Fracture evolution and pressure relief gas drainage from distant protected coal seams under an extremely thick key stratum

Longwall mechanized top coal caving mining (LMTCCM) in extra-thick coal seams has its own characteristics. The law of mining pressure and overlying strata failure height in extra-thick coal seams are much larger than those of medium-thick and thick coal seams. The key stratum structure morphology also has an important influence on the law of overlying strata movement and stability of surrounding rock. Based on the engineering geological conditions, this paper used the method of theoretical analysis and numerical simulation to study the key stratum structure morphology of LMTCCM in extra-thick coal seams. The results show that under the condition of LMTCCM in extra-thick coal seams, the key stratum forms the structure of low cantilever beam and high hinged rock beam. With the increase of coal seam thickness, the breaking position of cantilever beam is closer to the coal wall. Through theoretical calculation, it is obtained that the breaking length of cantilever beam is 31.5 m and the breaking position of cantilever beam is 15.4 m away from coal wall. With the increase of cycle, key strata will undergo the evolution law from the generation of longitudinal cracks to the hinged structure and then to the cantilever beam structure. The breakage of key strata will cause the expansion of longitudinal cracks and the overall synchronous movement of overlying strata. With the increase of coal seam thickness, the distribution of longitudinal cracks will gradually transfer from the upper part of goaf to the deep part of coal body in space and increase in quantity. This research is of great significance for improving the stability of overlying strata and ensuring the safe and efficient mining of extra-thick coal seams.

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Improvement of Gas Drainage Efficiency of Low-Permeability Coal Seams Using Ultra-High Pressure Hydraulic Cutting Technique

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/472/1/012084 ◽

2019 ◽

Vol 472 ◽

pp. 012084 ◽

Cited By ~ 1

Author(s):

Yongjiang Zhang

Keyword(s):

High Pressure ◽

Low Permeability ◽

Coal Seams ◽

Gas Drainage ◽

Ultra High Pressure

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A Gas–Solid–Liquid Coupling Model of Coal Seams and the Optimization of Gas Drainage Boreholes

Energies ◽

10.3390/en11030560 ◽

2018 ◽

Vol 11 (3) ◽

pp. 560 ◽

Cited By ~ 7

Author(s):

Yuexia Chen ◽

Jiang Xu ◽

Shoujian Peng ◽

Fazhi Yan ◽

Chaojun Fan

Keyword(s):

Coupling Model ◽

Coal Seams ◽

Gas Drainage ◽

Solid Liquid

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Experimental and Numerical Study of the Influence of Gas Pressure on Gas Permeability in Pressure Relief Gas Drainage

Transport in Porous Media ◽

10.1007/s11242-018-1107-1 ◽

2018 ◽

Vol 124 (3) ◽

pp. 995-1015 ◽

Cited By ~ 9

Author(s):

Cun Zhang ◽

Lei Zhang ◽

Shihao Tu ◽

Dingyi Hao ◽

Teng Teng

Keyword(s):

Gas Permeability ◽

Numerical Study ◽

Gas Pressure ◽

Pressure Relief ◽

Gas Drainage

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Mining Gassy Coal Seams with a Three-Entry Panel Layout

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.524-527.613 ◽

2012 ◽

Vol 524-527 ◽

pp. 613-617

Author(s):

Jun Hua Xue ◽

Sheng Xue

Keyword(s):

Coal Mine ◽

Methane Concentration ◽

Ventilation System ◽

Coal Mines ◽

Distribution Characteristics ◽

Coal Seams ◽

Gas Drainage ◽

Gas Emissions ◽

Underground Coal Mines

To address the issue of high gas emissions in mining gassy coal seams in underground coal mines, the concept of a three-entry panel layout with a retained goaf-edge gateroad and a “Y” type ventilation system is introduced in this paper. With the layout and ventilation system, distribution characteristics of methane concentration in the panel goaf is analyzed, technologies of gas drainage with boreholes drilled from the retained goaf-edge gateroad and into stress-relieved overlying and underlying seams are described, and an application case of such layout in a coal mine is also presented in this paper.

