Study on the Influence of Two-Step Filling Mechanic Characteristics on the Stability of Single-Side Exposed Cemented Backfill

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript examines the influence of two-step filling mechanics on the stability of single-side exposed cemented backfill, focusing on a mine in Shandong Province. A 3D mechanical model is developed to analyze the lateral pressure effects of weakly cemented fill on strongly cemented fill, considering key mechanical properties such as elastic modulus, cohesion, internal friction angle, and Poisson's ratio. Numerical simulations reveal the displacement patterns and their correlation with the mechanical parameters of the fill materials. The study aims to provide theoretical guidance for designing stable backfill structures under unilateral exposure in mining applications.

The text needs some revision regarding standardized notations, corrections on the reference presentation and, format according to the journal.

Some questions and notes related to the text are presented in the following items:

• The abstract lacks a clear presentation of the problem and methodology. While it summarizes the findings, it fails to emphasize the specific numerical analyses conducted and the considerations made during the study;
• The manuscript does not mention the software used for numerical simulations. Specifying the software and its version is necessary for reproducibility and credibility;
• Material Parameters (Table 1): The source of the material parameters is unclear. Were these obtained from laboratory tests, field studies, or literature?
• Figure 1: The schematic diagram of the stope structure is difficult to interpret. It requires better labeling, clearer resolution, and additional explanations in the caption to improve readability;
•  The discussion on the displacement distribution influenced by mechanical parameters (elastic modulus, cohesion, etc.) could be expanded to include implications for real-world applications;
• The figures presenting horizontal displacement distributions (e.g., Figures 4–7) are informative but would benefit from annotations or trendline summaries to highlight key findings;
• The manuscript does not explain how the figures were generated. Were they obtained directly from the simulation software or processed using additional tools?
• The conclusions section does not sufficiently connect the findings to practical engineering applications. How can the results inform design choices for stope stability in real mining projects? What are the implications for determining optimal mechanical properties of filling materials?

Author Response

Comments 1:The abstract lacks a clear presentation of the problem and methodology. While it summarizes the findings, it fails to emphasize the specific numerical analyses conducted and the considerations made during the study;

Response 1:I have annotated the abstract based on your feedback and added suggestions for improving the expression of research questions, method description, and numerical analysis details.

Comments 2:The manuscript does not mention the software used for numerical simulations. Specifying the software and its version is necessary for reproducibility and credibility;

Response 2:Information about numerical simulation software and its version has been added in relevant locations, clearly indicating that FLAC 3D 6.0060 was used for numerical simulation. If further adjustments or supplements are needed, please let us know at any time!

Comments 3:Material Parameters (Table 1): The source of the material parameters is unclear. Were these obtained from laboratory tests, field studies, or literature?

Response 3:These material parameters are derived from the mine's previous research projects, including indoor tests and field tests, and are obtained by weakening the indoor test data in historical scientific research projects.

Comments 4:Figure 1: The schematic diagram of the stope structure is difficult to interpret. It requires better labeling, clearer resolution, and additional explanations in the caption to improve readability;

Response 4:Figure 1: Schematic diagram of stope structure has been modified.

Comments 5:The discussion on the displacement distribution influenced by mechanical parameters (elastic modulus, cohesion, etc.) could be expanded to include implications for real-world applications;

Response 5:When the elastic modulus of the two-step weakly cemented filling body increases from 100MPa to 500MPa, the maximum horizontal displacement of the one-step cemented filling body exposed on one side decreases from 116mm to 32mm, a decrease of approximately 72%. When the elastic modulus parameters of the two-step filling body are 200MPa, 300MPa and 400MPa, the maximum horizontal displacements of the one-step filling body are 91mm, 69mm and 47mm respectively. Studies have shown that increasing the elastic modulus and cohesion of weakly cemented filling bodies can significantly reduce the displacement of unilaterally exposed cement filling bodies. This discovery provides a basis for the strength design of filling bodies in mining engineering, especially in the context of the demand for reducing ore pillars and improving mining efficiency. The research results provide data support for solving the slip risk of unilaterally exposed filling bodies or reducing material costs.

Comments 6:The figures presenting horizontal displacement distributions (e.g., Figures 4–7) are informative but would benefit from annotations or trendline summaries to highlight key findings;

Response 6:Thank you to the reviewer for their careful review and constructive suggestions on this article. We have taken note of the reviewer's suggestion to highlight key findings through annotations or trend lines regarding the improvement of the horizontal displacement distribution map (as shown in Figure 4-7). The cloud map in this article aims to visually display the maximum horizontal displacement points and their distribution patterns under different working conditions. In each image, the maximum displacement point area can be directly compared and observed.We have clearly stated the value of the maximum horizontal displacement in the text by exporting numerical simulation monitoring data. Therefore, we have not added additional trend lines in the cloud map to avoid overly complex graphical information.

Comments 7:The manuscript does not explain how the figures were generated. Were they obtained directly from the simulation software or processed using additional tools?

