Research on the Pressure Relief Mechanism of Gently Inclined Long-Distance Lower Protective Layer Mining and Cooperative Gas Control Technology

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1- Regarding to the abstract, If there is a word limit, prioritize the most important facts .

2- Consider including a brief reference to novelty (e.g., "This study advances understanding of...") to emphasize uniqueness.

3-Clearly indicate how this work adds prior understanding (e.g., "This study resolves spatial coupling challenges in...").

Author Response

1- Regarding to the abstract, If there is a word limit, prioritize the most important facts.

Response: In the revised version, we have restructured the abstract to ensure it concisely summarizes both the scientific background and key findings of our study. The abstract now highlights the main objectives, methodology, results, and implications of the research, providing a clearer overview of the study's contributions to the field of coal spontaneous combustion.

2- Consider including a brief reference to novelty (e.g., "This study advances understanding of...") to emphasize uniqueness.

Response: We have revised the concluding statement of the abstract to explicitly highlight the novelty of our work. The updated sentence now reads:

“The work advances understanding of pressure-relief and permeability enhancement in gently inclined remote lower protective layer mining.”

3-Clearly indicate how this work adds prior understanding (e.g., "This study resolves spatial coupling challenges in...").

Response: We appreciate your feedback and have refined the Conclusions to better articulate the advancement over prior research. The following addition has been incorporated:

“This methodology effectively resolves the spatial-temporal coordination challenges between gas extraction efficiency and operational safety in deep protective layer mining operations.”

 

Reviewer 2 Report

Comments and Suggestions for Authors

The paper presents a detailed investigation into the pressure-relief mechanism of gently inclined long-distance lower protective layer mining. The methodology is sound, and the results are thoroughly analyzed. The language is generally academic, although some phrases could be refined for improved clarity and conciseness. Further specific comments are attached.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

1. The manuscript is good but does not follow the formal format which must be followed for better understanding like with the sections of materials and methods, results and discussion.

Response: This study represents an applied research in engineering technology, focusing on the pressure relief effects of gently inclined remote protective layer mining on upper outburst-prone coal seams. Taking Pingdingshan Tianan Coal Industry's No. 1 Mine as the engineering case, we systematically investigated the pressure-relief influence range of lower protective layer mining through integrated theoretical analysis and field measurements. Specifically, a dual verification approach combining theoretical modeling of protective seams with in-situ geotechnical parameter measurement was adopted to examine the stress evolution patterns and dilatational deformation characteristics of protected coal seams. Given the significant empirical engineering nature of this research, the paper adopts an organizational framework that transcends traditional linear "materials-methods-results" structure. An innovative framework was developed, comprising Project Overview, Theoretical Analysis of the Protective Range of Protective layer mining, Field Parameter Testing Layout Plan, and Analysis of the Effect of Remote Protective layer mining, thereby achieving effective integration between theoretical research and engineering practice.

2. Page 1, Abstract: The abstract presents a good overview of the research, but it might benefit from a slightly more detailed explanation of the "theoretical modelling and multidimensional in-situ monitoring" methodologies. Consider adding a brief phrase explaining the significance of "lower protective seam" for readers who may be less familiar with this specific mining technique.

Response: The theoretical framework of this study is established in accordance with Detailed Rules for Preventing Coal and Gas Outbursts, theoretical calculating the pressure-relief boundaries in lower protective seam mining. The multi-dimensional field testing framework integrates gas pressure measurement and precise roof Expansion Deformation. As these methodologies have formed a complete theoretical-practical demonstration chain in the main text, technical details will not be reiterated in the abstract.   It should be noted that the engineering definition of lower protective layer mining have been systematically elucidated in the introduction section(lines 41-45).

3. Page 2, Introduction: The introduction effectively establishes the context of coal mining challenges and the importance of gas control. The authors could briefly elaborate on why accurately delineating pressure relief zones is a "critical engineering imperative." It might be helpful to provide a concise explanation of "FLAC3D numerical modelling" for readers outside of this specialization. The authors highlight the limitations of existing research, which justifies the need for this study.

Response: The engineering geological behavior induced by protective seam mining in adjacent outburst-prone coal seams is fundamentally governed by stress redistribution mechanisms: The mining disturbance disrupts the original geostatic equilibrium, leading to pressure relief failure in the outburst-prone seams. This process triggers significant gas desorption effects, rapidly transforming adsorbed gas into free-state gas that migrates through newly developed fracture networks. Crucially, this multi-physics coupling mechanism enhances the permeability characteristics of the protected seam by orders of magnitude, forming dominant seepage channels towards the mining face, consequently causing the gas concentration to exceed safety thresholds. In response to these engineering phenomena, the study emphasizes the establishment of a dynamic gas drainage system synchronized with spatiotemporal pressure relief evolution.

