Numerical Stability Analysis of Large Section Tunnels Using the Double-Side Heading Method: A Case Study of Xiamen Haicang Evacuate-Channel

Round 1

Reviewer 1 Report

1.      The authors have studied the large cross section tunnel; however, the size is not included in the abstract.

2.      Split lengthy paragraphs and sentences for better understanding.

3.      Include the FLAC modelling results having contours description.

4.      Excavation sequence not only affect the stability in large tunnel section, but have a dominant role in small scale tunnel stability. For reference, the authors can refer the following article;

Numerical evaluation of new Austrian tunneling method excavation sequences: A case study

5.      Geological section of the study area is missing.

6.      How the material properties were selected?

7.      Discuss the relaxation sequencing in numerical models at each step of construction.

8.      How the authors validated their model?

9.      Conclusion must be concise and be based on the results of this study.

10.   Figure 1 is labeled extensively. Include the information’s which are relevant to this study.

11.   Show the project location from the country map.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

 Reviewer’s introduction

The impacts of the excavation sequencing, second primary lining support period, temporary support dismantling, and supplementary lining support time of the double-side heading method on large section tunnel stability were investigated in this paper. The tunnel of Xiamen Haicang Evacuate-channel served as the case study for this research. Three excavation patterns were investigated. The first pattern involves excavating from the right to the middle of the tunnel, followed by the left side. This arrangement prevents lining deformation and regulates horizontal displacement at the tunnel's mid-arch. The second pattern proposes beginning excavation from the tunnel's centre and working outwards towards the tunnel's wings. This arrangement preserves the carrying capacity of the concrete towards the back of the arch. The third pattern implies that excavation begins at the tunnel's two ends and moves towards its centre. As a result, it keeps the concrete at the arch waist. The other three parameters, which are second primary lining support time, temporary support disassembly time, and secondary lining support time, have varying effects on the stress and deformation of rock and support structures. As a result, these characteristics are site-specific and must be verified throughout the construction process. This study can be used as a guide for designing the double-side heading approach for huge section tunnels.

 The article is interesting. However, it is lengthy and sometimes confusing. Before considering publication, extensive review is required.

 

Reviewer’s comments

1.       The title should reflect the scope of the research. It is suggested to read as: “Numerical stability analysis of large section tunnels using the double-side heading method: a case study of Xiamen Haicang Evacuate-channel”.

2.       Line 134 should be removed; it is duplicated on Line 131.

3.       What is the tunnel diameter?

4.       Line 160: Give the definition of C3D8R (e.g., Eight-node brick element with reduced integration).

5.       What are the boundary conditions (BCs) of the model?

6.       Citation of Table 2.

7.       Table 3: excavation sequences are unclear.

8.       What is the size (X. Y. Z) for each excavated part at once.

9.       Table 3: it is suggested to rewritten as: pattern, step 1 to 9 (or 7 steps) in case pattern II, dimensions. More steps should be added to include the support system.

 

Excavation Step or sequence	Modelled Pattern (See Fig. 3)
	I (Right, Left, Centre)	Block Size, (X. Y. Z) Or in  m3	II (Right + Left, Centre)	Block Size, (X. Y. Z) Or in m3	III (Centre, Right, Left)	Block Size, (X. Y. Z) Or in  m3
Step 1	Part 1		Parts 1+3		Part 5
Step 2	Part 2		Parts 2+4		Part 6
Step 3	Part 3		Part 5		Part 7
Step 4	Part 4		Part 7		Part 8
Step 5	Part 5		Part 6		Part 1
Step 6	Part 6		Part 8		Part 2
Step 7	Part 7		Part 9		Part 3
Step 8	Part 8				Part 4
Step 9	Part 9				Part 9

 

10.   The extent of yielding zones following each excavation step could be evaluated and compared to the anchorage length of rock (bolt) support or liner thickness.

11.   Fig. 5: Tunnel section only, zoomed in.

12.   At each excavation condition, what is the maximum vertical displacement of the rock mass surrounding the tunnel section?

13.   Line 234: “three stages were divided by two red vertical lines”. The two red lines are missing to identify the three-step construction sequence.

14.   Is there a surface settlement threshold at which serviceability or tunnel performance will be regarded unstable in relation to the excavation condition?

15.   According to Fig. 8, what is the maximum deformation that occurs at both the primary and temporary linings under varied excavation conditions?

16.   Does Fig. 9 show the vertical settlement of primary and temporary lining at various stages of construction?

17.   Why don't you pick four reference points (e.g., two points on the tunnel sides for horizontal displacement, one point at the back/roof, and one point on the tunnel floor for vertical displacement) to monitor the deformations with respect to the excavation sequence?

18.   Line 302: t arch?

19.   Fig. 11: Why is there such a sharp increase and decrease in horizontal displacement between steps 8 and 11?

20.   According to Figs. 12 & 13: What are the maximum vertical stresses that can develop at the primary and temporary linings under different excavation conditions?

21.   How was temporary and primary support simulated in FLAC3D?

22.   Figs. 16 & 17: Please zoom in exclusively on the tunnel section.

23.   Describe the magnitude of displacements (e.g., horizontal, and vertical) of nearby rock mass for the two modelled secondary support scheduling conditions?

24.   Line 404: Why is condition 2 effective at controlling rock deformation?

25.   For the two simulated scenarios (e.g., different support timing), what are the vertical stresses on the second primary and temporary lining?

26.   Fig. 20: horizontal stress of second primary support NOT vertical stress.

27.   Lines 440-441: secondary lining was usually carried out approximately 50 m after the primary lining was applied. Do you mean 50 cm?

28.   Figs. 23 and 24: What are the maximum horizontal lining displacements after removing and reinstalling the second temporary support?

29.   The results should bring the various parametric scenarios to a close. For example, based on the facts, it can be concluded that the excavation sequence of condition 2, is the most conservative as it gives least stresses (…Pa), deformation (…m). In terms of support time, it is most advised to install primary lining first, followed by secondary temporary lining because ….

Comments for author File: Comments.docx

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

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Reviewer 2 Report

Thank you for your thorough revision, authors. Every single comment has been addressed and revised. I have no other questions or concerns about this article.