Research on Leakage Mechanism of Underwater Shield Tunnels with Different Soil Layers during Operation Period

Round 1

Reviewer 1 Report

Please see the Word file uplaoded for detailed comments. 

Comments for author File: Comments.pdf

Author Response

Reviewer comments reply instructions

First of all, I would like to thank the chief editor and the reviewers for their important and pertinent comments, which have provided a constructive direction for the further improvement of this paper. According to the opinions of the reviewers, the author revised this paper article by article, and re-analyzed and modified this paper in detail. Detailed changes can be found in the text and "Reviewer Comments Reply". Thanks again to the chief editor and reviewers for their affirmation and suggestions.

Reviewer comments reply

This paper studied the influence mechanism of different soil layer properties and different degrees of lining deterioration on tunnel leakage. To explore the leakage mechanism of underwater tunnels in different soil layer properties, finite element analysis software is used to establish a calculation model. The working conditions of different soil layer properties and different degrees of lining deterioration are established by means of soil layer permeability coefficient and lining permeability coefficient, and the law of tunnel leakage under each working condition is analyzed. Finally, taking a section of Dinghuaimen tunnel in Nanjing, China as an example, the leakage law and leakage mechanism are verified and analyzed. The Reviewer has some concerns regarding the introduction, project overview, numerical models, and discussions. Generally, in this paper the English language is good, but some sentence should be more clear (too long).

Thank you for your suggestion. The author has revised all the long and misleading sentences in each part of the article. The modification is as follows:

" In recent years, with the rapid development of China's infrastructure scale and infrastructure technology, a large number of underwater shield tunnels across rivers are being constructed and operated. Due to the long-term service in the working environment of complex stratum and high water pressure, underwater shield tunnels are prone to leakage diseases." Was changed to " Different soil layer properties have great influence on tunnel leakage. "

" In this paper, the influence mechanism of different soil layer properties and different degrees of lining deterioration on tunnel leakage is studied. In order to explore the leakage mechanism of underwater tunnels in different soil layer properties, finite element analysis software is used to establish a calculation model." was changed to " In this paper, the finite element software is used to analyze the homogeneous leakage model of different soil layers and different degrees of lining deterioration.".

" Finally, taking a section of Dinghuaimen tunnel in Nanjing, China as an example, the leakage law and leakage mechanism are verified and analyzed. the result shows:." was changed to" This paper innovatively explores the relationship between the severity of tunnel seepage caused by different lining deterioration and the soil layer properties of the tunnel. Finally, by comparing the field survey data of Dinghuaimen with the leakage law and mechanism summarized by the model, the reliability and feasibility of the model method to explore the leakage mechanism are verified. The model test results are consistent with the project survey data. In this paper, the seepage law and mechanism of underwater shield tunnel are explored and the result shows:".

 

 

 

Other comments are as follows:

1. Introduction

The leakage of segmental joints in shield tunnels should be described with wider range. Below you

can find some papers about this aspect.

⚫ Performance of a new waterproof system with double sealing gaskets outside bolt hole of segment. Tunn. Undergr. Space Technol. 2022, 119, 104206.https://doi.org/10.1016/j.tust.2021.104206

⚫ Waterproofing behavior of sealing gaskets for circum-ferential joints in shield tunnels: A full−scale experimental investigation. Tunn. Undergr. Space Technol. 2021, 108, 103682. https://doi.org/10.1016/j.tust.2020.103682

⚫ A novel test setup for determining waterproof perfor-mance of rubber gaskets used in tunnel

segmental joints: Development and application. Tunn. Undergr. Space Technol. 2021, 115, 104079. https://doi.org/10.1016/j.tust.2021.104079

Thank you for your suggestion. My description of shield tunnel joint leakage is not very comprehensive, so I gave a more detailed description in the introduction of the paper. The following paragraph has been added to make the description more comprehensive.

“The waterproof structure of joint sealing gasket has been improved by some scholars, for example, a new double sealing gasket waterproof system has been designed by by Hongming Xie. In addition, a series of new testing devices were proposed to explore the correlation between the waterproof performance and mechanical performance of joint gaskets.”

2. It is necessary to supplement more details for the project example, and adding some figures may be a good choice.

Thank you for your valuable advice. The figure 8 and figure have been added to the 4.2 part of the paper, and the corresponding description has been added to perfect the engineering details. The description is as follows:

Nanjing Dinghuaimen Yangtze River Tunnel is a tunnel in Nanjing City, Jiangsu Province, China. It consists of a southern line and a northern line. The total length of the northern line is 7014m, including the underwater shield tunnel section of 4135m. The to-tal length of the southern line is 7363m, including the underwater shield tunnel section of 3557m. The tunnel is designed as a double-pipe double-deck eight-lane structure with a design speed of 80 km/h.

