Study on the Co-Evolution Mechanism of Key Strata and Mining Fissure in Shallow Coal Seam Mining

Round 1

Reviewer 1 Report

 

1-      Use some numerical results in the abstract and conclusion sections.

3-      Improve the literature review and mention more previous works.

4-      What was the gap of the previous studies and what is your novelty in this study?

5-      Draw a schematic figure for explanation of section 2.1.

6-      Explain lines 171-174. Why these values were selected as constants? On which basis these values were selected? geometric similarity constant =1:100, bulk density similarity constant= 1.56, stress similarity constant= 156; the time similarity constant =10?

7-      Use references for all equations.

8-      Define all parameters in the equations carefully.

9-      The paper lacks numerical results. In addition, the paper is too theoretical and parametric. Use some numerical results in the “results and discussion” section.

10-   Compare the obtained results with the results of the previous studies and discuss them.

11-   Add a table for Hanjiawan Coal Mine soil properties in lines 636-641 instead of writing them in these lines.

 

 

1-      Improve the English. For example:

 rewrite lines: 33-35

Change “kth” and “jth” to “k^th” and “j^th”.

Change the reference format. For example: “mine disasters [1-3]” is correct not “mine disasters ^[1-3]”.

Author Response

Dear editorial department and reviewers:

Hello! I am the corresponding author with the title “Study on the co-evolution mechanism of key strata and mining fissure in shallow coal seam mining” (ID applsci-2482105).

Thank you very much for your support and review of the manuscript. You have raised many valuable manuscript questions and provided important help to manuscript revision and development of ideas.

At present, the manuscript has carefully revised the following issues based on the reviewers' comments, and the revision of the comments has been explained in detail as follows.

 

[Reviewer]

1. Use some numerical results in the abstract and conclusion sections.

In view of the lack of data description in the abstract and conclusion, the author has written the theoretical calculation data of the evolution height of mining fissures in combination with the manuscript, and supplemented them in the 21-22 lines of the abstract, the 774-775 lines and the 782-785 lines of the conclusion, which improves the problem of insufficient data.

 

 

2. Improve the literature review and mention more previous works.

Relevant literature has been added to the manuscript according to the requirements, and the literature numbers are [41] and [42]. Because the research background of this paper is shallow buried coal seam, the special geological conditions cause the related research to have a certain regionality, so the references of foreign scholars are relatively few.

 

 

3. What was the gap of the previous studies and what is your novelty in this study?

In view of the differences between the research content of this manuscript and the research of relevant scholars, firstly, the calculation results of this manuscript are more accurate, considering the rock failure process caused by mining operations, and focusing on the tensile action of the surface and the tensile and shear stress action of the working face. In the past, the height of fissures caused by mining operations was mostly predicted by traditional empirical formulas. Due to the large differences in lithology of different mines, there was a large error in the predicted height of traditional fissure development, and the accuracy was low.

The novelty of this study, this manuscript obtained the migration and fracture characteristics of key blocks based on field and experiment. At the same time, the failure mode of fracture mechanics materials and the fracture characteristics of this research content are combined to realize the application of the formation reason and solution idea of fracture mechanics fissures to the fracture of rock and soil layers in mining operations, so as to obtain the evolution height of fissures under different lithology. The calculated results are more accurate, which is conducive to on-site production and research on fissures.

 

 

4. Draw a schematic figure for explanation of section 2.1.

In view of the layout of the working face and the characteristics of the stratum in Section 2.1, Figure 1. Stratum layout of the working face has been drawn in the manuscript, and the parameters of the stratum and the working face are marked in detail in the figure, as shown in the following figure.

 

Figure 1. Stratum layout of the working face

 

 

5. Explain lines 171-174. Why these values were selected as constants? On which basis these values were selected? geometric similarity constant =1:100, bulk density similarity constant= 1.56, stress similarity constant= 156; the time similarity constant =10?

