Study on Fracture Behavior of Directly Covered Thick Hard Roof Based on Bearing Capacity of Supports
Round 1
Reviewer 1 Report
The research of this manuscript aims to further explore the fracture behavior of directly covered thick hard roof based on bearing capacity of supports. The combination of simulation experiments, mechanical analysis, numerical simulation and field engineering practice is worthy of recognition in the article. But there are still some issues to be solved.
1. Please add reference to prove the correctness of the statement ‘Directly covering thick and hard roof leads to large range of rock pressure in working face, and large impact load when unstable’ in the line 156.
2. The variables of a formula should be written in a uniform font when interpreted.
3. Please give a brief explain for each graph in Figure 4 and label (a), (b) and (c).
4. Please delete the redundant unit representation in Table 4.
5. Please list the simulation, simulation or analysis software used in this article.
6. Some grammar errors of the whole article need to be improved.
7. Please add the illustration and explanation of Figure 15 to the article.
Therefore, I think this article can be considered for publication under minor revision.
Author Response
Thank you very much for giving us an opportunity to revise our manuscript (manuscript ID: applsci-2220442) entitled "Study on Fracture Behavior of Thick Hard Roof with Direct Covering Based on Support Bearing Capacity". The concerns and opinions of all reviewers are valuable, which is very helpful for us to revise and improve the manuscript. According to your comments and questions, we have carefully evaluated the reviewe report and made corresponding amendments to solve these problems.Please refer to the revised version uploaded again for specific changes (the changes are marked in red font). At the same time, explain the changes brought by your comments in the form of answers as follows:
Point 1: 1. Please add reference to prove the correctness of the statement ‘Directly covering thick and hard roof leads to large range of rock pressure in working face, and large impact load when unstable’ in the line 156.
Response 1: Thanks for your excellent suggestion. After the coal seam is mined, it is not easy to break the thick hard roof plate directly under its own weight. Industry scholars believe that the greater the thickness of the roof plate, the greater the breaking step, the longer the cantilever formed by the roof plate in the mining area, and at the same time, the impact load generated by the movement of the thick hard roof plate causes the risk of mine pressure at the working face to rise significantly.
Point 2: The variables of a formula should be written in a uniform font when interpreted.
Response 2:Thanks for your excellent suggestion. After checking, we have modified the writing font of formula variables in the paper to unify the writing font style.
Point 3: Please give a brief explain for each graph in Figure 4 and label (a), (b) and (c).
Response 3: Thanks for your excellent suggestion. After checking, we have revised and explained Figure 4 in the paper.
Point 4: Please delete the redundant unit representation in Table 4.
Response 4: Thanks for your excellent suggestion. After re-checking the content of the thesis, in the initial incoming pressure step statistics table of the roof, the incoming pressure duration of the hydraulic support measuring station in each part is not very relevant to the overall research content of this thesis, so the incoming pressure duration in Table 4 can be deleted, while the incoming pressure influence distance in the thesis can reflect the effect of mine pressure control on the straight overlying thick hard roof working face by using pre-cracked cut roof at the engineering site.
Point 5: Please list the simulation, simulation or analysis software used in this article.
Response 5: Thanks for your excellent suggestion. In this paper, we combine physical similar simulation and numerical simulation by FLAC3D software to obtain pre-cracking top cutting structure, and use the theory of plate structure for mechanical analysis to obtain the analytical equation of CFCS plate deflection, and use ORIGIN software to analyze the effect of each influencing factor according to this equation, and finally substitute the actual engineering parameters, and use MATLAB software to invert the maximum allowable thick hard roof breaking step to ensure the safety of the working face. Under the condition of ensuring the safety of the working face, the maximum allowable thick hard roof breaking step, and use this step as the top cutting step, use UDEC software to compare the overburden collapse and stress state before and after the top cutting, in order to verify the effect of top cutting according to the calculated step, and apply to the site, combined with the analysis of the site support monitoring data, pre-cracking top cutting achieved good results. So the main simulation software used in this paper is FLAC3D and UDEC, and the main analysis software is MATLAB software and ORIGIN software.
Point 6: Some grammar errors of the whole article need to be improved.
Response 6: Thanks for your excellent suggestion. In view of some grammatical errors in the article, it has been revised.
Point 7: Please add the illustration and explanation of Figure 15 to the article.
Response 7: Thanks for your excellent suggestion. The hydraulic bracket working resistance and dynamic load coefficient, as two major technical indicators of hydraulic bracket, can better reflect the mine pressure situation at the working face. Figure 15 shows the change of hydraulic bracket working resistance and dynamic load factor, where Figure 15(a) shows the hydraulic bracket working resistance and dynamic load factor of hydraulic bracket before and after the initial pressure coming from the straight overlying thick hard roofing slab after roof cutting, and Figure 15(b) shows the hydraulic bracket working resistance and dynamic load factor of hydraulic bracket before and after the periodic pressure coming from the straight overlying thick roofing slab after roof cutting. These data can better illustrate the incoming pressure condition of the working face on 13121 after pre-cracking and roof cutting and the load-bearing stability of the hydraulic support.
Thanks so much for your kind comments! We have amended the manuscript according to your suggestions, and hope the amended manuscript meets your requirement.
Thank you again for your comments and suggestions!
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The contribution to fracture mechanics is very good. Before publication needs to revise as per the following issues:
(1) The mathematical equation all are cited from known literature, is there any new mathematical formulae derived newly?
(2) Abstract is too long. It should be concise.
(3) Sensitivity analysis is missing. What is the most sensitive factors that should be found?
(4) Figure 14 is very tough to read. More explanation need for the figure with a clear picture.