Response 7:The horizontal displacement data provided in the paper comes from displacement cloud maps and monitoring data in simulation software, which reflect the displacement distribution under the conditions defined in the simulation scheme.

Comments 8:The conclusions section does not sufficiently connect the findings to practical engineering applications. How can the results inform design choices for stope stability in real mining projects? What are the implications for determining optimal mechanical properties of filling materials?

Response 8:Enhancing the mechanical properties of weakly cemented fillings, such as increasing elastic modulus (optimal range: 300-400 MPa) or internal friction angle (>27°), can significantly reduce horizontal displacement and improve stope stability. These opti-mizations mitigate collapse risks and contribute to safer mining operations.The find-ings suggest that adopting stronger filling materials allows for reducing the arm pillar thickness, increasing ore recovery rates by up to 15%, thereby improving both safety and economic efficiency.These results are most applicable to deep mines utilizing sublevel filling methods with stopes exposed to significant lateral pressure.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper Study on the Influence of Two-step Filling Mechanics Characteristics on the Stability of Single-side Exposed Cemented Backfill, presents a comprehensive study on the influence of two-step filling mechanics on the stability of single-side exposed cemented backfill. The research integrates numerical simulations and theoretical modeling to assess the stability of backfill structures under varying mechanical properties. The study is methodologically sound and addresses a relevant topic in mining and geotechnical engineering. The paper has some strong points: it is well-structured with clear segmentation into introduction, methodology, results, and conclusion sections; the numerical simulations are robust and provide insightful data on the influence of elastic modulus, internal friction angle, cohesion, and Poisson's ratio on backfill stability; the inclusion of three-dimensional mechanical models adds depth to the analysis, reflecting real-world complexities in backfill mechanics; figures and tables are effectively utilized to visualize data and results.

However, there are areas that could benefit from further clarification and expansion to enhance the overall quality and impact of the paper:

1. The abstract provides a concise summary but could be enhanced by specifying key quantitative results or observations. For example, include specific findings on how variations in elastic modulus or cohesion impact displacement.

2. While the introduction explains the context well, there is limited discussion on recent advancements or similar studies conducted internationally. Expanding this section with a broader literature review would strengthen the justification for the study. I recommend a more diverse geographic spread of the authors (ie outside PR of China) and try to increase the references up to 40 articles for the level of this journal, as the current 24 is too low. Please clarify the novelty of the study by explicitly stating in a phrase how it advances the current state of knowledge.

3. The methodology section is comprehensive but could benefit from more detailed explanations of the assumptions made in the numerical simulations. For example, further clarify the rationale behind the choice of the Mohr-Coulomb model. Also, i think a flowchart / schema summarizing the steps taken in the numerical simulation process would enhance readability.

4. The results section is presented clearly, but the discussion section should delve deeper into the implications of the findings. How can these results influence practical mining operations or future research? Provide more comparative analysis with existing studies to highlight consistencies or discrepancies.

5. Figures are generally clear but could benefit from more detailed captions explaining the key takeaways from each image.

6. Table 1 lists mechanical parameters but lacks detailed explanations of how these parameters were derived or referenced.

7. The conclusion effectively summarizes the findings but should emphasize broader implications and potential applications in mining engineering.

8. Consider adding a brief section on future research directions to encourage further exploration of the topic.

9. As a final note, there are minor grammatical errors throughout the text, and I think a thorough proofreading would improve overall readability.

10. Standardize the citation format and ensure all references (current and the ones to be added) are complete and follow the journal's guidelines.

In conclusion the paper presents significant contributions to the field and should be accepted with minor revisions. Addressing the above points will enhance the clarity, depth, and impact of the manuscript.

Comments on the Quality of English Language

There are minor grammatical errors throughout the text, and I think a thorough proofreading would improve overall readability. You could ask assitance either from a native speaker / colleague in the field, or use MDPIs' English language services.

Standardize the citation format and ensure all references (crrent and the ones to be added) are complete and follow the journal's guidelines.

Author Response

Comments 1:The abstract provides a concise summary but could be enhanced by specifying key quantitative results or observations. For example, include specific findings on how variations in elastic modulus or cohesion impact displacement.

Response 1:Thank you for your insightful advice. We have revised the abstract to include the key quantitative results of our study. The revised abstract now emphasizes the influence of changes in elastic modulus and cohesive force on the displacement of the next step bonding filling material under single-sided exposure conditions. Specifically, increasing the elastic modulus of the two-step weakly bonded filling material from 100 MPa to 500 MPa can reduce the maximum horizontal displacement of the one-step bonded filling material from 116 mm to 32 mm (a reduction of 72%). Similarly, the cohesion increased from 0.09MPa to 0.21MPa, and the displacement decreased from 96mm to 33mm (a decrease of 66%).

