A Study of Vibration Reduction Effects of TBM and NATM Parallel Construction Methods according to Tunnel Depth and Size

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

First, I would like to thank you for the invitation to review this interesting work. However, some aspects deserve to be highlighted. The comments aim to contribute to the technical and didactic content of the research:

1.     The abstract (The new Austrian tunnelling method (NATM) and tunnel boring machine (TBM) are methods for excavating underground spaces. The NATM construction method has noise and vibration problems, and excavation using TBM has the disadvantage of high initial cost and is limited by ground conditions. A parallel TBM & NATM construction method has been developed to overcome these limitations. However, research on the TBM & NATM parallel construction method is lacking, and it is crucial to identify the applicability of the TBM & NATM parallel construction method in advance by applying it to various ground and blasting conditions. In this study, based on the vibration measurement data of the excavation site using the NATM construction method, the vibration measurement values ​​generated when excavating the top surface using the existing NATM construction method and the TBM & NATM parallel construction method were compared. Lastly, the vibration reduction effect of the two construction methods was analysed according to the tunnel excavation depth and tunnel size through 3D numerical analysis) could contain some numerical value of the results obtained in the search. This helps to draw the reader's attention to the paper.

2.      In the introduction, a good literature review and description of the state of the art were made. However, it is important to make it clear whether the work was a computational and/or experimental simulation of the excavation conditions of the TBM and NATM methods. Another issue is that the chosen excavation methods, TBM and NATM, are conceptually different. In the introduction, it is not clear if both were studied from the same perspective or not.

3.     In the Literature Review it was mentioned that: In this study, 3D numerical analysis was used based on the vibration data measured on the upper ground surface of the site using the NATM blasting construction method to compare the existing blasting method and the TBM & NATM parallel construction method. For the application of the TBM & NATM parallel construction method, the vibration generated during blasting of the upper halves was compared, and the reduction rate of vibration measured on the ground surface according to the excavation depth of the tunnel was analyzed. In addition, based on the experiment conducted in [10], blasting vibration reduction effect due to pilot tunnel sizes for a total of six cases was predicted by modeling pilot tunnels of 3.0 m and 5.0 m excavated using TBM, and 10.0-m, 15.0-m, and 20.0-m using NATM tunnels. I suggest moving this paragraph to the end of the introduction. Still in the literature review item, it would be advisable to better detail both excavation methods, NATM and TBM. For the lay reader in the subject, the revolution caused by both constructive methods can make it difficult to understand the purpose of this research.

4.     In item 3, Field Measurement of Blasting Vibration, I suggest editing Figure 1 about the placement of vibration sensors and the location of blasting. I also suggest improving the description of the caption of Figure 1. Question: how do buildings located in the region of these measurements interfere with the measured values? Could the authors make any comments on this issue?

5.     In the same way as suggested for Figure 1, Figure 2 can have its caption better described.

6.     Although the authors have commented at the end of the work that this study was conducted based on the measurement data of a specific site, and further research on various ground and blasting conditions is needed. Hence, when excavating an underground tunnel, we plan to analyze the impact of blasting according to the groundwater level, and to study a method to protect the TBM backup device from blasting rockslide during the TBM & NATM parallel construction method, they could bring some considerations of the presence of groundwater in the bibliographic review, as this condition of the study is not clear in the text.

7.     In the item3.2. the authors described that: The measurement data comprised blasting data for a total of four days from June 20 to 23, 2022, and the vibration meter was measured every minute for 24 h. The day of blasting at the closest offset to the measurement point was the 21st. On days other than the 21st, vibrations of less than 0.1 cm/s occurred, and the maximum vibration was measured at 0.11 cm/s during blasting on the 21st (Fig. 4). The measured result values were less than 0.2 cm/s, which corresponds to the domestic standard for cultural assets and vibration sensitive structures, and vibration was not felt at the time of measurement (MOLIT, 2016). Tables 1 and 2 show domestic and foreign vibration regulation values. Observation: both in the Figures and in the Tables, absolute numbers are presented without the due uncertainty of these measurements. Likewise, they do not comment on the measurement instruments and their relative uncertainties. In this way, I suggest complementing this information by presenting the equipment used in the same vibration measurements.