Besides, it should be specifically clarified that the theoretical-field measurement dual verification methodology adopted in this study differs from conventional numerical simulation approaches. During the literature review phase, we systematically analyzed previous research advancements in numerical simulation of protective seam mining, with particular emphasis on evaluating the technical merits and limitations of Flac3D numerical simulation methodology in reconstructing coal seam stress fields. However, regarding the technical route of this research, we focus on establishing quantitative response relationships between mining disturbances and gas migration through the construction of engineering geomechanical analytical models combined with a self-developed multi-source information fusion monitoring system. This research paradigm not only ensures engineering accuracy but also significantly enhances field applicability.

4. Page 3, Introduction: The description of the Pingdingshan mining area is detailed, but consider rephrasing "a quintessential deep-mining scenario" to sound less colloquial. Defining "thrust-nappe tectonics" would make this section more accessible to a broader audience. A brief explanation of "remote protective layer mining operations" would be useful here.

Response: Revised "quintessential deep-mining scenario" to "representative deep-mining geological conditions." Defined thrust-nappe tectonics as "compression-induced overlapping rock strata" and explained remote protective seam mining as "interlayer spacing exceeding 60 meters between protective and protected strata."

5. Page 3, 1 Project Overview: The description of the mine and working face overview is detailed.

Response: Thank you for your positive feedback. We have ensured that the detailed description of the mine and working face overview provides a solid foundation for understanding the subsequent technical analyses and field testing procedures.

6. Page 4, 2 Theoretical Analysis of the Protective Range of Protective layer mining: The explanation of "stress-redistribution mechanism" is clear, but adding a sentence on the potential hazards if this mechanism is not well understood could add impact. The use of specific values for pressure-relief angles is good, but briefly mentioning the implications of these differences (77° vs. 83°) could be insightful. The phrase "engineered spatial arrangement" could be rephrased for better clarity.

Response: We appreciate your constructive suggestions. A sentence has been added to highlight potential hazards if the stress-redistribution mechanism is inadequately understood.

The variation in pressure-relief angles results from differences in coal seam dip. The presence of coal seam dip creates elevation disparity between two sides of the working face. This variation leads to distinct mining-induced effects on overlying strata following longwall mining operations, as empirically demonstrated in Table 1.

The phrase "engineered spatial arrangement" has been revised to " Under the engineering disturbance caused by mining the Wu₈ coal seam " for clarity.

7. Page 5, 2.2 Along the Strike Direction: The rationale for the 3-month interval is well explained.

Response: Thank you for acknowledging the explanation of the 3-month interval. This interval was determined based on empirical stability thresholds for stress redistribution and gas migration in similar coal seams, ensuring reliable data collection.

8. Page 5, 3 Field Parameter Testing Layout Plan: The description of the borehole layout is thorough.

Response: We are grateful for your recognition of the thoroughness of the borehole layout description. The design prioritizes spatial coverage and geological representativeness to ensure accurate monitoring of pressure-relief effects.

9. Page 6, 3.1.2 Sealing Method: The explanation of the sealing method is detailed.

Response: Thank you for your comment. The sealing method was elaborated to emphasize its role in minimizing gas leakage and ensuring measurement accuracy, which is critical for validating pressure-relief effectiveness.

10. Page 7, 3.2 Expansion Deformation Testing in the Ding6 Coal Seam: The purpose of expansion deformation testing is clearly stated.

Response: We appreciate your acknowledgment. The purpose of expansion deformation testing was explicitly stated to link mechanical behavior with gas migration dynamics, which is essential for evaluating protective layer efficacy.

11. Page 8, 3.3 Design of Pressure Relief Gas Extraction Boreholes in the Ding Coal Seam: The description of the borehole array design is comprehensive.

Response: Thank you. The comprehensive design of the borehole array ensures systematic gas extraction and aligns with theoretical predictions of stress-relief zones, maximizing operational safety and efficiency.

12. Page 9, 4 Analysis of the Effect of Remote Protective layer mining: The gas pressure test results are presented clearly, and the observation of distinct zonal characteristics is important.

Response: We are pleased that the gas pressure test results and zonal characteristics were clearly conveyed. These findings underscore the spatial heterogeneity of pressure relief, which directly informs gas extraction strategies.

13. Page 10, 4.2 Expansion Deformation of the Ding Coal Seam: The authors effectively explain the "compression and then expansion" process.

Response: Thank you. The "compression and then expansion" process was emphasized to illustrate the dynamic response of the coal seam to mining-induced stress changes, a key factor in gas desorption and flow.

14. Page 11, 4.3 Pressure Relief Gas Extraction Volume in the Ding6 Coal Seam: The analysis of gas extraction volume over time is logical.

Response: We appreciate your feedback. The temporal analysis of gas extraction volume highlights the effectiveness of the protective layer over time, correlating with theoretical models of pressure-relief gas release.

15. Further, no discussion was found which makes the manuscript’s authentication very weak. Please add the discussion while comparing previous studies with yours.

