Determining a Suitable Reinforcement Strategy for TBM Advance in a Gully Fault Zone Without Jamming—A Numerical Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This research develops a 3D numerical model to investigate reinforcement strategies for Tunnel Boring Machines (TBMs) passing through fault zones prone to jamming. The study evaluates the effectiveness of various pre-reinforcement methods, identifying surface pre-grouting as the most effective in reducing deformation and improving safety. 

The topic of this research is highly interesting; however, the following questions and comments need to be addressed in the manuscript:

1) Could you provide more details about the numerical model's unique features and methodology in the abstract?

2) What specific research gap does this study address compared to previous works?

3) How do the numerical simulation results quantitatively compare to the on-site measurements?

4) Can you include a flowchart or schematic to clarify the TBM cutterhead jamming mechanism and torque-related calculations?

5) Could you enhance figures by including more annotations, legends, and detailed captions for clarity?

6) What criteria were used for selecting the four treatment methods for evaluation?

7) Could you elaborate on the assumptions made in the numerical model and their potential limitations?

8) How does the surface pre-grouting technique compare in cost and implementation feasibility with other methods?

9) Can you discuss the sensitivity of the model's results to variations in the input parameters?

10) At the end of the introduction, the manuscript refers to "chapters" instead of sections, which is not appropriate for a scientific manuscript. Could you revise this to correctly reference the corresponding sections of the paper?

 

Author Response

I would like to express my sincere gratitude for your valuable feedback. Your comments have been incredibly insightful and have greatly benefited my work. I have made substantial revisions based on your suggestions, and the specific changes are outlined as follows:

 

• Could you provide more details about the numerical model's unique features and methodology in the abstract?

Thank you for pointing this out. We agree with your comment. Therefore, we have added more details about the unique features and methodology of the numerical model in the abstract. Specifically, we have provided a more detailed explanation regarding the modeling of the grouting zone and the supporting system within the grouting area. This includes refined models for different working conditions, such as the face chemical grouting, TBM shield tail small conduit installation, advanced pipe canopy grouting, and double-layer pipe canopy. These refined models allow for further calculations on the stability of surrounding rock and the stress characteristics of the supporting system under various treatment measures.

The abstract has been revised to reflect this change, and the detailed explanation can be found on page 1, lines 10-15 of the revised manuscript.

• What specific research gap does this study address compared to previous works?

Thank you for pointing this out. We agree with your comment. Therefore, we have clarified the specific research gap addressed by this study in comparison to previous works. In engineering practice, geological forecast analysis indicates that TBM is prone to jamming when passing through fractured zones like fault zones in gully areas. Previous studies have primarily focused on using pipe canopy pre-reinforcement to ensure smooth TBM passage, but this approach has limited applicability for fault zones in gully areas. This study specifically addresses the issue of TBM passage through fractured fault zones in gully areas, emphasizing pre-reinforcement measures that ensure smooth passage without jamming.

The revision has been made to the manuscript, and the updated text can be found on page 2, lines 83-96 of the revised manuscript.

• How do the numerical simulation results quantitatively compare to the on-site measurements?

Thank you for your valuable comment. We agree with your observation. Therefore, we have added a comparison between the on-site measurement curves and the numerical simulation results. The analysis reveals that the deformation error between the two is generally less than 20%, indicating that the model is reasonable and provides a good fit for the actual conditions.

The revision has been made to the manuscript, and the updated text can be found on page 17, lines 511-512 of the revised manuscript.

• Can you include a flowchart or schematic to clarify the TBM cutter head jamming mechanism and torque-related calculations?

Thank you for your insightful suggestion. We agree that a flowchart or schematic would help clarify the TBM cutterhead jamming mechanism and torque-related calculations. Therefore, we have included a flowchart in Figure 2, along with additional annotations to enhance understanding.The revision has been made to the manuscript, and the updated content can be found on page 4, lines 145-149 of the revised manuscript.

• Could you enhance figures by including more annotations, legends, and detailed captions for clarity?

Thank you for your helpful suggestion. We have expanded the annotations, legends, and captions for the figures to improve clarity. Specifically, we have added more detailed titles and annotations to Figures 2, 4, 5, 6, 10, and 11. Additionally, other figures in the manuscript are explained within the text. The revisions can be found in the updated figures and captions throughout the manuscript.

