Study on Deformation Characteristics of Surrounding Rock of Roadway with Coal–Rock Interface

Round 1

Reviewer 1 Report

The paper investigates the causes of discontinuous deformation of roadway, and presents the deformation and stress characteristics of roadway with coal rock interface at different burial depths. Meanwhile, the characteristics of discontinuous deformation caused by coal-rock interface at different positions in the roadway were studied. However, from the point of view of the innovation, novelty and research contents, there are some grammatical shortcomings or disadvantages in this paper. Following is my comments for better presentation of this investigation: accept after minor revision.

（1） In Section 2, (Page 6, line 144), “because the role of the interface between coal seam and roof rock is not considered, ……cannot be accurately described. ”The sentence is long and with repeated expression. Should be “due to the lack of consideration of the role of the coal seam and roof rock interface, the deformation state and stress deformation characteristics of the surrounding rock of the roadway cannot be accurately described.”

（2）In Section 2, (Page 6, line 150), “The length×the width×the height is 83m×15m×55m of the model, which is divided into 27000 units and 33124 nodes……” The expression is weird.

（3）Line 327, page 15, the label of table is weird. Why is there table 4-4? It should be table 2 ?

（4）Line 426, page 20, there is no figure 19.

 

Author Response

Dear Editors and Reviewers:

Thank you very much for these days of work. In accordance with the suggestions of the reviewers, the paper has been revised in detail. At the same time, I am very grateful for the suggestions of reviewers. Your suggestions are very important for improving the level of the paper. For the reviewers’ questions, we have made the following detailed reply:

 

（1） In Section 2, (Page 6, line 144), “because the role of the interface between coal seam and roof rock is not considered, ……cannot be accurately described. ”The sentence is long and with repeated expression. Should be “due to the lack of consideration of the role of the coal seam and roof rock interface, the deformation state and stress deformation characteristics of the surrounding rock of the roadway cannot be accurately described.”

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

（2）In Section 2, (Page 6, line 150), “The length×the width×the height is 83m×15m×55m of the model, which is divided into 27000 units and 33124 nodes……” The expression is weird.

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

（3）Line 327, page 15, the label of table is weird. Why is there table 4-4? It should be table 2 ?

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

（4）Line 426, page 20, there is no figure 19

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Review comments

Title: Deformation Characteristics and Control Principle of Surrounding Rock of Roadway with Coal-Rock Interface

In this paper, the authors conducted a roadway model with coal-rock interface, and the non-uniform and discontinuous deformation of the roadway was revealed, which has significance to guide the engineering application. Reviewer recommendation term: accept after minor revision. Some specific review comments are shown below.

1. In the summary section, (Page 1, line 9), “Roadway surrounding rock with coal-rock interface is the common……” , should be “Surrounding rock of Roadway with coal-rock interface is the common……” this should be corrected.

2. In Section 2, (Page 6, line 144), “Mohr Coulomb constitutive model is selected in this paper ” should be “ Mohr Coulomb constitutive model was selected”.

3. In Section 2, (Page 6, line 150), “Where, γis the average unit weight of the model” ,the Fonts of γ is not Times New Roman.

4.  Line 327, page 15, the label of table is weird. Why is there table 4-4? It should be table 2 ?

5. In Section 3, Page 17, line 364, “It can be seen in the Fig.5 that ”, why ?

6. section 3, line 290, “Figure 11 (a) shows the roof deformation increment under the comparison between the coal rock interface and the roadway without coal rock interface.” The sentence is repeated expression.

Author Response

Dear Editors and Reviewers:

Thank you very much for these days of work. In accordance with the suggestions of the reviewers, the paper has been revised in detail. At the same time, I am very grateful for the suggestions of reviewers. Your suggestions are very important for improving the level of the paper. For the reviewers’ questions, we have made the following detailed reply:

 

1. In the summary section, (Page 1, line 9), “Roadway surrounding rock with coal-rock interface is the common……” , should be “Surrounding rock of Roadway with coal-rock interface is the common……” this should be corrected.

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

2. In Section 2, (Page 6, line 144), “Mohr Coulomb constitutive model is selected in this paper ” should be “ Mohr Coulomb constitutive model was selected”.

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

3. In Section 2, (Page 6, line 150), “Where, γis the average unit weight of the model” ,the Fonts of γ is not Times New Roman.

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

4.  Line 327, page 15, the label of table is weird. Why is there table 4-4? It should be table 2 ?

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

5. In Section 3, Page 17, line 364, “It can be seen in the Fig.5 that ”, why ?

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

6. section 3, line 290, “Figure 11 (a) shows the roof deformation increment under the comparison between the coal rock interface and the roadway without coal rock interface.” The sentence is repeated expression.