Response: The framework design of this study transcends the linear "materials-methods-results" narrative paradigm prevalent in traditional experimental science, aligning inherently with the empirical nature of engineering research. While omitting a dedicated discussion section, the paper manifests its intellectual innovation through a multidimensional demonstration system: First, addressing the engineering challenge of identifying pressure-relief boundaries in gently inclined remote protective seams, we established a three-pronged research methodology integrating theoretical modeling, in-situ monitoring, and engineering verification. Second, through comparative analysis of field monitoring parameters, we validated the spatiotemporal evolution patterns governing pressure-relief protection ranges. This empirical revelation directly informs the refinement of effectiveness evaluation criteria for protective seams.

 

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is well-written and concise. The authors effectively outline their study's research method, theoretical foundations, and results. Lastly, they conducted a discussion summarizing their findings and briefly commented on their work in the Conclusions section.

The Abstract is too long.

Lines should be numbered throughout the Manuscript.

In the Abstract is “… extraction scheduling (8-month duration)”, but in the Conclusions Chapter is “…extraction lasting 7 months…, please explain it in more detail.

Table 1 shows that for a dip angle of 14°, the values of the pressure-relief angles are d1 between 77-73, and d2 83 and 87. Is it true to take 77 and 83 accordingly

Table 2 is not mentioned in the text.

Figure 5 could be more readable.

Figure 5 is not mentioned in the text.

Figure or Fig., please decide on one notation.

Please provide the accuracy of the measurement equipment used.

Figure 7 is not mentioned in the text.

“Article 55 of the “Detailed Rules for Preventing Coal and Gas Outbursts,”” – should be placed in the References Chapter.

“These precise pressure relief range and angle data provide an important theoretical basis for optimizing the design of protective seam mining and reasonably arranging gas extraction boreholes, helping to further improve gas extraction efficiency and effectiveness, and achieve efficient and safe mining of the mine. „ – Don’t the authors think that there are too many “and” in this sentence?

References:

• Please provide DOI numbers.

Author Response

The manuscript is well-written and concise. The authors effectively outline their study's research method, theoretical foundations, and results. Lastly, they conducted a discussion summarizing their findings and briefly commented on their work in the Conclusions section.

1. The Abstract is too long.

Response: We have revised the Abstract to make it more concise by removing redundant details while retaining the core objectives, methods, and conclusions.

2. Lines should be numbered throughout the Manuscript.

Response:  Lines numbers have been added in the manuscript.

3. In the Abstract is “… extraction scheduling (8-month duration)”, but in the Conclusions Chapter is “…extraction lasting 7 months…, please explain it in more detail.

Response: Thank you for catching this inconsistency. The total extraction period spanned 8 months. We have standardized the description of the extraction duration in both the Abstract and Conclusions.

4. Table 1 shows that for a dip angle of 14°, the values of the pressure-relief angles are δ₁ between 77-73, and δ₂ 83 and 87. Is it true to take 77 and 83 accordingly

Response: The pressure relief angles corresponding to different coal seam dip angles in Table 1 are recommended reference values derived from engineering experience. These values must be validated through field measurements. No matter δ₁=77° (δ₁=73°) or other values, the value may not correct. In this study, we adopted the principle of proximate verification for parameter selection, with subsequent validation to be performed using in-situ measurement data.

5. Table 2 is not mentioned in the text.

Response: Table 2 has been mentioned in lines 159-160.

6. Figure 5 could be more readable.

Response: Fig. 5 has been modified to make it more readable.

7. Figure 5 is not mentioned in the text.

Response: Fig. 5 has been mentioned in lines 166-167.

8. Figure or Fig., please decide on one notation.

Response: We have standardized all instances to “Fig.” (e.g., Fig. 5, Fig. 7).

9. Please provide the accuracy of the measurement equipment used.

Response: Testing accuracy parameters for the pressure gauge are specified in Lines 172-174; accuracy data of the stratigraphic displacement monitor is detailed in Line 186.

10. Figure 7 is not mentioned in the text.

Response: Fig. 7 has been mentioned in lines 194-195.

11. “Article 55 of the “Detailed Rules for Preventing Coal and Gas Outbursts,”” – should be placed in the References Chapter.

Response: This regulation has now been properly cited in the References section as:

[44] National Coal Mine Safety Administration. Detailed Rules for Preventing Coal and Gas Outbursts. Beijing: China Coal Industry Publishing House, 2019.

https://www.gov.cn/xinwen/2019-08/21/content_5423024.htm.

12. “These precise pressure relief range and angle data provide an important theoretical basis for optimizing the design of protective layer mining and reasonably arranging gas extraction boreholes, helping to further improve gas extraction efficiency and effectiveness, and achieve efficient and safe mining of the mine. „ – Don’t the authors think that there are too many “and” in this sentence?

Response: The sentence has been revised to:

“These precise pressure relief range and angle data provide an important theoretical basis for optimizing protective layer mining design and rationally arranging gas extraction boreholes. This methodology effectively resolves the spatial-temporal coordination challenges between gas extraction efficiency and operational safety in deep protective layer mining operations.”

13. References: Please provide DOI numbers.

Response: All applicable DOI numbers have been added to the reference entries. For sources without DOIs, we have provided ISBNs or official publication links.