• What criteria were used for selecting the four treatment methods for evaluation?

Thank you for pointing this out. We agree with your comment. Therefore, we have revised the manuscript to clarify the criteria used for selecting the four treatment methods for evaluation. Specifically, we considered the following factors:

Stability of Surrounding Rock and Support Stress Characteristics: We evaluated the stability of the surrounding rock and the stress characteristics of the support system under different treatment methods to ensure the method could effectively maintain stability and withstand pressures.

Stratum Displacement: We also analyzed the potential displacement of the strata under each treatment method to ensure that the method chosen would minimize displacement during construction.

Cost Analysis: In line with your valuable suggestion, we have emphasized the importance of economic analysis. We conducted a detailed cost comparison of each treatment method to ensure the selected scheme is not only technically sound but also cost-effective.

Based on these criteria, we identified the optimal pre-reinforcement support scheme. The cost analysis has been added on page 18, section 6, lines 522-574 in the revised manuscript.

• Could you elaborate on the assumptions made in the numerical model and their potential limitations?

Thank you for pointing this out. We agree with your comment. Therefore, we have revised the manuscript to provide a more detailed explanation of the assumptions made in the numerical model and their potential limitations.

The assumptions made in the model are as follows:

Uniform Surrounding Rock Parameters: We assumed the surrounding rock parameters used in the numerical model are uniform, based on the typical geological conditions of the tunnel site. This approach is intended to ensure that the parameters in the numerical model are reasonable and representative of the actual conditions.

Final Displacement as the Criterion for Parameter Determination: The surrounding rock parameters were determined using the final displacement value. This method was chosen to ensure that the parameters are appropriate for the numerical model, although small errors may arise during the entire tunnel excavation process. This is because the real strata are more complex than those assumed in the model, which could lead to some discrepancies.

The details of the parameter selection method can be found on page 10, lines 273-279 of the revised manuscript.

• How does the surface pre-grouting technique compare in cost and implementation feasibility with other methods?

Thank you for pointing this out. We agree with your comment. Therefore, we have revised the manuscript to include a more detailed comparison of the surface pre-grouting technique with other methods in terms of both cost and implementation feasibility. We have added a discussion on the cost comparison, considering material, labor, and equipment costs, as well as the economic feasibility of adopting this technique. Additionally, we addressed the implementation difficulty of the surface pre-grouting technique compared to other methods, highlighting factors such as construction time, technical complexity, and potential challenges. These updates can be found on page 18, Section 6, lines 522-574 of the revised manuscript.

• Can you discuss the sensitivity of the model's results to variations in the input parameters?

Thank you for pointing this out. We agree with your comment. Therefore, we have revised the manuscript to clarify the approach we used in determining the input parameters for the model. Specifically, we used final displacement comparisons to identify the optimal parameter inputs, but we did not conduct a sensitivity analysis on the variations of these parameters. For a detailed explanation of the method and process used to select the model parameters, please refer to page 10, lines 273-279 in the revised manuscript.

• At the end of the introduction, the manuscript refers to "chapters" instead of sections, which is not appropriate for a scientific manuscript. Could you revise this to correctly reference the corresponding sections of the paper?

Thank you for your comment. We have revised the manuscript to replace the term "chapters" with the correct reference to "sections." The necessary adjustments can be found on page 3, lines 97-106 in the revised manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Please see the attached document.

Comments for author File: Comments.pdf

Author Response

I would like to sincerely thank you for your thoughtful review of my paper. I deeply appreciate your encouraging comments and am grateful for the time and effort you put into reviewing my work. Your positive feedback has been a great source of motivation, and I am truly honored by your kind words. I have carefully reviewed your suggestions and made significant improvements to further strengthen the paper. Once again, thank you for your support and encouragement—it means a great deal to me.

