Seismic Damage Analysis of Box Metro Tunnels Accounting for Aspect Ratio and Shear Failure
Round 1
Reviewer 1 Report
This paper presented the research on assessment of seismic damage of box tunnels according to aspect ratio and shear failure by using commercial software SAP2000. The numerical results are genuine, initiative and practically useful, in particular for enhancing the design and analysis of multi-box tunnels. The conclusions are sound, inclusive and convincing. The paper was well prepared, including table and figures. The paper is technical and provides much new information so it is worthwhile to publish. However, there are some technical, editorial and grammatical issues which affect the reading and understanding and need to be further addressed and corrected before the paper can be published.
Technical and editorial issues
1. In Line 117 and other places, the definition for the term “Vs” is not given until Conclusions. This should be mentioned earlier.
2. In all figures, it is worthwhile to move all the legends out of the figures and use them as subtitles.
3. In Line 135 and other places, you used the term “columns”. Does this mean internal walls because you used 2D models? You didn’t explain this clearly. If this is true, you should revise all “column” to “internal wall”.
4. The rest typos and editorial/grammatical mistakes are clearly marked in the paper to help the authors revise the paper.
Comments for author File: 
Comments.pdf
Author Response
1. In Line 117 and other places, the definition for the term “Vs” is not given until Conclusions. This should be mentioned earlier.
► The definition of Vs (shear wave velocity) was specified in the line 89 (section 3). The second sentence of the second paragraph in section 3 was updated in the revised manuscript, as follow.
“Five uniform site profiles with shear wave velocities (Vs) of 50, 100, 200, 300, and 400 m/s are used”.
2. In all figures, it is worthwhile to move all the legends out of the figures and use them as subtitles
► The figures were updated in the revised manuscript.
3. In Line 135 and other places, you used the term “columns”. Does this mean internal walls because you used 2D models? You didn’t explain this clearly. If this is true, you should revise all “column” to “internal wall”.
► The term “columns” used in this study is represented the internal columns in the multi-box tunnels (double and triple tunnels). Because these structural elements were designed with an equal spacing between them, therefore, it is called “column”. The authors also described this column in the section 2 of the manuscript.
4. The rest typos and editorial/grammatical mistakes are clearly marked in the paper to help the authors revise the paper.
► The authors have revised all the mistakes throughout the manuscript.
Reviewer 2 Report
This study conducts a series of seismic damage analysis for several tunnel structure configurations, and shows failure mechanisms and damage indices.
Damage mechanisms and indices for tunnel configurations shown in this study may be of interest to South Korean practitioners of tunnel design.
However, I am not sure of the generality of the conclusions as it is drawn from computation of only a limited configuration of tunnels following South Korean design standards.
As a scientific paper, I would like to have seen analyses and discussion of the generality of the conclusions (e.g. will the same damage mechanism or damage indices occur if the tunnel beam or column configuration is changed for another design standard?)
Author Response
This study conducts a series of seismic damage analysis for several tunnel structure configurations, and shows failure mechanisms and damage indices.
Damage mechanisms and indices for tunnel configurations shown in this study may be of interest to South Korean practitioners of tunnel design.
However, I am not sure of the generality of the conclusions as it is drawn from computation of only a limited configuration of tunnels following South Korean design standards.
As a scientific paper, I would like to have seen analyses and discussion of the generality of the conclusions (e.g. will the same damage mechanism or damage indices occur if the tunnel beam or column configuration is changed for another design standard?)
► The purpose of this study was focused on the investigation of damage mechanisms of box tunnels in South Korea. The selected tunnel shapes are typical for cut-and-cover subway tunnels in the country. Also, a wide range of surrounding soil conditions/stiffness was considered in this research. A comparison of the present R-F relationships and the published curves, which were developed for box tunnels over the world, was conducted, highlighting that the model used in this study was in line with the previous works (see Fig. 4). Additionally, a comparison of updated damage indices and previous indices was presented in Table 1. Therefore, the findings of this study can be readily applied for similar box tunnel configurations located in different soil stiffness regardless using South Korean design standards.