Comments 2:While the introduction explains the context well, there is limited discussion on recent advancements or similar studies conducted internationally. Expanding this section with a broader literature review would strengthen the justification for the study. I recommend a more diverse geographic spread of the authors (ie outside PR of China) and try to increase the references up to 40 articles for the level of this journal, as the current 24 is too low. Please clarify the novelty of the study by explicitly stating in a phrase how it advances the current state of knowledge.

Response 2:Thank you for your constructive feedback and valuable suggestions. The initial report provided limited discussion on recent developments and international research. In the revised manuscript, we have expanded the introduction to include a broader literature review. Following your suggestion, we have increased the number of references from 24 to 40, incorporating research from different geographical locations and disciplines.

To clearly emphasize the novelty of our research, we have added the following statement in the introduction:This study advances current research by developing a three-dimensional mechanical model that integrates the lateral pressure effect of weakly cemented backfill on single-sided exposed cemented backfill. Unlike previous work, our model explicitly considers the interaction between front wall exposure and rear wall compression, providing new insights into displacement patterns and stability mechanisms under different mechanical properties. This clarification emphasizes the unique contribution of our research to this field.

Comments 3:The methodology section is comprehensive but could benefit from more detailed explanations of the assumptions made in the numerical simulations. For example, further clarify the rationale behind the choice of the Mohr-Coulomb model. Also, i think a flowchart / schema summarizing the steps taken in the numerical simulation process would enhance readability.

Response 3:Thank you for your valuable feedback. We have revised the methodology section and provided a more detailed explanation of the assumptions in the numerical simulation. Specifically, we elaborated on the basic principles of using the Mohr Coulomb constitutive model, as follows: "The Mohr Coulomb constitutive model was chosen because it effectively represents the shear strength characteristics of rocks and backfill soil under various stress conditions. The model assumes that failure occurs on a plane where the shear stress reaches a critical value defined by cohesive force and internal friction angle. This method is highly consistent with the mechanical behavior of the studied material, where the surrounding rock is treated as an isotropic linear elastic material. This assumption simplifies the analysis while capturing the main deformation characteristics related to mining engineering applications

 

Comments 4:The results section is presented clearly, but the discussion section should delve deeper into the implications of the findings. How can these results influence practical mining operations or future research? Provide more comparative analysis with existing studies to highlight consistencies or discrepancies.

Response 4:In this study, we demonstrated that the mechanical properties of weakly cemented backfill materials significantly affect the stability of cemented fill under unilateral exposure. Improving the mechanical strength of two-step weakly cemented filling can not only enhance the stability of one-step cemented filling when exposed on one side, but also reduce the risk of collapse in complex mining environments. These findings provide practical guidance for designing safer filling methods in segmented mining operations, especially in mines with poor geological conditions. Improving the mechanical properties of two-step weakly cemented filling can significantly reduce tailings collapse, thereby minimizing the harm to personnel and equipment. These improvements can also reduce the required pillar thickness, potentially improving ore recovery and overall mining efficiency.

 

Comments 5:Figures are generally clear but could benefit from more detailed captions explaining the key takeaways from each image.

Response 5:Thank you for your valuable feedback . We have revised the captions to provide more detailed explanations of the key findings from each image, as follows:

Figure 4: Horizontal displacement distribution of the two-step weakly cemented filling material under varying elastic modulus values (E=100 MPa to 500 MPa). The figure shows that as the elastic modulus increases, the horizontal displacement of the one-step cemented filling body significantly decreases, indicating enhanced stability of the filling material.

Figure 5: Horizontal displacement distribution of the one-step cemented filling body exposed to one side under varying internal friction angles of the weakly cemented filling body (φ=21° to 29°). The results demonstrate a negative correlation between the internal friction angle and horizontal displacement, with greater angles leading to reduced displacement and improved stability.

Figure 6: Horizontal displacement distribution of the two-step weakly cemented filling material with different cohesion values (c=0.09 MPa to 0.21 MPa). The data suggest that higher cohesion values significantly reduce horizontal displacement, highlighting the role of particle bonding strength in stabilizing the filling material.

Figure 7: Horizontal displacement distribution of the two-step weakly cemented filling material with varying Poisson's ratio values (μ=0.31 to 0.39). The analysis indicates that an increased Poisson's ratio improves the self-stabilizing ability of the filling material, resulting in reduced lateral pressure and horizontal displacement.

Comments 6:Table 1 lists mechanical parameters but lacks detailed explanations of how these parameters were derived or referenced.

Response 6:The horizontal displacement data provided in the paper comes from displacement cloud maps and monitoring data in simulation software, which reflect the displacement distribution under the conditions defined in the simulation scheme.

Comments 7:The conclusion effectively summarizes the findings but should emphasize broader implications and potential applications in mining engineering.

Response 7:In the revised paper, we expanded the conclusions and emphasized the broader implications and practical applications of our findings in mining engineering. Specifically, we emphasize the following points: the optimal range of mechanical properties for weakly cemented fill materials, such as elastic modulus (300-400MPa) and internal friction angle (>27 °), can significantly reduce horizontal displacement and improve mining stability.