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript presents research on optimizing reinforcement strategies for a tunnel located in the gully fault zone. Numerical simulations were employed to investigate the rock mass behavior around the tunnel and the effectiveness of the selected reinforcement measures. This study is expected to provide valuable insights for TBM tunnel construction in similar geological conditions. Although the manuscript covers an interesting topic, many aspects require further explanation and discussion. Revisions are required to enhance the overall quality of manuscript. Below are some constructive suggestions and comments:

1. Since your study focuses primarily on the engineering solution, it is suggested to revise the title to: Determining a Suitable Reinforcement Strategy for TBM Advance in a Gully Fault Zone Without Jamming – A Numerical Analysis.
2. The Abstract and Introduction chapters lack a clearly defined research aim. Additionally, the method-based code employed for the research should also be mentioned.
3. The geological and geotechnical characteristics of the studied site are missing. An exemplary geological profile should be provided, including details on the gully fault.
4. Figures 2, 4, 7, 11, 14, 15, and 19 (text and legends) require improvements to enhance their presentation quality.
5. The input data (mechanical parameters) for the Mohr-Coulomb criterion is missing.
6. The model description and calculation variations should be rewritten in more detail.
7. Please provide a justification for the selected reinforcement strategies.
8. Expand the Conclusions section to include the research goal, tools or methodologies applied, major findings, limitations, and suggestions for future work.
9. In general, the manuscript would benefit from verifying and calibrating the numerical model and its input parameters in the initial stages. Subsequently, predictions for tunnel stability analysis and reinforcement optimization can be made.
10. The References section needs updating. Please incorporate more references published in English from 2020 to 2025.
11. Additional minor comments can be found in the PDF.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English could be improved and double-checked by a native speaker.

Author Response

I would like to express my sincere gratitude for your valuable feedback. Your comments have been incredibly insightful and have greatly benefited my work. I have made substantial revisions based on your suggestions, and the specific changes are outlined as follows:

 

• Since your study focuses primarily on the engineering solution, it is suggested to revise the title to Determining a Suitable Reinforcement Strategy for TBM Advance in a Gully Fault Zone Without Jamming – A Numerical Analysis.

Thank you for your suggestion. We have revised the title of the manuscript to better reflect the focus of the study. The new title is: "Determining a Suitable Reinforcement Strategy for TBM Advance in a Gully Fault Zone Without Jamming – A Numerical Analysis." This change is reflected in the first line of the manuscript.

• The Abstract and Introduction chapters lack a clearly defined research aim. Additionally, the method-based code employed for the research should also be mentioned.

Thank you for your valuable feedback. We have revised both the Abstract and Introduction to clearly define the research aim. Additionally, we have included a mention of the method-based code used in the research. These revisions can be found on page 1, lines 8-18, and page 3, lines 83-96 in the revised manuscript.

• The geological and geotechnical characteristics of the studied site are missing. An exemplary geological profile should be provided, including details on the gully fault.

Thank you for your comment. Due to the nature of the engineering project, we are unable to provide the geological profile as a cross-sectional diagram.

• Figures 2, 4, 7, 11, 14, 15, and 19 (text and legends) require improvements to enhance their presentation quality.

Thank you for your suggestion. We have made improvements to Figures 2, 4, 7, 11, 14, 15, and 19 by enhancing both the text and legends to improve their presentation quality. These revisions have been incorporated into the revised manuscript.

• The input data (mechanical parameters) for the Mohr-Coulomb criterion is missing.

Thank you for pointing this out. The missing input data, including the mechanical parameters for the Mohr-Coulomb criterion, has been added. You can find this information on page 10, Table 4 in the revised manuscript.

• The model description and calculation variations should be rewritten in more detail.

Thank you for your feedback. The model description and calculation variations have been rewritten in more detail to provide a clearer understanding. These revisions can be found in Section 4.2 on page 8 of the revised manuscript.

• Please justify the selected reinforcement strategies.

Thank you for your suggestion. The justification for the selected reinforcement strategies has been provided in more detail. The study concludes that grouting pre-reinforcement at the surface is the most effective measure to prevent TBM jamming, particularly in trench fault zones. While the simplification of strata parameter variations in the study may introduce minor errors, these were controlled through displacement indicators. The final model showed less than a 20% discrepancy from field data. Future research should focus on refining the modeling process and using advanced optical measurement technologies to improve accuracy in simulating tunnel excavation conditions. Umbrella grouting saves around 6.82 million RMB in investment but comes with challenges like longer construction times, greater technical difficulty, and potential risks, especially at greater tunnel depths. Surface pre-grouting, on the other hand, reinforces the ground before the TBM reaches fault zones, preventing delays and jamming. For tunnel depths under 70 meters, surface pre-grouting is more cost-effective, safer, and efficient. The choice of grouting method should depend on the project's specific conditions and economic factors for optimal outcomes. Specific changes can be found in lines 434-442, 456-476, and 615-626 of the revised manuscript.