Reviewer 3 Report
In this paper the concrete damage mechanisms of the box tunnels investigated.
Please consider the following comments. The revisions in the paper must be highlighted for the easier navigation:
+ please remove citation from abstract.
+ fix the order of the citation and follow the journal template for citation and referencing.
+introduction to the seismic damage analysis and box metro tunnels are weak.
+clear the state of the contribution and organization of the paper in the last two paragraphs of the paper.
+literature review is not adequate. Please add at least 10 relevant references, search MPDI data base as well for the relevant papers.
+elaborate on results and explain the figures more.
+make the conclusions shorter and more efficient.
Author Response
1. Please remove citation from abstract.
► We removed the citation from the abstract. The abstract was updated in the revised manuscript.
2. Fix the order of the citation and follow the journal template for citation and referencing.
► The order of the citation was updated. Also, the authors corrected all references according to the journal template.
3. Introduction to the seismic damage analysis and box metro tunnels are weak.
► An introduction to the seismic damage analysis and box metro tunnels was added into Section 1 (Introduction). The following paragraphs were also updated in the revised manuscript.
“Seismic damage analyses of box tunnels can be performed by using experimental or/and numerical methods. Zou et al. [12] conducted a series of numerical simulations and a verified shaking table test to investigate the seismic response and damage of a multi-story subway station. Then, they defined four damage states based on the damage parameter, which depends on the ductility of structural members. Chen et al. [13] studied the effect of pulse-like ground motions on seismic responses of a multi-story subway station using shaking table test. Based on experimental results, they pointed out that the center columns were sensitive structural members, which can be suffered a significant vulnerability under earthquake excitations. Chen et al. [14] investigated the effects of axial compression ratio of interior columns on failure modes and damage patterns of a multi-story underground structure using a series of numerical pushover analyses. Recently, some studies employed numerical approach to analyze the seismic failure and collapse mechanism of Daikai subway station [15-20]. They both gave a mutual conclusion that the structure was completely collapsed due to an extreme failure and loosing load capacity of the center column. Furthermore, an extensive summary of previous studies on the seismic analysis of tunnels are presented by Hashash et al. [1] and Lee et al. [21]. The previous studies dealt with a specific tunnel and soil stiffness. A wide range of tunnel shapes and soil conditions is needed to consider in seismic damage analyses.
The dynamic analysis is recognized to provide the most realistic estimate of the seismic response of tunnels. However, it was reported that the difference between the dynamic and pseudo-static analyses is insignificant [22,23]. Therefore, the numerical pseudo-static method is widely used in practice and also in research [1,12,22-36].”
4. Clear the state of the contribution and organization of the paper in the last two paragraphs of the paper.
► In the last two paragraphs of the paper, the authors would like to show the effects of shear failure of the interior column and aspect ratio on the damage index (DI) and then update the DIs that proposed in our previous study (Lee et al. 2016). It is again noted that the previous study (Lee et al. 2016) did not consider a shear failure model of the tunnel linings and a variation of aspect ratio of tunnels. The authors re-organized and improved Section 4.3 for a clarity. Section 4.3 was intensively updated in the revised manuscript.
5. Literature review is not adequate. Please add at least 10 relevant references, search MPDI data base as well for the relevant papers.
► The authors have updated more relevant references (12 journal papers) in the revised manuscript. A detailed introduction to seismic damage analysis of box metro tunnels was also added in Section 1. Following references were newly added in the paper.
- Roy, N.; Sarkar, R. A Review of Seismic Damage of Mountain Tunnels and Probable Failure Mechanisms. Geotechnical and Geological Engineering 2017, 35, 1-28, doi:10.1007/s10706-016-0091-x.
- Chen, Z.; Chen, W.; Li, Y.; Yuan, Y. Shaking table test of a multi-story subway station under pulse-like ground motions. Soil Dynamics and Earthquake Engineering 2016, 82, 111-122.