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

This paper aimed to study the deformation of roadway using FLAC3D simulate method by considering the coal-rock interface. By comparing the results obtained by the models with and without coal-rock interface under different burial depth, different shear stiffness of the interface and the different position of the interface, this manuscript studied the influence of coal-rock interface on the deformation of roadway. However, the Introduction, the innovation, the theory, the model, and the writing are poor. Obviously, the quality of the manuscript is below the acceptance standard of this journal, and therefore, I regret to recommend that the manuscript is declined publication in this journal. Some major comments are as follows:

1. For the Title, I think it is inappropriate for the content of the manuscript. The control principle is hardly discussed in this paper.

2. Concerning the term “coal-rock interface”, in the whole text, the term should be consistent, but the authors also call it “coal rock interface” in many places. 

3. The INTRODUCTION should be improved, all references are introduced in a paragraph, lack of a summary for different parts of the research.

4. The innovation is can not be seen in the manuscript, at least in comparison to the previous research. I suggest the authors emphasize the shortcomings of the related research and the innovation points of the manuscript in the section of INTRODUCTION.

5. Some references in the texts are errors, e.g., Page 2 Line 60: “Zhao Pengxiang” should be “Zhao Pengxiang et al. (2020)”. Page 3 Line 74: “(Li Wenfeng)” the publish year is lost. 

6. In Section 2, the introduced theory of the constitutive model is wrong described by the authors. (1) the Page 4 Line 120, the “shear Fsmax”? what does it mean? The Fsmax is the shear force or shear strength? (2) Page 5 Line 124, the Fsi is actually not the shear stiffness as the author said, according to equation (1), the Fsi should be the shear force, please understand the meaning of parameters introduced in the FLAC. (3) Line 131-134, the Fs should be the shear force, not the shear stiffness as described in the text. 

7. For the FLAC model shown in Fig.3. the name of the block group should be modified to the corresponding stratum, not “deep1”, “deep2”, etc. The readers can not understand the stratum in the model.

8. Why the model only considers the coal-rock interface in the roof of roadway, as shown in Figure 1, the floor of the roadway is also the interface of coal and Sandrock stratum, why not establish the coal-rock interface on the floor of roadway? 

9. How to determine the parameters of the rock stratums used in the model, especially the shear stiffness? Do you refer to an actual engineering project? Please clarify it in the text. 

10. In Section 2.1, Line 184 and Line 194, what is the definition of the stress concentration factor? And what does the value represent? The comparison of the stress concentration factor values of roadway with and without interface should be analyzed. 

11. Line 200, “Fig.1” should be “Fig. 6”, and the introduction of the monitoring points should be described in the model, before Section 2.1. 

12. Line 201, it is said the deformation and displacement of the monitoring points are obtained. Does the deformation mean the total deformation or lateral deformation? Please clarify it. 

13. Fig. 7 is poorly exhibited, (1) the figure title contains “with coal rock interface”, but the figure contains (a) without interface. (2)Line 221 said “ the maximum deformation is 1.11 cm”, but the data point can not be seen in the figure. (3) The burial depth is not stated for the cloud figures shown in the figure. 

14. In the analysis of the deformation of the roof and floor of roadway, why the comparison to the model without the interface is not analyzed? 

15. Line 281, it is said “when there is interface at the junction of roadway sidewalls and roof”, is there interfaces set on the sidewalls? 

16. The engineering significance is ambiguous for the studying of shear stiffness of the interface on the roadway deformation. The parameters of different actual interfaces are not different only for the stiffness, but also the friction angle and cohesion. The stiffness was changed from 5MPa to 50GPa in the model, what is it based on? I think the value of 50 GPa is too large for an actual stratum. 

17. Line 426, the control approach was only simply proposed, I suggest adding some content about studying the control effectiveness evaluation by carrying out simulations. 

Author Response

Dear editor and reviewer

Thank you very much for your work these days. I am very grateful to the reviewers for their suggestions. Your suggestion is very important to improve the level of the thesis. For the questions of the reviewers, we have given detailed answers in the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

### Overall review

The introduction is clear and understandable. However, it presents basically an enumeration of previous works which does not depict a trajectory of the knowledge previously gained in the subject under study. The objectives are vage and the sustainability is not adressed in any part of the work. The description of the problem in physical terms is not clear, and the same occurs with the description of the numerical methodology. The numerical method is not validated, which deprecates the quality of the work. Conclusions made from numerical data are well explained and presented, though.

### Mayor corrections

The introduction only presents an enumeration of previous works. The general problem under study should be more clearly presented and assuming that the work will be published in a __Sustainability__ journal, the sustainability should be addressed somehow. The objectives are not clear and should be improved.

Section 2 presents the problem under study. The description of the physical problem addressed in lines 96-110 should be illustrated with a scheme representing the material, forces, stress and deformation states, etc. The problem description should be improved. 

