The Influence of Construction Methods on the Stability of Tunnels and Ground Structures in the Construction of Urban Intersection Tunnels

Round 1

Reviewer 1 Report

This article presents the development of a numerical model pertaining to an underground tunnel located at an urban intersection. The model is established with reference to a circular roadway initiative implemented within a central business district. The authors engage in numerical simulations of excavation procedures, employing three distinct methodologies: the full-section approach, the stepwise technique, and the center cross diagram (CRD) approach. It is demonstrated that, although disparate construction techniques do not alter the overall trends in parameters such as the stress and displacement of surrounding rock, deformation of nearby building structures, and convergence of the pre-existing tunnel, they do influence the extent of these variations. Notably, the CRD method induces the least magnitude of maximum compressive and tensile stresses within the surrounding rock. These findings underscore the suitability of the CRD method for urban intersection tunnel projects from a safety standpoint.

The paper has been written in good format and organized well and can be accepted after revising/answering flowing comments.

-          Major comment: Authors have compared three approaches based on just a single numerical example. From statistics point of view, it is not a valid. how do they justify that for some different numerical examples, their results are still valid?

-          Minor comment: A paragraph must be added to the end of Section 1 to briefly describe next sections of the paper. (e.g. Section 2 described the urban tunnel construction method. Project overview is presented in Section 3. ….)

 

Author Response

Response to Reviewer 1
We would very much like to thank the reviewer for his/her supportive comments. The questions, suggestions and other constructive opinions greatly promote this paper. As it follows, our responses to the reviewer’s comments are provided in black text, the reviewer’s comments are shown in blue bold text, the specific revises are displayed in red text in the revision paper (marked-up version).
This article presents the development of a numerical model pertaining to an underground tunnel located at an urban intersection. The model is established with reference to a circular roadway initiative implemented within a central business district. The authors engage in numerical simulations of excavation procedures, employing three distinct methodologies: the full-section approach, the stepwise technique, and the center cross diagram (CRD) approach. It is demonstrated that, although disparate construction techniques do not alter the overall trends in parameters such as the stress and displacement of surrounding rock, deformation of nearby building structures, and convergence of the pre-existing tunnel, they do influence the extent of these variations. Notably, the CRD method induces the least magnitude of maximum compressive and tensile stresses within the surrounding rock. These findings underscore the suitability of the CRD method for urban intersection tunnel projects from a safety standpoint.
The paper has been written in good format and organized well and can be accepted after revising/answering flowing comments.
1. Major comment: Authors have compared three approaches based on just a single numerical example. From statistics point of view, it is not a valid. how do they justify that for some different numerical examples, their results are still valid?
Based on an underground circular roads engineering project located in the Central Business District of Chongqing, China, we establish a numerical model of urban intersection tunnel to analyze the influence of different construction methods on the stability of tunnels and ground structures. The numerical simulation results are rigorously verified by field monitoring data. Finally, we get the conclusion that the CRD method stands out as the most suitable choice for urban intersection tunnel engineering, particularly in terms of safety considerations. It is crucial to underline that the foundation of this study is the specific engineering project mentioned, and all the numerical simulation parameters have been tailored to match the characteristics of
this project, including the properties of the rock strata, tunnel dimensions, supporting materials, and more. Consequently, the results and conclusions drawn from this research are intended to be directly applicable to the underground circular roads engineering project. While the findings may not possess universal applicability, they serve as a valuable reference and foundation for similar projects.
This study represents a segment of our ongoing research efforts. We plan to continue our investigations by examining construction methods for urban intersection tunnels under varying geological conditions, different burial depths, and diverse intersection angles. Our goal is to establish a comprehensive research framework focusing on construction methods for urban intersection tunnel projects.
2. Minor comment: A paragraph must be added to the end of Section 1 to briefly describe next sections of the paper. (e.g. Section 2 described the urban tunnel construction method. Project overview is presented in Section 3. ….)
A paragraph describing sections of the paper is added to the end of Section 1. As follows:
This paper comprises six interrelated sections, each providing a comprehensive perspective on the research. Section 1 offers an overview of the research's significance and its current status. Section 2 describes the NATM theory and common urban tunnel construction methods. Project overview of urban intersection tunnel is presented in Section 3. Information of the numerical model and simulation results are showed in Section 4. Section 5 provides an assessment of the three construction methods, along with a description of the field monitoring process. Finally, Section 6 wraps up our study with a comprehensive conclusion.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript is well written, I have just a minor comment for improving the Conclusion section.