It is possible to reduce the thickness of the arm column and increase the ore recovery rate by 15%, thereby improving safety and economic benefits. We have revised the conclusion to provide a more comprehensive summary, linking the research findings with the practical applications and future research directions of mining engineering. If there are any other areas that need to be modified or further clarified, please let us know. Thank you again for your insightful suggestions.

Comments 8:Consider adding a brief section on future research directions to encourage further exploration of the topic.

Response 8:Building upon the findings of this study, future research could explore the following areas.Dynamic Stability under Real-Time Mining Conditions.While this study focuss on static analysis of cemented backfill stability, real-time mining introduces dynamic factors such as vibrations, gradual subsidence, and operational disturbances. Future studies could integrate dynamic simulations to assess the long-term performance and adaptability of cemented backfill structures.

 

Comments 9:As a final note, there are minor grammatical errors throughout the text, and I think a thorough proofreading would improve overall readability.

Response 9:In response to your note regarding minor grammatical errors, we will perform a detailed proofreading of the entire manuscript to ensure improved readability and linguistic accuracy. This step will help us address the issues you mentioned and enhance the overall quality of the text.Should you have any additional specific examples or areas of concern, please feel free to share them, and we will prioritize those as part of our revisions.

Comments 10:Standardize the citation format and ensure all references (current and the ones to be added) are complete and follow the journal's guidelines.

Response 10:We have reviewed the current references and formatted them to align with the journal's prescribed style. Additionally, we have verified the completeness of all citations and will ensure any new references added during the production stage are also compliant.Please let us know if there are any specific aspects of the reference format that require further attention.

Reviewer 3 Report

Comments and Suggestions for Authors

Dear authors!

The topic you have presented in your article, the influence of two-step filling mechanics characteristics on the stability of single-side exposed cemented backfill, is very interesting. Although your article is well structured, some minor corrections are needed:

Line 78: You are stating that the dimensions of the stope height is17.5 m and the width of room and pillar is 15m as shown in the figure. But in the figure 1 the dimensions are not stated.

Line 106: In the figure 2 the pillar width is not stated, also the Py, Px and b are not explained below the figure. The symbols are explained later in line 112 and forward. In this way the figure is not understandable. The “Potential Slip Plane” is only mentioned in this figure but later in the article you are calculating your models based on the influence of internal friction angle (chapter 5.2). The Potential Slip Plane should be explained.

Line 120: the F in the formula (3) is not explained

Line 140: the dimensions of the model are only stated in the text and for better understanding of the model the dimensions should be stated on the model

Line 146: the grid size is not shown in the model as stated.

Line 154: in the table 1 the symbols for the Internal friction angle, Cohesive force, Poisson's ratio and Compressive strength are not stated.

Line 158: the method (numerical calculation scheme is designed by using the method of control variables) is not adequately explained. Did you use some specialised software in the method for calculating the models?

Line 163: what methodology was used in the values determination in the table 2? Explain in more detail how the values in the table 2 are determined.

Line 307-309: the statement is not based on the data presented in the article.

Best regards.

Author Response

Comments 1:Line 78: You are stating that the dimensions of the stope height is17.5 m and the width of room and pillar is 15m as shown in the figure. But in the figure 1 the dimensions are not stated.

Response 1:Updated Figure 1: We have revised Figure 1 to include annotations for the stope height and the width of the room and pillar, ensuring consistency with the text.

Comments 2:Line 106: In the figure 2 the pillar width is not stated, also the Py, Px and b are not explained below the figure. The symbols are explained later in line 112 and forward. In this way the figure is not understandable. The “Potential Slip Plane” is only mentioned in this figure but later in the article you are calculating your models based on the influence of internal friction angle (chapter 5.2). The Potential Slip Plane should be explained.

Response 2:To ensure clarity, we will directly add the missing information about pillar width to the text (Px represents lateral pressure, Pz represents pressure, A represents pillar width, B represents pillar length)

Comments 3:Line 120: the F in the formula (3) is not explained

Response 3:To ensure the clarity of the formula expression, we have added a detailed explanation of F in the revised version.Among them, F represents the resultant force due to the overlying rock pressure acting on the filling body.

 

Comments 4:Line 140: the dimensions of the model are only stated in the text and for better understanding of the model the dimensions should be stated on the model

Response 4:Regarding your comment on Line 140, we appreciate your suggestion to include the model dimensions directly on the figure to enhance clarity and understanding.

We will update Figure 3 to explicitly display the dimensions of the model alongside the visual representation.

Comments 5:Line 146: the grid size is not shown in the model as stated.

Response 5:Thank you for your valuable feedback on the paper! Regarding the grid size used in the numerical model mentioned in line 146, we have indeed specified a grid size of 0.5m in the paper. However, due to the small grid size, it affects the display effect of Figure 3. In order to improve the display quality of the image, we have blurred the grid lines in Figure 3 and hidden them in the displacement cloud map. This is done to ensure that the image is clearer and easier to understand, while preserving the accuracy of the grid size.