For the problem of why the relevant data of lines 171-174 in the manuscript are selected as constants, the main reason is that in mining engineering, because the research scale is usually 100 meters or kilometers under the actual geological conditions in the field, in order to realize the indoor experiment to verify the actual production conditions in the field, it is necessary to scale the field and indoor experiments in a certain proportion. For example, the scale of a map, you can use drawings to describe the actual terrain. Similarly, the indoor similarity simulation experiment selected in this paper is to use a certain proportion for scaling. For example, the geometric similarity constant in the manuscript is 1:100, which means that the 1 cm in the experiment represents the actual geological condition of the site is 1 m. Similarly, the actual bulk density, stress and field working face advancing time in the corresponding strata must be set in the experiment. The above proportional coefficient is usually called the similarity constant in mining.

 

 

6. Use references for all equations.

For the problem of using references for manuscript equations, because the equation references in the original manuscript are cited in the introduction, some formulas are not cited again. In this paper, the missing documents in the manuscript are supplemented in lines 307, 402, 583 and 661 of the manuscript, and marked in red font. The reason why some equations do not continue to use references is that the subsequent equations are derived from the secondary derivation in the reference literature or the further writing of the above equations, and there is no intellectual property problem.

 

 

7. Define all parameters in the equations carefully.

For the problem of defining parameters in the equation, the manuscript has been tested and combed again, and the parameters defined in lines 498-502 and 774 of the manuscript have been corrected and marked in red font.

 

 

8. The paper lacks numerical results. In addition, the paper is too theoretical and parametric. Use some numerical results in the “results and discussion” section.

First of all, we are very grateful for your question about the lack of numerical results of the manuscript. The main reason is that the manuscript is mainly theoretical research, so there are many theoretical calculation equations. In order to make the manuscript more readable and repeatable, the article has added the relevant data calculation and parameter description in the abstract, conclusion and text lines 745-748.

 

 

9. Compare the obtained results with the results of the previous studies and discuss them.

Since the research background of this manuscript is a shallow coal seam, according to the previous research on this background by scholars at home and abroad, it is generally believed that mining fissures directly develop to the surface. However, the study in this paper shows that when the mining fissures are I-I type, the mining fissures are not connected with the surface. When the mining fracture is I-II type, the mining fracture is connected with the surface. The field measurement in the working face shows that it conforms to the conclusion of this study. Therefore, compared with the previous research results, this study is more accurate and conducive to the later research.

 

 

10. Add a table for Hanjiawan Coal Mine soil properties in lines 636-641 instead of writing them in these lines.

Regarding the characteristic parameters of rock and soil layers in Hanjiawan Coal Mine, the relevant text descriptions have been converted into Table 3, and the lines 636-641 have been rearranged. The specific parameters are shown in Table 3.

Table 3. The occurrence characteristic parameters of rock and soil layers in Hanjiawan Coal Mine

Soil layer related parameters	Average bulk density (kN/m3)	Poisson ratio	Cohesion (MPa)	Angle of internal friction (°)	Elastic modulus (MPa)	Critical tensile deformation of ground surface (mm/m)
	23	0.35	0.077	36	32.45	-0.003
Related parameters of rock strata	Average bulk density (kN/m3)	Fracture angle of rock stratum (°)	Cohesion (MPa)	Angle of internal friction (°)	Buried depth of key strata (m)	/
	26	68	1.2	37	54.89	/

 

 

11. Improve the English. For example:

rewrite lines: 33-35

Change “kth” and “j_th” to “kth” and “j_th”.

Change the reference format. For example: “mine disasters [1-3]” is correct not “mine disasters^[1-3]”.

The full text of English expression has been collated and modified, and the problems mentioned will be modified. First, rewrite lines 33-35. Secondly, the subscript problem is modified, and the modified part is located in line 498-502 of the manuscript. Finally, the full-text reference of the manuscript has been rewritten, ^[1-3] has been changed to [1-3], and the modified position has been marked red.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper focuses on the mining of shallow coal seams and its impact on the surrounding rock and surface fissures. It investigates the relationship between broken rock beam structures and mining fissures in the key strata of shallow coal seam mining. The study uses field observations, simulations, and calculations to analyze the characteristics and connectivity of mining fissures, as well as their activation period and expansion patterns. The research findings identify different types of mining fissures and establish formulas for calculating their activation period and penetration. The study provides insights into the formation and evolution mechanisms of mining fissures in shallow coal seam mining and offers a theoretical foundation for further research in this field.

