Prediction and Application of the Height of Water-Conducting Fracture Zone in the Composite Roof: A Case Study of Jinxinda Coal Mine
Round 1
Reviewer 1 Report
Based on theoretical analysis, numerical simulation, and field measurement, the movement law of composite roof overlying rock is analyzed. Taking the 201 working face of the No. 2 coal seam in Jinxinda Coal Mine as an example, the height of the water-conducting fracture zone is determined, and the water hazard prediction and prevention is carried out by transient electromagnetic method, which enriches the relevant experience of water hazard prevention and control. However, there are still some deficiencies in the work, which are as follows:
1. Abstract: There is no summary description of Section 3, which leads to the independent content. It is recommended to add related descriptions in the Abstract.
2. Introduction: The research on the development of overburden fractures caused by mining is not clear. For example, "In the aspect of mining overburdened rock lead to water crack development." It is suggested that the text of this part should be rearranged.
3. It is suggested to unify the titles 4.1 and 4.2.
4. In Section 5.2, according to the crack evolution law of composite roofs, the advance distance selected by vertical displacement and crack distribution cannot be completely corresponding, which fails to form a strict comparison. Please explain the reasons for choosing different advancing distances.
5. In Section 6.1, the working principle of the transient electromagnetic detection method should be briefly introduced, and it is suggested to supplement this part.
6. Conclusion: Conclusion (1) The logical relationship is not strong, the description is not complete, and the description of the development law of water-conducting fissure is lacking.
7. Numbers and units should be written separately according to the MDPI editing requirements.
8. Some figures and tables in this work do not meet MDPI requirements, as shown in Figure 5 and Table 4. It is suggested to modify them according to relevant requirements.
9. There are some grammatical problems in this work, so it is suggested to modify the grammar.
10. The proportion of Chinese journals in the reference literature is a little high, the authors can refer to some relevant international journal papers, such as follows: “Fracture characteristics of basic roof and mechanism of strata behavior in a pillarless working face”, “The influence of advance speed on overburden movement characteristics in longwall coal mining: insight from theoretical analysis and physical simulation”,”Evolution mechanism of water-flowing zones and control technology for longwall mining in shallow coal seams beneath gully topography”
There are some grammatical problems in this work, so it is suggested to modify the grammar
Author Response
Response to Reviewer 1 Comments
Point 1：Abstract: There is no summary description of Section 3, which leads to the independent content. It is recommended to add related descriptions in the Abstract.
Response 1: In Section 3, the fracture conditions of hard rock and soft rock are analyzed and the height of the water-conducting fracture zone is calculated. The breaking conditions of hard rock and soft rock in this section are completed based on the overburden stability in Section 2. The calculation of the height of the water-conducting fracture zone is also completed based on the key strata characteristics and identification in Section 2. In addition, it provides a comparison for the numerical simulation of the fracture zone height in Section 4. Based on the above, the Abstract is reorganized.
Point 2：Introduction: The research on the development of overburden fractures caused by mining is not clear. For example, "In the aspect of mining overburdened rock lead to water crack development." It is suggested that the text of this part should be rearranged.
Response 2: The first part is the research background of water-conducting fracture zone; the second part is the research status of overburden deformation and fracture; the third part is the research status of fracture development under the influence of mining; the fourth part is the research content and significance of this paper. Based on this, the Introduction is rearranged and modified.
Point 3：It is suggested to unify the titles 4.1 and 4.2.
Response 3: Section 4.1 is the hard rock fracture analysis, and Section 4.2 is the soft rock fracture analysis. These two sections are the analysis of fracture conditions for different lithology strata. Based on this, the two sections of the title of the unified expression.
Point 4：In Section 5.2, according to the crack evolution law of composite roofs, the advance distance selected by vertical displacement and crack distribution cannot be completely corresponding, which fails to form a strict comparison. Please explain the reasons for choosing different advancing distances.
