Comprehensive technical support for safe mining in ultra-close coal seams: A case study

In order to mine the coal seam under super-thick hard roof, improve the utilization rate of resources and prolong the remaining service life of the mine, a case study of the Gaozhuang Coal Mine in the Zaozhuang Mining Area has been performed in this paper. Based on the specific mining geological conditions of ultra-close coal seams (#3up and #3low coal seams), their joint systematic analysis has been performed, with the focus made in the following three aspects: (i) prevention of rock burst under super-thick hard roof, (ii) deformation control of surrounding rock of roadways in the lower coal seam, and (iii) fire prevention in the goaf of working face. Given the strong bursting tendency observed in upper coal seam and lower coal seam, the technology of preventing rock burst under super-thick hard roof was proposed, which involved setting of narrow section coal pillars to protect roadways and interleaving layout of working faces. The specific supporting scheme of surrounding rock of roadways in the #3low1101 working face was determined, and the grouting reinforcement method of local fractured zones through Marithan was further proposed, to ensure the deformation control of surrounding rock of roadways in lower coal seams. The proposed fire prevention technology envisaged goaf grouting and spraying to plug leaks, which reduced the hazard of spontaneous combustion of residual coals in mined ultra-close coal seams. The technical and economic improvements with a direct economic benefit of 5.55 million yuan were achieved by the application of the proposed comprehensive technical support. The research results obtained provide a theoretical guidance and technical support of safe mining strategies of close coal seams in other mining areas.

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Cooperative Control Mechanism of Long Flexible Bolts and Blasting Pressure Relief in Hard Roof Roadways of Extra-Thick Coal Seams: A Case Study

Applied Sciences ◽

10.3390/app11094125 ◽

2021 ◽

Vol 11 (9) ◽

pp. 4125

Author(s):

Zhe Xiang ◽

Nong Zhang ◽

Zhengzheng Xie ◽

Feng Guo ◽

Chenghao Zhang

Keyword(s):

Coal Seam ◽

Cooperative Control ◽

Field Tests ◽

Surrounding Rock ◽

Deep Hole ◽

Coal Seams ◽

Thick Coal Seam ◽

Structure Damage ◽

Hard Roof

The higher strength of a hard roof leads to higher coal pressure during coal mining, especially under extra-thick coal seam conditions. This study addresses the hard roof control problem for extra-thick coal seams using the air return roadway 4106 (AR 4106) of the Wenjiapo Coal Mine as a case study. A new surrounding rock control strategy is proposed, which mainly includes 44 m deep-hole pre-splitting blasting for stress releasing and flexible 4-m-long bolt for roof supporting. Based on the new support scheme, field tests were performed. The results show that roadway support failure in traditional scenarios is caused by insufficient bolt length and extensive rotary subsidence of the long cantilever beam of the hard roof. In the new proposed scheme, flexible 4-m-long bolts are shown to effectively restrain the initial expansion deformation of the top coal. The deflection of the rock beam anchored by the roof foundation are improved. Deep-hole pre-splitting blasting effectively reduces the cantilever distance of the “block B” of the voussoir beam structure. The stress environment of the roadway surrounding rock is optimized and anchorage structure damage is inhibited. The results provide insights regarding the safe control of roadway roofs under extra-thick coal seam conditions.

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Surrounding Rock Movement of Steeply Dipping Coal Seam Using Backfill Mining

Shock and Vibration ◽

10.1155/2021/5574563 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Wenyu Lv ◽

Kai Guo ◽

Jianhao Yu ◽

Xufeng Du ◽

Kun Feng

Keyword(s):

Numerical Simulation ◽

Coal Seam ◽

Surrounding Rock ◽

Maximum Deflection ◽

Coal Seams ◽

Physical Similarity ◽

Working Face ◽

Rock Structure ◽

Backfill Mining ◽

The Stability

The movement of the overlying strata in steeply dipping coal seams is complex, and the deformation of roof rock beam is obvious. In general, the backfill mining method can improve the stability of the surrounding rock effectively. In this study, the 645 working face of the tested mine is used as a prototype to establish the mechanical model of the inclined roof beam using the sloping flexible shield support backfilling method in a steeply dipping coal seam, and the deflection equation is derived to obtain the roof damage structure and the maximum deflection position of the roof beam. Finally, numerical simulation and physical similarity simulation experiments are carried out to study the stability of the surrounding rock structure under backfilling mining in steeply dipping coal seams. The results show the following: (1) With the support of the gangue filling body, the inclined roof beam has smaller roof subsidence, and the maximum deflection position moves to the upper part of working face. (2) With the increase of the stope height, the stress and displacement field of the surrounding rock using the backfilling method show an asymmetrical distribution, the movement, deformation, and failure increase slowly, and the increase of the strain is relatively stable. Compared with the caving method, the range and degree of the surrounding rock disturbed by the mining stress are lower. The results of numerical simulation and physical similarity simulation experiment are generally consistent with the theoretically derived results. Overall, this study can provide theoretical basis for the safe and efficient production of steeply dipping coal seams.