The findings of this research can inform the design and planning of mining operations in shallow coal seams. Understanding the relationship between broken rock beam structures and mining fissures can help engineers develop strategies to stabilize the surrounding rock, prevent excessive fissure expansion, and ensure the integrity of the mining structure. Overall, the study of mining fissures in shallow coal seam mining contributes to enhancing safety, minimizing environmental impact, optimizing resource utilization, and improving engineering design in mining operations.

 

Issue 1.

Please provide answers for important questions regarding methodology and provide lines where it is discussed in the paper:

1.1. How were the rotation and stress distribution characteristics of the rock beam structure analyzed, and what analytical techniques or models were utilized to derive the different types of mining fissures observed (up and down Ⅰ-Ⅰ type and Ⅰ-Ⅱ type)?

1.2. In the field measurement results, how were the obtained formulas for fissure activation period, rock formation fracture angle, mining fracture lag distance, and fissure penetration validated? What specific measurement techniques or instruments were employed to verify these formulas and their applicability to real-world conditions?

1.3. Could you elaborate on the process of theoretical derivation and calculation used to establish the relationship between mining fissures and mining rock beam structure? What mathematical or computational models were employed?

1.4. Can you provide more information about the field measurement techniques used to validate the formulas for fissure activation period, rock formation fracture angle, mining fracture lag distance, and fissure penetration? How were these measurements conducted and what instruments were employed?

 

Issue 2.

Please provide answers for important questions regarding discussion and provide lines where it is discussed in the paper:

2.1. Based on the findings and results, what are the practical implications of the study for the mining industry? How can the co-evolution mechanism between broken rock beam structures and mining fissures be utilized to improve mining operations and ensure safety?

2.2. Could you provide further details about the theoretical derivation and calculation methods used to establish the mechanical calculation model for key strata mining fractures?

2.3. Based on the research outcomes, what are the potential areas for future research or further investigation? Are there any specific aspects or variables that were not covered in this study but could enhance our understanding of mining fissures in shallow coal seam mining?

 

Issue 3.

What about the influence of leaving rock underground after coal mining? Can such actions make influence on evolution law of surface mining fissures? Please consider mentioned below research in your study as it can affect further research direction.

Smoliński, A.; Malashkevych, D.; Petlovanyi, M.; Rysbekov, K.; Lozynskyi, V.; Sai, K. Research into Impact of Leaving Waste Rocks in the Mined-Out Space on the Geomechanical State of the Rock Mass Surrounding the Longwall Face. Energies, 2022, 15, 9522. https://doi.org/10.3390/en15249522

Malashkevych, D.; Petlovanyi, M.; Sai, K.; Zubko, S. Research into the coal quality with a new selective mining technology of the waste rock accumulation in the mined-out area. Min. Miner. Depos. 2022, 16, 103-114. https://doi.org/10.33271/mining16.04.103

 

Issue 4.

All references are from China. Enhance literature review of studies conducted outside of China.

 

Issue 5.

The references are presented not in MDPI style. You need to reformat existing references with a proper guide.

 

Issue 6.

 

In general, I must admit that a very good study was performed, and I will recommend your paper for publication after careful revision.

Author Response

Dear editorial department and reviewers:

Hello! I am the corresponding author with the title “Study on the co-evolution mechanism of key strata and mining fissure in shallow coal seam mining” (ID applsci-2482105).

Thank you very much for your support and review of the manuscript. You have raised many valuable manuscript questions and provided important help to manuscript revision and development of ideas.

At present, the manuscript has carefully revised the following issues based on the reviewers' comments, and the revision of the comments has been explained in detail as follows.

 

[Reviewer]

1. Please provide answers for important questions regarding methodology and provide lines where it is discussed in the paper:

1.1. How were the rotation and stress distribution characteristics of the rock beam structure analyzed, and what analytical techniques or models were utilized to derive the different types of mining fissures observed (up and down Ⅰ-Ⅰ type and Ⅰ-Ⅱ type)?