Response 4: In Section 5.2, the roof migration law and crack evolution law are analyzed by numerical simulation. The roof migration law is expressed by vertical displacement, and the crack evolution law is reflected by the joint failure state. FIG. 6 shows the evolution process of vertical displacement of overlying rock at the working face, reflecting the vertical displacement of the roof at different lengths. Taking large vertical displacement of roof strata as the standard, the working face is selected to advance 80 m, 120 m, 140 m, 170 m, 190 m, and 300 m, respectively. Figure 7 shows the dynamic development characteristics of mining-induced overburden fracture and water-conducting fissure, reflecting the joint state of the roof strata. When failure occurs, it is divided into fissure generation. Therefore, the working face is selected to advance 100 m, 130 m,160 m, 190 m,220 m, and 260 m. Vertical displacement and fracture do not occur at the same time, so the advancing length of the selected working face is not consistent, which mainly reflects the migration characteristics of the overburden and fracture evolution process.
Point 5：In Section 6.1, the working principle of the transient electromagnetic detection method should be briefly introduced, and it is suggested to supplement this part.
Response 5: In Section 6.1, there is the analysis of the geophysical anomaly area in the working face. The transient electromagnetic method is adopted for geophysical exploration of the working face, and its basic working method is as follows: a transmitting coil with a certain waveform current is set in the well to generate a primary magnetic field in the surrounding space, and an induced current is generated in the underground conductive rock orebody. Because the water resistance rate is lower than that of coal, the low resistance abnormal area is the key prevention and control area of water disasters. Based on the above, the relevant content is added.
Point 6：Conclusion: Conclusion (1) The logical relationship is not strong, the description is not complete, and the description of the development law of water-conducting fissure is lacking.
Response 6: The conclusion part is reorganized according to the research content. There are three main conclusions: (1) Stability characteristics and fracture zone height of 201 working face are obtained through theoretical analysis. (2) The migration and fracture evolution law of mining-induced overburden are analyzed by using discrete element software simulation. (3) Study on the assessment and prevention of water damage in working face. Detailed conclusions are in the manuscript.
Point 7：Numbers and units should be written separately according to the MDPI editing requirements.
Response 7: According to the editing rules of MDPI, the full text has been checked and relevant problems have been modified.
Point 8：Some figures and tables in this work do not meet MDPI requirements, as shown in Figure 5 and Table 4. It is suggested to modify them according to relevant requirements.
Response 8: According to the rules of MDPI, check the full text, and modify the problems existing in the related ffigures and tables.
Point 9：There are some grammatical problems in this work, so it is suggested to modify the grammar.
Response 9: Check the full text and correct the grammar problems.
Point 10：The proportion of Chinese journals in the reference literature is a little high, the authors can refer to some relevant international journal papers, such as follows: “Fracture characteristics of basic roof and mechanism of strata behavior in a pillarless working face”, “The influence of advance speed on overburden movement characteristics in longwall coal mining: insight from theoretical analysis and physical simulation ”,” Evolution mechanism of water-flowing zones and control technology for longwall mining in shallow coal seams beneath gully topography”
Response 10: We carefully read the references recommended by the reviewers and collected relevant references. The relevant international references are added, which mainly include three aspects: overburden migration law, roof fracture analysis, and water-conducting fracture zone prediction. The proportion of international literature in the reference is increased.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The article of the authors is devoted to an important and topical issue related to the study of the roof of coal mines.
The causes of accidents and accidents at mining enterprises are of a general nature: low labor and technological discipline among the performers of work, lack of technical means to ensure safe working conditions, insufficient qualifications of personnel, lag in reconstruction and technical re-equipment, aging of fixed assets. For mines, the main task is to update fixed assets (replacement of main ventilation fans, stationary and mining equipment, equipping mines with new aero-gas control equipment), degassing of coal seams and mined-out spaces to ensure aerological safety and utilization of methane for subsequent energy generation or other use.
