Seismic Stability of Dual Tunnels in Cohesive–Frictional Soil Subjected to Surcharge Loading

Round 1

Reviewer 1 Report

Carrying out workings in the rock mass, which is susceptible to dynamic loads, is extremely difficult due to the multiplicity and variability of mainly geological conditions. Therefore, the proposed issue is important due to the stability of tunnel workings. Numerical research is interesting both in terms of science and technology. Below are some comments and suggestions:

1. In the introduction, please write that the assessment of the stability of underground workings has been performed for many years using numerical methods. In particular, they are important for a rock mass for which numerous excavations are made, such as in the case of room and pillar methods, in which the destructive stresses in the roof are summed up (doi.org/10.3390/en13143564).
2. In the second Chapter, it should be written what values ​​an earthquake acceleration factor kh to the soil domain takes.
3. Line 76, check the entry "FELA".
4. For Figure 2, it should be written whether the mesh compaction directly between tunnels is performed automatically or whether the number of divisions can be determined.
5. In the fourth Chapter, it is necessary to write in a few sentences what the shock energy in kJ can be simulated corresponds to the data presented in Figure 3.
6. Figures 9-12, it should be added units, legend description and indicated the maximum ranges.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The article addresses an important topic of the seismic stability of dual tunnels in cohesive-frictional soil subjected to surcharge loading, which is appreciated. The study include the numerical analysis of the sensitivity analyses of series of influential factors, including the distance between the dual tunnels, the depth of the tunnels, the cohesion, internal friction angle, unit weight of the soil and the seismic acceleration factor, were presented. The reviewer appreciates the efforts done in this paper, however, the reviewer has some concerns regarding the introduction, description of methods, numerical modelling, results and conclusions. The English language should be improved for Native Speaker. In my opinion this paper should be reject.

Other comments.

1. Please explain the differences between your article and this article https://doi.org/10.1016/j.compgeo.2012.12.008.
2. Introduction is really poor and should be improved of papers about the seismic analysis based on experiment and numerical analysis (made of RC, soil-steel tunnel etc).
3. The aim of this research is not clear. What is new?
4. The numerical model should be detailed description. Please shown numerical model with boundary condition, seismic load etc.
5. Please add the properties of soil and seismic load.
6. The reviewer has concerns about the correctness and accurate of these results, they are true?
7. Please add in numerical analysis additional seismic records (minimum 3 records are requirement according to Eurocode 8, Canadian and American Code) e.g. El Centro, Loma Prieta, Ancona, Fukushima etc.
8. Conclusion is really poor. Please improve it.
9. Please used the template of this journal (https://www.mdpi.com/journal/applsci/instructions).

And the end I hope that my comments will be helpful for the authors.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

there are some weaknesses through the manuscript which need improvement. Therefore, the submitted manuscript cannot be accepted for publication in this form, but it has a chance of acceptance after a major revision. My comments and suggestions are as follows:

 

1- Abstract gives information on the main feature of the performed study, but some details about the obtained results must be added.

2- Authors must clarify necessity of the performed research. Objectives of the study must be clearly mentioned in introduction.

3- The literature study must be enriched. In this respect, authors must read and refer to the following papers: (a) FE analysis: https://doi.org/10.1016/j.eml.2020.100692 (b) Urbanization: https://doi.org/10.1016/j.uclim.2021.100961 and other research works.

4- It would be nice, if authors could add some figures to show concept and some conditions.

5- The main reference of each formula must be cited. Moreover, each parameters in equations must be introduced. Please double check this issue.

6- Input parameters of the numerical simulation must be presented in a table.

7- Details of internal friction angle on the failure mechanism must be explained.

8- Standard deviation is the presented curves must be discussed. In addition, error in calculation must be considered and discussed.

9- In its language layer, the manuscript should be considered for English language editing. There are sentences which have to be rewritten.