(5) Motivation and novelties should be written in a separate subsection after giving the subsection name.
(6) The applications of this study should be written more briefly by adding a section like future research scope.
(7) A flow chart is needed for describing the whole presented work.
(8) Several equations like equation (2), if we consider the coefficient value 241 rather than 241.3 what happens? Is it numerical approximated or any assumed value?
(9) Each and every equation and figure needed more description and discuss their necessity.
Author Response
Thank you very much for giving us an opportunity to revise our manuscript (manuscript ID: applsci-2220442) entitled "Study on Fracture Behavior of Thick Hard Roof with Direct Covering Based on Support Bearing Capacity". The concerns and opinions of all reviewers are valuable, which is very helpful for us to revise and improve the manuscript. According to your comments and questions, we have carefully evaluated the reviewe report and made corresponding amendments to solve these problems.Please refer to the revised version uploaded again for specific changes (the changes are marked in red font). At the same time, explain the changes brought by your comments in the form of answers as follows:
Point 1: The mathematical equation all are cited from known literature, is there any new mathematical formulae derived newly?
Response 1: Thanks for your excellent suggestion. The mechanical calculation methods and mechanical theories applied in the paper are quoted from known literature. In this paper, the mechanical model of two pairs of solid support, one side free and the other side simply supported is established in combination with the structure of thick hard roof plate after pre-cracking roof cutting on the working face of 13121, but due to the special conditions of the first mining of this working face, the influence of other dynamic loads is not considered, and only the overlying uniform load of thick hard roof plate is analyzed as the force on the roof plate. Formally, the formulas in the paper do not see obvious innovative formulas, but it is still very necessary for the subsequent research. Meanwhile, in the previous research, there is a lack of discussion about hydraulic bracing and roof breakage step, and this study proposes a bracing resistance solution formula based on roof breakage step, which provides reference value for similar engineering applications.
Point 2: Abstract is too long. It should be concise.
Response 2: Thanks for your excellent suggestion. The abstract has been simplified according to the content of the paper.
Point 3: Sensitivity analysis is missing. What is the most sensitive factors that should be found?
Response 3: Thanks for your excellent suggestion. According to the formula for calculating the deflection of roof and the method for calculating the resistance of hydraulic support in the manuscript, formulas (10) and (11), the relationship between the working resistance of hydraulic support and the size of the broken body of thick and hard roof can be obtained, such as formula (12), and the related influencing factors are analyzed, and the influence curve of each factor is made. The slope represents the sensitivity of each factor to the resistance of support, in which the resistance of support responds more obviously to the changes of K, L and q0.
Point 4: Figure 14 is very tough to read. More explanation need for the figure with a clear picture.
Response 4: Thanks for your excellent suggestion. Figure 14 shows the cycle pressure step for the upper, middle and lower working face of 13121 in the process of 18 cycles of pressure, in which the main monitoring data of the upper part of the working face comes from the data of 8#, 16#, 24#, 32#, 40# hydraulic supports, the main monitoring data of the middle part of the working face comes from the data of 48#, 56#, 64#, 72#, 80 #The main monitoring data of the lower part of the working face is from the data of 88#, 96#, 104#, 112# and 120# hydraulic supports, combined with Figure 14 to reflect the top plate cycle step situation. And according to your suggestion, we redraw Figure 14 to make it more clear.
Point 5: Motivation and novelties should be written in a separate subsection after giving the subsection name.
Response 5: Thanks for your excellent suggestion. According to your suggestion, add a separate section to sort out the motivation and novelty of this study.
Point 6: The applications of this study should be written more briefly by adding a section like future research scope.
Response 6: Thanks for your excellent suggestion. At present, this study is only based on field engineering practice, and the future application of this study will be studied in the future.
Point 7: A flow chart is needed for describing the whole presented work.
Response 7: Thanks for your excellent suggestion. In this paper, the physical similarity simulation and FLAC3D software are combined to carry out numerical simulation to obtain the pre-splitting and top-cutting structure, and the mechanical analysis is carried out by using the relevant theory of plate structure, and the analytical formula of the deflection of CFCS plate is obtained, and according to this formula, the influence effect of various influencing factors is analyzed by using ORIGIN software. Finally, the actual engineering parameters are substituted, and the maximum allowable breaking step of thick hard roof can be deduced by using MATLAB software under the condition of ensuring the safety of the working face. Taking this step as the cutting step, UDEC software is used to compare the caving and stress state of overlying strata before and after cutting, so as to verify the cutting effect according to the calculated step, and it is applied to the site. Combined with the analysis of the monitoring data of the site support, the pre-splitting cutting has achieved good results. Therefore, the simulation software used in this paper is FLAC3D and UDEC, and the main analysis software is MATLAB and ORIGIN software.
Point 8: Several equations like equation (2), if we consider the coefficient value 241 rather than 241.3 what happens? Is it numerical approximated or any assumed value?
Response 8: Thanks for your excellent suggestion. Equation (2) is a kind of deformation under the assumption of Equation (1), and the coefficient in Equation (2) is 241.3, which comes from the method of calculating the initial pressure equivalent of roof in the book Mine Pressure and Strata Control by Academician Qian Minggao. It is an empirical calculation method obtained by fitting a large number of field data, and it is used as a constant at present.
Point 9: Each and every equation and figure needed more description and discuss their necessity.
Response 9: Thanks for your excellent suggestion. Combined with your suggestion, the equations and figures in this paper have been supplemented.
Thanks so much for your kind comments! We have amended the manuscript according to your suggestions, and hope the amended manuscript meets your requirement.
Thank you again for your comments and suggestions!
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The paper is now acceptable.