Thank you again for your understanding and support. If you have any further questions or suggestions, we would be happy to continue improving.

Comments 6:Line 154: in the table 1 the symbols for the Internal friction angle, Cohesive force, Poisson's ratio and Compressive strength are not stated.

Response 6:In response to your comment regarding Table 1, I have updated the table to include the symbols for the internal friction angle, cohesive force, Poisson's ratio, and compressive strength. These symbols are now clearly stated in the revised version of the table.

Bulk density γ(kN/m3)

Elastic modulus E(GPa)

Internal friction angle(°)

Cohesive force(MPa)

Poisson's ratio

Compressive strength (MPa)

 

 

Comments 7:Line 158: the method (numerical calculation scheme is designed by using the method of control variables) is not adequately explained. Did you use some specialised software in the method for calculating the models?

Response 7:In this study, we used FLAC 3D numerical simulation software for model calculations, and conducted three-dimensional mechanical simulations of the model using the software. We also conducted experiments on different mechanical parameters using the controlled variable method to evaluate their effects on the stability of the filling material.

Comments 8:Line 163: what methodology was used in the values determination in the table 2? Explain in more detail how the values in the table 2 are determined.

Response 8:The mechanical parameters listed in Table 2 were determined based on experimental measurements and data simplification. Elastic Modulus (E): The elastic modulus values were derived from laboratory compression tests on weakly cemented backfill samples. These samples were prepared with varying cement-tailings ratios to simulate actual site conditions. The tests were conducted using a universal testing machine, and the modulus values were calculated from the linear portion of the stress-strain curves.

Internal Friction Angle (φ): This parameter was obtained using direct shear tests performed on weakly cemented backfill samples. The tests followed the Mohr-Coulomb failure criterion, and the friction angles were derived by plotting shear stress versus normal stress and fitting a straight line.

Cohesion (c): Cohesion values were determined through uniaxial compression tests on the same samples used for shear tests. The peak compressive strength of the samples was correlated with cohesion values using standard geotechnical equations.

Poisson's Ratio (ν): The Poisson's ratio was estimated using biaxial testing. Axial and lateral deformations were recorded, and ν was calculated as the ratio of lateral strain to axial strain within the elastic deformation range.

Comments 9:Line 307-309: the statement is not based on the data presented in the article.

Response 9:Thank you for your valuable feedback. In response to your point 9, lines 307-309, I have reviewed the content of the paragraph again and made modifications to it: The results show that with the increase of cohesion, the horizontal displacement moderately decreases, which is consistent with the results shown in Figure 6, where the maximum horizontal displacement of the cementitious filler decreases with the increase of cohesion

Thank you for your guidance. I have made revisions to this paragraph based on your suggestions.

Reviewer 4 Report

Comments and Suggestions for Authors

In the article presented to me for evaluation, Study on the influence of two-step filling mechanics characteristics on the stability of single-side exposed cemented back-fill, the authors address a very important element of a miner's work, which is ensuring the safety of the crew working underground. Extraction of mineral resources, especially at greater depths, is associated with deformation of the rock mass and difficulties in ensuring the stability of the surrounding rocks. The research was conducted on the example of exploitation in the Shandong mine. Using the developed three-dimensional mechanical model, the effectiveness of filling goafs with rock material with the possible addition of cement as a binding agent was examined.

 

In my opinion, the solved aspect of rock mechanics and mineral resource extraction technology is an original and new step in understanding the issue. Each element that increases the knowledge of the hazardous work environment of miners is important for both a wide group of practical mining engineers and theoreticians. Successive solving of subsequent unknown mechanisms will enable the development of effective technologies and proper prevention of mining hazards.

The developed three-dimensional mechanical model allows for understanding of further unexplored mechanisms of the behavior of the rock mass directly disturbed by mining exploitation. The presented results of model tests may facilitate the preparation of safe technology for the extraction of subsequent exploitation plots. Despite the great contribution of the authors to the research, the presented form of their presentation is very insufficient. The presented text is very difficult to understand even for a mining engineer. In the review of literature thematically related to the analyzed problem, the authors very briefly described scientific research in related fields. Without underestimating the significance of the study presented to me for evaluation, I believe that such a narrow approach to research on the issue, limited only to Chinese publications, may reduce its potential impact on global knowledge. I suggest analyzing the research and presenting the scientific achievements of other research centers as well. At least several European or American centers conduct similar research, which should be taken into account when describing the background of the research problem being solved. The study itself lacks a background describing the exploitation system in the Shandong mine. It is not clear what is being mined in this mine and what hazards occur there. In order to understand the presented text, please supplement this aspect. The drawing attached to the description of the exploitation system is, in my opinion, clear, but unfortunately unclear to the reader. I suggest adding a comment to this drawing. The description of the lateral action is very unclear, I suggest a correction. Similarly, I ask for more comments when describing the methodology for calculating lateral pressure. It is difficult to say whether the model proposed by the authors is correctly selected due to the lack of a description of the exploitation system, which I have already informed about earlier. In its current form, the description of the model is completely illegible. I suggest the authors comprehensively modernize the presented text. Similarly, the numerical simulation scheme is incomprehensible due to the very limited scope of the text. Please add the necessary comments. The next chapter describes research on the impact of mechanical properties of the flooring material. I believe that this fragment is also unclear and difficult to understand. I suggest a comprehensive correction.