8.     Both in Table 1 and Table 2, I suggest improving the information in the caption by adding more information about the property that is the objective of the standard used as a reference for the considered parameters.

9.     It is known from the literature that: The concept of the New Austrian Tunneling Method (NATM) is that surrounding rock plays a certain role in tunnel support. The solution should be to find the correct relationship between shaft lining thickness and rock strength, which is related to the interaction between the surrounding rock and concrete lining. The plane strain mechanics model is introduced to calculate lining thickness. Shaft lining design of Cixi Colliery in China is completed with the mechanics-based method proposed in specific study. The lining design is verified through numerical simulation and field monitoring. The simulation results show that the maximum mises stress is located at the inner edge of the shaft lining. The increase of lining thickness cannot effectively reduce concrete grade. The monitoring results indicate that lining design, thickness of 900mm with C60 concrete, is safe and reliable in the shaft over 1000 meters. This analytical design method can be well referenced in similar deep shaft project. Question: The authors could comment on the influence of the "shaft" in this study?

10.  In item 4, Numerical Analysis According to Tunnel Depth, the authors mentioned that: we used the FLAC 3D numerical analysis program, a widely verified program developed by ITASCA as a 3D continuum analysis program for mechanical analysis of rocks, soil, and structures. FLAC 3D is a program with strengths in dynamic analysis based on time-do-main analysis techniques as well as continuum analysis, discontinuity analysis, and mechanical-hydraulic coupling analysis considering fluid flow [14]. I suggest that the authors build a legend with the main abbreviations of names used in the work.

11.  On the other hand, I also suggest that the authors highlight what are the main limitations of the computational simulation model employed (FLAC 3D program) and that eventually can lead to values that are very different from the experimental results (field).

12.  The Figures 5, 6 e 7 show, respectively, Figure 5. Numerical modeling equivalent to field conditions, Figure 6. Top surface excavation numerical analysis modeling based on field conditions and Figure 7. Numerical analysis modeling of top surface excavation using TBM & NATM parallel construction method. It is clearly observed that the surfaces are delimited by meshes that represent a series of geometric figures. Question: how were these geometric figures chosen? What are your characteristics?

13.  In the item 4.1.2. Blasting Load Calculation, it was established that: In this study, only the tamping was calculated here to interpret the same as the field conditions. For application as a dynamic load, the time history of vibration generated by blasting must be considered as well. As for the blasting load time history, the hysteresis curve of [16] was mainly used, and the calculated time history curve is shown in Fig. 8. In this analysis, the equivalent blasting loads for the charge holes (centre cut hole A, centre cut hole B, and expanded hole) were calculated as 150.58 kg/cm2 , 191.65 kg/cm2 , and 119.78 kg/cm2 , respectively [17]. Moreover, referring to [18], the duration was set as 0.001 s, and the equivalent frequency and ground damping ratio were 830 Hz and 1.0%, respectively. Question: Could the authors comment on what are the implications of variations in the equivalent frequency and ground damping ratio on the simulation results?

14.  I suggest that the captions of Figures 8, 9 and 10 be revised and implemented in terms of what the curves presented in these same figures refer to (parameters).

15.  In item 4.2, analysis of results, more specifically in 4.2.1. Comparison of Field Measurement Data and Numerical Analysis Results, the calculated measured results and those measured in the field are presented. Suggestion: once again, I note that the uncertainties of measurements and equipment used in the field to raise these parameters can directly influence this analysis. Therefore, I ask that you consider taking these uncertainties into account.

16.  The same observation from the previous topic applies to item 4.2.2. Numerical Analysis Results According to Tunnel Depth.