 

Figure 1 is too small and the images present very blurry images, they should be updated and improved.

 

The presentation of the computational domain should be illustrated, idem as before. The utilization of a computational tools for the simulation of the problem needs to explain the method used by the solver. The numerical methodology is far from being clear.

 

The presented results are clear and understandable. But there is no validation or explanation of the numerical code which deprecates the quality of the results and the conclusions drawn from the numerical data. The validation of the code should be presented. The presentation of field data supporting the conclusions made would be a plus

Author Response

Dear Editors and Reviewers:

Thank you very much for these days of work. In accordance with the suggestions of the reviewers, the paper has been revised in detail. At the same time, I am very grateful for the suggestions of reviewers. Your suggestions are very important for improving the level of the paper. For the reviewers’ questions, we have made the following detailed reply:

 

The introduction only presents an enumeration of previous works. The general problem under study should be more clearly presented and assuming that the work will be published in a __Sustainability__ journal, the sustainability should be addressed somehow. The objectives are not clear and should be improved.

Thank you very much for your suggestion.

The INTRODUCTION has been modified as follows,

For the study of coal-rock interface, scholars (Yu et al. 2018, Chen et al. 2021, Zhao et al. 2016, Zuo et al. 2016, Yin et al, 2019) conducted mechanical strength tests on combinations with different coal rock proportions and combinations, and analyzed the mechanical parameters of the combination specimens. Zhao carried out mechanical and energy analysis on the whole process of deformation and failure of like coal rock materials with different combinations under uniaxial load, and the evolution law of elastic properties and dissipated energy in the full stress-strain process of the specimen was revealed (Zhao et al. 2020). The influence of interface dip angle and fractal dimension on the combination by designing 25 combinations with different interface fractal dimensions and dip angles were revealed (Cao et al. 2018). The mechanical structure model of coal and rock is established, the influence of different interface connection modes on coal and rock was analyzed, and the mechanical properties (plastic zone, stress and displacement) and energy of coal rock composite structure under different interface connection modes were studied through numerical simulation (Tian et al. 2022). The slip failure mechanism of coal rock structure under horizontal unloading biaxial compression was studied (Liu et al. 2022). The influence of interface cohesive strength, rock strength and stress level on the failure behavior of the composite model was revealed (Zhao et al. 2015). The above studies explain the influence of the interface on the mechanical properties of coal and rock from the perspective of the constraint effect of the coal-rock interface and the dip angle of the coal-rock interface, and lack the research on the shear resistance of the coal and rock interface.

For the study of coal bearing interface roadway in coal and rock mass, the influence of mechanical parameters of coal-rock interface on the stability of sidewalls was analyzed, and the deformation mechanism of this type of roadway includes the mechanism of interlaminar shear failure of coal-rock interface and the mechanism of inducing interlaminar instability of interface were revealed (Wang et al. 2017). The stress, deformation and failure law of the roadway under the main control factors such as different dip angles of coal-rock interface were studied, and the deformation failure instability mechanism of the surrounding rock of deep half coal rock roadway was revealed(Jin et al. 2015, Zhao et al. 2017). The asymmetric distribution characteristics of the failure in the surrounding rock of the steeply inclined coal-rock interbedding roadway was analyzed, and the large deformation of the sidewalls caused by the staggered deformation of the structural planes between the lower layers under the horizontal stress was revealed (Chang et al. 2022). Through a series of uniaxial compression tests on inclined coal rock combination specimens (with inclination angle of coal and rock contact surface 15 °, 30 ° and 45 °) with and without anchors in the horizontal direction, the failure mechanism of coal rock anchor combination solid formed by support structure and coal rock mass is deeply studied (Yu et al. 2020). Through the direct shear test on the natural coal-rock interface specimen, the stress effect and lithologic effect of the coal rock combination specimen affected by the interface are revealed (Li et al. 2018). The influence of rock in coal rock sample on coal mechanical behavior was revealed, and it is obtained that the greater the proportion of coal body, the lower the strength of the combination (Liu et al. 2018). For the roadway with coal-rock interface, most of the research focuses on the research and control of roadway deformation with inclined interlayer structural plane, while the research on the constraint effect of horizontal coal-bearing rock interface on roadway instability is less.

The model test of the effect of interface shear stiffness on the anti-sliding ability of the sidewall during the deformation and instability of the coal-bearing rock interface roadway is carried out, which is innovative. Firstly, the deformation of the roadway with and without coal-rock interface are compared, and it is pointed out that the coal-rock interface deformation is more in line with the actual situation. Then, the deformation of single-interface roadway and multi-interface roadway is analyzed respectively, which is consistent with the deformation of roadway in different coal and rock strata thickness and interlayer state. It also points out the deformation state of the coal-rock interface at different positions of the roadway sidewall, which provides reference for the deformation of the semi-coal-rock roadway, and the determination of weak points in roadway with coal-rock interface has certain practical value for formulating targeted support methods.