10- The conclusion must be more than just a summary of the manuscript. List of references must be updated based on the proposed papers. Please provide all changes by red color in the revised version.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

Here are comments that the authors could consider after I reviewed this manuscript:

• Line 25, this “cannot” is too strong. Revise
• Lines 30-50, here, the authors reviewed papers saying who did what, which is not useful I think. Provide insights into those reviewed studies.
• Line 51, "few" here means there have. if so, please review and introduce, if not say "no", so overall, the novelty is not clear to me.
• so, Fig. 1 in this study, no rock considered? if so, wonder the cases only have soils where the tunnel will be built.
• Line 67, not sure how far the tunnel is from the lateral BC.
• 1 this is simga_s used to simulate the overlying?
• 2, is this lambda a function? why minimize a variable?
• 2, are you looking at plane strain or plane stress here? wonder if 2D is reasonable to use. 3D might be better.
• Line 116, give a number, how large.
• 3, need to explain why at high S/D values, this study was underestimated.
• Line 149, “it reasons” weird to use this, use because
• Line 283, I think it is a bit difficult to understand the failure patterns mentioned in Tables 1-4
• Line 300, again, why different having this deviation.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Thank you for your improving. In my opinion this paper have still a one big problem of numerical model (boundary condition), thus in my opinion this paper should be reject.  Below you can see more detail comments:

 

(4) The numerical model should be detailed description. Please shown numerical model with boundary condition, seismic load etc

Authors’ reply:

Thanks for the reviewer’s suggestion. We have described the boundary condition and seismic load in problem definition. The bottom surface and the lateral surfaces are fixed in all directions, the top surface is free, and the seismic load is applying to the soil domain. In addition, it should be noted that the AFELA code used in this study is developed by the authors. We haven’t developed a visual interface for this code therefore, numerical model only can be established by command stream. So we feel sorry that we cannot show a more detailed model including the information about the boundary condition and seismic load.

Reviewer reply:

Thank you for your comments. Your assumption of boundary condition is wrong. In seismic analysis “The bottom surface and the lateral surfaces are fixed in all directions” are not acceptable! Very important is wave propagation, thus for these results are not true. In seismic excitation we can observed the surface move (soil). In the case when the fixed boundary condition was used the surface move is not possible. So, if you cannot show the boundary condition from numerical analysis the Reviewer cannot verified these results.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Authors have addressed the comments, and answered the questions, but reference format must be checked:

Author's Last Name, First name. Article title. Journal Title, Year, Volume Number, Page Numbers.

The revised version of your manuscript appears to be suitable for publication.

 

 

Author Response

Thanks for the reviewers kind suggestion. We have updated the reference format by the reviewer's guidance. Thanks for your time and patience again.

Reviewer 4 Report

Here are comments that the authors could consider after I reviewed this manuscript:

1) Eq. 2, is this lambda a function? why minimize a variable? Very confused, here the authors say lambda is the soil unit weight, but in the paper, line 112, lambda is the load multiplier.

2) Fig. 2, are you looking at plane strain or plane stress here? wonder if 2D is reasonable to use. 3D might be better. First, the authors need to clarify your assumption that infinite length was assumed. BTW, do you have infinite tunnel length? You assumed, so Not regarded, assumed.

3) Fig. 3, need to explain why at high S/D values, this study was underestimated. In fig.3 you compared your results with literature results, at high S/D values, you results were underestimated compared to the literature results, need to explain.

4) Line 300, again, why different having this deviation. Again, in line 343, you mentioned you had 7% relative error, why you have this error, what is the reason for causing this, need to explain.

Author Response

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Author Response File: Author Response.docx

Round 3

Reviewer 2 Report

Dear Authors, thank you for your improving and explanations. I am afraid I cannot agree with the Authors explanations. In soil we haven't fixed surface i.e. please improve or change in the text this name. In soil fixed surface is impossible, thus you can name this boundary condition as "rigid halfspace" or something like "hinge support".In my opinion this is big error in this article and it can be significant impact of the occured results. In addition please check all paper with references because of is carelessly preparted (template, language mistakes (misspelling)). In opinion of Reviewer this paper should be subjected major revision.

I hope that my comments will be helpful for the Authors.

Author Response

Dear reviewer, thanks for your kind suggestion. It helps us a lot, and we have corrected the boundary condition by your guidance. Owing to this manuscript has been accepted by all of other reviewers, the text of the whole manuscript would be checked and polished by the paid MDPI editing service if you can kindly accept it. I hope that the final edition will satisfy you.

Reviewer 4 Report

no comments any more

Author Response

Dear reviewer, thanks for your patience and time!

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The paper presents an interesting study performed by a finite element limit analysis code to investigate the seismic bearing capacity of dual tunnels in cohesive-frictional soil subjected to surcharge loading and seismic action.

The paper is interesting because it deals with the interaction between two tunnels and, until now, there are only few information about the seismic stability of dual tunnels in c-φ soil.

