A New Hydro-Mechanical Coupling Numerical Model for Predicting Water Inflow in Karst Tunnels Considering Deformable Fracture

Round 1

Reviewer 1 Report

My comments are in the pdf file.

Comments for author File: Comments.pdf

Moderate editing of English language required

Author Response

Review of Submission, ID: sustainability-2512468, "Numerical study of fracture-induced water inrush in tunnels construction considering unsaturated-saturated flow". Although the topic is of interest to the readership of the Journal ; however, the results, discussion section, and verification needs deeper interpretation. The revision of the paper is proposed as follows:

（1）The paper title should be more concise and briefer. Please, modify it.

Response: As suggested by the reviewer, we have condensed the title of this article again.

（2）It is critical to validate the results against observations. Through this way, one could know the validity of the models. In my view, the authors should add more detailes on validation section and verification needs deeper interpretation. Include a separate section in the paper titled verification and verify this numerical study. This matter is very important me.

Response: Your proposal is very reasonable. We have rewritten the discussion and engineering background sections and compared in detail the differences between numerical analysis results and actual observation results.

（3）What distinguishes this study from others that have been published in the scholarly literature? As there are numerous other studies in the body of research that are comparable to these studies, kindly compare them. Write out the similarities and differences, with an emphasis on your uniqueness. It is crucial to emphasise in the beginning how special this piece of study is.

Response: Your proposal is very reasonable. We have rewritten the results and discussion section and conducted comparative analysis with other literature, highlighting the innovation and theme of this paper.

（4）The paper does not present a high level of innovation. Justify this matter. The novel contributions of this study are not addressed well in the manuscript. It is required to be reorganized in order to become more apparent. The authors must emphasize the novelty of the their research and that their work can be successfully used in other regions and settings, because this justify the publication in an international journal.

Response: Your proposal is very reasonable. We have rewritten the Instruction, Discussion section, and delved into the innovative aspects of this paper, as shown in the revised draft in lines 81-83.

（5）The introduction is generally. It is desired to rephrase this part to emphasize the objective of the study. In this reviewer's opinion, the introduction should be rewritten and extended with more and new refs.

Response: As suggested by the reviewer, we rewrote the Instruction section, see Section 1 of the revised version.

（6）The manuscript requires some language corrections to avoid any editorial errors and also needs the edition for proper English language, grammar, punctuation, spelling, and overall style. It's recommended to be checked by a native person. Else, I will reject the paper in the next time.

Response: Thanks for your careful checks. We have carefully reviewed the grammar issues in this paper and also ask people from English native to improve and check the grammar.

（7） In Table 1, How the value of the parameters is taken from field date or from any literature? what is the rationality behind the range of these variable parameters? The authors should add new more explanations and justify this selection of values.

Response: Your proposal is very reasonable. The parameters used in the numerical model in this article mainly come from two aspects: (1) obtained through indoor experiments; (2) Obtained after referencing other literature or conducting sensitivity analysis. The detailed content has been added to the revised manuscript.

（8）The authors should improve discussion sections. Clearer presentation and discussion of the results should be provided. The reported claims should be adequately discussed in the context of the literature.

Response: As suggested by the reviewer, we rewrote the discussion section, see Section 5 of the revised version.

（9）Although the paper objectives are mentioned in introduction part, additional information are provided, making it difficult to comprehend these objectives. It should be uniquely stated what the aim is then the importance should be appreciated by those who are interested in this paper. I suggest splitting this part into two paragraphs or numbering the objectives, in order to be clear. Please, apply.

Response: As suggested by the reviewer, we rewrote the Instruction section.

（10）The author should add more explanations related software and modeling. The authors said almost nothing on the modeling. A sketch including the information of the arrangement of meshes, the boundary conditions and the number of elements, …should be presented for a better readability. The following studies should be mentioned to enhance the impact of the article for numerical modeling: https://doi.org/10.1007/s40808-022-01543-y.

Response: As suggested by the reviewer, we have added detailed information on the construction of numerical models in Section 4 of the revised manuscript and cited the literature.

（11） How did the mesh was calibrated? Where is diagram related to the validation of the meshes? The meshing refinement should be stopped after checking that the results do not change. Authors should include a separate section for verifing of the meshing in the paper by related diagram.

Response: As suggested by the reviewer, we have discussed in detail the basis for grid division in lines 261-269 of the revised manuscript, as shown in Figure 10.

