Mathematical equations for pressure relief angle of protective seam inclination in outburst coalmine

Abstract Protective seam mining is one kind of most effective measure to reduce coal and gas outburst risk. The pressure relief angles along inclination (δm) are key parameters for evaluating the effect of protective seam mining. However, the numerical relation between δm and coal seam dip (a) is defined by discrete data and is difficult to determine δm accurately. In this study, the variations of δm with respect to seam dips are analyzed to derive analytical equations that can be used to accurately calculate δm. The relationship between δm and seam dip (a) can be expressed as parabolic or inverted parabolic curves. Mathematical equations for δm are derived by curve fitting technique. Furthermore, polynomial equations are determined as the most appropriate for δm calculation when the polynomial order is selected as 7, 6, 4 and 5 respectively. These derived equations are computationally solved and verified using actual and field test data of δm. with satisfactory consistency and accuracy. The equations are suggested as supplement and improvement for Detailed Rules on Prevention of Coal and Gas Outburst.

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The elimination of coal and gas outburst disasters by long distance lower protective seam mining combined with stress-relief gas extraction in the Huaibei coal mine area

Journal of Natural Gas Science and Engineering ◽

10.1016/j.jngse.2015.08.068 ◽

2015 ◽

Vol 27 ◽

pp. 346-353 ◽

Cited By ~ 29

Author(s):

Haibo Liu ◽

Yuanping Cheng

Keyword(s):

Coal Mine ◽

Stress Relief ◽

Coal And Gas Outburst ◽

Gas Extraction ◽

Long Distance ◽

Mine Area ◽

Gas Outburst ◽

Protective Seam ◽

Seam Mining ◽

Protective Seam Mining

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Researches of fracture evolution induced by soft rock protective seam mining and an omni-directional stereo pressure-relief gas extraction technical system: a case study

Arabian Journal of Geosciences ◽

10.1007/s12517-018-3666-4 ◽

2018 ◽

Vol 11 (12) ◽

Cited By ~ 3

Author(s):

Xiang Cheng ◽

Guangming Zhao ◽

Yingming Li ◽

Xiangrui Meng ◽

Chunliang Dong ◽

...

Keyword(s):

Soft Rock ◽

Technical System ◽

Gas Extraction ◽

Pressure Relief ◽

Fracture Evolution ◽

System A ◽

Protective Seam ◽

Seam Mining ◽

Protective Seam Mining

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Elimination of Coal and Gas Outburst Dynamic Disasters in Dengfeng Coalfield through Gas Extraction Based on Extremely Thin Protective Coal Seam Mining

Advances in Civil Engineering ◽

10.1155/2021/8675060 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Haibo Liu ◽

Xucheng Xiao ◽

Zhihang Shu

Keyword(s):

Coal Seam ◽

Coal And Gas Outburst ◽

Comprehensive Treatment ◽

Cross Layer ◽

Gas Extraction ◽

Pressure Relief ◽

Gas Outburst ◽

Geological Conditions ◽

Fracture Development ◽

Seam Mining

No. 21 coal seam is a full-thickness structured soft coal in Dengfeng coalfield. The coal seam gas-bearing capacity is high, and the permeability is poor, thus resulting in serious coal and gas outburst dynamic disasters. According to the gas geological conditions of Baoyushan Mine, No. 17 coal seam without outburst danger, which is 0.5 m thick and 23.4 m under No. 21 coal seam, was mined in advance as the lower protective seam. At the same time, a gas extraction roadway was constructed in No. 21 coal seam floor. Cross-layer boreholes were constructed to extract the pressure relief gas of No. 21 coal seam for comprehensive treatment of mine gas. The mobile deformation of the overburden coal and rock mass after mining No. 17 coal seam, the fracture development characteristics of No. 21 coal seam, the pressure relief gas migration of the coal seam, the gas extraction, and the outburst danger elimination were studied. The research findings showed the following: (1) after mining No. 17 coal seam, the overburden hard and extremely thick limestone roof sagged slowly, albeit leading to no craving zone. (2) The permeability of No. 21 coal seam was increased by about 394 times, from 0.0012 mD to 0.4732 mD. (3) After the extraction of pressure relief gas through the gas extraction roadway on the floor through the cross-layer borehole, the gas pressure of No. 21 coal seam decreased from 1.17 MPa to 0.12 MPa, while the gas content decreased from 9.74 m3/t to 3.1 m3/t, which suggested that the coal and gas outburst dynamic danger of No. 21 coal seam was totally eliminated and the goal of safe and efficient mining in the mine was realized.

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Analysis of the Influence of Upper Protective Layer Mining on the Effect of Pressure Relief and Protection of Coal and Rock Masses between the Lower Overburden Layers

Advances in Civil Engineering ◽

10.1155/2021/8682156 ◽

2021 ◽

Vol 2021 ◽

pp. 1-16

Author(s):

Jiaxin Dang ◽

Min Tu ◽

Xiangyang Zhang ◽

Qingwei Bu

Keyword(s):

Numerical Simulation ◽

Rock Mass ◽

Expansion Ratio ◽

Pressure Relief ◽

Protection Effect ◽

Protective Seam ◽

Coal Wall ◽

Seam Mining ◽

Protective Seam Mining ◽

Relief Effect

Protective seam mining is an effective gas pressure relief method in deep mining. Effective theoretical calculation methods in the current studies on the prediction of pressure relief protection effect of interbed coal and rock masses and their distribution laws are lacking. Thus, the evaluation and research with respect to pressure relief effect in protective seam mining relatively lag behind. This situation restricts the engineering feasibility evaluation and decision making in the protective seam mining. Therefore, the influence of upper protective seam mining on the pressure relief protection effect of coal and rock mass between underlying beds was investigated in this study. On the basis of an analysis of concrete engineering projects, a mechanical model was constructed for the pressure relief protection effect of upper protective seam mining on the coal and rock mass between underlying beds. The distribution equation of pressure relief expansion ratio in the underlying protected seam was also derived. The influence laws of main influencing factors on the pressure relief protection effect of the protected seam were revealed as well. In the end, the pressure relief effect was analyzed and verified for the protected seam before and after mining through numerical simulation and similarity simulation test. The pressure relief effect of upper protective seam mining on the coal and rock mass between underlying beds and the distribution characteristics were deeply explored in this study, which could provide a theoretical reference for the decision making in the gas extraction engineering design and pre-evaluation of extraction effect. Results show that the effective pressure relief zone (expansion rate>0.3%) of the protected seam beneath the goaf is located within the range of approximately 40 m from the coal wall to the rear part. It also presents an approximate “Λ-shaped distribution characteristic,” that is, it experiences migration and evolution with the advancement in the working face. Moreover, the peak pressure relief lags behind the coal wall on the working face by nearly 10–20 m. In the numerical simulation, the expansion ratio in the goaf also presents an approximate “Λ-shaped distribution.” Its effective pressure relief zone is the 50 m range from the coal wall to the rear part of the goaf, and the peak value lags behind the coal wall by around 15 m. The theoretical results and numerical simulation results are basically consistent with the physical experiment results. The expansion rates are 1.25%, 1.268%, and 1.32%, respectively. The elastic modulus E of coal seam and interbed spacing H are the main influencing factors of the swelling deformation and are negatively correlated with the expansion ratio. In the actual mining process, E and H of the protected layer can be measured to infer the expansion deformation of the protected layer.

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