The authors are required to provide a comprehensive explanation of the limits of their study, discuss the significance of their research findings for future studies, and offer suggestions for further research.

Minor editing of English language required

Author Response

Response to Reviewer 2
We would very much like to thank the reviewer for his/her supportive comments. The questions, suggestions and other constructive opinions greatly promote this paper. As it follows, our responses to the reviewer’s comments are provided in black text, the reviewer’s comments are shown in blue bold text, the specific revises are displayed in red text in the revision paper (marked-up version).
The manuscript is well written, I have just a minor comment for improving the Conclusion section. The authors are required to provide a comprehensive explanation of the limits of their study, discuss the significance of their research findings for future studies, and offer suggestions for further research.
First, we proofread and revise the writing language and norms in detail, and then we re-edit the conclusion of the manuscript: added an explanation of the limits, clarified the research significance, and offered suggestions for future research. As follows:
In this study, we established a numerical model of urban intersection tunnel based on an underground circular roads project and conducted simulations of the excavation process using three construction methods (full-section method, step method and CRD method). We analyzed the stability of tunnels and ground building, and verified the simulation results with field monitoring data. It was essential to clarify that the foundation of our study was the underground circular roads project, and all numerical simulation parameters were tailored to this specific project. Consequently, the conclusions were primarily applicable to underground circular roads engineering. While these research findings might not be universally applicable, they served as valuable references and a foundation for similar projects. To enhance the research comprehensiveness, it was suggested to conduct research on the construction methods of urban intersection tunnels with diverse geological conditions, varying burial depths and different intersection angles.

Author Response File: Author Response.pdf

Reviewer 3 Report

1-   The authors discussed the impact of the three construction methods (full-section method, step method, and centre cross diagram (CRD) method) on the safety and stability of urban intersection tunnel construction which is an interesting topic for tunnel engineers.

The title is appropriate and reflects the content of the article. The abstract section is clear and it gives the summary of the work.

2-   The introduction and literature review has been explained well. The advantages and disadvantages of the three methods have been explained accurately.

3-   The numerical simulation & model, results analysis and evaluation have been explained well.

4-   The Tables and Figures clearly and easily show data visually, and discussion done well.  

5-   The conclusions perform the findings of the present study in a concrete manner.

6-   The article adequately referenced.

Author Response

Response to Reviewer 3
We would very much like to thank the reviewer for his/her supportive comments. The questions, suggestions and other constructive opinions greatly promote this paper. We proofread and revise the writing language and norms in detail, the specific revises are displayed in red text in the revision paper (marked-up version).
1-The authors discussed the impact of the three construction methods (full-section method, step method, and center cross diagram (CRD) method) on the safety and stability of urban intersection tunnel construction which is an interesting topic for tunnel engineers.
The title is appropriate and reflects the content of the article. The abstract section is clear and it gives the summary of the work.
2-The introduction and literature review has been explained well. The advantages and disadvantages of the three methods have been explained accurately.
3-The numerical simulation & model, results analysis and evaluation have been explained well.
4-The Tables and Figures clearly and easily show data visually, and discussion done well.
5-The conclusions perform the findings of the present study in a concrete manner.
6-The article adequately referenced.

Author Response File: Author Response.pdf

Reviewer 4 Report

This paper presented an interesting study on the risk analysis of urban intersection tunnels through different construction methods. The contents are clearly presented and well-organized. Some comments are provided for authors to consider:

1)     Is there any monitoring data to compare with the simulated results?

2)     According to Fig. 2, bolts are used in the construction, so how is the effect of bolt supporting on the simulation results? Some detailed information is suggested.

3)     Some detailed parameters are missing, such as geometric information of ground, geotechnical parameters, concrete parameters, bolt information etc.

4)     Fig. 6-11, the legend is not clearly seen.

5)     It would be very appreciate if some of the following literatures can be reviewed: Structural Concrete 22(4) (2021) 2167-2183; Structural Concrete 22(6) (2021) 3430-3445; Engineering Structures 188 (2019) 418-429;