（12）How many elements are in mesh? How many nodes? Which criteria have been used to build it?

Response: As suggested by the reviewer, we have added detailed information of numerical models in Section 4 of the revised manuscript.

（13）Numerical algorithms and solutors that are used by the software to solve the equations need to be declared, analyses need to be described or at least declared.

Response: As suggested by the reviewer, we have added this declaration at the end of Section 2.3 (Line 176-177).

（14） The authors should show used mesing in the numerical simulation in a separate figure.

Response: As suggested by the reviewer, we have added this part in revised manuscript Line 261-269 and Figure 9-Figure 10.

（15）"The distance from the lateral boundary of the model and the distance between the lower bound of the model from top should be taken sufficient, so that the effects of the boundaries in the numerical model on the results was minimized. The displacement and the stress contours in the finite element software indicate that this distance is suficient [1-2]". The authors should add above sentence in Numerical model and calculation parameters section and then author should cite the following researches (two items): 1) https://doi.org/10.1007/s41062-022-00861-5. 2) https://doi.org/10.1007/s12517-022-09454-z

Response: As suggested by the reviewer, we have added this information on lines 261-264 of the revised manuscript and cited the literature.

（16）Insert refs for the used numerical software in ref section.

Response: As suggested by the reviewer, we have inserted references to the numerical software used in this article (Line 180.)

（17） Write all the notations that were used in the research.

Response: As suggested by the reviewer, we have re standardized the character expression in this article.

（18） All of the equations and parameters should be checked again.

Response: As suggested by the reviewer, we have thoroughly reviewed all parameters and formulas.

（19） Some text within the figures is too small, please revise them based on the requirement of the journal.

Response: Thanks for your careful checks. We have improved the quality of figures in this paper.

（20） The authors should substitute all of the poor-quality figures with more representable version.

Response: Thanks for your careful checks. We have improved the quality of figures in this paper.

（21）All of the parmeters in text, figures, and tables, ... should be italics. Check all of the parameters.

Response: As suggested by the reviewer, we have edited according to the requirements of the journal.

（22） Referencs, Figures, Tables should be listed in the order in which they are mentioned in the text.

Response: Thanks for your careful checks. We have listed the references, charts, and tables in order in the revised manuscript.

（23）Conclusions sections should be re-arranged as Conclusion and Recommendations. In this section limitations and recommendations of this study should be listed.

Response: Your proposal is very reasonable. We have written the conclusion section and described the limitations and future research directions of this article (Section 6).

（24） The references list is inconsistent, composed of several writing styles and punctuation errors, which is unacceptable. Rewrite all references according to the style of the journal's format.

Response: Thanks for your careful checks. We have carefully edited the references according to the journal format requirements based on Endnote software.

（25） I think in the section References the digital object identifiers (DOIs) are completely missing. Please insert them in cases of all references where the DOIs are available.

Response: As suggested by the reviewer, we have added the DOIs to the references.

Reviewer 2 Report

This paper provides an equivalent fracture model to predict the tunnel construction inflow under unsaturated conditions. The model can consider complete failure mechanisms, including shear failure and tensile failure. This method is based on the TOUCH-FLAC3D. The authors apply this model to predict the water inflow in the construction process of Jianxin Tunnel in Guizhou and conduct the sensitivity analysis to study the impact of key parameters. However, this paper lacks the data comparison between the simulation results and the data observed in the field. There are only a few qualitative descriptions of the prediction accuracy. In addition, this study contains the randomness of fracture distribution. The authors might consider summarizing the regularity from a probabilistic perspective to avoid the contingency of a single simulation. In summary, the method presented in this paper may provide accurate predictions of flows during tunnel construction in the future, but more work still needs to be done.

 

Specific comments can be found below:

 

1.      The last sentence in the Introduction should be ‘were’. (Furthermore, the effects of fracture density, dip angle, stress anisotropy, and initial fracture width was analyzed through sensitivity analysis.)

2.      Please check the meaning of ?? (‘steadyy’?)

3.      ‘Intact rocks consist of pure matrix, while fracture element consist of intact rocks and fractures.’ should be ‘elements’. It is better to add the lines number.

4.      Do A and V mean cross-sectional area and volume in equation 8. There seems no definition about the symbols.

5.      Does author mean equation 11 in ‘Under purely tensile or compressive stresses, the increase in fracture width increment can be estimated according to Eq. 12.’

