Floor Heave Mechanism of Gob-Side Entry Retaining with Fully-Mechanized Backfilling Mining
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Abstract:
Serious floor heave in gob-side entry retaining (GER) with fully-mechanized gangue backfilling mining affects the transportation and ventilation safety of the mine. A theoretical mechanical model for the floor of gob-backfilled GER was established. The effects of the mechanical properties of floor strata, the granular compaction of backfilling area (BFA), the vertical support of roadside support body (RSB), and the stress concentration of the solid coal on the floor heave of the gob-backfilled GER were studied. The results show that the floor heave increases with the increase of the coal seam buried depth, and decreases with the increase of the floor rock elastic modulus. The development depth of the plastic zone decreases with the increase of the c and φ value of the floor rock, and increases with the increase of the stress concentration factor of the solid coal. The development depth of the plastic zone in the test mine reached 2.68 m. The field test and monitoring results indicate that the comprehensive control scheme of adjusting backfilling pressure, deep grouting reinforcement, shallow opening stress relief slots, and surface pouring can effectively control the floor heave. The roof-floor displacement is reduced by 73.8% compared to that with the original support scheme. The roadway section meets the design and application requirements when the deformation stabilizes, demonstrating the rationality of the mechanical model. The research results overcome the technical bottleneck of floor heave control of fully-mechanized backfilling GER, providing a reliable basis for the design of a floor heave control scheme.Keywords:
Gangue
To investigate the failure mechanisms of coal bursts in the longwalls of underground coal mines, a case study based on the real coal burst in the Tangshan coal mine occurring on 2 August 2019 was carried out to analyze the cause and basic theories of the coal burst and, thus, propose approaches and methods to mitigate the damage. The coal burst occurred mainly due to the sliding of coal from the longwall ribs and the simultaneous uplifting of the floor. As a result of the longwall retraction, the roof above the coal seam was too stable to collapse, forming a long hanging roof behind the longwall. Because the longwall acted as a fulcrum, the hanging roof acted like a saw, exerting massive loads on the longwall. As a result, the roof in front of the longwall tended to slope upward, leaving the underlying coal seam unconfined. Due to the horizontal stresses, the longwall ribs collapsed into the longwall, causing the coal seam to break out. These findings could help improve the fundamental understanding of the failure mechanisms of coal breakouts and, thus, aid in the development of measures to prevent such occurrences.
Longwall mining
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Coal bursts caused by mining-induced seismicity occur in the working face in steeply inclined and extra thick coal seams (SIETCSs). This article presents a case study in SIETCS through discrete element simulation as well as field investigation. The evolution of the coal burst was studied from the perspective of stress distribution, crack propagation and coal fragment ejection. The results showed that dynamic failure mainly occurred in the coal near the roof. The deep bottom coal and the top coal near the roof are under high static stress due to the clamping effect of the roof and floor and the rotation of the deep roof. The coal burst in the working face was triggered by mining-induced seismicity. The coal burst occurred when the sum of the static stress and the dynamic stress caused by the mining-induced seismicity exceeds the sum of the ultimate strength of the coal and the support strength, which was called the 'clamping-rotation-dynamic loads' mechanism. During the coal burst, the cracks developed rapidly into the deep bottom coal and the top coal on the roof side. The results can serve as an important reference for the coal burst failure mechanism in the working face in SIETCSs.
Stress field
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Longwall mining
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The movement rule of top roof and top coal is very complex in the mining of deeply inclined thick coal seam.The research on the damage and movement of top roof and top coal is rebound to confirm the difficulty degree of top coal caving,control coal slide and roof fall,confirm rational coal caving parameters,maintain rationally the roof of deeply inclined thick coal seam,get the rule of underground pressure and instruct production.The movement of top coal and top roof is discussed with the data observed from the caving mining of deeply inclined thick coal seam with horizontal section in Zhaogezhuang colliery of Kailuan Group.
