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

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

Energy Exploration & Exploitation ◽

10.1177/01445987211009390 ◽

2021 ◽

pp. 014459872110093

Author(s):

Wei Zhang ◽

Jiawei Guo ◽

Kaidi Xie ◽

Jinming Wang ◽

Liang Chen ◽

...

Keyword(s):

Coal Seam ◽

Technical Support ◽

Surrounding Rock ◽

Coal Seams ◽

Deformation Control ◽

Hard Roof ◽

Working Face ◽

Close Coal Seams ◽

Safe Mining

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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A numerical simulation of realistic top coal caving intervals under different top coal thicknesses in longwall top coal caving working face

10.21203/rs.3.rs-243080/v1 ◽

2021 ◽

Author(s):

Chuang Liu ◽

Huamin Li

Keyword(s):

Numerical Simulation ◽

Coal Seam ◽

Distinct Element ◽

Simulation Models ◽

Simulation Software ◽

Thick Coal Seam ◽

Coal Recovery ◽

Working Face ◽

Longwall Top Coal Caving ◽

Selection Of

Abstract In the process of longwall top coal caving, the selection of the top coal caving interval along the advancing direction of the working face has an important effect on the top coal recovery. To explore a realistic top coal caving interval of the longwall top coal caving working face, longwall top coal caving panel 8202 in the Tongxin Coal Mine is used as an example, and 30 numerical simulation models are established by using Continuum-based Distinct Element Method (CDEM) simulation software to study the top coal recovery with 4.0 m, 8.0 m, 12.0 m, 16.0 m, 20.0 m and 24.0 m top coal thicknesses and 0.8 m, 1.0 m, 1.2 m, 1.6 m and 2.4 m top coal caving intervals. The results show that with an increase in the top coal caving interval, the single top coal caving amount increases. The top coal recovery is the highest with a 0.8 m top coal caving interval when the thickness of the top coal is less than 4.0 m, and it is the highest with a 1.2 m top coal caving interval when the coal seam thickness is greater than 4.0 m. These results provide a reference for the selection of a realistic top coal caving interval in thick coal seam caving mining.

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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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Case study on the mining‐induced stress evolution of an extra‐thick coal seam under hard roof conditions

Energy Science & Engineering ◽

10.1002/ese3.733 ◽

2020 ◽

Vol 8 (9) ◽

pp. 3174-3185 ◽

Cited By ~ 1

Author(s):

Cong Li ◽

Heping Xie ◽

Mingzhong Gao ◽

Jing Xie ◽

Guangdi Deng ◽

...

Keyword(s):

Coal Seam ◽

Stress Evolution ◽

Thick Coal Seam ◽

Hard Roof ◽

Induced Stress

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The Parameter Identification of the Steep Seam Goafs Structural Characteristics of the Coal and Rock Based on GPR

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.390.403 ◽

2013 ◽

Vol 390 ◽

pp. 403-407 ◽

Cited By ~ 1

Author(s):

Sheng Jun Miao ◽

Chao Long ◽

Guan Lin Huang ◽

Han Chen

Keyword(s):

Coal Seam ◽

Structural Characteristics ◽

Steep Seam ◽

Rock Mass Structure ◽

Thick Coal Seam ◽

Detection Range ◽

Rock Structure ◽

Mining Design ◽

Information Image ◽

Ground Penetrating

Identifying the rock mass structure is crucial for disaster control and safe mining.In the south tunneling lane of the original +600 level, using detection method of GPR (Ground Penetrating Radar ) to implement the sophisticated detection of failure characteristics, groundwater and rock structure of the upper goaf. It determines the goaf structure parameters and water conditions through the comparative analysis of the information image. The result shows: there is no large goaf, the coal seam is broken seriously in part section and water is rich in the detection range (200m) from 2650 to 2850. The coal is hypostatic and whole in the section above 20m. It has a great significance to the safety of deep mining design and the prevention for disasters of the steep thick coal seam.

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Control of Gob-Side Roadway with Large Mining Height in Inclined Thick Coal Seam: A Case Study

Shock and Vibration ◽

10.1155/2021/6687244 ◽

2021 ◽

Vol 2021 ◽

pp. 1-14

Author(s):

Xie Fuxing

Keyword(s):

Numerical Simulation ◽

Coal Pillar ◽

Simulation Software ◽

Surrounding Rock ◽

Mine Pressure ◽

Thick Coal Seam ◽

Working Face ◽

Rock Structure ◽

Large Mining Height ◽

Mining Height

The gob-side roadway of 130205, a large-mining-height working face in the Yangchangwan coal mine, was investigated in terms of the mine pressure law and support technology for large mining heights and narrow coal pillars for mining roadways. The research included field investigations, theoretical analysis, numerical simulation, field tests, and other methods. This paper analyzes the form of movement for overlying rock structure in a gob-side entry with a large mining height and summarizes the stress state and deformation failure characteristics of the surrounding rock. The failure mechanism of the surrounding rock of the gob-side roadway and controllable engineering factors causing deformation were analyzed. FLAC3D numerical simulation software was used to explore the influence law of coal pillar width, working face mining height, and mining intensity on the stability of the surrounding rock of the gob-side roadway. Ensuring the integrity of the coal pillar, improving the coordination of the system, and using asymmetric support structures as the core support concept are proposed. A reasonably designed support scheme for the gob-side roadway of the working face for 130205 was conducted, and a desirable engineering effect was obtained through field practice verification.

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Stability Analysis and Protection Measures of Large Section Tunnel in Coal Rich Weak Rock Stratum

Geofluids ◽

10.1155/2021/9394145 ◽

2021 ◽

Vol 2021 ◽

pp. 1-15

Author(s):

Guannan Zhou ◽

Zijiang Zhao ◽

Zhanping Song ◽

Hongjian Wang

Keyword(s):

Coal Seam ◽

Large Scale ◽

Economic Benefits ◽

Surrounding Rock ◽

Tunnel Construction ◽

Weak Rock ◽

Large Section ◽

Tunnel Face ◽

Finite Element Software ◽

Geological Conditions

Due to poor engineering geological conditions of Liujiazhuang tunnel on Shanghai-Kunming Passenger Dedicated Line, the large deformation of weak rock occurs repeatedly during tunnel construction. In this paper, the large-scale finite element software ABAQUS is used to simulate the construction process of a large-section tunnel in weak surrounding rock. It is found that when tunnel face passes through the coal seam, the displacement and stress simulated by the bench method increase abruptly. The maximum stress reaches up to 18 MPa, and displacement reaches 45 mm, which is about twice when without crossing coal seam. It is technically feasible to use the bench method for tunnel construction, under the condition when large settlements is allowed; additionally, the bench method has better technical and economic benefits than that of the CD method. Through the comparative analysis of onsite monitoring data and numerical simulation results, it can be seen that the tunnel is in a dangerous state when passing through the coal seam and measures such as strengthening support or auxiliary advance support should be taken immediately to control the surrounding rock and to ensure tunnel construction safety.

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