6.      What is Δ?? in Equation 14. Does author mean Δ?n?

7.      Does ? mean the direction vector of the boundary in Eq. 15?

8.      In Figure 10, the pressure cloud map shows similar results from 10-50 hours, which indicates that the inflow reached a steady state within 10 hours. Can authors show more detailed information about the inflow in 10 hours to let the readers understand the evolution of the entire process from the start to the steady state?

9.      Can authors consider being able to eliminate the interference of randomness (as assumed in Figure 16 and Figure 19) by repeating simulations multiple times or other methods?

10.   In Figure 20, why do K0 = 0.4, 0.8, and 1.0 show similar pressure distributions, while K0 = 0.6 shows a different distribution?

11.   Can authors provide any comparison between the predictions and the data observed in the field to prove the reliable performance of the new method?

Author Response

 

（1）The last sentence in the Introduction should be ‘were’. (Furthermore, the effects of fracture density, dip angle, stress anisotropy, and initial fracture width was analyzed through sensitivity analysis.)

Response: Thanks for your careful checks. We have made corrections to Line 80 of the revised manuscript.

（2）Please check the meaning of ?? (‘steadyy’?)

Response: Thanks for your careful checks. We have made corrections to Line 92 of the revised manuscript.

（3）Intact rocks consist of pure matrix, while fracture element consist of intact rocks and fractures.’ should be ‘elements’. It is better to add the lines number.

Response: Thanks for your careful checks. We have made corrections to Line 102-103 of the revised manuscript. At the same time, we have also added line numbers in the revised manuscript

（4）Do A and V mean cross-sectional area and volume in equation 8. There seems no definition about the symbols.

Response: Thanks for your careful checks. We have added the specific meanings of variables A and V in Line 118-119 of the revised manuscript.

（5）Does author mean equation 11 in ‘Under purely tensile or compressive stresses, the increase in fracture width increment can be estimated according to Eq. 12.’

Response: Thanks for your careful checks. We have made corrections to Line 133 of the revised manuscript.

（6）What is Δ?? in Equation 14. Does author mean Δ?n?

Response: Thanks for your careful checks. We have made corrections to Line 147 of the revised manuscript.

（7）Does ? mean the direction vector of the boundary in Eq. 15?

Response: Thanks for your careful checks. We have added the specific meanings of variables ? in Line 154 of the revised manuscript.

（8）In Figure 10, the pressure cloud map shows similar results from 10-50 hours, which indicates that the inflow reached a steady state within 10 hours. Can authors show more detailed information about the inflow in 10 hours to let the readers understand the evolution of the entire process from the start to the steady state?

Response: Your proposal is very reasonable. We have supplemented the pressure contours map within 0-10 hours (Figure 11).

（9）Can authors consider being able to eliminate the interference of randomness (as assumed in Figure 16 and Figure 19) by repeating simulations multiple times or other methods?

Response: Your proposal is very reasonable. Random networks have a significant impact on water inflow prediction. Based on your suggestion, we have conducted multiple repeated experiments in the modified version to seek general patterns.

（10）In Figure 20, why do K0 = 0.4, 0.8, and 1.0 show similar pressure distributions, while K0 = 0.6 shows a different distribution?

Response: Thanks for your careful checks. Due to the incorrect use of the contour map corresponding to  in the initial manuscript, the initial fracture network is different from the other three, resulting in different pore pressure distributions. We have corrected this in the revised manuscript.

（11）Can authors provide any comparison between the predictions and the data observed in the field to prove the reliable performance of the new method?

Response: Your proposal is very reasonable. We have compared the differences between actual observation and simulation results in detail in the discussion section and conducted in-depth analysis Line 330-342.

Reviewer 3 Report

The article deals with a very interesting topic regarding the 'Numerical study of fracture-induced water inrush in tunnels construction considering unsaturated-saturated flow'. Overall, it is a comprehensive article, well referenced and the findings provided indicate that a great deal of effort was put in.

Suggestions for some improvements that could be performed to the manuscript prior to its publication are the following:

- Introduction: It would be interesting to highlight the novelty that this specific article presents compared to previous studies.

- Governing Equation: It is suggested to add some more relevant references regarding the equations/maths used based on the literature. What type of SW was used to perform the previous calculations/display? Elaborate more on this (analyse more the TOUGH-FLAC3D framework). In addition, make sure to use relevant references when using other figures.

