Study of Prevention and Control Technology for Roadway Excavation under the Soft and Extra-Thick Coal Roof in Luling Coal Mine

Round 1

Reviewer 1 Report

I do not see any scientific merit of this study.  I do not feel that readers will be engaged with the study. Authors do not inform  well about benefit of the study or why they have to study. 

Author Response

Response 1: We thank the reviewer for his/her affirmative comments to our paper. In this paper, The range of stress concentration area and plastic zone was studied by numerical simulation. The reasonable water injection could improve the cohesion and shear strength of coal body, which were effective measures to prevent and control the wall of soft coal seam. The advanced Metal roof frame was used to maintain the stability of roadway according to the engineering condition. The support technology of "water injection + advanced metal roof frame + U-type shed" was formed to ensure the safe and efficient tunneling of roadway. This study provides reference significance for similar projects.

Reviewer 2 Report

Dear Authors,

overall, I found the article very interesting and well positioned. It deals with an interesting and topical topic and we believe will make a great contribution to literature. I would suggest the authors make some minor changes that perhaps could make the article more accessible and attract a wider readership.

First of all, I advise you to slightly improve the section containing the abstract, introduction, and conclusions.
  In conclusion, try to combine your results with a slightly larger group of readers. The results are very interesting, but the aim is to highlight your research in this article and to improve the presentation of this interesting scientific research. The article has great scientific and practical value.

GOOD LUCK,

Reviewer

Author Response

Response 1: We thank the reviewer for his/her affirmative comments to our paper. Based on your comments and in conjunction with the relevant literature, I have revised the abstract, introduction and conclusion sections to better read them for everyone. Thanks again to the reviewer.

Author Response File: Author Response.docx

Reviewer 3 Report

0- Literature Review is weak and few studies are mentioned in this connection.

1- Section “Engineering general situation” is not clear.

2- The quality of Figure 1 is low and is not clear.

3- The text is very poor in terms of editing, grammar and spelling.

4- The parameters in Table 1 are not defined (B, C, T ?)

5- The geometry of the numerical model and its details are not known.

6- Figure 4 is not referenced in the manuscript.

7- How was the excavation done and what was the support system for the walls?

8- Ground settlement profiles should be added during excavation.

9- What mean’s “past shear” and “present shear”?

10- Equation 2 is the Terzaghi’s effective stress relation and does not need to be proved again.

11- Although water injection reduces the applied pressure and may contribute to stability, it causes a drastic reduction in shear strength, which causes instability. Has this issue been investigated in this regard?

12- The structure of the manuscript is weak and the contents presented in different sections are not related to each other.

13- The purpose of the manuscript is not clear and there is no innovation in it.

Author Response

Response 1: We thank the reviewer for his/her affirmative comments to our paper. According to the opinions of reviewers, we added relevant literature categories to enrich this paper. The revised part has been marked in the paper.

Response 2: We thank the reviewer for his/her affirmative comments to our paper. We describe the project in detailed, so that the reader can have a clearer understanding of the project background. It's better to read the study below.

Response 3: We thank the reviewer for his/her affirmative comments to our paper. We have edited Figure 1 to see it more clearly.

Response 4: We thank the reviewer for his/her affirmative comments to our paper. We have carefully revised the manuscript according to the reviewers' comments, and the whole paper has been carefully reviewed and the grammatical errors have been corrected. The revised part has been marked in red.

Response 5: We thank the reviewer for his/her affirmative comments to our paper. We have defined the parameters, and has been marked in red.

Response 6: We thank the reviewer for his/her affirmative comments to our paper. We have added geometry of the numerical simulation to make it easier for you to read. The revised part has been marked in red.

Response 7: We thank the reviewer for his/her affirmative comments to our paper. We have referenced the Figure 4 in the manuscript.

Response 8: We thank the reviewer for his/her affirmative comments to our paper. Excavate coal (rock) by tunneling machine，After cutting forming, knock on the top, roof temporary support, using metal front probe beam, hat point column, impact wedge as advanced temporary support.

Response 9: We thank the reviewer for his/her affirmative comments to our paper. This paper mainly studies the block problem in the process of roadway excavation. Thanks for the guidance of the review experts, this part will be added in the following study.

Response 10: We thank the reviewer for his/her affirmative comments to our paper. Past shear means that the unit have been shear failure in the past. Present shear means that the unit is undergoing shear failure.

