An Experimental Investigation of the Gas Permeability of Tectonic Coal Mineral under Triaxial Loading Conditions

Round 1

Reviewer 1 Report

The article deals with the subject of gas permeability of coal. This subject is very important from the point of view of gas hazards in hard coal mines. The authors have made a good literature research (I also suggest to refer to the article: Kudasik M.: Investigating Permeability of Coal Samples of Various Porosities under Stress Conditions, https://doi.org/10.3390/en12040762). The paper presents in detail the research material and its origin. The paper is clear, the diagrams are described accurately In my opinion, several elements need improvement:

1. In chapter 2.1., line 93, please describe the word "remodeled" more precisely or replace it with a more unambiguous word.
2. In chapter 2.1, line 98, please specify the unit of the sieve mesh size.
3. In Chapter 2.1, line 101, please complete the description of figure (b).
4. In Chapter 2.1, lines 103-110, please describe the sample preparation process in more detail.
5. In Chapter 2.1, Table 1, please explain the authors' reasons for dividing the samples into three groups A, B and C?
6. In chapter 2.2, lines 115-118, I propose to indicate in the figure the described elements.

Author Response

Thans for your reviewing. Please check the attachment for author's response.

Author Response File: Author Response.pdf

Reviewer 2 Report

Overall, the paper is well-written and clearly outlines the knowledge gap it is attempting to address regarding the measurement of gas-permeability evolution and stress-strain response for tectonic coal. Technically, the study may have benefitted from a ‘designed experiment’ approach, as opposed to ‘one-factor-at-a-time’, however, this does not greatly impact the usefulness of the results. Below are some comments the authors should clarify.

1. There is no description of how the permeability was actually calculated.
2. It is mentioned in the paper (lines 93-94) that this remodeled coal is widely employed, but how representative of tectonic coal is the remodeled coal? References would be useful for readers not directly within the topic area and to support the existing statement.
3. Lines 142-144, four stages are described and used throughout the text. It would be very useful to provide a visual definition as well (maybe within Figure 6) to help aid comprehension.
4. Line 145, what is meant by “the plasticity of the coal body is weakened”?
5. How was the radial strain measured?
6. Lines 183-184, it is stated that from the results in Figure 7 that the gas permeability evolution is closely related to the volumetric strain change. It is unclear to the reviewer how this conclusion was deduced and what the actual relationship is. A mention of this “obvious correlation” is also repeated in regards to Figure 10, but I still cannot understand what relationship the authors are trying to show.

Minor comments:

1. There should be a space between numbers and units of measure e.g. 0.47 MPa.
2. Line 56, should say “…it is more…”.
3. Lines 85 and 86 should say “…coal seam that is located…” or “…coal seam located…”.
4. Line 104, should the reference be to Figure 4b and not Figure 3b?
5. Line 106, should the reference be to Figure 4c and not Figure 3c?
6. Figure 4d is not referenced. Is it also necessary, since Figure 4c shows that the top section is circular?
7. Line 127, replace “fist” with “first”.
8. Replace “KN” with “kN” throughout the text.
9. In Figure 6, it may be beneficial to have the same axis values for the stress and strain.
10. Line 174, replace “triaxle” with “triaxial”.
11. Start of Line 183 should say “…is shown…”.
12. Line 211, should try and be consistent with the number of decimal places for all measurements.
13. Line 224, “repressing” may be better than “repress”?

Author Response

Thans for your reviewing. Please check the attachment for author's response.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have done a thorough job in addressing the reviewer's comments and I have nothing further to add.