The manuscript is mainly inspired by similar simulation experiments and previous studies. In the similar simulation experiments, the total station and the fissure width gauge are used to monitor the displacement of the rock beam structure and the mining fissures between the rock beam structures. The monitoring found that the broken rock blocks will rotate. At the same time, the stress sensor is laid under the experimental model to monitor the change of stress in the process of coal seam mining, so as to obtain the basic idea of this paper. Before the study of this manuscript, some scholars have done some research, mainly on the analysis of the force of rock beam. This manuscript uses the mechanical model of hinged rock beam and the mechanical model of step rock beam to analyze different mining fissures. According to the different causes of fissure formation, it is divided into I-I type and I-II type mining fissures.

  

• Total station                      (b) BJQF-1 fissure width gauge

  

• CL-YB-152 pressure monitoring equipment        (d) Simulation support

Figure 1. Similar simulation monitoring instrument

 

 

1.2. In the field measurement results, how were the obtained formulas for fissure activation period, rock formation fracture angle, mining fracture lag distance, and fissure penetration validated? What specific measurement techniques or instruments were employed to verify these formulas and their applicability to real-world conditions?

Because the layout of the mine working face is based on the latitude and longitude coordinates, in the process of advancing the working face, the specific latitude and longitude coordinates of the advancing position of the working face can be obtained according to the advancing distance. In this paper, the polar point measurement system is used to obtain the latitude and longitude coordinates of the location through satellite positioning, and the mutual position distance can be obtained according to the latitude and longitude coordinates and the latitude and longitude coordinates of the mine working face, so as to obtain the fissure activation cycle, rock breaking angle, mining fissure lag distance and so on. For the connectivity of fissures, the method of on-site measurement of ground drilling is used to obtain the fracture connectivity under different conditions. The specific monitoring instruments and monitoring process are shown in the following diagram.

 

• Host supporting equipment(b) Support tripod

 

• Field monitoring

Figure 2.  Pole measurement system

 

 

1.3. Could you elaborate on the process of theoretical derivation and calculation used to establish the relationship between mining fissures and mining rock beam structure? What mathematical or computational models were employed?

Thank you very much for your interest in the theoretical derivation process of this manuscript, which is our honor. This manuscript mainly adopts rock stratum control theory and fracture mechanics. The specific derivation process has been deduced in this paper, and the literature has been cited in the relevant formula part, which is conducive to the further understanding of the manuscript.

 

 

1.4. Can you provide more information about the field measurement techniques used to validate the formulas for fissure activation period, rock formation fracture angle, mining fracture lag distance, and fissure penetration? How were these measurements conducted and what instruments were employed?

This problem is described in detail in Question 1.2.Since the mining-induced fissures are irregular arcs, the field measured data are more complicated, which is not conducive to the overall combing of the article. The relevant data have been processed and drawn in the manuscript Figure 1 and Table 1.

The field measurement instrument is mainly the pole measurement system, and the specific monitoring instrument and measurement process have been listed in the figure of problem 1.2. By determining the mutual displacement coordinates between fixed points, the formation position of fissures can be determined, and the fixed points on the ground can be designed according to the needs of field research.

 

 

2 Please provide answers for important questions regarding discussion and provide lines where it is discussed in the paper:

2.1. Based on the findings and results, what are the practical implications of the study for the mining industry? How can the co-evolution mechanism between broken rock beam structures and mining fissures be utilized to improve mining operations and ensure safety?

Regarding the inspiration of this study to the mining industry, the manuscript research content can more accurately predict the evolution height of mining fissures and the distance between fissures and working faces, which is conducive to the prediction and treatment of water inrush and air leakage by field operators. Through this study, the subsequent quantitative research on mining fissures can be improved to a certain extent.

The problem of cooperative operation of breaking key strata and mining fissures is mainly to control the advancing speed of working face in the process of advancing working face, so as to control the breaking position of rock strata to a certain extent, and then control the distance of mining fissures lagging behind working face, so as to realize certain safety guarantee for on-site production.