- It is also suggested to add a flow chart including the general steps that were followed in order to facilitate reading.

- Conclusions: It would be interesting to comment more on the restrictions/challenges that may arise according to the selected area of interest and the corresponding solutions that could be followed (if another area is selected, how successful would the proposed methodoly be?). It is also suggested to underline the novelties that the proposed methods offer.

Are there any other factors/limitations that should be taken into account? It is also suggested to elaborate more on the future work paths.

 

 

Moderate to minor editing of English language is required.

Author Response

（1）Introduction: It would be interesting to highlight the novelty that this specific article presents compared to previous studies.

Response: Your proposal is very reasonable. We have rewritten the introduction section and highlighted the innovative points and themes of this article.

（2）Governing Equation: It is suggested to add some more relevant references regarding the equations/maths used based on the literature. What type of SW was used to perform the previous calculations/display? Elaborate more on this (analyse more the TOUGH-FLAC3D framework). In addition, make sure to use relevant references when using other figures.

Response: Your proposal is very reasonable. We have made detailed modifications to this section.

（3）It is also suggested to add a flow chart including the general steps that were followed in order to facilitate reading.

Response: Your proposal is very reasonable. We have added the HM method constructed in this article and provided a brief description, as shown in Figure 4 (Line 179-188).

（4）Conclusions: It would be interesting to comment more on the restrictions/challenges that may arise according to the selected area of interest and the corresponding solutions that could be followed (if another area is selected, how successful would the proposed methodoly be?). It is also suggested to underline the novelties that the proposed methods offer.

Response: Your proposal is very reasonable. We have rewritten the conclusion section and covered the content mentioned above.

（5）Are there any other factors/limitations that should be taken into account?

Response: The accurate construction of geological models is the main limitation of the proposed method in this article, and the randomness of the model is also an inevitable problem, which has been discussed in the conclusion section.

（6）It is also suggested to elaborate more on the future work paths.

Response: Your proposal is very reasonable. We described the limitations and future research directions of this article in the last paragraph of the conclusion (Line 442-447).

Reviewer 4 Report

Paper "Numerical study of fracture-induced water inrush in tunnels construction considering unsaturated-saturated flow" presents research related to the tunnel engineering, in general. Likewise, the research belongs to the field of engineering geology, as well as hydrogeology, considering of water inflow.

 

Several suggestions will be emphasized:

 

-        Generally related to keywords and abstract: keywords should not be words from the title, but terms from the abstract. On the other hand, the abstract should not detail the research results and discuss which methods are better.

-        The introduction is not very representative. You cannot just list references, without details of previous research (eg 1-6; 8-11 …).

-        In the second chapter, only the described methodology should remain, without presenting the input parameters for the model. This should be transferred to the results section, as the basis of the model.

-        On the other hand, in the chapter related to methodology, more specific things that the authors applied are needed. The general theory and basic geotechnical and geomechanical equations shown are redundant. The basis here is a methodology that determines water inflow and that has a potential advantage over some previous methods and research in tunnel engineering.

-        Regarding the presentation of the research area, it is necessary to add data on hydrogeological setting. As the main problem is groundwater, it is necessary to describe the aquifer. The values of parameters such as hydraulic conductivity should also be added.

-        The map shows the spring (Fig. 8), i.e. the natural recharge. Fracture and the like are emphasized in the abstract. Spring can really create a big hazard. Here you need to add more details about the spring, according to the previous suggestion related to the description of the aquifer and hydraulic parameters.

-        Chapter 4 is too short. It is necessary to harmonize with the other chapters where the results and discussion are. Why was the 3D model not applied?

-        The discussion is really very limited.

-        Why were steady-state groundwater data used for the sensitivity analysis? The results are more representative for the transient period.

-        The conclusion needs to be refined. It should not be in summary form. Here, it is necessary to emphasize the scientific contribution that the authors make to their research. Likewise, as the issue of tunnel construction is complex, it is necessary to add a contribution to the academic community.

-        I propose an interesting paper in a really complicated geological structure: Berisavljević, Z.; Bajić, D.; Jovičić, V. Development and Application of Methodology for Quantification of Overbreaks in Hard Rock Tunnel Construction. Appl. Sci. 2023, 13, 1379. https://doi.org/10.3390/app13031379

Author Response

（1）Generally related to keywords and abstract: keywords should not be words from the title, but terms from the abstract. On the other hand, the abstract should not detail the research results and discuss which methods are better.