But no geotechnical data is specified, so the geotechnical characterization of the involved soil has to be added, because an accurate soil geotechnical characterization is a key-aspect for a realistic evaluation of the tunnel-soil behavior.

The following corrections have to be made in the text.

Introduction: 

As for the references about numerical methods investigating the seismic behavior of a single tunnel, the following recent works can be added:

• Wang, Z.; Gao, B.; Jiang, Y.; Yuan, S. Investigation and assessment on mountain tunnels and geotechnical damage after the Wenchuan earthquake. China Ser. E Technol. Sci. 2009, 52, 546–558.
• Abate, G., Grasso, S., Massimino, M.R. The role of shear wave velocity and non-linearity of soil in the seismic response of a coupled tunnel-soil-above ground building system. Geosciences (Switzerland), 2019, 9(11), 473.

As for experimental studies, the following works can be cited, such as:

• Lanzano, G.; Bilotta, E.; Russo, G.; Silvestri, F.; Madabhushi, S.P.G.; Madabhushi, S.P.G. Centrifuge Modeling

of Seismic Loading on Tunnels in Sand. Geotech. Test. J. 2012, 35, 104348.

• Abate, G.; Massimino, M.R.; Maugeri, M. Numerical modelling of centrifuge tests on tunnel-soil systems. Bull. Earthq. Eng. 2015, 13, 1927–1951.

Par. 2 “Problem definition”: 

Row 72: the symbol of internal friction angle is missing

Rows 72-73: why do the Authors chose these boundary conditions (“The bottom surface and the 72 lateral surfaces are fixed horizontally and vertically simultaneously”)?

Par. 3 “AFELA model”: 

Row 95: the symbol of the load multiplier is missing.

Row 124: how did the Authors characterize the soil? Which values of the parameters of the Mohr-Coulomb criterion were adopted? The description of the model is missing of the soil characterization. No geotechnical data is specified. The Authors should add this important information.

Par. 4 “Results and discussions”: 

Row 146: a symbol regarding Fig. 4 is missing. The same is in the caption of Figure 4.

From row 174 to row 184 many symbols are missing.

For a clearer understanding of Figure 5, the same scale should be adopted in the x-axis (i.e. the S/D values) and, if possible, in the y-axis (i.e. the Ncs values).

A symbol is missing in the caption of Figure 5.

Row 192: a symbol is missing, regarding the comments to Figure 6. The same is in the caption of Figure 6.

For a clearer understanding of Figure 6, the same scale should be in the y-axis (i.e. the Ncs values). Moreover, it is not convenient that Figure 6 is divided into two pages.

From row 205 to row 215 many symbols are missing.

For a clearer understanding of Figure 7, the same scale should be in the x-axis (i.e. the f values) and in the y-axis (i.e. the Ncs values). Moreover, the caption of Figure 7 should be insert in the same page of the Figure.

Figure 7: a symbol is missing in the caption

From row 236 to row 237 two symbols are missing.

For a clearer understanding of Figure 8, the same scale should be in the y-axis (i.e. the Ncs values).

Figure 8: a symbol is missing in the caption

Par. 5 “Failure mechanisms”: 

Row 246: a symbol is missing, regarding the comments to Figure 9.

Figure 9: It is necessary to specify “a”, “b”, “c” and “d” in the figure. Moreover, it is not convenient that Figure 9 is divided into two pages.

Figure 9: a symbol is missing in the caption.

Figure 10: It is necessary to specify “a”, “b” and “c” in the figure.

Figure 10: a symbol is missing in the caption

Row 278: a symbol is missing, regarding the comments to Figure 11.

Figure 11: It is necessary to specify “a”, “b”, “c” and “d” in the figure. Moreover, it is not convenient that Figure 11 is divided into two pages.

Figure 11: a symbol is missing in the caption.

From row 300 to row 302 two symbols are missing.

Figure 12: It is necessary to specify “a”, “b”, “c” and “d” in the figure. Moreover, it is not convenient that Figure 12 is divided into two pages.

Figure 12: symbols are missing in the caption

Par. 6 “Design tables”: 

It is not convenient that Tables 1-4 are divided into two pages.

Par. 7 “Conclusions”: 

Row 335: a symbol is missing.

Row 345: a symbol is missing.

 

Reviewer 2 Report

There are lots of spelling and grammatical mistakes. 
Validation of the methodology is missing
 The novelty of the study is also in question.