Response 11: We thank the reviewer for his/her affirmative comments to our paper. According to your coment, we have modified the description part of Equation 2.

Response 12:After the pressure water is injected into the coal wall, the pressure water will quickly enter the coal body along the favorable channels such as primary and secondary joints fissures and spread to the surrounding. Connecting tiny coal particles makes the brittleness of the wetted coal body weaken and the plasticity increases. The force between the molecular clusters changes the physical and mechanical properties of the coal body itself and improves the cohesion between the coal particles. In order to support the theoretical support of coal wall water-flooding and anti-plate help, this paper adds relevant references.

Response 13: We thank the reviewer for his/her affirmative comments to our paper. In order to improve the cohesion of each chapter, we add a transitional part between chapters. The revised part has been marked in red.

Response 14: We thank the reviewer for his/her comments to our paper. The range of stress concentration area and plastic zone was studied by numerical simulation. The reasonable water injection could improve the cohesion and shear strength of coal body, which were effective measures to prevent and control the wall of soft coal seam. The advanced Metal roof frame was used to maintain the stability of roadway according to the engineering condition. The support technology of "water injection + advanced metal roof frame + U-type shed" was formed to ensure the safe and efficient tunneling of roadway. This study provides reference significance for similar projects.

Author Response File: Author Response.docx

Reviewer 4 Report

-My major concern about this manuscript is its novelty. Contribution of authors about this subject need to be mentioned.

-Also, results of numerical model need to be validated.

- Why did you use FLAC3D? Compare this numerical software with other software that you can use instead (in a table).

Author Response

Response 1: In this paper, The location of rib spalling and the development law of plastic zone in the process of excavation of soft and extra-thick coal seams were studied. And use the water injection technology to alleviate the coal wall, Improve support quality. Ensure safe and efficient excavation of working face. It would play a demonstration role for the excavation of the roadway with similar conditions, and had certain reference significance and social benefits. FLAC3D can simulate the mechanical change of rock mass under the tectonic stress. The application in mining is mainly to analyze the failure characteristics and possibility of coal rock by simulating the change of surrounding rock of coal rock disturbed by mining.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I do not read it as a scientific research. Instead it is a mining cite operation project that can be solved within the mine company.  

Author Response

Response 1: The co-authors and I would like to thank you for the time and effort spent in reviewing the manuscript. As you ever said before, This paper is based on the engineering problem for intensive study. The stress, displacement and plastic zone were studied by numerical simulation to analyze the approximate location of coal wall slab. And through the coal wall water injection to strengthen the loose and broken coal body, improve the stability of the coal wall, and inhibit the coal wall fragmentation. The water injection parameters were determined by measuring the water content of the coal body. And the roof protection metal skeleton was used for support to enhance the later stage stability of the coal wall and ensure the long-term stability of the roadway. This support system of loosely broken coal is importantly referred for the similar kinds of projects. In terms of grammar, I had a professional team polish it to make it more convenient for readers to read. We sincerely hope that this revised manuscript has addressed all your comments and suggestions. We appreciated for reviewers’ warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.

Author Response File: Author Response.docx

Reviewer 3 Report

1- Literature Review is weak and few studies are mentioned in this connection.

2- Section “Engineering general situation” is not clear.

3- The text is very poor in terms of editing, grammar and spelling.

4- The legend is not clear in Figure 2.

5- The specifications of each 10 layers should be given in the article for the numerical model.

6- The geometry of the numerical model and its details are not known.

7- How was the excavation done and what was the support system for the walls?

8- Ground settlement profiles should be added during excavation.

9- Equation 2 is the Terzaghi’s effective stress relation and does not need to be proved again.

10- Although water injection reduces the applied pressure and may contribute to stability, it causes a drastic reduction in shear strength, which causes instability. Has this issue been investigated in this regard?

11- The structure of the manuscript is weak and the contents presented in different sections are not related to each other.

Author Response

Point 1: Literature Review is weak and few studies are mentioned in this connection.

Response 1: We thank the reviewer for his/her affirmative comments to our paper. According to the opinions of reviewers, we added relevant literature categories to enrich this paper. The revised part has been marked in the paper.

Point 2: Section “Engineering general situation” is not clear.

Response 2: We thank the reviewer for his/her affirmative comments to our paper. We describe the project in detailed, so that the reader can have a clearer understanding of the project background. It's better to read the study below.

Point 3: The text is very poor in terms of editing, grammar and spelling.