In my opinion, the conclusions in which the authors summarized the research they conducted should also be fully corrected. It is difficult to assess whether the presented conclusions result from the author's own research, due to the difficult to understand form of the text.

The list of literature attached to the text contains 24 bibliographic items, unfortunately mainly Chinese. I believe that in order to improve the quality of the analysis, the bibliography and literature review should be supplemented with items from other scientific centers related to mining.

A very important and extremely significant addition to the text are the attached figures (7 pieces) and 2 tables. They should facilitate the understanding of the text. Unfortunately, only tables fulfill this task. Without diminishing the quality of the prepared figures, I believe that their understanding will be possible after including their broader comments in the text. In my opinion, Figure 1 lacks elements describing the exploitation system. I suggest modifying both the figures and the texts describing them.

Comments on the Quality of English Language

I do not feel competent to assess the Quality of English Language

Author Response

Comments 1:In the article presented to me for evaluation, Study on the influence of two-step filling mechanics characteristics on the stability of single-side exposed cemented back-fill, the authors address a very important element of a miner's work, which is ensuring the safety of the crew working underground. Extraction of mineral resources, especially at greater depths, is associated with deformation of the rock mass and difficulties in ensuring the stability of the surrounding rocks. The research was conducted on the example of exploitation in the Shandong mine. Using the developed three-dimensional mechanical model, the effectiveness of filling goafs with rock material with the possible addition of cement as a binding agent was examined.

In my opinion, the solved aspect of rock mechanics and mineral resource extraction technology is an original and new step in understanding the issue. Each element that increases the knowledge of the hazardous work environment of miners is important for both a wide group of practical mining engineers and theoreticians. Successive solving of subsequent unknown mechanisms will enable the development of effective technologies and proper prevention of mining hazards.

The developed three-dimensional mechanical model allows for understanding of further unexplored mechanisms of the behavior of the rock mass directly disturbed by mining exploitation. The presented results of model tests may facilitate the preparation of safe technology for the extraction of subsequent exploitation plots. Despite the great contribution of the authors to the research, the presented form of their presentation is very insufficient. The presented text is very difficult to understand even for a mining engineer. In the review of literature thematically related to the analyzed problem, the authors very briefly described scientific research in related fields. Without underestimating the significance of the study presented to me for evaluation, I believe that such a narrow approach to research on the issue, limited only to Chinese publications, may reduce its potential impact on global knowledge. I suggest analyzing the research and presenting the scientific achievements of other research centers as well. At least several European or American centers conduct similar research, which should be taken into account when describing the background of the research problem being solved. The study itself lacks a background describing the exploitation system in the Shandong mine. It is not clear what is being mined in this mine and what hazards occur there. In order to understand the presented text, please supplement this aspect. The drawing attached to the description of the exploitation system is, in my opinion, clear, but unfortunately unclear to the reader. I suggest adding a comment to this drawing. The description of the lateral action is very unclear, I suggest a correction. Similarly, I ask for more comments when describing the methodology for calculating lateral pressure. It is difficult to say whether the model proposed by the authors is correctly selected due to the lack of a description of the exploitation system, which I have already informed about earlier. In its current form, the description of the model is completely illegible. I suggest the authors comprehensively modernize the presented text. Similarly, the numerical simulation scheme is incomprehensible due to the very limited scope of the text. Please add the necessary comments. The next chapter describes research on the impact of mechanical properties of the flooring material. I believe that this fragment is also unclear and difficult to understand. I suggest a comprehensive correction.

In my opinion, the conclusions in which the authors summarized the research they conducted should also be fully corrected. It is difficult to assess whether the presented conclusions result from the author's own research, due to the difficult to understand form of the text.

The list of literature attached to the text contains 24 bibliographic items, unfortunately mainly Chinese. I believe that in order to improve the quality of the analysis, the bibliography and literature review should be supplemented with items from other scientific centers related to mining.

A very important and extremely significant addition to the text are the attached figures (7 pieces) and 2 tables. They should facilitate the understanding of the text. Unfortunately, only tables fulfill this task. Without diminishing the quality of the prepared figures, I believe that their understanding will be possible after including their broader comments in the text. In my opinion, Figure 1 lacks elements describing the exploitation system. I suggest modifying both the figures and the texts describing them.