Section (typography)
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Aiming at the problem of coal face failure of lower coal seam under the influence of repeated mining in close coal seams, with the working face 17,101 as a background, the coal samples mechanics test clarified the strength characteristics of the coal face under repeated mining, through similar simulation experiments, the development of stable roof structure and surrounding rock cracks under repeated mining of close coal seams are further explored. And based on this, establish a coal face failure mechanics model to comprehensively analyze the influence of multiple roof structural instabilities on the stability of the coal face. Finally, numerical simulation is used to further supplement and verify the completeness and rationality of similar simulation experiment and theoretical analysis results. The results show that: affected by repeated mining disturbances, the cracks in the coal face are relatively developed, the strength of the coal body is reduced, and the coal face is more prone to failure under the same roof pressure; During the mining of coal seam 17#, the roofs of different layers above the stope form two kinds of "arch" structures and one kind of "voussoir beam" structure, and there are three different degrees of frequent roof pressure phenomenon, which is easy to cause coal face failure; Under repeated mining of close coal seams, the roof pressure acting on the coal face is not large. The main controlling factor of coal face failure is the strength of the coal body, and the form of coal face failure is mostly the shear failure of soft coal. The research results can provide a theoretical basis for coal face failure under similar conditions.
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To adopt fully mechanized top caving method for the shallowly-buried thick coal seam,the hard top coal and roof fracturing and moving were observed and analyzed and the mechanical model of roof breaking established.Based on the deep-base point method,the underground pressure observing station was set up in the full mechanized top caving workface 4101 of Anjialing Mine to observe the top coals and roofs of different levels.The data about fracturing and movement condition of the top coal and roof were obtained and the movement rule was analyzed.The result shows that the top coal falls with workface advancing,and the points at which the top coal and roof start to move is quite close to the working face,with the top coal being 10 m and the roof,15 m,ahead of the working face,and the displacement of the top coal is small.Because the top coal and roof of workface 4101 can timely fall down with workface advancing,no artificial measure is needed.
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This paper presents bolt supporting of retain strip pillar in strip top coal mining in Jinqiao colliery where the coal seam is occupied by villages, the retain trip coal pillar can support the roof effectively and over a long period of times, the coal rate of recovery can be improved between 40% 55%, so the better economic and social benefit can be improved.
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Aiming at the situation of mining short-range coal seams in Fenxi mining area,we analyze the factors affecting the re-distribution of stress of coal-rock mass near the coal pillar and its adjacent area.In addition,we study the mechanism of load-transfer between coal pillars and in coal-rock mass using the finite difference program FLAC3D.The result indicates that the effect of stress concentration in coal pillars on the re-distribution of floor stress is greater than that on the roof stress;the stress concentration factors of coal and rock within the coal pillars with different widths is different from those in the roof and floor,and as the increase of width of the coal seam,the maximum principal stress in the coal seam increases first and then decreases;as the width of the coal seam increases,the stress influence diffusion angle of the coal and rock under the coal pillar decreases and gradually reaches a constant.The stress re-distribution in the 10#~11# coal seams at the Shuiyu coal mine is obviously affected by the 9# coal seam mining.Based on the calculation of the stress influence diffusion angle of the coal pillars in the 9# coal seam,the layout of the roadways in the 10#~11# coal seams is designed following the main principle that the layout of the roadways should be in the area with a relatively low stress.And the in-situ monitoring results show that the deformation is not severe and the supporting effect is good.
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Fully mechanized caving is the most popular method for safe and efficient coal mining in China. In this study, based on the geological and mining conditions of Workface 822 of the Yuandian No. 1 Mine, we used theoretical analysis and numerical simulation to analyze the crushing mechanism of gangue-containing coal seam roofs, discuss the mechanical model of stability of gangue-containing coal seams to simulate different methods and caving intervals, and optimize the caving parameters of coal from gangue-containing coal seams. The results indicated that under the action of mining-induced stress, the peak pressure on the support is less than the rupture stress of the gangue, and relying on the mine support pressure alone can promote the rupture of the roof coal. However, it is difficult to rupture the gangue in the roof; owing to the gangue-containing coal seams, the area where the damage coefficient of the roof coal at the upper end of the support is lower than 1 is further expanded from the front of the support to the entire upper area of the support, and the crushing effect of roof coal is greatly weakened. After comparing the effects of five caving modes, we finally decided to use the single-cycle interval caving mode. The minimum gangue content of Workface 822 of the Yuandian No. 1 Mine is 54.35%. The results of this study can provide a theoretical basis and experience-based reference for the safe and efficient mining of gangue-containing coal seams.
Gangue
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