 

 

Section 2 presents the problem under study. The description of the physical problem addressed in lines 96-110 should be illustrated with a scheme representing the material, forces, stress and deformation states, etc. The problem description should be improved.

 

The field test adopts the form of drilling, including horizontal drilling, vertical drilling and inclined drilling. Geological radar detection is also used, and the relevant detection is shown in Figure 1.

 

Fig. 1 Site detection

 

Fig. 2 Field observation and borehole detection

Through field observation and borehole detection, it can be seen that the side wall has slipped and deformed, and the side wall and roof have separated. The borehole detection shows that there is also a gap between the roof and the sidewall of the side.

Relevant expressions have been added to the manuscript as follows

The inclined observation borehole was drilled on the side wall, and the borehole penetrated into the coal seam roof from the side wall as shown in Figure 1. The observation showed that the side wall and roof of the roadway also had a certain degree of separation in the coal pillar.

Figure 1 is modified as follows.

 

Figure.1 Detection and deformation characteristics of roadway along roof under high stress

 

Figure 1 is too small and the images present very blurry images, they should be updated and improved.

Thank you very much for your suggestion. The Figure.1 has been modified.

 

 

The presentation of the computational domain should be illustrated, idem as before. The utilization of a computational tools for the simulation of the problem needs to explain the method used by the solver. The numerical methodology is far from being clear.

Mohr Coulomb constitutive model was selected in this paper. The length×the width×the height is 83m×15m×55m of the model, and the model was divided into 27000 units and 33124 nodes, the width×the height is 3m×3m of the roadway, which is excavated for 5 times, 3m each time. Six groups of loads with different burial depth are applied, which are 300m, 350m, 400m, 450m, 500m and 550m respectively. The boundary conditions of the tunnel model are set as follows: the fixed constraints are imposed on the bottom boundary of the model, and the horizontal displacement constraints are imposed in the model, and the equivalent load of overburden is applied on the top of the model. The coal-rock interface between the wall and the roof added. The shear stiffness of the weakened coal-rock interface is 0.05GPa·m^-1.

 

The presented results are clear and understandable. But there is no validation or explanation of the numerical code which deprecates the quality of the results and the conclusions drawn from the numerical data. The validation of the code should be presented. The presentation of field data supporting the conclusions made would be a plus.

The code verification will be submitted in the system, and we have done it in the field test verification. However, the manuscript studies the influence of the interface on the deformation of the roadway, and lacks a more detailed comparative analysis of support control schemes, which will be analyzed in another article. Thank you very much for your suggestion.

Author Response File: Author Response.pdf

Reviewer 5 Report

The Authors attempted to assess the effects of coal-rock interface on the performance of a roadway tunnel. They demonstrated this through finite element analysis. The study has several shortcomings, particularly on the details of the field case study, the modelling techniques, the choice of constitutive model, modelling parameters, the validation of the model, and how the model reflects the real world behaviour. Therefore, the results from modelling are dubious.

This reviewer is of the opinion that the manuscript requires significant improvement. Therefore, this reviewer recommends for this manuscript to undergo MAJOR REVISION.

 

The following are comments for the Authors to address:

 

