A Study on the Maximum Scour Depth of River-Crossing Tunnels
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsReview of "A study on the maximum scour depth of river-crossing tunnels". The manuscript deals with a two-dimensional hydro-sediment mathematical model to investigate the characteristics of bedrock maximum scouring changes. While the analysis is well-conducted and the writing is clear and engaging, here are some suggestions and comments that need to be addressed to ensure the manuscript is publishable.
1. Introduction: 1st paragraph: How do construction costs change with depth of tunnel? Is there a trade-off between depth and economic feasibility?
2. I recommend strengthening the literature review with recent references.
3. Section 2.2: The authors need to revise this section taking into consideration of Governing Equations. The Hydrodynamic Equations (that capture the movement of water, considering factors like river geometry, water depth, and flow velocity) and Sediment Transport Equations (that include equations of the erosion, entrainment, transport, and deposition of sediment particles. Factors like particle size, flow shear stress, and bed slope are included) must be clearly distinguished and presented.
4. Bathymetry data is absolutely required for moving-bed mathematical models used in simulating river sediment transport. However, no information has been provided related to this.
5. Section 3.1.1: The authors focusing solely on fixed-bed and mobile-bed model debugging might be too narrow. There could be other model components requiring debugging, such as initial conditions, boundary conditions, or numerical solution methods. Justify
6. Discuss the physical meaning and implications of the main channel roughness of the calculated river section (0.019~0.023). Why and How these ranges were derived.
7. Section 5: Provide specific conclusions based on the results that have been obtained. The limitations of the 2D model used for the simulations should be discussed. The effectiveness of potential riverbed protection measures needs further evaluation and hence could be suggested as future scope of work.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsIn this work, the authors used a two-dimensional hydro-sediment mathematical model to study the scoring changes in the Line 6 of the Nanning Metro in Guangxi, China. The authors investigated the impacts of sediment particle sizes and flow rate, and explored how the Froude number alters bed sedimentation. In general, the authors provided some useful insights for practical engineering safety for river flow system in urban environment. However, more details are requested to elaborate the methodology and improve the manuscript. Details are included in the following.
1. The authors obtain the flow speed and particle dynamics by solving the equations (1-7). For the flow speed part, this is similar to a 2D N-S equation. How were the equations solved? Did the author check the mesh sensitive to ensure that the mesh grid is sufficient?
2. Following the previous comment, the equations (1-7) include many parameters, including flow speeds and channel depths as a function of both x and y directions, and time. The authors are expected to provide more details of the convergence condition of the numerical simulation results. Also, the authors did not mention how these parameters change across time, although the time term is included in equations (1-7). Are all the results based on the time-average of the simulation? If that is the case, I recommend that the authors point this out in the governing equation and remove all the time-depended terms (i.e., similar to RANS equation).
3. Minor comments, the authors used the term ‘distance’ for horizontal axis in many plots. I assume it refers to the y axis along the span of the channel, but the authors should point it out clearer. Meanwhile, the plots in figure 8 is stretched.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for Authors1. The expression should be improved to meet the scientific report.
2. Details of the simulation should be provided, e.g. the mesh resolution, the boundary condition of water flow and sediment.
3. Which bedload formula was used in the simulation ?
4. How to quantify the sediment initial suspending contidions ?
5. In the case studies, how long does the flood last ?
6. With the flow velocity increases, the capability of flow will increase, what contributes to the decrease of the scour depth ?
7. During the flood, is the sediment from upstream considered ? Whether the sediment from upstream will affect the local scouring ?
8. Definetly, it is difficult to accurately simulate the riverbed evolution due to complex hydrodynamic conditions and the sand bed composition. Figure 3 represents very accurate simulation, what is the critical technique ?
Comments on the Quality of English LanguageThe expression is difficult to read.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsReview of revised manuscript "A study on the maximum scour depth of river-crossing tunnels". The authors have made a significant effort to revise the manuscript in response to the reviewers' suggestions and comments. They have addressed all the points raised in a positive and constructive manner, incorporating the feedback into the revised manuscript. However, I have identified a few additional concerns that need to be addressed before the manuscript can be considered for acceptance. Hope they consider all suggestions and revise efficiently.
1. How is the "critical depth" calculated based on the Froude number threshold? Is it simply the water depth at the threshold point, or is there a more complex formula involved?
2. What are the ideal conditions for tunnel placement regarding water depth and critical depth? Should they be exactly the same, or can there be some tolerance?
3. How does a significant difference between water depth and critical depth indicate potential safety risks? Does it mean the riverbed is more likely to scour or silt up excessively?
4. In my previous feedback, I recommended reviewing recent literature to strengthen the background section of your study. Unfortunately, I haven't observed any changes reflecting this suggestion. Therefore, I strongly recommend reviewing and incorporating the following papers : https://doi.org/10.1038/s41598-024-54261-z ; https://doi.org/10.1061/JHEND8.HYENG-13305 ; https://doi.org/10.1016/j.tust.2024.105964 )
5. The statement "Safety is paramount in tunnel construction, with efforts focused on minimizing costs while ensuring safety standards are upheld. Deeper tunnels entail more complex geological conditions, heightened ground pressure, and increased construction costs due to elevated technical requirements, greater support and lining expenses, groundwater control challenges, and intensified safety measures. Therefore, tunnel design should meticulously determine a burial depth below the scouring limit to avoid excessive depth, which would escalate construction complexity and costs" must be cited with relevant references.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have addressed all my comments and I can recommend publication of this manuscript.
Author Response
Thank you very much for your opinions and suggestions!
Reviewer 3 Report
Comments and Suggestions for AuthorsThe reqired questions have been answered.
Comments on the Quality of English LanguageThe language should be furtherly edited.
Author Response
Thank you very much for your opinions and suggestions!