Response 1:

Thank you for your constructive and detailed feedback on our paper. Below, we have discussed each point raised and outlined the revisions we have implemented: we have revised the paper, continued to annotate necessary technical symbols, and improved overall readability. Expand the literature review to provide a more comprehensive overview of global research on two-step filling mechanics and cemented filling stability. Lateral pressure and method explanation: We have annotated the symbols of lateral pressure and added detailed titles and explanations to the chart to improve its interpretability. Improve the numerical simulation scheme to provide a more detailed description of the methods, parameters, and the correlation between the model and the studied problem. The conclusions have been revised to ensure that they are a clear and logical summary of our research findings. The references will be updated to include key works from internationally recognized journals and institutions related to mining and backfill mechanics.

Thank you again for your valuable feedback. We look forward to resubmitting a revised version of our manuscript for your consideration.

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

In the article Study on the influence of two-step filling mechanics characteristics on the stability of single-side exposed cemented back-fill, presented to me for review again, the authors address a very important element of a miner's work, which is ensuring the safety of the crew working underground and increasing the use of the deposit by reducing the volume of pillars left. Extraction of mineral resources, in this case iron ore, especially at greater depths, is associated with deformation of the rock mass and difficulties in ensuring the stability of the surrounding rocks. The research was carried out using the example of mining and geological conditions in the Shandong mine. In the research, the authors used a three-dimensional mechanical model to study the stability of goafs filled with material with the addition of a binding agent.

 

I maintain my opinion from the previous review and believe that the resolved aspect of rock mechanics and mineral resource extraction technology is an original and new small step in understanding the influence of various backfill materials on the development of extraction technology. Each element that increases the knowledge of the hazardous work environment of miners is important for both a wide group of practical mining engineers and theoreticians. Successive solving of the next unknown aspects of rock mass mechanics will enable the development of effective, efficient and safe technologies for the extraction of raw materials.

 

I maintain my opinion from the previous stage of the review and believe that the developed three-dimensional mechanical model allows for the understanding of the next unexplored mechanisms of the behavior of the rock mass directly disturbed by mining. The presented results of model tests may facilitate the preparation of a safe technology for the extraction of subsequent exploitation plots.

 

Compared to the previous version, the text has been significantly improved. Despite these corrections and the authors' great contribution to the research, the presented form of their presentation, in my opinion, is still very insufficient. The presented text is still very difficult to understand even for a mining engineer. In accordance with the previous suggestion, the authors have slightly increased the scope of the description of the research environment itself, in which they conduct simulations. Right at the beginning, you can learn that the Shandong mine is an ore mine and extraction is carried out using pillar systems. Unfortunately, it is only on line 203 that the reader learns that this is an iron ore mine, which is very important information that should have been included at the beginning of the text. The authors still have not described the pillar mining system and the deposit conditions, which would have helped the reader understand the model studies conducted. The authors reserve that the model does not take into account the influence of, for example, faults, etc., but information about their existence would significantly increase the understanding of mining problems and the purpose of the simulations conducted. It is not clear from the text whether the filling of post-mining spaces is intended to protect the excavations fenced in the filling material or to protect the stability of the overlying rock mass. I assume that this is about the latter aspect and the possibility of reducing the number of pillars left from the unselected deposit. I kindly ask the authors to comment on this, because it is not the reader's task to guess. I kindly ask the authors to provide additional information on what filling material is used, I assume that it is waste rock, and in the case of segments with a reinforced cement structure, sand. The review of the literature thematically related to the analyzed problem has been modified. Unfortunately, the authors still described very briefly the scientific research of other research centers conducting similar studies, although in the text I indicate that similar studies are conducted in other research centers, but even a short description is missing. Figure no. 1 attached to the description of the exploitation system is unfortunately still unclear to the reader. I suggest adding a comment to this figure. Due to the lack of a description of the exploitation system, which I have already informed about earlier, it is still not clear to me whether the model proposed by the authors is correctly selected. The scheme of numerical simulations is still unclear due to the lack of a description of the method of filling the goafs. Due to the admixture of binding materials, I assume that the filling material is fed to the exploited space through pipelines, and the carrier is water, but I may be wrong. Please add the necessary comments and I suggest a comprehensive correction of the text (e.g. in lines 65 to 67).

 

I maintain my opinion from the previous stage of the review and it is difficult to assess whether the presented conclusions result from the author's research, due to the difficult to understand form of the text. In my opinion, yes, but I suggest that the previously signalled comments be applied.

 

The list of references attached to the text contains 45 bibliographic items. The list of references has been supplemented compared to the previous version and in my opinion does not require any major corrections in this version.

 

The authors have attached 7 figures and 2 tables to the text. I maintain my opinion from the previous stage of the review and suggest modifying both figures 1 and 3 so that they better describe the issue. I consider the remaining figures to be well designed and prepared, but their better understanding will be possible after including their broader comments in the text. The modifications already applied by the authors have improved the situation, but in my opinion they are insufficient. The attached tables facilitate understanding of the text and in my opinion do not require corrections.