Figure 8. N-line geological cross-section

3. It is suggested to conduct the convergence study on the impact of the mesh size on the numerical results.

Thank you for your valuable advice. In this paper, the influence of mesh accuracy on numerical results is not enough. In this paper, the selection of model size is fully considered according to the references, and the influence of model size on the calculation results is reduced as much as possible, and the mesh near the tunnel lining is uniformly encrypted. However, the influence of this treatment on the calculation results is not discussed in this paper. Now it has been supplemented and perfected. Add the following corresponding part:

The accuracy of the calculation results is affected by the form of meshing. Through the author's experiment, when the mesh element size is approximately 4m, the calculation results cannot converge. In this paper, the mesh element size approximately 1~3m is called mesh accuracy 1~3. In order to explore a reasonable grid division form, The four mesh partitioning methods selected in this paper are shown in Figure 1: all grids are uniformly set to grid accuracy 1, 2 and 3, or mesh accuracy 1 or 3 is selected according to the mesh position. (The mesh accuracy is 1 when the element is located near the tunnel. The mesh accuracy is 3 when the element is far away from the tunnel.)

As can be seen from the figure 2, four different meshing methods lead to different calculation results. By comparing the vertical stress on the outside of the lining, it can be seen that the calculation results of mesh accuracy 1 and mesh accuracy 2 are similar and the most accurate, but both of them take too long to calculate. The calculation result of mesh accuracy 3 is quite different from that of mesh accuracy 1 and mesh accuracy 2, so the calculation result of mesh accuracy 3 is not accurate enough. The calculation result of mesh accuracy 1&3 is accurate enough, and the calculation process is also time-consuming, so this form of meshing is selected in this paper. In this paper, mesh accuracy 1&3 is adopted. That is, the mesh size is approximately 1m when the element is located near the tunnel. When the element is far away from the tunnel, the mesh size is approximately 3m.

(a) mesh accuracy 1                  (b) mesh accuracy 2

(c) mesh accuracy 3                  (d) mesh accuracy 1&3

Figure 1. Mesh division diagram of numerical calculation model.

Figure 2. Mesh division diagram of numerical calculation model.

4. Figures 2, 5, 7, 9 are not clear enough, especially for the legend, which should be improved.

Thank you for your suggestion. More high-definition pictures have been replaced in the original text, and the legend has been enlarged. Please check

5. The discussions in section 4.2 about the leakage analysis is not deep enough. Please improve it.

Thank you for your suggestion. Now the corresponding part of the result analysis has been added in 4.2. The analysis is also combined with engineering examples to make the result analysis more logical. The additions are as follows.

According to the geological survey report of Dinghuaimen Tunnel, the fine sand layer passed by N-Line is 1273.25m long, accounting for 35.76% of the total length of the north-ern line. The silty clay layer accounted for 449.78m, accounting for 12.63% of the total length. In addition, the upper half layer of 760.64m tunnel is fine sand. the northern line has a total of 1782 ring lining. According to the field statistics since 2019, the number of leakage points and the percentage of section rings in the tunnel can be used to understand the severity of N-line leakage in Dinghuai Men tunnel under different geological condi-tions. The percentage of the number of seepage points and the number of cross section rings in the fine sand formation is as high as 51.52%. The silty sand layer is 41.76%. Silty clay is 28.23%. The tunnel severity data of different strata investigated in the field are highly consistent with the simulation conclusion in the third part of the paper, which shows the feasibility of the calculation model for the leakage simulation of the Dinghuaimen tunnel.

6. What is the next step of your research? Please add this aspect in the conclusion.

Thank you for your suggestion. There is no mention of the research plan for the next step in this paper, and the corresponding part has been added now.

The method adopted in this paper is reasonable, and the results reach the expectation, which proves the reliability and feasibility of this modeling method. In the next step, the author will use this method to further explore the leakage mechanism of different leakage forms under different strata, such as the influence of different stratum properties on annular seam leakage, longitudinal seam leakage and bolt hole leakage.

7. The format of scientific counting should be uniform.

Thank you for your suggestion. The counting format in the table and the article has been changed, and the units have also been unified.

8. The title of Section 3 should be results analysis or discussions, instead of conclusion analysis.

Thanks for your suggestion. The title of section 3 has been revised.