 

 

2.2. Could you provide further details about the theoretical derivation and calculation methods used to establish the mechanical calculation model for key strata mining fractures?

The manuscript mainly uses rock stratum control theory and fracture mechanics for mechanical derivation. The central derivation idea of the manuscript is as follows:

• Based on the mining of coal mine working face, the upper rock stratum is broken. Due to the difference of bearing capacity of rock stratum, different fracture structures will be produced, which can be divided into two categories hinged structure and step structure.
• When the hinged structure is formed by breaking the key rock block, the rock stratum rotates, resulting in tensile failure of the rock stratum and loose soil layer.
• When the key block is broken to form a step structure, dislocation is formed at the breaking position, resulting in shear failure. Because the lower part of the rock layer has been mined out, it is inevitable to form partial rotation. The larger the disturbance radius of the loose soil layer, the larger the rotation amount, and the more obvious the tensile failure.
• According to the form of rock formation combined with the theory of fracture mechanics, the length of fissures can be further derived.
• According to the sum of the fracture values formed by the rock stratum and the loose soil layer, the permeability of the fracture can be judged, and the unpenetrated position and the height of the rock and soil layer can be reasonably obtained.

 

 

2.3. Based on the research outcomes, what are the potential areas for future research or further investigation? Are there any specific aspects or variables that were not covered in this study but could enhance our understanding of mining fissures in shallow coal seam mining?

Regarding the areas where the research content of this manuscript can be further studied in the future, there are mainly the following aspects.

(1) It can realize the gradual transformation of mining fissures from shallow coal seams to deep coal seams.

(2) Through the further analysis of mining fissures, it is possible to predict the development of fractures in advance and make some help for the subsequent closure of mining fissures.

Regarding the aspects not covered in this study, it is believed that mining fissures can be controlled from the method of filling mining. The author of this manuscript has been exploring specific related fields, but has not achieved great results.

 

 

3. What about the influence of leaving rock underground after coal mining? Can such actions make influence on evolution law of surface mining fissures? Please consider mentioned below research in your study as it can affect further research direction.

Smoliński, A.; Malashkevych, D.; Petlovanyi, M.; Rysbekov, K.; Lozynskyi, V.; Sai, K. Research into Impact of Leaving Waste Rocks in the Mined-Out Space on the Geomechanical State of the Rock Mass Surrounding the Longwall Face. Energies, 2022, 15, 9522. https://doi.org/10.3390/en15249522

Malashkevych, D.; Petlovanyi, M.; Sai, K.; Zubko, S. Research into the coal quality with a new selective mining technology of the waste rock accumulation in the mined-out area. Min. Miner. Depos. 2022, 16, 103-114. https://doi.org/10.33271/mining16.04.103

Thank you very much for your help and suggestions for this manuscript. We read the first article of your recommendation in detail. After reading, we found that it was indeed helpful to this manuscript, but unfortunately we did not retrieve the second article. Therefore, we decided to quote the first article you recommended to read, and in the follow-up study, we will combine the research content of the above article to carry out a more in-depth analysis.

 

 

4. All references are from China. Enhance literature review of studies conducted outside of China.

The relevant literature has been added as required, and the literature numbers are [41] and [42]. Because the research background of this paper is shallow buried coal seam, the special geological conditions cause the related research to have a certain regionality, so the reference references of foreign scholars are relatively few, please the editorial department and the external audit teacher understand.

 

 

5. The references are presented not in MDPI style. You need to reformat existing references with a proper guide.

The references have been modified according to the MDPI format, and the modified literature has been marked red. Thank you for your help.

 

 

6. In general, I must admit that a very good study was performed, and I will recommend your paper for publication after careful revision.

Thank you very much for your valuable comments on the manuscript, and thank you for your affirmation of the article. We will continue to work hard in the direction of manuscript research, and hope to further exchange relevant academic issues with you.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

1-Insert the gap of the previous works and your novelty in the manuscript.

2- As mentioned, some equations such as Eq. (23) have no references.

3- Check to define all parameters in the equations carefully.