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Surrounding rock deformation control of asymmetrical roadway in deep three-soft coal seam: a case study

Journal of Geophysics and Engineering ◽

10.1088/1742-2140/aabb2a ◽

2018 ◽

Vol 15 (5) ◽

pp. 1917-1928 ◽

Cited By ~ 10

Author(s):

Wei Zhang ◽

Ziming He ◽

Dongsheng Zhang ◽

Dahong Qi ◽

Weisheng Zhang

Keyword(s):

Coal Seam ◽

Surrounding Rock ◽

Rock Deformation ◽

Deformation Control ◽

Soft Coal ◽

Soft Coal Seam ◽

Surrounding Rock Deformation

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Stability of "Support-Surrounding Rock" System for Fully Mechanized Longwall Mining in Steeply Dipping Coal Seams

10.21203/rs.3.rs-403141/v1 ◽

2021 ◽

Author(s):

Luo Shenghu ◽

tong wang ◽

Wu Yongping ◽

Huangfu Jingyu ◽

Zhao Huatao

Keyword(s):

Coal Seam ◽

Longwall Mining ◽

Stability Control ◽

Surrounding Rock ◽

Coal Seams ◽

Physical Test ◽

Rock System ◽

Working Face ◽

The Stability ◽

Mining Height

Abstract The key to the safe and efficient longwall mining of steeply dipping seams lies in the stability control of the "support-surrounding rock" system. This paper analyzes the difficulty of controlling the stability of the support during the longwall mining process of steeply dipping coal seams in terms of the characteristics of the non-uniform filled-in gob using a combination of physical test, theoretical analysis and field measurements. Considering the floor as an elastic foundation, we built a "support-surrounding rock" mechanical model based on data obtained on "support-surrounding rock" systems in different regions and the laws of support motion under different load conditions. Our findings are summarized as follows. First, depending on the angle of the coal seam, the caving gangue will roll (slide) downward along the incline, resulting in the formation of a non-uniform filling zone in the deep gob in which the lower, middle, and upper sections are filled, half-filled, and empty, respectively. In addition, an inverted triangular hollow surface is formed on the floor of the gob in the middle and upper sections behind the support. Furthermore, as the angle of the coal seam, length of the working face, and mining height increase, the characteristics of the non-uniform filled-in gob are enhanced. Second, we found that, as a result of support by the gangue, the "support-surrounding rock" system is relatively stable in the lower part of the working face while, in the middle and upper sections of the working face, the contact method and loading characteristics of the support are more complicated, making stability control difficult. Third, the magnitude and direction of the load, action point, and mining height all affect the stability of the support to varying degrees, with the tangential load and action position of the roof load having the most significant impacts on the stability of the support. Under loading by the roof, rotation and subsidence of the support inevitably occur, with gradually increasing amplitude and effects on the inter-support and sliding forces. Finally, we found that it is advisable in the process of moving the support to adopt "sliding advance of support" measures and to apply a "down-up" removal order to ensure overall stability. These research results provide reference and guidance of significance to field practice production.

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Analysis of coal face stability of lower coal seam under repeated mining in close coal seams group

Scientific Reports ◽

10.1038/s41598-021-04410-5 ◽

2022 ◽

Vol 12 (1) ◽

Author(s):

Yu Xiong ◽

Dezhong Kong ◽

Zhijie Wen ◽

Guiyi Wu ◽

Qinzhi Liu

Keyword(s):

Coal Seam ◽

Shear Failure ◽

Coal Seams ◽

Coal Face ◽

Soft Coal ◽

Mechanics Model ◽

Roof Structure ◽

Working Face ◽

Close Coal Seams ◽

Similar Simulation

AbstractAiming 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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Study on Law of Overlying Strata Breakage and Migration in Downward Mining of Extremely Close Coal Seams by Physical Similarity Simulation

Advances in Civil Engineering ◽

10.1155/2020/2898971 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Xiaobin Li ◽

Wenrui He ◽

Zhuhe Xu

Keyword(s):

Coal Seam ◽

Coal Pillar ◽

Coal Seams ◽

Monitoring Point ◽

Rock Stratum ◽

Working Face ◽

Roof Fall ◽

And Migration ◽

Close Coal Seams ◽

Overlying Strata

Extremely close coal seam groups are widely distributed in China, and the main mining method is downward mining. In the downward mining process of extremely close coal seam groups, the violent movement of overlying strata will cause the redistribution of surrounding rock stress. It not only produces stress concentration on the pillar but also causes the roof of the lower coal seam to be broken and difficulty in maintaining the mining roadway. In this study, the physical similitude modeling method and field observations were used to study the breakage and migration law of overlying strata in the downward mining of extremely close coal seams. Results show that in the process of mining upper coal seam, the first weighting step of the main roof is 37.5 m and the periodic weighting step is 12.5 m. The occurrence of strata separation is beneficial to the prediction of roof weighting. When the working face advances to 25 m, the rock stratum approximating a parallelogram of height 5 m does not collapse, and the working face is relatively dangerous. When mining the lower coal seam, the overall pressure of the working face is large, but the periodic weighting of the working face is not obvious. The first collapse step of the immediate roof is 15 m. When mining the upper and lower coal seams, the subsidence of the monitoring point increases significantly at 17.5 and 15 m, respectively. The roof collapse of the lower coal seam occurs 2.5 m ahead of that of the upper coal seam. The hydraulic value of the support, roof fall height, and sloughing depth in the entire working face reach the maximum at the coal pillar, and the extreme points at the coal pillar are relatively concentrated. This research provides some guidance for the safe and efficient mining of extremely close coal seams in the future.

