Effect of Pressure Relief Hole Spacing on Energy Dissipation in Coal Seam at Various Mining Depths

Round 1

Reviewer 1 Report

In the past, the research work with borehole pressure relief was mainly focused on stress, plastic deformation, and loose failure. But this paper mainly studies the effect of pressure relief hole spacing at different mining depths on coal seam energy dissipation to reflect the effect of pressure relief. The issue with borehole pressure relief is analyzed from the angle of energy, which is obviously innovative. Therefore, the paper can be published after minor revision. However, the following problems still need to be corrected or explained:

1.      It is necessary to explain the specific meaning of P and λ in Figure 1.

2.      The size of captions for Figures 3 and 4 are too small to read and needs to be enlarged.

3.      During the content analysis, sometimes it is necessary to add a serial number to increase the readability of the content. For example, “ the energy dissipation law of coal is analyzed as follows: (1), (2), (3), … ”.

4.      “ Under the conditions of 600 m mining depth and 0.5 m, 1.0 m, 1.5 m, 2.0 m, and 2.5 m pressure relief holes spacing separately. ” , “ The larger the spacing, the smaller the decreasing range of dissipated energy. ” There are grammatical errors in these sentences. Such grammatical errors should be corrected in the paper.

5.      Please supplement the engineering application diagram of pressure relief holes to better explain the engineering background.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

    The author adopting the method of combining theoretical analysis with numerical simulation to study the accumulation and dissipation law of coal seams in the condition of different mining depths and different spacings of pressure relief holes. The quantitative relationship between mining depth, spacing of pressure relief holes and dissipated energy is proposed. The figures and tables are is clear and the data is sufficient. It is innovative that analyzing energy dissipation to reveal pressure relief effect of large diameter boreholes on coal seam. But there are still some problems that need to be corrected or explained.

1)   Properly supplement some engineering background of pressure relief boreholes, which is more beneficial to understanding the theme of the article.

2)    Please explain why the numerical model is designed with a hole depth of 1m instead of 20m in the project.

3)   Some of the terminology used in mining engineering is inaccurate and should be corrected. For example, the phrase “Rib spalling and floor heavy” should be replaced with “wall caving and floor heave”.

4)  There are some syntax errors such as lack of predicate, illogical tense and morbid sentence structure in this paper. Please check them to improve the readability of the paper.

5)   The meanings of the conclusion is not clear enough. Please optimize the sentence structure to make the main idea clearer.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Based on the actual engineering background, the article establishes the mechanical model of energy dissipation in coal bodies with large diameter pressure relief holes through theoretical analysis, obtains the approximate calculation formula of energy dissipation, and combines with numerical simulations to study the influence law of different mining depth and pressure on energy dissipation. The results of the study can provide some theoretical basis for the optimization of pressure relief hole parameters for rock explosion prevention and control. However, this paper still has some shortcomings that can be improved. It is recommended that the manuscript be adopted with minor modifications.

 

1: The title covers two variables, and the effect of different mining depths on energy dissipation is discussed in the latter part of the paper. However, the research results of most scholars on the size and spacing of pressure relief holes are described in a large part of the introduction, and the research results on the energy dissipation of coal seams by mining depth are rarely discussed. It is suggested that the authors can add this part of the discussion in the introduction.

 

2： “For the coal seams of rock burst risk, the localized hazard-relief measures are often used for effective prevention and control” This section suggests adding literature to support the ideas.

 

3： “However, the degree of energy dissipation in the coal seam varies under the conditions of various mining depths and various hole spacings.” This section suggests adding literature to support the ideas.

 

4: In the introduction section, it is stated that this paper will use a combination of theoretical analysis and numerical simulation. However, the research progress and methods related to theoretical analysis and numerical simulation analysis are not introduced throughout the introduction. It is not convincing to introduce why this approach is adopted. It is suggested to revise this part of the introduction to make it more coherent and to improve the persuasiveness of the article.

 

5： “The deep coal seam is in an environment with the complex and intense stress field, which makes the deep coal rock to accumulate a large amount of elastic strain energy.” This section suggests adding literature to support the ideas.

 

6： “As shown in Figure 1, after the formation of large diameter pressure relief holes, a part of elastic strain energy stored in the coal around the hole is released into the free space in the form of deformation and failure, another part is consumed by plastic deformation and the remaining part is still stored in the coal.” This section suggests adding literature to support the ideas.

 

7： “If the finite element analysis approach is applied to divide the coal seam into unit grids, FLAC3D can be used for numerical simulation calculation.” Why should the FEA method be used and what are the advantages of using FEA instead of other numerical simulation methods. Additional discussion is recommended.

 

8: In the modeling part of 3.1, the size of the coal seam model is 10m×1m×2.5m. The setting of the coal seam burial depth parameter why the interval of 200m is selected and the setting basis of the pressure relief hole spacing and diameter parameters, and the selection basis of the top load parameter values are not explained. It is suggested that the setting of this part of the parameters be supplemented.

 

9: Table1 numerical simulation scheme lacks the description and basis for the combination of schemes between different parameters. It is suggested that additional explanation of the basis for the combination of scenarios be carried out.

 

10: Table2 coal in the physical parameters, this part of the data source of parameters is unknown, it is recommended to add a description.

 

11: The fonts in Figure3, 4 and 5 pictures are small, so it is recommended to enlarge them slightly.

 

12: In part 3.3, there is a lack of analytical discussion on why only 600m depth was chosen, and it is suggested to add.

 

13： “Typically, the spacing of pressure relief holes for weak rock burst hazard is 3m, 2m for medium rock burst hazard, and 1m for high rock burst hazard coal seam. The diameter of the pressure relief hole is 120~150 mm and the hole depth is around 20 m.” This section suggests adding literature for better support.

 

14: The fourth part is too short, and it is recommended to discuss it in detail and add literature to support the corresponding ideas.

Author Response

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Author Response File: Author Response.pdf