None

Author Response

Response to Reviewer 4
We would very much like to thank the reviewer for his/her supportive comments. The questions, suggestions and other constructive opinions greatly promote this paper. As it follows, our responses to the reviewer’s comments are provided in black text, the reviewer’s comments are shown in blue bold text, the specific revises are displayed in red text in the revision paper (marked-up version).
This paper presented an interesting study on the risk analysis of urban intersection tunnels through different construction methods. The contents are clearly presented and well-organized. Some comments are provided for authors to consider:
1) Is there any monitoring data to compare with the simulated results?
In Section 5.3, we engage in a rigorous comparison between the monitoring data with the simulated results, and verify the correctness of the simulated results. Specifically, we focus the monitoring efforts on section K0+415 of branch tunnel 1#, where we closely observe and record the vault subsidence and horizontal convergence over a 30-day period. The characteristic curves of cumulative vault subsidence and cumulative horizontal convergence both are divided into three stages: rapid deformation stage, slow deformation stage and stable stage. Based on these monitoring observations, it is obtained that the maximum vault subsidence amount and maximum horizontal convergence value of section K0+415 are 2.480 mm and 2.110 mm. The numerical simulation shows that the corresponding deformation values are 2.361 mm and 2.157 mm, respectively, as shown in Fig. 14. Notably, the simulated results are in close agreement with the monitoring data. The error between simulation results and monitoring data remains below 5%, as shown in Table 9. This consistency validates the accuracy of the numerical simulation.
Fig. 14 Simulated results, the deformation of the branch tunnel 1# after main tunnel excavated by the CRD methods.
Table 9 Results comparison of numerical simulation and field monitoring.
The maximum vault settlement
The maximum horizontal convergence
Field monitoring
2.480 mm
2.110 mm
Numerical simulation
2.361 mm
2.157 mm
Results error
4.7%
2.2%
2) According to Fig. 2, bolts are used in the construction, so how is the effect of bolt supporting on the simulation results? Some detailed information is suggested.
We re-edit Section 4.2 and add information such as anchor bolt parameters and model mesh division to enhance the comprehensiveness of the numerical model.
Anchor bolt support, as a commonly employed support method, plays a role in enhancing the stability of the surrounding rock. It assists the shotcrete to complete the surrounding rock supporting in the intersection tunnel engineering.
The primary objective of this study is to reveal the construction method with the least construction disturbance by analyzing the stability of both ground building and tunnels under different construction methods. In order to effectively evaluate the stability of the structures, we refer to two China's national standards (GB50007-2011 and GB50911-2013), and take the concrete stress, the gradient and subsidence of the ground building, the deformation of the tunnel as evaluation parameters. Consequently, our research has centered on examining the stress levels in the surrounding rock and the deformation characteristics of structures. While the deformation of anchor bolt and its influence on surrounding rock are not the research objects. Upon careful consideration, we have determined that analyzing the deformation and stress of anchor bolts would not contribute to the core objective of this study. In fact, it could potentially divert our focus from the primary research areas.
As a result, we have made the deliberate decision to omit the analysis of anchor bolt deformation and stress results within this study, with anchor bolts primarily serving as a supplementary support element within the numerical model.
3) Some detailed parameters are missing, such as geometric information of ground, geotechnical parameters, concrete parameters, bolt information etc.
In Section 4.2, the detailed parameters of the numerical model are supplemented, including the simplification of the model, the geometric relationship of the objects, the physical and mechanical parameters of the materials, etc.
4) Fig. 6-11, the legend is not clearly seen.
The figures have been re-edited and the new legends are clear enough to read smoothly.
Fig. 6. Vertical displacement of rock strata after the main tunnel excavation. (a) Excavated by full-section method, (b) excavated by step method, (c) excavated by CRD method.
Fig. 7. The minimum principal stress of surrounding rock after the main tunnel excavation. (a) Excavated by full-section method, (b) excavated by step method, (c) excavated by CRD method.
Fig. 8. The maximum principal stress of surrounding rock after the main tunnel excavation. (a) Excavated by full-section method, (b) excavated by step method, (c) excavated by CRD method.
Fig. 9. The settlement of ground affected commercial building after the main tunnel excavation. (a) Excavated by full-section method, (b) excavated by step method, (c) excavated by CRD method.
Fig. 10. Vault subsidence of branch tunnel #1 after main tunnel excavated by the three methods. (a) Full-section method, (b) step method, (c) CRD method, (d) vault subsidence affected amount of branch tunnel #1.
Fig. 11. Horizontal convergence of branch tunnel #1 after main tunnel excavated by the three methods. (a) Full-section method, (b) step method, (c) CRD method, (d) horizontal convergence affected amount of branch tunnel #1.
5) It would be very appreciate if some of the following literatures can be reviewed: Structural Concrete 22(4) (2021) 2167-2183; Structural Concrete 22(6) (2021) 3430-3445; Engineering Structures 188 (2019) 418-429;
The literatures provide references and suggestions in the mechanical analysis of supporting structures and the establishment of numerical simulation, which promote this paper.