Author Response File: Author Response.pdf

Reviewer 2 Report

Paper entitled ‘’Research on Leakage Mechanism of Underwater Shield Tunnels with Different 1 Soil Layers during Operation Period’’ authors study the influence mechanism of different soil layer properties and different degrees of lining deterioration on tunnel leakage, by applying finite element method analysis. There are few issues that need to be addressed by authors before this manuscript could be reconsidered for publication:

1.       The first two sentences should be removed from the Abstract.

2.       English proof reading by English native speaker is essential and required since there are many vague sentences. Example: ’’However, scholars have 49 not paid enough attention to the influence of strata on tunnel leakage.‘‘

3.       From the current version of the manuscript, it is not clear what the novelty of the paper is. Application of FEM for solving engineering problems is over 50 years old, and the problem of tunnel leakage is known and already investigated. Moreover, authors investigate homogeneous soil model, which is the most simple case in the real conditions.

4.       Authors chose only a single value of soil parameters in Table 1. How about the variations of the parameter values in real conditions? It is common to examine range of values for the soil parameters.

5.       Figures 2 (a and b) and 5,  are very vague and should be provided in higher resolution and with higher font size.

6.       In (49) authors are calling Theorem 3 – where is Theorem 3? There is no Theorem 3 given in text.

7.       Regarding Section 4.2 – are there any data on the measured quantity of the tunnel leakage, which should be compared to the output results of the analysis?

8.       Section Conclusion should be significantly expanded by the numerical data of the presented research, and with clear indication of the novelty of the presented paper in comparison to the previous studies, including guidance for further research.

 Once these suggestions are taken into account, I will be pleased to review the revised manuscript and reconsider my decision.

Author Response

Reviewer comments reply instructions

First of all, I would like to thank the chief editor and the reviewers for their important and pertinent comments, which have provided a constructive direction for the further improvement of this paper. According to the opinions of the reviewers, the author revised this paper article by article, and re-analyzed and modified this paper in detail. Detailed changes can be found in the text and "Reviewer Comments Reply". Thanks again to the chief editor and reviewers for their affirmation and suggestions.

 

Reviewer comments reply

Paper entitled ‘’Research on Leakage Mechanism of Underwater Shield Tunnels with Different 1 Soil Layers during Operation Period’’ authors study the influence mechanism of different soil layer properties and different degrees of lining deterioration on tunnel leakage, by applying finite element method analysis. There are few issues that need to be addressed by authors before this manuscript could be reconsidered for publication:

1. The first two sentences should be removed from the Abstract.、

Thanks for your suggestion, the first two sentences have been removed from the abstract of the original manuscript.

2. English proof reading by English native speaker is essential and required since there are many vague sentences. Example: ’’However, scholars have 49 not paid enough attention to the influence of strata on tunnel leakage.„

Thank you for reminding me that the original description of the paper is indeed vague. We have changed the original sentence to " The influence of strata on tunnel leakage haven't been studied by researchers." according to your suggestion.

In addition, the long and easily ambiguous sentences in the article were corrected, for example, " In this paper, the influence mechanism of different soil layer properties and different degrees of lining deterioration on tunnel leakage is studied. In order to explore the leakage mechanism of underwater tunnels in different soil layer properties, finite element analysis software is used to establish a calculation model." was changed to" In this paper, the finite element software is used to analyze the homogeneous leakage model of different soil layers and different degrees of lining deterioration.".

" Finally, taking a section of Dinghuaimen tunnel in Nanjing, China as an example, the leakage law and leakage mechanism are verified and analyzed. the result shows:." was changed to" This paper innovatively explores the relationship between the severity of tunnel seepage caused by different lining deterioration and the soil layer properties of the tunnel. Finally, by comparing the field survey data of Dinghuaimin with the leakage law and mechanism summarized by the model, the reliability and feasibility of the model method to explore the leakage mechanism are verified. The model test results are consistent with the project survey data. In this paper, the seepage law and mechanism of underwater shield tunnel are explored and the result shows:".

3. From the current version of the manuscript, it is not clear what the novelty of the paper is. Application of FEM for solving engineering problems is over 50 years old, and the problem of tunnel leakage is known and already investigated. Moreover, authors investigate homogeneous soil model, which is the most simple case in the real conditions.

Thanks for your suggestions. The conclusion and abstract of this paper have been modified to strengthen the description of innovation. The main innovation of this paper is that the feasibility and reliability of the homogeneous leakage model to explore the mechanism of leakage are proved by using the Dinghuaimen tunnel project. We also studied the mechanism of tunnel leakage in different soil layers under different degrees of lining deterioration.

