Coal Pillar Stress Weakening Technology and Application by Gob-Side Entry Driving and Hydraulic Roof Cutting in Deep Shafts Mines

Round 1

Reviewer 1 Report

In the paper 'Coal Pillar Stress Weakening Technology and Application by Gob-Side Entry Driving and Hydraulic Roof Cutting in Deep Shafts' the authors present their recent results about hydraulic roof cutting structural model for the roof structure of narrow gob-side coal pillars in kilometer-deep shafts.

In general, the paper is well written and organized. The figures are quite clear. I have only one minor concern related to the references which are, in my opinion, too synthethic. Therefore, I suggest to the authors to increase the number of references.

Author Response

Dear reviewer,

We would like to thank you for your careful reading, helpful comments, and constructive suggestions, which has significantly improved the presentation of our manuscript.

We have carefully considered the comments from you and revised our manuscript accordingly. In the revised manuscript, we added references where literature support is needed and revised the existing references. Thank you very much.

 

Yours sincerely,

Mr. Zhi Zhang

Shandong University of Science and Technology, 266590, China Qingdao,

[email protected].

Author Response File: Author Response.docx

Reviewer 2 Report

Very interesting article. The subject is very important both for the safety of mining works - the selection of large-thickness seams in the case of hanging roof rocks and the necessity to cause their fall as a result of hydraulic fracturing of rocks. This issue is also important in terms of the protection of the land surface in the area of coal mining in the underground mine.

The authors put a lot of work into the development of the computational model and conducted simulation tests that allowed them to determine the hydraulic fracturing roof cutting parameters (angle and height) due to the stresses of the surrounding rocks. The results of the tests were confirmed experimentally during the tests carried out in the mine.

Comments:

1) Shouldn't the end of the title rather read "... in Deep Shaft Mines"?

2) Check the correctness of the data in the References (authors' names) - items: 6, 7, 9, 10.

3) It does not follow from the content what the quantities represent: m_Z, m_E, γ_Z, γ_E. The first two quantities are shown in Fig. 3, but for the sake of order, it would be good to give their meaning under the formula (5).

4) What does figure 8a show?

5) Lines: 438 and 440 - there is: Table 4, it should be: Table 5

Author Response

Dear reviewer,

We would like to thank you for your careful reading, helpful comments, and constructive suggestions, which has significantly improved the presentation of our manuscript.

We have carefully considered all comments from you and revised our manuscript accordingly. All changes to the manuscript are marked using the "Track changes" feature. We hope our revised manuscript can be accepted for publication.

1) Shouldn't the end of the title rather read "... in Deep Shaft Mines"?

Response:

We are very sorry for the mistakes in this manuscript and inconvenience they caused in your reading. We have thoroughly checked and corrected the grammatical errors and typos we found in our revised manuscript. The title has been revised to “Coal Pillar Stress Weakening Technology and Application by Gob-Side Entry Driving and Hydraulic Roof Cutting in Deep Shafts Mines”.

 

2) Check the correctness of the data in the References (authors’ names) – items: 6, 7, 9, 10.

Response:

Thank you very much for pointing out this mistake. In the revised manuscript, we carefully checked all references and corrected the errors. For items: 6, 7, 9, 10:

6. PR, C.; OL, M.; Marcelo, S.; MA, M.; LJN, G. Hydro-mechanical coupled modeling of hydraulic fracturing using the mesh fragmentation technique. Computers and Geotechnics 2020, 124.

Cleto, P.R.; Manzoli, O.L.; Sánchez, M.; Maedo, M.A.; Beserra, L.B.; Guimarães, L.J. Hydro-mechanical coupled modeling of hydraulic fracturing using the mesh fragmentation technique. Comput. Geotech. 2020, 124, 103591.

7.Ingrid, T.; Marte, G. Micromechanics of hydraulic fracturing and damage in rock based on DEM modeling. Granular Matter 2020, 22.

Tomac, I.; Gutierrez, M. Micromechanics of hydraulic fracturing and damage in rock based on DEM modeling. Granular Matter 2020, 22, 1-17.

9. MS, K.; Seshagiri R. Empirical methods to estimate the strength of jointed rock masses. Engineering Geology 2004, 77.

Singh, M.; Rao, K.S. Empirical methods to estimate the strength of jointed rock masses. Eng. Geol. 2005, 77, 127-137.

10.BC, H.; FH, C. ISRM Suggested Methods for rock stress estimation—Part 3: hydraulic fracturing (HF) and/or hydraulic testing of pre-existing fractures (HTPF). International Journal of Rock Mechanics and Mining Sciences 2003, 40.

Haimson, B.; Cornet, F. ISRM suggested methods for rock stress estimation—part 3: hydraulic fracturing (HF) and/or hydraulic testing of pre-existing fractures (HTPF). Int. J. Rock Mech. Min. Sci. 2003, 40, 1011-1020.

 

3) It does not follow from the content what the quantities represent: mZ, mE, γZ, γE. The first two quantities are shown in Fig. 3, but for the sake of order, it would be good to give their meaning under the formula (5).

Response:

Thank you for pointing out this problem in our manuscript. According to the revised content, we give their meaning under the formula (5).

where γZ: volumetric weight of the immediate roof, kN/m3; mZ: thickness of the imme-diate roof, m; γE: volumetric weight of the basic roof, kN/m3; mE: thickness of the basic roof, m.

4) What does figure 8a show?

Response:

I'm sorry for the inaccuracy statements here. We corrected it in the revised manuscript. In the simulation, we recorded the vertical stresses of monitoring point at two sides of roadway. Figure8a show the vertical stress at different distances from roadway sidewall in the solid coal; Figure8b show the vertical stress at different distances from roadway sidewall in the coal pillar. In Figure 8a, as the height of the roof cutting increases, the vertical stress at the solid coal side of the roadway along the goaf gradually decreases, and the reduction rate is also gradually reduced.

 

5) Lines: 438 and 440 - there is: Table 4, it should be: Table 5

Response:

We thank the reviewer for pointing out this issue. We have replaced Table 4 in lines 438 and 440 with Table 5 in the revised manuscript.

 

Yours sincerely,

Mr. Zhi Zhang

Shandong University of Science and Technology, 266590, China Qingdao,

[email protected].

Author Response File: Author Response.docx