- Chen, Z.; Chen, W.; Zhang, W.; Lou, M. Effects of Axial Compression Ratio of Central Columns on Seismic Performance of a Multi-Story Underground Structure. International Journal of Computational Methods 2016, 13, 1641014.
- Li, W.; Chen, Q. Seismic performance and failure mechanism of a subway station based on nonlinear finite element analysis. KSCE Journal of Civil Engineering 2017, 1-12.
- Ma, C.; Lu, D.-C.; Du, X.-L.; Qi, C.-Z.; Zhang, X.-Y. Structural components functionalities and failure mechanism of rectangular underground structures during earthquakes. Soil Dynamics and Earthquake Engineering 2019, 119, 265-280.
- Lu, C.-C.; Hwang, J.-H. Nonlinear collapse simulation of Daikai Subway in the 1995 Kobe earthquake: Necessity of dynamic analysis for a shallow tunnel. Tunnelling and Underground Space Technology 2019, 87, 78-90.
- Sayed, M.A.; Kwon, O.-S.; Park, D.; Van Nguyen, Q. Multi-platform soil-structure interaction simulation of Daikai subway tunnel during the 1995 Kobe earthquake. Soil Dynamics and Earthquake Engineering 2019, 125, 105643.
- Liu, J.; Liu, X. Pushover analysis of Daikai subway station during the Osaka-Kobe earthquake in 1995. In Proceedings of 14th world Conference on earthquake engineering, Beijing, China; pp. 12-17.
- Liu, T.; Chen, Z.; Yuan, Y.; Shao, X. Fragility analysis of a subway station structure by incremental dynamic analysis. Advances in Structural Engineering 2016, 1369433216671319.
- Nguyen, D.-D.; Park, D.; Shamsher, S.; Nguyen, V.-Q.; Lee, T.-H. Seismic vulnerability assessment of rectangular cut-and-cover subway tunnels. Tunnelling and Underground Space Technology 2019, 86, 247-261.
- Xu, Z.; Du, X.; Xu, C.; Jiang, J.; Han, R. Simplified equivalent static methods for seismic analysis of shallow buried rectangular underground structures. Soil Dynamics and Earthquake Engineering 2019, 121, 1-11.
- Huh, J.; Tran, Q.H.; Haldar, A.; Park, I.; Ahn, J.-H. Seismic Vulnerability Assessment of a Shallow Two-Story Underground RC Box Structure. Applied Sciences 2017, 7, 735.
6. Elaborate on results and explain the figures more.
► The authors added more discussions on the results and associated figures in Section 4. Specifically, section 4.3 was significantly improved for a better understanding.
7. Make the conclusions shorter and more efficient.
► The conclusions were re-written more shortly and concisely.
Round 2
Reviewer 2 Report
Thank you for your comments.
I prefer to have such discussion explicitly put into the manuscript such that the readers can understand easier.
Author Response
The authors are again so grateful to the reviewers and editors for their insightful comments. We believe that the comments have much enhanced the quality of our paper.
The detailed responses to the comments are described in the following. They are written in the red font.
Reviewer 2
I prefer to have such discussion explicitly put into the manuscript such that the readers can understand easier.
► The following paragraph was newly added at the end of Section 4 in the manuscript.
“The purpose of this study is focused on the investigation of damage mechanisms of one-story box tunnels in South Korea. The selected tunnel shapes are typical for cut-and-cover subway tunnels in the country. Also, a wide range of surrounding soil conditions/stiffness is considered in this research. A comparison of the present R-F relationships and the published curves, which were developed for worldwide box tunnels, is conducted, highlighting that the model used in this study is in line with the previous works (see Figure 4). Additionally, a comparison of updated damage indices and previous indices is presented in Table 1. Therefore, the findings of this study can be readily applied for similar box tunnel configurations located in different soil stiffness regardless using South Korean design standards.”