Coal mining is associated with such hazardous factors as the collapse of the roof and walls of mine workings, coal dust, the release of methane and other harmful gases generated during the development process.
Detection and measurement of the parameters of fracture systems, which largely determine the stability of rocks around mine workings, is an important technological task in monitoring and predicting the geomechanical state of the massif.
The work uses modern methods of theoretical analysis and numerical simulation to control water disaster on the roofs of coal seams.
The studies presented in the paper are undoubtedly of interest to readers in the field under consideration.
However, it would be necessary to clarify a number of comments that are available to the article:
1. In the introduction, the article presents an incomplete literary review of the problems that may be in coal mines and the study of which is very relevant in the works of various scientists. In particular, different gases are emitted in coal seams: most often methane (CH4), less often hydrogen sulfide (H2S) and carbon dioxide (CO2). These gases rarely cause death or serious illness. An explosive mixture of air with methane and coal dust, which is highly flammable. The problem of ensuring safety in mines developing methane-bearing coal seams continues to be relevant. Methane explosions occur as a result of exceeding the intensity of methane release compared to the predicted one. It would be possible to consider the work of:
Bosikov I.I., Martyushev N.V., Klyuev R.V., Savchenko I.A., Kukartsev V.V., Kukartsev V.A., Tynchenko Y.A. Modeling and complex analysis of the topology parameters of ventilation networks when ensuring fire safety while developing coal and gas deposits. Fire 2023, 6, 95. https://doi.org/10.3390/fire6030095.
Along with these, it is important to study the aerodynamic processes occurring in coal mines, as can be seen from the work of:
Balovtsev S.V., Skopintseva O.V., Kolikov K.S. Aerological risk management in preparation for mining of coal mines. Sustainable Development of Mountain Territories. 2022;14(1):107-116. DOI: 10.21177/1998-4502-2022-14-1-107-116.
2. According to Table 2, for greater clarity, it would be necessary to present a mathematical model of the dependence of thickness on the depth of embedment for a more extensive analysis in various operating conditions.
3. In formulas (3), (4) not all components are described. A number of parameters should be disclosed in more detail, in particular, h, E, etc.
4. It was necessary to describe in more detail the implementation of the methodology shown in Figure 3. Is it possible to have a wider variation of the parameters according to the applied methodology?
5. Interesting data are presented in Figure 6, however, it would be necessary to carry out mathematical modeling of the studied indicators with the reduction of models that can be used to calculate and predict the output parameters.
6. The quality of figure 7 needs to be improved, practically nothing is visible.
7. Are there any patents on the methods used in the article and is it planned to test the results obtained on other similar objects?
Author Response
Response to Reviewer 2 Comments
Point 1：In the introduction, the article presents an incomplete literary review of the problems that may be in coal mines and the study of which is very relevant in the works of various scientists. In particular, different gases are emitted in coal seams: most often methane (CH4), less often hydrogen sulfide (H2S) and carbon dioxide (CO2). These gases rarely cause death or serious illness. An explosive mixture of air with methane and coal dust, which is highly flammable. The problem of ensuring safety in mines developing methane-bearing coal seams continues to be relevant. Methane explosions occur as a result of exceeding the intensity of methane release compared to the predicted one. It would be possible to consider the work of: Bosikov I.I., Martyushev N.V., Klyuev R.V., Savchenko I.A., Kukartsev V.V., Kukartsev V.A., Tynchenko Y.A. Modeling and complex analysis of the topology parameters of ventilation networks when ensuring fire safety while developing coal and gas deposits. Fire 2023, 6, 95. https://doi.org/10.3390/fire6030095. Along with these, it is important to study the aerodynamic processes occurring in coal mines, as can be seen from the work of: Balovtsev S.V., Skopintseva O.V., Kolikov K.S. Aerological risk management in preparation for mining of coal mines. Sustainable Development of Mountain Territories. 2022;14(1):107-116. DOI: 10.21177/1998-4502-2022-14-1-107-116.