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The Study of Key Stratum Location and Characteristics on the Mining of Extremely Thick Coal Seam under Goaf

Advances in Civil Engineering ◽

10.1155/2021/8833822 ◽

2021 ◽

Vol 2021 ◽

pp. 1-9

Author(s):

Gaochuan Guo ◽

Yongkang Yang

Keyword(s):

Coal Seam ◽

Longwall Mining ◽

Maximum Principal Stress ◽

Engineering Practice ◽

Coal Seams ◽

Thick Coal Seam ◽

Key Strata ◽

Key Stratum ◽

Arch Structure ◽

Overlying Strata

The basis of traditional ground pressure and strata control techniques is the key strata theory, wherein the position of the key stratum can easily be determined for coal seams with regular thickness and without goaf. However, in the case of mining ultrathick coal seams underneath goaf, the traditional methods used for the calculation of key stratum position need to be improved in order to account for the additional coal seam thickness and the presence of an upper goaf. This study analyzed the failure height and collapse characteristics of overlying strata during excavation for determining the structure of the failed overlying strata. The results indicate that the intercalation and overlying strata gradually evolve into a large “arch structure” and a small “arch structure” during longwall mining, respectively. A mechanical model of the bearing characteristics of the interlayer key strata structure was established according to the structure of the intercalation rock layer, which is a hinged block structure. The results of the model indicate that the maximum principal stress occurs when the key strata portion of the arch structure bears the overlying load. Consequently, the movement and position of the interlayer key strata can be evaluated throughout the mining process of the ultrathick coal seams underneath goaf. This method was used to determine the position of interlayer key stratum of overlying strata in Xiegou coal mine. And the results agree with that of the engineering practice. The results are significant to determine the key strata position during ultrathick coal seam underneath goaf longwall mining.

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Research on the Reasonable Spacing of Holes in Gas Drainage along Coal Seams in Consideration of the Superimposed Effect of Drainage

Journal of Engineering Science and Technology Review ◽

10.25103/jestr.091.16 ◽

2016 ◽

Vol 9 (1) ◽

pp. 102-110

Author(s):

Li Bo ◽

◽

Wei Jianping ◽

Sun Donghui ◽

Zhang Lulu ◽

...

Keyword(s):

Coal Seams ◽

Gas Drainage ◽

Superimposed Effect

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Research and Application of Hydraulic Punching Pressure Relief Antireflection Mechanism in Deep “Three-Soft” Outburst Coal Seam

Shock and Vibration ◽

10.1155/2021/7241538 ◽

2021 ◽

Vol 2021 ◽

pp. 1-10

Author(s):

Beifang Gu ◽

Yanling Wu

Keyword(s):

Coal Seam ◽

Large Scale ◽

Water Pressure ◽

Pressure Relief ◽

Gas Drainage ◽

Technical Problems ◽

Soft Coal ◽

Coal Rock ◽

Outburst Coal Seam ◽

Soft Coal Seam

To solve the problems of gas predrainage in deep seams with “three softs” and low-air permeability, hydraulic punching pressure relief antireflection technology is proposed on the basis of the research background of gas predrainage technology in Lugou Mine to alleviate technical problems, such as low gas drainage efficiency, in this mine. Through the analysis of the mechanism of hydraulic punching and coal breaking, combined with FLAC3D software, a hydraulic punching pressure relief antireflection model is established. Then, the fracture radii of coal rock are simulated and calculated. The results show that, under hydraulic punching with a water pressure of 10 MPa and coal outputs of 3 m3, 6 m3, 9 m3, and 12 m3, the fracture radii of coal and rock are 3.4 m, 4.8 m, 5.5 m, and 5.9 m, respectively. Using the software to fit the relationship between coal output V and hydraulic punching fracture radius R under the same water pressure, R = 2.32479 V0.3839 is obtained. The field test is carried out in the bottom drainage roadway of 32141 in Lugou Mine. The application effect is as follows: the gas concentration of hydraulic punching with a coal output of 3 m3 is twice that of ordinary drilling, and the coal output of hydraulic punching with a coal output of 6 m3 is four times that of ordinary drilling. The extraction concentration is four times that of ordinary drilling, and the extraction concentration of hydraulic punching with a coal output of 9 m3 is 6.4 times that of ordinary drilling. Combining the results of the numerical simulation and taking into account the actual construction situation on site, the coal output of water jetting from the borehole is 9 m3, and the fracture radius is 5.5 m. This outcome means that the effective half radius is 5.5 m, and the borehole spacing is 7.7 m. These values are the construction parameters for large-scale applications. This proposal provides effective technology and equipment for gas drainage in the deep three-soft coal seam. Consequently, it has promotion and reference significance for gas drainage in coal seam of the same geological type.

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