• General
• Please correct the in-text referencing style. Only the last name of the authors should be shown in the in-text reference.
• Please include the DOI for the references.
• One of the references in the bibliography (ZHAO Z H, LV X, WANG W, et al. Damage evolution of bi-body model composed of weakly cemented 535 soft rock and coal considering different interface effect[J]. Springer Plus, 2016, 5(1): 292-311) should have the authors’ names spelled out in full to be consistent with other references. Also, “et. al” is not appropriate in the bibliography.
• Please clarify the meaning of “[J]” in a number of the references.
• There is an issue with multiple uses of the word “the”, which usually refers to a subject that is well-known or described earlier in the manuscript. 
• It is unclear why “coal-rock” is of significant interest, and how this interface would change depending on the type of rock interacting with the coal.
• 1 Introduction
• Lines 66 – 67: Please clarify what “angles” are being referred to.
• The literature is just a quick review of references, without sharing insights or relevance to the current study. For example, in the statement “The influence of rock in coal rock sample on coal mechanical behavior was revealed (Liu XS et al. 2018).”, the Authors should explain what was revealed, and how this behaviour is relevant to the current study.
• There is also an absence of a knowledge gap or a problem statement.
• 2 Roadway model and analysis
• This section appears to be written as a case study. Please provide the important details of the case study, including location, geological + geotechnical conditions, geological assessments of the rock surrounding the tunnel (please include assessments of joints, fractures, weathering and other structural geology factors), details about the rock-coal interface, tunnel construction details, equipment used, etc.
• Line 113: Please justify the suitability and necessity of FLAC 3D in the analysis of the problem.
• Lines 119 – 120: Please clarify whether this is the Mohr-Coulomb strength criterion, or Coulomb as mentioned. Also, it may not be appropriate to model the rock masses as continuum if the rock formations are highly weathered or fractured. This is especially important in tunnel modelling, where stress relief can result in other phenomena such as arching, rock squeezing, or rock bursting. These are all mechanisms which require consideration of rocks being dislodged, i.e. discontinuous.
• Fig. 3: Please justify the bedding/joint direction of the coal-rock interface with in-situ observations. The assumption of one continuous joint set running infinitely long into the rock mass is also unrealistic. Please provide dimensions and levels for the model.
• Lines 150 – 151: Please clarify what is meant by “groups of loads”. Are these uniformed distributed loads to model the effect of vertical overburden pressure? If so, then this is not appropriate since overburden pressure increases with depth.
• Lines 154 – 158: Please provide justifications for the mechanical parameters of the coal-rock interface. Were any strength and stiffness/modulus tests performed?
• Table 1: Please explain how the mechanical parameters were obtained. Also, the c values are incredibly high.
• Figs 4 and 5: The colour scales are not discernible even at 100% zoom. Please plot all according to the some colour scale for direct comparison between the stress concentration maps.
• Lines 184, 186, 194 and 195: Please define “concentration factor”.
• Lines 196 – 198: Are these “monitoring points” referring to the model or to a field instrumentation scheme?
• Line 200: Error in numbering of figure.
• 3 Interface stiffness and position
• Please clarify where the interface is located.
• Fig. 12: Please justify the range of values used in interface stiffness. Are these reflective of values used in other research? Would be advisable to adopt a range of values based on the literature.
• Fig. 12: It is unexpected for the horizontal stresses to reduce at points closest to the roof, and at the floor. Please explain why this is the case. The Authors may wish to consider the orientation of principle stresses.

Author Response

Dear Editors and Reviewers:

Thank you very much for these days of work. In accordance with the suggestions of the reviewers, the paper has been revised in detail. At the same time, I am very grateful for the suggestions of reviewers. Your suggestions are very important for improving the level of the paper. For the reviewers’ questions, we have made the following detailed reply:

 

Please correct the in-text referencing style. Only the last name of the authors should be shown in the in-text reference.

 

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

Please include the DOI for the references.

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

One of the references in the bibliography (ZHAO Z H, LV X, WANG W, et al. Damage evolution of bi-body model composed of weakly cemented 535 soft rock and coal considering different interface effect[J]. Springer Plus, 2016, 5(1): 292-311) should have the authors’ names spelled out in full to be consistent with other references. Also, “et. al” is not appropriate in the bibliography.

Thank you very much for your patience and meticulous review. It has been revised in the manuscript.

 

Please clarify the meaning of “[J]” in a number of the references.

Thank you very much for your patience and meticulous review. The symbol [J] has been removed from the manuscript.

 

There is an issue with multiple uses of the word “the”, which usually refers to a subject that is well-known or described earlier in the manuscript.

Thank you. The manuscript has been revised.

 

It is unclear why “coal-rock” is of significant interest, and how this interface would change depending on the type of rock interacting with the coal.

If there is no interface between coal and rock, the roadway will not slide and deform along the interface. The greater the shear stiffness of the interface, the more likely the roadway will be deformed in the complete rock. Therefore, it is meaningful to study the interface parameters of different shear stiffness in the manuscript.

 

1 Introduction

Lines 66 – 67: Please clarify what “angles” are being referred to.

Thank you very much for your patience and meticulous review. The angle refers to the inclined angle of coal and rock contact surface.

 

The literature is just a quick review of references, without sharing insights or relevance to the current study. For example, in the statement “The influence of rock in coal rock sample on coal mechanical behavior was revealed (Liu XS et al. 2018).”, the Authors should explain what was revealed, and how this behaviour is relevant to the current study.

There is also an absence of a knowledge gap or a problem statement.

Thank you very much for your suggestion.