Response 1: In the introduction part, the research status is analyzed from two aspects of overburden fracture and water-conducting fracture zone development. Therefore, this work takes the water disaster prevention of the No.2 coal seam roof of Jinxida Coal Mine as the research background, the development rule of composite roof fracture, and the maximum height of the water-conducting fracture zone are analyzed by the combination of theoretical analysis and numerical simulation. Transient electromagnetic exploration technology was used to explore the working face, and to prevent the influence of water disasters in the abnormal areas during mining, drilling verification was carried out in the abnormal areas. he expected research results can not only enrich the rock formation control theory and roof water inrush mechanism but also have important practical significance to guide the safety production of a coal mine.
Point 2：According to Table 2, for greater clarity, it would be necessary to present a mathematical model of the dependence of thickness on the depth of embedment for a more extensive analysis in various operating conditions.
Response 2: Table 2 is the rock mechanics parameters table, which is the material parameters for the establishment of numerical models, generally obtained through laboratory tests.
Point 3：In formulas (3), (4) not all components are described. A number of parameters should be disclosed in more detail, in particular, h, E, etc.
Response 3: Relevant instructions are supplemented in formulas (3) and (4), where E is elastic modulus, h is rock thickness, γ is bulk density, and q is load.
Point 4：It was necessary to describe in more detail the implementation of the methodology shown in Figure 3. Is it possible to have a wider variation of the parameters according to the applied methodology?
Response 4: Figure 3 is a flow chart, which illustrates the whole implementation process in detail, and the parameters used are described in the manuscript.
Point 5：Interesting data are presented in Figure 6, however, it would be necessary to carry out mathematical modeling of the studied indicators with the reduction of models that can be used to calculate and predict the output parameters.
Response 5: Figure 6 has been modified to add related descriptions in the manuscript.
Point 6：The quality of figure 7 needs to be improved, practically nothing is visible.
Response 6: Figure 7 was redrawn to increase the clarity of the figure, and a ruler was added to the figure to clearly reflect the height of the roof fracture development. The figure shows all states of the joint. In UDEC, the states of joints are divided into slip and tension. In general, longitudinal joints slip and transverse joints are tensile.
Point 7：Are there any patents on the methods used in the article and is it planned to test the results obtained on other similar objects?
Response 7: The method used in this work does not have any patent at present. Similar tests are planned to analyze the results and explore the applicability of the method.
Author Response File: Author Response.docx
Reviewer 3 Report
In this work, based on the research background of water disaster prevention and control of 2 coal seam roofs in Jinxinda Coal Mine, the development law of composite roof fracture is analyzed by combining theoretical analysis and numerical simulation. This paper lacks innovation, science, reliability, logic and readability and I reject this paper for publication.
Please align the terminology in the text.
Author Response
Response to Reviewer 3 Comments
Point 1：In this work, based on the research background of water disaster prevention and control of 2 coal seam roofs in Jinxinda Coal Mine, the development law of composite roof fracture is analyzed by combining theoretical analysis and numerical simulation. This paper lacks innovation, science, reliability, logic and readability and I reject this paper for publication.
Response 1: Thank you for your comment on improving the quality of this work. Thank you for pointing out the inadequacies of this article, and We have revised it accordingly.
This work takes the water disaster prevention of the No.2 coal seam roof of Jinxida Coal Mine as the research background, the development law of composite roof fracture, and the maximum height of the water-conducting fracture zone are analyzed by the combination of theoretical analysis and numerical simulation. Transient electromagnetic exploration technology was used to explore the working face, and to prevent the influence of water disasters in the abnormal areas during mining, drilling verification was carried out in the abnormal areas.