Comments on the Quality of English Language

I am not competent to judge the quality of the English language used by the authors, but I think that the text would require linguistic correction in terms of vocabulary typical for mining.

Author Response

Thank you for your detailed review and valuable suggestions on our manuscript.In response to the issues you raised, we have implemented the following improvements and provided further clarification in the text highlighted in red.

Comment 1:

Compared to the previous version, the text has been significantly improved. Despite these corrections and the authors' great contribution to the research, the presented form of their presentation, in my opinion, is still very insufficient. The presented text is still very difficult to understand even for a mining engineer. In accordance with the previous suggestion, the authors have slightly increased the scope of the description of the research environment itself, in which they conduct simulations. Right at the beginning, you can learn that the Shandong mine is an ore mine and extraction is carried out using pillar systems. Unfortunately, it is only on line 203 that the reader learns that this is an iron ore mine, which is very important information that should have been included at the beginning of the text. The authors still have not described the pillar mining system and the deposit conditions, which would have helped the reader understand the model studies conducted. The authors reserve that the model does not take into account the influence of, for example, faults, etc., but information about their existence would significantly increase the understanding of mining problems and the purpose of the simulations conducted. It is not clear from the text whether the filling of post-mining spaces is intended to protect the excavations fenced in the filling material or to protect the stability of the overlying rock mass. I assume that this is about the latter aspect and the possibility of reducing the number of pillars left from the unselected deposit. I kindly ask the authors to comment on this, because it is not the reader's task to guess. I kindly ask the authors to provide additional information on what filling material is used, I assume that it is waste rock, and in the case of segments with a reinforced cement structure, sand. The review of the literature thematically related to the analyzed problem has been modified. Unfortunately, the authors still described very briefly the scientific research of other research centers conducting similar studies, although in the text I indicate that similar studies are conducted in other research centers, but even a short description is missing. Figure no. 1 attached to the description of the exploitation system is unfortunately still unclear to the reader. I suggest adding a comment to this figure. Due to the lack of a description of the exploitation system, which I have already informed about earlier, it is still not clear to me whether the model proposed by the authors is correctly selected. The scheme of numerical simulations is still unclear due to the lack of a description of the method of filling the goafs. Due to the admixture of binding materials, I assume that the filling material is fed to the exploited space through pipelines, and the carrier is water, but I may be wrong. Please add the necessary comments and I suggest a comprehensive correction of the text (e.g. in lines 65 to 67).

response 1:

Advance explanation on iron ore information: We have clearly stated in the project overview that the research object is an underground iron ore mine in Shandong Province, China, using segmented filling method.

The main purpose of strong filling after the first step of mining is to provide stable support for the subsequent second step of mining pillars, thereby enhancing the overall stability of the mining area, reducing the volume of unmined pillars, and improving resource recovery rate. In addition, this filling method also plays a role in protecting the stability of the overlying rock mass, especially under deep mining conditions, by reducing the risk of stress concentration and surrounding rock deformation caused by goaf.

The filling material is mainly composed of tailings and cementitious admixtures, transported through pipelines with water as the carrier.

The viewpoint of passive support for cemented backfill mainly focuses on the self-supporting effect of cemented backfill. The backfill plays a passive support role under its own weight and lateral pressure, that is, analyzing the influence of the exposed area and exposure time of the backfill on the stability of the mining site. This design approach is suitable for mining environments with large exposed areas and long support times. The active support viewpoint of cemented backfill focuses more on the ability of the backfill to withstand support pressure during pillar mining. The filling material reduces the deformation of the surrounding rock by supporting the distribution of compressive stress on the roof, thereby improving the overall stability of the mining area. This method is particularly suitable for deep mining scenarios that require effective sharing of roof pressure.

Comment 2:The authors have attached 7 figures and 2 tables to the text. I maintain my opinion from the previous stage of the review and suggest modifying both figures 1 and 3 so that they better describe the issue. 

response 2:Figures 1 and 3 have been modified and provided further clarification within the manuscript.

Author Response File: Author Response.docx

Round 3

Reviewer 4 Report

Comments and Suggestions for Authors

n the article Study on the influence of two-step filling mechanics characteristics on the stability of single-side exposed cemented back-fill, presented to me for the third time for evaluation, the authors address an important mining issue, namely the stability of retaining pillars and ensuring the stability of rocks in the rock mass. In previous reviews, I have extensively described the advantages and disadvantages of the text presented to me for evaluation. Now I will only refer to the corrections introduced by the authors. In my opinion, the biggest shortcoming of the previous versions of the text was the lack of a description of the mining technology in the Shandong mine. The authors have partially supplemented the description of the technology that I postulated. In my opinion, it should be a bit more extensive, but I understand that it is not the most important part of the evaluated text. The comments introduced by the authors have largely dispelled my doubts and I believe that they are sufficient for understanding the mining background of the research conducted by the authors. Ultimately, I accept the authors' response and congratulate them on a well-prepared report on their research.