The INTRODUCTION has been modified as follows,

For the study of coal-rock interface, scholars (Yu et al. 2018, Chen et al. 2021, Zhao et al. 2016, Zuo et al. 2016, Yin et al, 2019) conducted mechanical strength tests on combinations with different coal rock proportions and combinations, and analyzed the mechanical parameters of the combination specimens. Zhao carried out mechanical and energy analysis on the whole process of deformation and failure of like coal rock materials with different combinations under uniaxial load, and the evolution law of elastic properties and dissipated energy in the full stress-strain process of the specimen was revealed (Zhao et al. 2020). The influence of interface dip angle and fractal dimension on the combination by designing 25 combinations with different interface fractal dimensions and dip angles were revealed (Cao et al. 2018). The mechanical structure model of coal and rock is established, the influence of different interface connection modes on coal and rock was analyzed, and the mechanical properties (plastic zone, stress and displacement) and energy of coal rock composite structure under different interface connection modes were studied through numerical simulation (Tian et al. 2022). The slip failure mechanism of coal rock structure under horizontal unloading biaxial compression was studied (Liu et al. 2022). The influence of interface cohesive strength, rock strength and stress level on the failure behavior of the composite model was revealed (Zhao et al. 2015). The above studies explain the influence of the interface on the mechanical properties of coal and rock from the perspective of the constraint effect of the coal-rock interface and the dip angle of the coal-rock interface, and lack the research on the shear resistance of the coal and rock interface.

For the study of coal bearing interface roadway in coal and rock mass, the influence of mechanical parameters of coal-rock interface on the stability of sidewalls was analyzed, and the deformation mechanism of this type of roadway includes the mechanism of interlaminar shear failure of coal-rock interface and the mechanism of inducing interlaminar instability of interface were revealed (Wang et al. 2017). The stress, deformation and failure law of the roadway under the main control factors such as different dip angles of coal-rock interface were studied, and the deformation failure instability mechanism of the surrounding rock of deep half coal rock roadway was revealed(Jin et al. 2015, Zhao et al. 2017). The asymmetric distribution characteristics of the failure in the surrounding rock of the steeply inclined coal-rock interbedding roadway was analyzed, and the large deformation of the sidewalls caused by the staggered deformation of the structural planes between the lower layers under the horizontal stress was revealed (Chang et al. 2022). Through a series of uniaxial compression tests on inclined coal rock combination specimens (with inclination angle of coal and rock contact surface 15 °, 30 ° and 45 °) with and without anchors in the horizontal direction, the failure mechanism of coal rock anchor combination solid formed by support structure and coal rock mass is deeply studied (Yu et al. 2020). Through the direct shear test on the natural coal-rock interface specimen, the stress effect and lithologic effect of the coal rock combination specimen affected by the interface are revealed (Li et al. 2018). The influence of rock in coal rock sample on coal mechanical behavior was revealed, and it is obtained that the greater the proportion of coal body, the lower the strength of the combination (Liu et al. 2018). For the roadway with coal-rock interface, most of the research focuses on the research and control of roadway deformation with inclined interlayer structural plane, while the research on the constraint effect of horizontal coal-bearing rock interface on roadway instability is less.

 

 

2 Roadway model and analysis

This section appears to be written as a case study. Please provide the important details of the case study, including location, geological + geotechnical conditions, geological assessments of the rock surrounding the tunnel (please include assessments of joints, fractures, weathering and other structural geology factors), details about the rock-coal interface, tunnel construction details, equipment used, etc.

The field test adopts the form of drilling, including horizontal drilling, vertical drilling and inclined drilling. Geological radar detection is also used, and the relevant detection is shown in Figure 1.

 

Fig. 1 Site detection

Line 113: Please justify the suitability and necessity of FLAC 3D in the analysis of the problem.

FLAC 3D is a very important simulation software in the direction of rock and soil, and is a finite element numerical simulation software. The purpose of the manuscript is to find out the effect of different interface shear stiffness on roadway deformation, most previous studies did not consider the interface effect between rock layers when using FLAC 3D simulation software.

Therefore, the adoption of FLAC 3D is innovative, and also provides a reference for future research.

 

Lines 119 – 120: Please clarify whether this is the Mohr-Coulomb strength criterion, or Coulomb as mentioned. Also, it may not be appropriate to model the rock masses as continuum if the rock formations are highly weathered or fractured. This is especially important in tunnel modelling, where stress relief can result in other phenomena such as arching, rock squeezing, or rock bursting. These are all mechanisms which require consideration of rocks being dislodged, i.e. discontinuous.

Thank you very much for your suggestion.

The influence of possible joints and cracks in rock mass is not considered in the paper. The manuscript only distinguishes different shear stiffness as basic variables to analyze the basic law of variable change.

 

 

Fig. 3: Please justify the bedding/joint direction of the coal-rock interface with in-situ observations. The assumption of one continuous joint set running infinitely long into the rock mass is also unrealistic. Please provide dimensions and levels for the model.

 

Fig. 2 Field observation and borehole detection

Through field observation and borehole detection, it can be seen that the side wall has slipped and deformed, and the side wall and roof have separated. The borehole detection shows that there is also a gap between the roof and the sidewall of the side.

The length×the width×the height is 83m×15m×55m of the model, which is divided into 27000 units and 33124 nodes, the width×the height is 3m×3m of the roadway, which is excavated for 5 times, 3m each time.