This work focuses on the migration law and fracture development law of composite roofs by theoretical analysis, numerical simulation, and field monitoring. On the basis of fracture development, the relationship between the development height of the fracture zone and mining is explored to avoid the influence of water in overlying strata on the mining of the working face. The expected research results can not only enrich the rock formation control theory and roof water inrush mechanism but also have important practical significance to guide the safety production of a coal mine.
Author Response File: Author Response.docx
Reviewer 4 Report
Review comments,
In this paper, based on the research background of water disaster prevention and control of 2 coal seam roofs in Jinxinda Coal Mine, the development law of composite roof fracture is analyzed by combining theoretical analysis and numerical simulation. The research results have certain experimental value and engineering practice significance, but there are the following problems:
1. I would recommend avoiding group links [1-4], [5-9]. From my point of view, [11-12] or [11, 13] can be acceptable, up to three are acceptable, everything more needs to be deciphered. Each work you cite is unique and the studies you cite deserve more proper and careful review to demonstrate (and prove) its importance to current research. It is necessary to demonstrate in detail the essence of each study and their need for your work.
2. In Figure 5, the different rock strata should be indicated in the UDEC Numerical model.
3. In Figure 6, " Y Displacement" should be marked on the displacement cloud map.
In addition, the clarity of Figure 6 should be increased, and appropriate labels should be made to make the stratification of the rock strata shown in the Figure 6 better.
4. With the same problem, Figure 7 is fuzzy, it is difficult to see the joint failure situation clearly, the clarity should be increased. In addition, it is important that the height of mining-induced overburden fracture and water-conducting fractures be numerically indicated on the figure.
5. Figure 7 shows different failure forms of joints after excavation of the UDEC model, is it completely displayed?
6. In Section 6.1, the principle of TEM exploration for water-bearing fracture zone is low apparent resistivity anomaly under high resistance background should be added. I would recommend that transient electromagnetic inversion resistivity section can be added to the paper and analyzed, which may make the analysis more convincing.
7. For the same problem, Figure 8 should be clearer.
8. Please revise the conclusion in paragraphs. In the conclusions, in addition to summarizing the actions taken and results, please strengthen the explanation of their significance.
Author Response
Response to Reviewer 4 Comments
Point 1：I would recommend avoiding group links [1-4], [5-9]. From my point of view, [11-12] or [11, 13] can be acceptable, up to three are acceptable, everything more needs to be deciphered. Each work you cite is unique and the studies you cite deserve more proper and careful review to demonstrate (and prove) its importance to current research. It is necessary to demonstrate in detail the essence of each study and their need for your work.
Response 1: The references were reorganized and adjusted, and the way of quoting multiple references with group links was modified to quote three references at most. In the introduction part, the research status is analyzed from two aspects of overburden fracture and water-conducting fracture zone development. Therefore, this work takes the water disaster prevention of the No.2 coal seam roof of Jinxida Coal Mine as the research background, the development rule of composite roof fracture, and the maximum height of the water-conducting fracture zone are analyzed by the combination of theoretical analysis and numerical simulation. Transient electromagnetic exploration technology was used to explore the working face, and to prevent the influence of water disasters in the abnormal areas during mining, drilling verification was carried out in the abnormal areas. The expected research results can not only enrich the rock formation control theory and roof water inrush mechanism but also have important practical significance to guide the safety production of a coal mine.
Point 2：In Figure 5, the different rock strata should be indicated in the UDEC Numerical model.
Response 2: Updated Figure 5. Figure 5 shows the numerical calculation model, 700m in length and 320m in height, with a length scale, added. The mining boundary on the left and right sides of the model is 200m away from the left and right sides of the model respectively, and the mining area is represented by the red line frame in the figure. The coal seam floor line is marked in orange in the figure, and information such as roof displacement and fracture development height can be obtained by combining it with the model scale.
Point 3：In Figure 6, " Y Displacement" should be marked on the displacement cloud map. In addition, the clarity of Figure 6 should be increased, and appropriate labels should be made to make the stratification of the rock strata shown in the Figure 6 better.
