Pressure Relief by Blasting Roof Cutting in Close Seam Group Mining under Thick Sandstone to Enhance Gas Extraction for Mining Safety
Round 1
Reviewer 1 Report
The safety of underground miners' work is a very important issue all over the world. As the authors wrote, the most common causes of accidents are gas and coal dust explosions. The authors want to release the mine gas by forced explosions in the roof of the excavation. Here my doubts arise, what about the safety of the surface on which the exploitation is carried out? The aforementioned exploitation is very shallow (line 285), which causes significant changes in the surface with no information at all. Figure 6 (lines 148 and 149) is unclear. The chapter on analyzes and results (2.2) also raises doubts: The change in pressure in the following points 1, 2 and 3 is logical without the need to conduct an experiment !!! The name of the software used (line 70) should not appear in a scientific study. We do not know exactly what model is described.
The developed and described model was 3-dimensional (formula number 2), and the results are only 2-dimensional, why do the authors not refer to the full 3-dimensional analysis of the developed prototype (chapter 3.3)? Similarly, in the real environment, the authors did not describe the mechanism of gas dispersion in 3-dimensional space.
A final remark concerns the literature cited. The literature is only about studies on China, why don't the authors cite people from other parts of the world, or does no one else conduct such research and simulations?
Author Response
Reply 1.
In this study, the mechanism of pressure relief and permeability enhancement to enhanced gas extraction for mining safety.
To ensure that the cross-section of the roadway is not affected by blasting, a sufficiently long isolation zone must be left between the hole bottom and the roadway(line 285).In Table 5 of the paper, the information about the sealing length of blasting borehole is added.
Figure 6 (lines 148 and 149) is “histogram of â…¡7224N working face.” , not “Lithologic profiles of II 7224N coal face.” It's a translation error, which has been revised in the article. Figure 6 mainly describes the properties of the vertical strata of the coal seam, it mainly describes the thickness of hard strata overlying the coal seam. By enlarging Figure 6, the lithology and thickness of each layer can be seen clearly.
The change in pressure in the following points 1, 2 and 3 is logical, the purpose of the experiment is to verify the conclusion of the numerical simulation through physical simulation, and more truly observe the expansion of blasting cracks.
The name of the software used (line 70) has been deleted. The description of numerical model is added in this paper:
Two blasting holes are set in the numerical model, and the thickness of the model is 3 m. Three stress measuring points are set in the hard rock at the lower left of the blasting hole. The numerical model adopts the common node joint action mode to conduct stress. The boundary conditions of the calculated model are as followed: the upper boundary of the model is affected by gravity stress of coal and rock. The left and right boundaries were set as non-reflection boundary. The bottom was set as all sides constraint boundary.
The developed and described model was 3-dimensional (formula number 2), and the results are only 2-dimensional. Due to the limitation of the existing experimental equipment, it is difficult to observe the fracture development inside the experimental model. Therefore, the crack propagation and blasting effect can only be reproduced by the crack development on the surface. Similarly, the experimental device can not be sealed and filled with gas, the authors did not describe the mechanism of gas dispersion in 3-dimensional space. According to the experimental results, the migration law of gas in fracture can be analyzed theoretically in “4.2. Mechanism of Pressure Relief and Permeability Enhancement”.
China's coal mine geological conditions and gas occurrence are relatively complex, and foreign countries take closure measures for similar mines. Therefore, for high gas and low permeability mine gas drainage, only China has more reference literature.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors, you have done a very interesting and deep research. I would be curious to know how you took into account the scale factor when simulating post-explosion crack growth in the model (3.2 Experimental Model Construction) and how did you pressurize the model. I think it will be of interest to readers for future research on this topic.
Author Response
Comment 2.
Dear Authors, you have done a very interesting and deep research. I would be curious to know how you took into account the scale factor when simulating post-explosion crack growth in the model (3.2 Experimental Model Construction) and how did you pressurize the model. I think it will be of interest to readers for future research on this topic.
Author Response File: Author Response.pdf
Reviewer 3 Report
Respected Authors
I'd strongly recommend to publish your contribution after some minor revisions. I found some editorial shortcomings and also I have some methodological suggestions that do not need special changes in the scientific merit of presented work.
Personally, I appreciate very much articles that are composed that way, with clear introduction to the subject, brief description of the methods, results and discussion followed by presentation of practical implementation of proposed technology (or methodology). I found all these issues in reviewed article so it has my very positive recommendation.
A number of comments and suggestions for your paper are listed below:
Lines 40, 46, 54, 57 - please avoid multiple references, even if they are justified. It is better to refer individually to every cited paper, showing what it bring to the area of knowledge.
Line 74 - please check the quality of the Figure 1, provide some more description of its content.
Line 148 - please remove some of the horizontal frames from the third column to show the real layer thicknes. It is not mandatory but will make the table look better.
Line 319 - please provide better quality of Figure 13 (if possible) and some more detailed description of its content.
Best regards
Author Response
Comment 3.
I'd strongly recommend to publish your contribution after some minor revisions. I found some editorial shortcomings and also I have some methodological suggestions that do not need special changes in the scientific merit of presented work.
Personally, I appreciate very much articles that are composed that way, with clear introduction to the subject, brief description of the methods, results and discussion followed by presentation of practical implementation of proposed technology (or methodology). I found all these issues in reviewed article so it has my very positive recommendation.
A number of comments and suggestions for your paper are listed below:
Lines 40, 46, 54, 57 - please avoid multiple references, even if they are justified. It is better to refer individually to every cited paper, showing what it bring to the area of knowledge.
Line 74 - please check the quality of the Figure 1, provide some more description of its content.
Line 148 - please remove some of the horizontal frames from the third column to show the real layer thicknes. It is not mandatory but will make the table look better.
Line 319 - please provide better quality of Figure 13 (if possible) and some more detailed description of its content.
Reply 3.
Lines 40, 46, 54, 57 references were modified and deleted in the paper.
The description of stress boundary is added to figure 1in the paper.
The horizontal frames from the third column of the figure 6 has been modified.
Figure 13 shows the observation of blasting cracks in the borehole by using borehole camera, so the image quality is not good, but there is no redundant image. Its purpose is to observe the development of blasting cracks. The description of image is added in the article.
Author Response File: Author Response.pdf