 

Lines 150 – 151: Please clarify what is meant by “groups of loads”. Are these uniformed distributed loads to model the effect of vertical overburden pressure? If so, then this is not appropriate since overburden pressure increases with depth.

Thank you very much for your suggestion.

It is true that the overburden pressure increases with the increase of depth. The load applied by the model in the paper is based on the same lateral pressure coefficient and different buried depth.

 

Lines 154 – 158: Please provide justifications for the mechanical parameters of the coal-rock interface. Were any strength and stiffness/modulus tests performed?

Table 1: Please explain how the mechanical parameters were obtained. Also, the c values are incredibly high.

Thank you very much for your suggestion.

The strength/modulus test of rock mechanics is mainly based on a previous article published by us for specific test analysis (Wang et al. 2020). Quoted statements were also added to the manuscript.

Mohr-Coulomb criterion has wide acceptance for the description of rock failure under conventional triaxial conditions. In this paper(Wang et al. 2020), uniaxial and multistage confining pressure mechanical tests are carried out, and the mechanical parameters of rock are obtained by linear fitting of different test data using Mohr-Coulomb criterion.

Wang, Tuo, Zhanguo Ma, Peng Gong, Ning Li & Shixing Cheng. 2020. Analysis of Failure Characteristics and Strength Criterion of Coal-Rock Combined Body with Different Height Ratios. Advances in Civil Engineering 2020.1-14.

 

Figs 4 and 5: The colour scales are not discernible even at 100% zoom. Please plot all according to the some colour scale for direct comparison between the stress concentration maps.

Lines 184, 186, 194 and 195: Please define “concentration factor”.

Thank you very much for your suggestion.

The red area in the figure is the stress concentration area. It can be seen that the stress concentration area changes with the buried depth or whether there is an interface. The expression of stress concentration has also been shown in the manuscript.

Formula 1 defines the stress concentration factor K as the ratio of roadway stress σ after roadway opening and original rock stress σ_p, reflecting the degree of stress concentration in the roadway area.

                                (5)

Lines 196 – 198: Are these “monitoring points” referring to the model or to a field instrumentation scheme?

These “monitoring points” referring to the model.

 

Line 200: Error in numbering of figure.

We are sorry for the mistakes.

 

3 Interface stiffness and position

Please clarify where the interface is located.

Assuming that the distance between the coal seam and the rock stratum interface and the roadway floor is a, the roadway width and height are still 3m × 3m, a is 3m, 2m, 1.5m and 0.5m respectively.

 

Fig. 12: Please justify the range of values used in interface stiffness. Are these reflective of values used in other research? Would be advisable to adopt a range of values based on the literature.

Fig. 12: It is unexpected for the horizontal stresses to reduce at points closest to the roof, and at the floor. Please explain why this is the case. The Authors may wish to consider the orientation of principle stresses.

The roadway is loaded horizontally and vertically. The points closest to the roof, and at the floor of the roadway are within the range of plastic zone, and it can be seen that the smaller the shear stiffness is, the smaller the horizontal stress value of the roadway is. However, with the increase of shear stiffness, the stress value of the roof increases greatly, which conforms to the stress distribution law of the roadway^[1-3].

[1] Li, Xuejia, Baoyang Wu, Yanzhao Zhu, Junting Guo & Zhaolong Li. 2023. Numerical Study on Deformation and Failure Characteristics of Rectangular Roadway. GEOFLUIDS 2023.1-14.

[2] Feng Wei, Han Lijun, Liu Cancan. Influence of horizontal stress on stress distribution and deformation characteristics of surrounding rock of semi-circular arch roadway. China Science and Technology of Work Safety, 2012,8 (12): 21-26.

[3] Zhu Liu Research on deformation mechanism of surrounding rock of coal roadway in different directions under high horizontal stress. Shandong University of Science and Technology, 2018. DOI: 10.27275/d.cnki.gsdku.2018.001239.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The revised manuscript has corrected some errors, but the innovation, the theory, the model and the English writing are still very poor. Especially, some comments were responded, but the manuscript were not revised, the attitude towards the revision is very bad. The numerical model was not modified, the introduced theory of the constitutive model is still wrong. The innovation of the study the effect of shear stiffness of the coal- rock interface on the deformation of surrounding rock has no engineering significance. And the English writing has many syntax errors. As such, I still suggest to reject this revised manuscript. Some detail reasons are as follows:

 

1.      Some errors were still not corrected as you responded. (1) The comment 11 in last review, I said the “Fig. 1” should be the “Fig. 6”, the figure number was wrong, but it was still wrong in the revised manuscript. (2) For the Comment 6, the description of the Eq. (1) was not revised, and the “shear Fsmax” was still wrong. If the simple and important errors were not taken seriously by the authors, I think this paper can not be accepted forever.