Author Response File: Author Response.pdf

Reviewer 5 Report

This paper employs numerical simulation to discuss the sequence of impacts of three construction methods on construction stability. It concludes that the CRD method is the most suitable for ensuring safety in urban intersection tunnel engineering. Nevertheless, there are some recommended modifications.

1. The manuscript title is not sufficiently straightforward.

2. Line 240, the numerical model is not clearly introduced. This should include details such as the selection of solid elements, contact surfaces, mesh generation, and how buildings are treated within the model.

3. Table 8, there is inconsistency in the units used for building height.

4. Line 365, the author provides standard values for six safety assessment indicators. In practical engineering, these indicators may have varying degrees of impact on stability. It is recommended to include relevant discussions in the manuscript.

5. Figure 12, the building subsidence induced by the three construction methods are all very small, within 1mm. It is advisable to adjust the scale of building subsidence indicators in the figure to more clearly demonstrate the degree of influence of the three methods.

The writing is readable but a careful proofreading must be practiced before the revised version is submitted for re-review. 

Author Response

Response to Reviewer 5
We would very much like to thank the reviewer for his/her supportive comments. The questions, suggestions and other constructive opinions greatly promote this paper. As it follows, our responses to the reviewer’s comments are provided in black text, the reviewer’s comments are shown in blue bold text, the specific revises are displayed in red text in the revision paper (marked-up version). Additionally, we have proofread and revised the writing language and norms in detail.
This paper employs numerical simulation to discuss the sequence of impacts of three construction methods on construction stability. It concludes that the CRD method is the most suitable for ensuring safety in urban intersection tunnel engineering. Nevertheless, there are some recommended modifications.
1. The manuscript title is not sufficiently straightforward.
The title is changed to “The influence of construction methods on the stability of tunnels and ground structures in the construction of urban intersection tunnels”.
2. Line 240, the numerical model is not clearly introduced. This should include details such as the selection of solid elements, contact surfaces, mesh generation, and how buildings are treated within the model.
In Section 4.2, the detailed numerical model introduction is supplemented, including the selection of solid elements, mesh generation, the model simplification, etc.
3. Table 8, there is inconsistency in the units used for building height.
We proofread the manuscript carefully and correct irregularities.
Table 8 Deformation allowable value of affected ground building.
Height of building
(m)
Allowable gradient value
Allowable foundation settlement gradient (mm)
Safety coefficient
24 < H ≤ 60
0.003
20
0.5
4. Line 365, the author provides standard values for six safety assessment indicators. In practical engineering, these indicators may have varying degrees of impact on stability. It is recommended to include relevant discussions in the manuscript.
We add relevant discussions for the assessment indicators in Section 5.1, appearing in lines 414 to 438.
5. Figure 12, the building subsidence induced by the three construction methods are all very small, within 1mm. It is advisable to adjust the scale of building subsidence indicators in the figure to more clearly demonstrate the degree of influence of the three methods.
The scales of building subsidence and building gradient are adjusted based on the advice.
Fig. 12. The safety of excavating tunnel, the stability of existing tunnel and ground affected building caused by full-section method, step method and CRD method, respectively.

Author Response File: Author Response.pdf

Reviewer 6 Report

Dear Authors, 

This is a very nicely written paper. I enjoyed reading the manuscript. The results are presented nicely. However, I see a lack of theoretical implications of this work. I would strongly suggest the authors to put a theoretical and practical implication section in the manuscript outlining the significant contributions of this study to the body of knowledge and to practice. 

 

 

Author Response

Response to Reviewer 6
We would very much like to thank the reviewer for his/her supportive comments. The questions, suggestions and other constructive opinions greatly promote this paper. As it follows, our responses to the reviewer’s comments are provided in black text, the reviewer’s comments are shown in blue bold text, the specific revises are displayed in red text in the revision paper (marked-up version).
This is a very nicely written paper. I enjoyed reading the manuscript. The results are presented nicely. However, I see a lack of theoretical implications of this work. I would strongly suggest the authors to put a theoretical and practical implication section in the manuscript outlining the significant contributions of this study to the body of knowledge and to practice.
We have added Section 2.1 to outline the New Austrian Tunneling Method theory and its applicability to urban tunnel engineering in the manuscript. Additionally, at the end of Section 1, we explain the research significance and engineering contribution, and briefly describe the subsequent sections respectively.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The paper can be accepted in the current

format.