Response 3: We thank the reviewer for his/her affirmative comments to our paper. This paper had undergone English language editing by MDPI. The text had been checked for correct use of grammar and common technical terms, and edited to a level suitable for reporting research in a scholarly journal.

Point 4:  The legend is not clear in Figure 2.

Response 4: We thank the reviewer for his/her affirmative comments to our paper. We have edited Figure 2 to see it more clearly.

Point 5: The specifications of each 10 layers should be given in the article for the numerical model.

Response 5: We thank the reviewer for his/her affirmative comments to our paper. The specifications of each layer can be seeing in the Figure 1.

Point 6: The geometry of the numerical model and its details are not known.

Response 6: We thank the reviewer for his/her affirmative comments to our paper. In order to study the stress, displacement and the development of plastic zone at different positions in the process of roadway excavation. The location of the heading head was 0m, 1.2m, 2.4m. Through numerical simulation, the stress environment of different positions in the process of excavation was understood, and the location of prone to slip was clear, so as to provide the theory instruction for rib spalling. We had added geometry of the numerical simulation to made it easier to read. The revised part had been marked in red.

Point 7:  How was the excavation done and what was the support system for the walls?

Response 7: We thank the reviewer for his/her affirmative comments to our paper. We have referenced the Figure 4 in the manuscript. The roadway excavation was closely followed by the 9# coal floor, and the tunnel-boring machines was used to break rock and coal. The metal front prob beams, capped point column and bump wedge support were used as temporary fore support. The support section is shown in Figure 1.

Fig.1 Roadway support section

Point 8:  Ground settlement profiles should be added during excavation.

Response 8: We thank the reviewer for his/her affirmative comments to our paper. Because the coal seam was buried deep, the roadway was supported in time during the process of excavation. So the ground did not appear obvious subsidence.

Point 9: Equation 2 is the Terzaghi’s effective stress relation and does not need to be proved again.

Response 9: We thank the reviewer for his/her affirmative comments to our paper. Equation 2 is the Terzaghi’s effective stress relation and we have simplified it.

Point 10: Although water injection reduces the applied pressure and may contribute to stability, it causes a drastic reduction in shear strength, which causes instability. Has this issue been investigated in this regard?

Response 10: We thank the reviewer for his/her affirmative comments to our paper. Through the coal seam water injection, With the help of water-filled coal joints and fissures to connect easily dispersed coal particles, The shear strength and plastic deformation of coal can be improved by increasing the internal friction angle and cohesion of coal. However, the superfluous water would lead to the reduction of coal shear strength^[1-5].

[1] Wang H Z. Research and Application of hydrostatic water injection technology in the tunneling roadway of third soft coal Seam to prevent caving and roof collapse [J]. Journal of Jiaozuo Institute of Technology, 2004, 23(4): 261-263.

[2] Wang S D, Wang S K, Zhou E X, et al. Water injection technology of Middle pressure deep hole in the wall of three soft coal seam [J]. China Energy and Environmental Protection, 2011 (9): 65-66.

[3] Song Q Y, Nie Z, Chen C Q, et al. Application of high pressure water injection in shallow hole of coal wall [J]. Journal of Mining And Strata Control Engineering, 2005, 10(5): 59-60.

[4] Wang G Q, Li J, Yang H, et al. Technology of anti-slicing rust junction in Loose coal seam mining face [J]. China Energy and Environmental Protection, 2012 (9): 87-88.

[5] Sang P M. Study on law and process parameters of water injection strengthening stability of soft coal wall [D]. Henan Polytechnic University, 2010.

Point 11:  The structure of the manuscript is weak and the contents presented in different sections are not related to each other.

Response 11: We thank the reviewer for his/her comments to our paper. In this paper, The range of stress concentration area and plastic zone was studied by numerical simulation. The reasonable water injection could improve the cohesion and shear strength of coal body, which were effective measures to prevent and control the wall of soft coal seam. The advanced Metal roof frame was used to maintain the stability of roadway according to the engineering condition. The support technology of "water injection + advanced metal roof frame + U-type shed" was formed to ensure the safe and efficient tunneling of roadway. This study provides reference significance for similar projects.

We sincerely hope that this revised manuscript has addressed all your comments and suggestions. We appreciated for reviewers’ warm work earnestly, and hope that the correction will meet with approval. Once again, thank you very much for your comments and suggestions.

Author Response File: Author Response.docx