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Optimization of roadway layout in ultra-close coal seams: A case study

PLoS ONE ◽

10.1371/journal.pone.0207447 ◽

2018 ◽

Vol 13 (11) ◽

pp. e0207447 ◽

Cited By ~ 4

Author(s):

Gang Wu ◽

Xinqiu Fang ◽

Hualin Bai ◽

Minfu Liang ◽

Xiukun Hu

Keyword(s):

Coal Seams ◽

Close Coal Seams

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Key Parameters of Roof Cutting of Gob-Side Entry Retaining in a Deep Inclined Thick Coal Seam with Hard Roof

Energies ◽

10.3390/en12050934 ◽

2019 ◽

Vol 12 (5) ◽

pp. 934 ◽

Cited By ~ 15

Author(s):

Jinzhu Hu ◽

Manchao He ◽

Jiong Wang ◽

Zimin Ma ◽

Yajun Wang ◽

...

Keyword(s):

Numerical Model ◽

Coal Seam ◽

Economic Benefits ◽

Surrounding Rock ◽

Thick Coal Seam ◽

Hard Roof ◽

Coal Recovery ◽

Rock Structure ◽

Different Depths ◽

Dip Angle

Gob-side entry retaining by roof cutting (GERRC) employed in a deep inclined thick coal seam (DITCS) can not only increase economic benefits and coal recovery, but also optimize surrounding rock structure. In accordance with the principles of GERRC, the technology of GERRC in DITCS is introduced and a roof-cutting mechanical model of GERRC is proposed to determine the key parameters of the depth and angle of RC. The results show that the greater the RC angle, the easier the caving of the goaf roof, but the length of cantilever beam increases. The depth of RC should account for the dip angle of the coal seam when the angle is above 20°. Increasing the coal seam dip angle could reduce the volume of rock falling of the goaf roof, but increase the filling height of the upper gangue to slide down. According to numerical model analysis of the stress and displacement of surrounding rock at different depths and angles of RC, when the depth of RC increased from 9 m to 13 m, the distance between the stress concentration zone and the coal side is increased. When the angle of RC increased from 0° to 20°, the value of roof separation is decreased. GERRC was applied in a DITCS with 11 m depth and 20° RC angle, and the field-measured data verified the conclusions of the numerical model.

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Mine Pressure Behavior Characteristics and Control Methods of a Reused Entry that Was Formed by Roof Cutting: A Case Study

Shock and Vibration ◽

10.1155/2020/4276730 ◽

2020 ◽

Vol 2020 ◽

pp. 1-15

Author(s):

Yajun Wang ◽

Haosen Wang ◽

Manchao He ◽

Qi Wang ◽

Yafei Qiao ◽

...

Keyword(s):

Deformation Zone ◽

Dynamic Pressure ◽

Field Application ◽

Surrounding Rock ◽

Mine Pressure ◽

Stress Increase ◽

Severe Deformation ◽

Working Face ◽

Roof Deformation

Noncoal pillar mining with automatic formation of a roadway is a new coal mining method that is tailored to improve the coal resource recovery rate and reduce the investment in roadway tunneling. Using this proposed method, a reuse entry is formed by roof cutting instead of tunneling. In this paper, the S1201-II working face of the Ningtiaota Coal Mine was used as a case study. The stress distribution of surrounding rock and the roof deformation characteristics of the reused entry during the mining process of the second working face were studied through FLAC3D numerical simulations combined with field measurements. The results indicate that the zone close to the reused entry led to higher stress in advance. If this stress is superimposed with the lateral pressure of the adjacent mined working face, it will be more difficult to maintain the reused entry. In the engineering case study described here, the reused entry created a stress increase zone and a severe deformation zone in the range of 0–80 m in front of the working face, and its range was approximately 37.5% larger than an ordinary entry. The stress peak in the stress increase zone increased by approximately 34.7% over that of an ordinary entry. The maximum amount of deformation within the severe deformation zone increased by 94.4% over that of an ordinary entry. To properly control the surrounding rock stress and deformation of the reused entry, a dynamic pressure bearing support in front of the working face with adaptability to the large roof deformation and high support strength is proposed here. Field application results showed that the final roof deformation with the dynamic pressure bearing support can be satisfactorily controlled within 110∼130 mm. These findings can provide a reference for researchers and field engineering technicians when engaging in the support work of reused entry.

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