The following section is added to the article :" In this paper, the finite element software is used to analyze the homogeneous leakage model of different soil layers and different degrees of lining deterioration. Through the analysis of tunnel seepage field and seepage velocity under different working conditions to judge the severity of tunnel leakage and explore the mechanism of leakage. This paper innovatively explores the relationship between the severity of tunnel leakage caused by different lining deterioration and the soil layer properties of the tunnel. The reliability and feasibility of using this model method to explore the mechanism of leakage are verified by the field survey data of Dinghuaimen tunnel. Finally, according to the actual working conditions of Dinghuaimen project, the seepage law and mechanism of Dinghuaimen tunnel under complex stratum conditions are discussed. The conclusion is as follows".

4. Authors chose only a single value of soil parameters in Table 1. How about the variations of the parameter values in real conditions? It is common to examine range of values for the soil parameters.

Thanks for your suggestion. The soil parameter value is indeed a range value under actual conditions. The soil parameter values adopted in this paper are the data in the site geological survey report of the Dinghuai Gate tunnel project, so the data used in this paper are the actual soil parameter values of this section, which is determined.

5. Figures 2 (a and b) and 5,  are very vague and should be provided in higher resolution and with higher font size.

Thanks for your suggestion. Figure 2 and Figure 5 are indeed very fuzzy. We have replaced them with higher definition and enlarged the legend font.

6. In (49) authors are calling Theorem 3 – where is Theorem 3? There is no Theorem 3 given in text.

Thank you for your suggestion and the contents of article in (49) have been revised.

7. Regarding Section 4.2 – are there any data on the measured quantity of the tunnel leakage, which should be compared to the output results of the analysis?

Thank you for your suggestion. Now the corresponding part of the result analysis has been added in 4.2. The analysis is also combined with engineering examples to make the result analysis more logical. The additions are as follows.

According to the geological survey report of Dinghuaimen Tunnel, the fine sand layer passed by N-Line is 1273.25m long, accounting for 35.76% of the total length of the north-ern line. The silty clay layer accounted for 449.78m, accounting for 12.63% of the total length. In addition, the upper half layer of 760.64m tunnel is fine sand. the northern line has a total of 1782 ring lining. According to the field statistics since 2019, the number of leakage points and the percentage of section rings in the tunnel can be used to understand the severity of N-line leakage in Dinghuaimen tunnel under different geological conditions. The percentage of the number of seepage points and the number of cross section rings in the fine sand formation is as high as 51.52%. The silty sand layer is 41.76%. Silty clay is 28.23%. The tunnel severity data of different strata investigated in the field are highly consistent with the simulation conclusion in the third part of the paper, which shows the feasibility of the calculation model for the leakage simulation of the Dinghuaimen tunnel.

8. Section Conclusion should be significantly expanded by the numerical data of the presented research, and with clear indication of the novelty of the presented paper in comparison to the previous studies, including guidance for further research.

Thank you for your suggestion. The conclusion has been expanded according to the research content, and the innovation and the next research plan have been clarified as follows:" The velocity inside the lining is much smaller than the velocity inside the soil layer. For example, in the silty clay homogeneous soil layer, the maximum velocity of the soil at the arch foot is 7.043×10-10m/s, and the maximum velocity of the lining with good wa-ter-proof performance is 5.933×10-11m/s." and " The velocity inside the lining is much smaller than the velocity inside the soil layer. For example, in the silty clay homogeneous soil layer, the maximum velocity of the soil at the arch foot is 7.043×10-10m/s, and the maximum velocity of the lining with good wa-ter-proof performance is 5.933×10-11m/s."

The method adopted in this paper is reasonable, and the results reach the expectation, which proves the reliability and feasibility of this modeling method. In the next step, the author will use this method to further explore the leakage mechanism of different leakage forms under different strata, such as the influence of different stratum properties on an-nular seam leakage, longitudinal seam leakage and bolt hole leakage.

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All the comments have been addressed, and the manuscript is suggested to be accepted.

Reviewer 2 Report

Authors provided answers to the questions. Still, I do not see clearly the novelty of the paper. In Abstract authors state ''This paper innovatively explores the relationship between the severity of tunnel seepage caused by different lining deterioration and the soil layer properties of the tunnel. Finally, by comparing the field survey data of Dinghuaimen with the leakage law and mechanism summarized by the model, the reliability and feasibility of the model method to explore the leakage mechanism are verified. The model test results are consistent with the project survey data. '' I do not see any novelty, since authors apply FEM to examine tunnel leaking problem, which is the standard procedure in engineering practice. Therefore, I cannot recommend publication of the presented manuscript.