17.  In item 5. Numerical Analysis According to Tunnel Size, I suggest editing Figure 18. Cases of analytical modeling according to size of NATM tunnel and TBM pre-excavation tunnel.

18.  In the conclusions of the work, the first paragraph (The purpose of this study was to minimise the effect of NATM widening blasting on the pilot tunnel and TBM surroundings by using a protective shield during TBM & NATM widening parallel excavation. Accordingly, after comparing the numerical analysis results 363 under the same conditions with the actual field measurement data, half section blasting was modelled and compared with the results using the TBM & NATM parallel construction method. In addition, the effect according to the tunnel excavation depth and NATM and TBM excavation cross-sectional size was compared and analysed. The main results are as follows) could be moved to the objective item, which would make it easier for the reader to better understand the study developed in this work.

Comments for author File: Comments.docx

Author Response

The authors deeply appreciate all the invaluable comments from the reviewers. These comments will be carefully considered in the manuscript.

Author Response File: Author Response.pdf

Reviewer 2 Report

Throughout the manuscript, it is found that the authors point out the construction characteristics of NATM and TBM. Then, according to the vibration measurement data, the existing NATM construction method and the TBM & NATM parallel construction method were compared. Finally, the vibration reduction effect of different excavation methods and construction conditions was studied by the results of numerical analysis. I think the research has a guiding significance for the development of underground space. But there are still some problems in the manuscript. It is suggested to be accepted after minor revisions.

1.      There is a lack of literature support in the introduction, which should be added. It is recommended to incorporate the literature review into the introduction, where there are repetitions (for example, line 83-85).

2.      There are language inaccuracies in the manuscript, please review the manuscript to improve English. For example, short extension (line 40); nature (line 182), and so on.

3.      The font and title of all the figures should be consistent and clear to add beauty. Simple figures together, such as Figures 1 and 2. Please check and modify.

4.      The specific content of model parameters is missing, which is suggested to be supplemented in the manuscript (Section 4.1.1).

5.      For international journals, consistent international unit standards should be use (table3).

6.      There are many ambiguities in the manuscript. For example, “at the rear and the excavation surface of the TBM”, what is the rear; What do 1 and 2 in Figure 5 refer to; What does A, B and expanded stand for (line 205), and so on.

7.      In lines 203-207, blasting load calculation details should appear to show the authenticity of the manuscript content.

8.      The discussion of the results in Section 5 is relatively simple. The purpose of this study should then be further discussed in conjunction with the results of Sections 4 and 5.

Author Response

The authors deeply appreciate all the invaluable comments from the reviewers. These comments will be carefully considered in the manuscript.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript studies numerical modeling results of tunnel construction in urban regions through NATM blasting and NATM TBM. The comparison is not fair as blasting may be compared with improved blasting methods and not with the mechanical excavation methods. The paper is weak, it needs extensive improvement before it can be considered for publication. I urge the authors to conduct an in-depth study on the topic which may be reflected in the re-submitted manuscript. Consider my general comments in the attached document.

Comments for author File: Comments.pdf

Author Response

The authors deeply appreciate all the invaluable comments from the reviewers. These comments will be carefully considered in the manuscript.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

No further comment.

Author Response

Thank you for your comment.

Reviewer 2 Report

This manuscript study the Vibration Reduction Effect of TBM & NATM Parallel Construction Methods by change tunnel depth and size. It is an interesting workd. Before receved it show further response  for the following questions:

1. The quality of figure should be imporved, such as Fig.3. It is hard to see the number in the figure.

2. Why not draw the lines, points in figures by color?

3. Is there any experimental data to support the correctness of the numerical simulation results?

Author Response

Thanks for the reviewer's comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors did a lot of hard work but the direction does not seem right. The title is not an attractive one for the audience. The paper has been improved but more work is needed. The novelty part needs to be explained in the manuscript as well. The modifications claimed in the author's reply do not reflect much on the manuscript. Do the changes clearly in the manuscript.

Author Response

Thanks for the reviewer's comments.

Author Response File: Author Response.pdf