• Expand the Conclusions section to include the research goal, tools or methodologies applied, major findings, limitations, and suggestions for future work.

Thank you for your feedback. The Conclusions section has been expanded to include the research goal, tools or methodologies applied, major findings, limitations, and suggestions for future work. These revisions can be found in lines 576-588 and 615-626 on page 19 of the revised manuscript.

• In general, the manuscript would benefit from verifying and calibrating the numerical model and its input parameters in the initial stages. Subsequently, predictions for tunnel stability analysis and reinforcement optimization can be made.

Thank you for the suggestion. The manuscript has been revised to include the verification and calibration of the numerical model and its input parameters in the initial stages. This will ensure that predictions for tunnel stability analysis and reinforcement optimization can be made effectively. These changes can be found in lines 273-279 on page 10 of the revised manuscript.

• The References section needs updating. Please incorporate more references published in English from 2020 to 2025.

Thank you for your suggestion. The References section has been updated to include more recent publications in English from 2020 to 2025. Most of the references are from this period, with a few representative older sources retained for their relevance. These changes can be found in lines 638-645 of the revised manuscript.

• Additional minor comments can be found in the PDF.

Thank you for your valuable comments on the manuscript. I have made the necessary revisions based on your feedback.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been noticeably improved.

Author Response

I would like to sincerely thank you for your thoughtful review of my paper. I deeply appreciate your encouraging comments and am grateful for the time and effort you put into reviewing my work. Your positive feedback has been a great source of motivation, and I am truly honored by your kind words. Once again, thank you for your support and encouragement—it means a great deal to me.

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for your responses

Here are some more comments:

Response no. 3 is not convincing and does not align with the data availability statement. Nevertheless, a detailed cross-sectional profile is not necessary; however, the rock layers, including the gully fault zone around the tunnel, should be clearly presented for the readers.

Response no. 4 is not satisfactory. In Table 3, the symbol c should represent cohesive strength or cohesion. Additionally, tensile strength is still missing. In Table 4, the name and unit are not appropriate. The unit kN/m³ is suitable for specific weight (as shown in Table 3); however, if you mean density, the unit should be kg/m³. Please clarify.

For Figures 11, 14, and 15, the text and legends are still blurred. Further improvements are required.

 

Comments on the Quality of English Language

The English seems fine to me. However, to ensure accuracy, it is suggested that the English be double-checked by native speakers

Author Response

I would like to express my sincere gratitude for your valuable feedback. Your comments have been incredibly insightful and have greatly benefited my work. I have made substantial revisions based on your suggestions, and the specific changes are outlined as follows:

 

Response no. 3 is not convincing and does not align with the data availability statement. Nevertheless, a detailed cross-sectional profile is not necessary; however, the rock layers, including the gully fault zone around the tunnel, should be clearly presented for the readers.

Thank you for your valuable feedback. I apologize for the oversight in my previous response. I have now added a schematic of the geological longitudinal profile around the tunnel as shown in Figure 1. Additionally, I have provided a more detailed description of the project in the text to address your concerns. Thank you again for your constructive suggestions.

 

Response no. 4 is not satisfactory. In Table 3, the symbol c should represent cohesive strength or cohesion. Additionally, tensile strength is still missing. In Table 4, the name and unit are not appropriate. The unit kN/m³ is suitable for specific weight (as shown in Table 3); however, if you mean density, the unit should be kg/m³. Please clarify.

I agree with your comments and have made the necessary revisions to the headings in Tables 3 and 4. Thank you for your valuable corrections.

 

For Figures 11, 14, and 15, the text and legends are still blurred. Further improvements are required.

Thank you for your valuable feedback. I agree with your suggestion. Due to image compression, I overlooked uploading clearer versions. I have now re-uploaded the images, and to improve the visibility of the legends, I have removed the background fill in Figure 15, making it easier to read.