English needs to be improved. For example:

Rewrite lines 701-702

Author Response

Dear editorial department and reviewers:

Hello! I am the corresponding author with the title “Study on the co-evolution mechanism of key strata and mining fissure in shallow coal seam mining” (ID applsci-2482105).

Thank you very much for your support and review of the manuscript. You have raised many valuable manuscript questions and provided important help to manuscript revision and development of ideas.

At present, the manuscript has carefully revised the following issues based on the reviewers' comments, and the revision of the comments has been explained in detail as follows.

 

 

1. Insert the gap of the previous works and your novelty in the manuscript.

The shortcomings and innovations of the manuscript have been supplemented after the conclusion of the manuscript, which is located in lines 781-814 of the manuscript. The supplementary contents are as follows.

Shortcomings and innovations of manuscripts

• This paper mainly studies the co-evolution of key strata and mining fissures in the working face, and the research on the control method of rock fracture is still insufficient, and no targeted weakening mining fissure evolution method is proposed. According to the research, the control of mining fissures should effectively reduce the free movement space of the overlying strata, so as to realize the overall control of the overlying strata, and relevant research will be carried out continuously in the follow-up work.
• In this paper, the pole measurement system is used to make a useful connection between the geometric parameters of the surface mining fissures and the mining position of the mine working face. Based on the mining position of the mine working face and the surface coordinate points, the field measured parameters such as the lag distance of the mining fissures and the breaking angle of the rock strata are obtained, which provides an effective measurement method for the prediction of the surface mining fissures position in the subsequent working face.
• In this paper, the field mining fissure development position and physical similarity simulation experiment are combined to realize the purpose of the field verification similarity simulation experiment and similarity simulation experiment to predict the field. At the same time, according to the evolution characteristics of the two, five dynamic activation processes of mining fissures are obtained. Based on the monitoring data, the formulas for calculating the lag distance of mining fissures, the breaking distance of rock strata, and the evolution time of mining fissures are obtained.
• Based on geotechnical mechanics and Griffith's criterion, the propagation characteristics of mining fissures are obtained by combining the micro-fissures in rock and soil with the macro-fissures in the working face. At the same time, considering that the coal mine strata are sedimentary rocks, and the evolution characteristics of mining fissures in rock mass are different, the calculation formula of the overall breaking angle of rock strata is obtained based on the control effect of key strata.
• According to the evolution characteristics of mining fissures in the field and similar simulation experiments, and according to the fracture characteristics of rock strata, the idea of upward and downward (I-I) and (I-II) mining fissures is proposed. Based on fracture mechanics and generalized Hooke's law, the mechanical calculation model of mining fissure evolution height is established. Based on the mechanical model, the calculation formula of mining fissure evolution value and the discriminant of mining fissure penetration are obtained.

 

 

2. As mentioned, some equations such as Eq. (23) have no references.

Thank you very much for your careful reading and review of the manuscript. For the problem that Eq. (23) does not add references in the manuscript, the manuscript has been checked and the relevant references have been supplemented, which are references [48] and [49].

 

 

3. Check to define all parameters in the equations carefully.

For the expression of all parameters in the equation, all the parameters of the manuscript have been checked and it has been found that the coefficient A in Eq. (1) is easy to be confused with the key block A.Therefore, the coefficient A is changed to F, which is located in the 264-266 lines of the manuscript and marked with red font.

 

 

4. English needs to be improved. For example:Rewrite lines 701-702

As for the grammar problem, the content of lines 701-702 in the manuscript has been rewritten, which is located in lines 696-699 of the manuscript, and the manuscript has been sorted out in full text, and the grammar and words and sentences have been further modified.

 

 

Thank you again for your valuable comments on the manuscript. Your comments make the manuscript more perfect. If there are still any problems in the manuscript, I hope you can contact us in time, hope to have the opportunity to communicate again, the most valuable greetings.

Author Response File: Author Response.docx

Reviewer 2 Report

Good work

Author Response

Thank the reviewers for their valuable comments on the manuscript. Your comments have further improved the manuscript. Because the reviewers have not raised specific questions, they have not made targeted amendments.