2.      For the theory of the constitutive model used in the FLAC model, I said the Fsi and the Fs should be the shear force, not the shear stiffness as said by the authors. Why not spending time in understanding the theory introduced in the FLAC? This is a very low-level error.

3.      For the numerical model, referring to the comment 8 in the last review, the floor is also the coal-rock interface. The neglect of the establish of the interface must have influence on the deformation of the surrounding rock. This paper is focused on the effect of the coal-rock interface, the numerical model should be modified, otherwise the analysis is unreasonable.

4.      For the innovation of this paper, as the author said, is the effect of shear stiffness of coal-rock interface on the deformation of the surrounding rock. I have said in the comment 16 in last revision, the study has no engineering significance. Because the parameters of different actual interfaces are not different only for the shear stiffness, but also the friction angle, cohesion, and so on. I think the effect of shear stiffness is even less than that of the friction angle. As such, if you only change the shear stiffness of the interface in the numerical model, the results can not be used for reference to other engineering projects.

Author Response

Dear editor, We are sorry for the mistakes. In accordance with the suggestions of the reviewers, the paper has been revised in detail. At the same time, I am still very grateful for the suggestions of reviewers. We will seek MDPI English editing service to help us correct grammar errors. Thank you very much. 1. Some errors were still not corrected as you responded. (1) The comment 11 in last review, I said the “Fig. 1” should be the “Fig. 6”, the figure number was wrong, but it was still wrong in the revised manuscript. (2) For the Comment 6, the description of the Eq. (1) was not revised, and the “shear Fsmax” was still wrong. If the simple and important errors were not taken seriously by the authors, I think this paper can not be accepted forever. Thank you very much for your patience and meticulous review. We are sorry for the mistakes. The label “Fig. 6” has been modified in the revised manuscript of the first reply. Shear force is not shear stiffness. The expression error has been corrected in the manuscript. Such as “maximum shear force Fsmax”, “shear force vector”. We are very sorry that we only modified the wrong expressions in 131 and 133 lines, but missed some wrong expressions in 120 line and line 124. 2. For the theory of the constitutive model used in the FLAC model, I said the Fsi and the Fs should be the shear force, not the shear stiffness as said by the authors. Why not spending time in understanding the theory introduced in the FLAC? This is a very low-level error. Thank you very much. We didn't have a good understanding of the theory introduced in the FLAC. As you said, shear force is not shear stiffness. Can we explain it from the linear relationship between interface shear stiffness and shear force? The shear stiffness can reflect the shear force between the two interfaces, under the condition that other parameters remain unchanged. Relevant statements were added to the article. Thank you again for your suggestion. 3. For the numerical model, referring to the comment 8 in the last review, the floor is also the coal-rock interface. The neglect of the establish of the interface must have influence on the deformation of the surrounding rock. This paper is focused on the effect of the coal-rock interface, the numerical model should be modified, otherwise the analysis is unreasonable. This is my understanding of this part, the interface can only be established when the floor and the roadway sidewall are not the same rock layer. When the roadway floor is also in a coal seam and has the same lithology as the sidewall, the sidewall and the floor can be regarded as a whole, and in this case, there is no need to add an interface. The manuscript is based on that situation to build a model, which is also corresponding to the site. Thank you for your understanding and support. 4. For the innovation of this paper, as the author said, is the effect of shear stiffness of coal-rock interface on the deformation of the surrounding rock. I have said in the comment 16 in last revision, the study has no engineering significance. Because the parameters of different actual interfaces are not different only for the shear stiffness, but also the friction angle, cohesion, and so on. I think the effect of shear stiffness is even less than that of the friction angle. As such, if you only change the shear stiffness of the interface in the numerical model, the results can not be used for reference to other engineering projects. Thank you very much. As you said, the friction angle and cohesion of the rock stratum also have a big impact on the roadway deformation, and cohesion and friction angle affect the deformation of rock stratum. Also,we think that shear stiffness of interface affects the shear dislocation between layers, and our research is based on the phenomenon of the staggered deformation of the roof at the site, which has on-site basis. As shown in the figure, the coal body at the sidewall is separated from the roof rock layer, and the sidewall also moves towards the roadway as a whole. The anchor cable tray has entered the gap between the sidewall and the top plate.

Author Response File: Author Response.pdf

Reviewer 4 Report

The authors have improved the manuscript and now is ready for publication

Author Response

Thank you very much for your review

Round 3

Reviewer 3 Report

The revised manuscript has been improved, and can be published after minor revision.

In line 209, the "Figure 1" should be "Figure 6", you still have not modified it in the revised version.

The English writing should be improved by native English speakers.

Author Response

Sorry, I found the problem. In the word version, only the number “Figure 6” in line 209 was used for automatic numbering, so when converting to pdf, the number is changed to “Figure 1”. The word version has been changed to “Figure 6” .

Author Response File: Author Response.docx