Response 3: Figure 6 has been modified to include the addition of model scale and label names and units. Figure 6 shows the evolution process of vertical displacement of overlying rock on the working face. Combined with the strata histogram, it can be seen from the figure that the displacement of each rock layer and the height of fracture. Through advancing the working face, the displacement of the roof is reflected, thus reflecting the overlying rock movement law and crack development law of the working face.
Point 4：With the same problem, Figure 7 is fuzzy, it is difficult to see the joint failure situation clearly, the clarity should be increased. In addition, it is important that the height of mining-induced overburden fracture and water-conducting fractures be numerically indicated on the figure.
Response 4: Figure 7 was redrawn to increase the clarity of the figure, and a ruler was added to the figure to clearly reflect the height of the roof fracture development.
Point 5：Figure 7 shows different failure forms of joints after excavation of the UDEC model, is it completely displayed?
Response 5: Figure 7 has been redrawn to show all states of the joint. In UDEC, the states of joints are divided into slip and tension. In general, longitudinal joints slip and transverse joints are tensile.
Point 6：In Section 6.1, the principle of TEM exploration for water-bearing fracture zone is low apparent resistivity anomaly under high resistance background should be added. I would recommend that transient electromagnetic inversion resistivity section can be added to the paper and analyzed, which may make the analysis more convincing.
Response 6: In Section 6.1, the transient electromagnetic method is used to detect the water content in the direction of the working face. The principle of TEM is to set up a transmitting coil with a certain waveform current in the well, so as to generate a primary magnetic field in the surrounding space and generate induced current in the underground conductive rock orebody, so as to obtain geoelectric characteristics of different depths. Because the resistance of water is lower than that of coal, the water-bearing area is an abnormal area of low resistance. Add relevant principles in the manuscript.
Point 7：For the same problem, Figure 8 should be clearer.
Response 7: Figure 8 has been updated. Figure 8 is a schematic diagram of the transient electromagnetic construction of 201 working face. One measuring line is arranged along the coal seam in each roadway on both sides, with a length of 2350m and spacing of measuring points of 10m. By moving the transmitting and receiving coils, two measured profiles are formed, as shown in Figure (a) and Figure (b).
Point 8：Please revise the conclusion in paragraphs. In the conclusions, in addition to summarizing the actions taken and results, please strengthen the explanation of their significance.
Response 8: The conclusion part is reorganized according to the research content. There are three main conclusions: (1) Stability characteristics and fracture zone height of 201 working face are obtained through theoretical analysis. (2) The migration and fracture evolution law of mining-induced overburden are analyzed by using discrete element software simulation. (3) Study on the assessment and prevention of water damage in working face. Detailed conclusions are in the manuscript.
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
In this work, based on the research background of water disaster prevention and control of 2 coal seam roofs in Jinxinda Coal Mine, the development law of composite roof fracture is analyzed by combining theoretical analysis and numerical simulation. This paper lacks innovation, science, reliability, logic and readability and I reject this paper for publication.
Need to be improved
Author Response
Based on the research on the prevention and control of water damage in the roof of No. 2 coal seam in Jinxinda Coal Mine, the work analyzes the height of water-conducting crack zone according to the theory of key strata. The combination of numerical simulation and field monitoring verifies the correctness of the theoretical analysis, but there are some shortcomings. In this work, the discussion section is added for explanation. Details are as follows:
(1) Numerical simulation. The development law of vertical displacement and fracture during mining is analyzed. Due to space limitation, this work does not analyze the fracture development law from the perspective of stress, which is relatively not detailed enough.
(2) On-site monitoring. Due to space limitation, the monitoring data, analysis process and drilling scheme of transient electromagnetic method will not be discussed here.
In the future research, we will focus on the above content.
Reviewer 4 Report
Accept in present form
Author Response
Thank you for your contribution to the quality check of this work, we will continue to work hard.
