam. In this paper, based on the Kalman filter principle, the dynamic characteristics of flying gangue were obtained, the mechanism of flying gangue hazards and the parameters of control element were studied, and a methodology about flying gangue damage control was proposed. The results show that when the flying gangue collides with facilities, its impact energy can be dissipated into various forms of energy, of which the deformation energy of the facility accounts for the largest amount. The impact energy of flying gangue before collision and the recovery coefficient of impact energy of equipment jointly affect the degree of flying gangue energy-loss. Therefore, the flying gangue damage control can be started from two aspects, including increasing the impact energy recovery coefficient of facilities and reducing the impact energy of flying gangue. Parameters of the control element for working face in steeply dipping coal seam with large mining height were determined by LA-DYNA, the diameter of the polyester was 6 mm and the size of the diamond mesh was 100×100 mm. Then thecontrol element was applied in field, the number of casualties caused by flying gangue was reduced and the problem of short usage period was effectively improved. [ABSTRACT FROM AUTHOR]

The artificial-caved rock composited backfilling approach can effectively restrain the dynamic phenomena in the coal seam and the associated roof and floor during mining operations, and can also improve the stability of the system of support and surrounding rock. In this study, based on the analysis of influencing factors affecting the surrounding rock movement and deformation of the composited backfilling longwall face in a steeply dipping coal seam, the roof mechanical model is developed, and the deflection differential equation is derived, to obtain the roof damage structure and the location of the roof fracture for the area without backfilling. The migration law of the roof under different inclination angles, mining depths, working face lengths, and backfilling ratios are analyzed. Finally, mine pressure is detected in the tested working face. Results show that the roof deflection, bending moment, and rotation drop with the increase of the inclination angle and backfilling ratio, whereas these parameters increase with greater mining depth and working face length. The roof failure location moves toward the upper area of the working face as the inclination angle and working face length increases, while it moves toward the center of the non-backfilling area with greater mining depth and backfilling ratio. Results from the proposed mechanical model agree well with the field test results, demonstrating the validity of the model, which can provide theoretical basis for a safe and efficient mining operation in steeply dipping coal seams.

The flying gangue is a kind of special derivative disaster in the steeply dipping coal seam, which seriously endangers the safety of the working face equipment and personnel. It is essential to discuss the disaster mechanism to establish the protection system in longwall face along strike when mining the steeply dipping coal seam. Laboratory simulation was carried out on the basis of disaster measurement of (lying gangue, the impact energy and energy recovery coefficient were used to characterize the flying gangue’ s hazard, impact energy were recorded and acquired by HDV and pressure sensors. The evolution characteristics of impact energy under different working conditions were analyzed by statistical principle. The risk discrimination model of flying gangue was established according to the curve of impact energy and energy recovery coefficient, and the damage level of flying gangue were divided. Then taking the energy of equipment (personnel) as the control object, the energy absorption steep point and extreme point as the boundary, the flying gangue damage risk discrimination model was established to divide the damage level. The mechanism of flying gangue disaster was discussed on the basis of above discussion. The results show that the hazard of flying gangue by the impact energy and energy recovery coefficient reaches to the corresponding hazard level under the coupling of collision path and mode. The disaster process is the accumulation of impact energy in the state of free fall, splash, rolling and sliding, meets the movement, height, collision position and contact with the equipment. The impact energy can be converted into the elasticity of the device and the vibration damping between the components, resulting in the deformation of the component is greater than its ultimate deformation when the damage occurs. Lastly, the rationality of the energy recovery coefficient in the studies of theory and experiment were verified by simulation method. [ABSTRACT FROM AUTHOR]

The evolution law of the spatial stress field in roof,and the space form of surrounding rock structure after the coal seam mining in steeply dipping seam mining is unconventionally complex compared with the mining of gently-inclined coal seam, which is due to the buried conditions of the steeply dipping seam. Based on the results of the physical simulation experiments and numerical simulation of steeply dipping seam mining, the basic mechanical characteristics of the space shape of arch shell after coal seam mining was analyzed. It revealed that the space shape of arch shell after coal seam mining, which is belong to mining disturbance, is an optimal structure. The shell structure is symmetric along coal seam strike but not along the inclination of coal seam. Accordingly, considering waste rock filling effect, the model of stress arch along coal seam strike and inclination of coal seam is established. The rational axis equation along coal seam strike and inclination of coal seam is obtained. The results show that when working face advancing distance is far greater than the length of the working face, the shell structure configuration is independent with the working face advancing distance. The arch height and span length of symmetric stress arch increase firstly and decrease later along the inclination of coal seam. The maximum caving height is in the middle and upper part of the inclination direction, and the arch height and span length of symmetric stress arch is the largest in that zone. [ABSTRACT FROM AUTHOR]

Many examples have shown that rockfalls can occur in underground coal mines. The presence of rockfalls in the long walls of a steeply dipping coal seam (SDCS) is harmful due to the cumulative damage effects of rockfall near active mining faces. Therefore, this study aims to assess rockfall hazards in SDCS mining and propose corresponding protective measures. The steps are as follows: Step 1 : The on-site coal wall spalling was investigated. Information such as the shape, size, and location of the detached block was collected. Step 2 : The risk indicators Ē and Ē COR,BE that characterize the cumulative damage effects of rockfall were proposed. Step 3 : A small-scale impact test was performed in the laboratory to study the rockfall characteristics, and a sensitivity analysis for the risk indicators under different block diameters, seam inclinations, and longwall floor Schmidt hardness was conducted. Step 4 : A risk assessment model for rockfall hazards was established. Rockfall risks can be divided into five degrees based on the distribution of Ē and Ē COR,BE. Among them, the laws of Ē and Ē COR,BE were obtained through Step 3. ΔE can be obtained under two scenes, with or without equipment, on the longwall floor. E d is the critical energy for equipment destruction, which is related to the equipment materials. Step 5 : The risk assessment method for rockfall in longwalls of an SDCS is proposed based on evaluating Ē and Ē COR,BE. Specifically, the risk assessment model was combined with the on-site damaged hydraulic support, and then, the verification of the risk assessment method was accomplished through a comparison of the small-scale impact test in the laboratory and on-site damage measurements. Finally, three protective principles were discussed. This study provides a method for risk assessment and for determining the principles of protective systems in underground steep coal seams. [ABSTRACT FROM AUTHOR]

The artificial-caved rock composited backfilling approach can effectively restrain the dynamic phenomena in the coal seam and the associated roof and floor during mining operations, and can also improve the stability of the system of support and surrounding rock. In this study, based on the analysis of influencing factors affecting the surrounding rock movement and deformation of the composited backfilling longwall face in a steeply dipping coal seam, the roof mechanical model is developed, and the deflection differential equation is derived, to obtain the roof damage structure and the location of the roof fracture for the area without backfilling. The migration law of the roof under different inclination angles, mining depths, working face lengths, and backfilling ratios are analyzed. Finally, mine pressure is detected in the tested working face. Results show that the roof deflection, bending moment, and rotation drop with the increase of the inclination angle and backfilling ratio, whereas these parameters increase with greater mining depth and working face length. The roof failure location moves toward the upper area of the working face as the inclination angle and working face length increases, while it moves toward the center of the non-backfilling area with greater mining depth and backfilling ratio. Results from the proposed mechanical model agree well with the field test results, demonstrating the validity of the model, which can provide theoretical basis for a safe and efficient mining operation in steeply dipping coal seams. [ABSTRACT FROM AUTHOR]