Response: Based on your suggestion, we have rewritten the abstract and title, and replaced some keywords.

（2）The introduction is not very representative. You cannot just list references, without details of previous research (eg 1-6; 8-11 …).

Response: Your proposal is very reasonable. We have rewritten the introduction section.

（3）In the second chapter, only the described methodology should remain, without presenting the input parameters for the model. This should be transferred to the results section, as the basis of the model.

Response: Your suggestion is very reasonable. In the second section, our main content still focuses on the principle of the method, with section 2.5 having input parameters to verify the rationality of considering fracture shear deformation behavior in the proposed method.

（4）On the other hand, in the chapter related to methodology, more specific things that the authors applied are needed. The general theory and basic geotechnical and geomechanical equations shown are redundant. The basis here is a methodology that determines water inflow and that has a potential advantage over some previous methods and research in tunnel engineering.

Response: Based on your suggestion, we have discussed the calculation formula for water inflow in Line 152-155.

（5）Regarding the presentation of the research area, it is necessary to add data on hydrogeological setting. As the main problem is groundwater, it is necessary to describe the aquifer. The values of parameters such as hydraulic conductivity should also be added.

Response: As suggested by the reviewer, we have supplemented the hydrological situation Line 227-244.

（6）The map shows the spring (Fig. 8), i.e. the natural recharge. Fracture and the like are emphasized in the abstract. Spring can really create a big hazard. Here you need to add more details about the spring, according to the previous suggestion related to the description of the aquifer and hydraulic parameters.

Response: As suggested by the reviewer, we added the details about the spring in Line 234-237.

（7）Chapter 4 is too short. It is necessary to harmonize with the other chapters where the results and discussion are. Why was the 3D model not applied?

Response: Your suggestion is very reasonable. We have rewritten the results and discussion sections, and compared the differences between the numerical analysis results and the actual observation values in depth.

（8）The discussion is really very limited.

Response: Your suggestion is very reasonable. We have rewritten the results and discussion sections.

（9）Why were steady-state groundwater data used for the sensitivity analysis? The results are more representative for the transient period.

Response: Your suggestion is very reasonable. We have rewritten the sensitivity analysis section and discussed the differences between steady-state and transient.

（10）The conclusion needs to be refined. It should not be in summary form. Here, it is necessary to emphasize the scientific contribution that the authors make to their research. Likewise, as the issue of tunnel construction is complex, it is necessary to add a contribution to the academic community.

Response: Based on your suggestion, we have rewritten the conclusion section.

（11）I propose an interesting paper in a really complicated geological structure: Berisavljević, Z.; Bajić, D.; Jovičić, V. Development and Application of Methodology for Quantification of Overbreaks in Hard Rock Tunnel Construction. Appl. Sci. 2023, 13, 1379. https://doi.org/10.3390/app13031379

Response: After reading your paper, we believe that its viewpoints are very valuable to this article and cite them to support the conclusion of this article (Line 33 and Line 469).

Round 2

Reviewer 4 Report

The version of the paper that is in the MDPI system is unrefined and very difficult to read. I must emphasize this in particular. On the other hand, the authors really did their best to improve the presentation of scientific research.

 

Several suggestions will be emphasized:

 

-        Check the equations again.

-        The same applies to the text - some smaller parts remain in the native language (eg below picture 21).

-        Instead of emphasizing what was not done during the research, and emphasizing that it will be analyzed in a future study, the conclusion should still emphasize the scientific and academic contribution of the research that was conducted and presented in the paper.

 

Once again, it was really a pleasure to read such an interesting paper.

Author Response

（1）Check the equations again.

Response: We have thoroughly reviewed the formulas in this article.

（2）The same applies to the text - some smaller parts remain in the native language (eg below picture 21).

Response: Thank you for carefully checking. We have removed this part of the native language.

（3）Instead of emphasizing what was not done during the research, and emphasizing that it will be analyzed in a future study, the conclusion should still emphasize the scientific and academic contribution of the research that was conducted and presented in the paper.

Response: Your suggestion is very reasonable. We have clearly stated in the conclusion section the outstanding contribution of this study, which is the applicability and accuracy of the HM coupling model considering crack deformation in predicting the water inflow of karst tunnels, and have conducted in-depth analysis of its influencing factors. The last paragraph of the conclusion section of this article only contains a few sentences describing the current shortcomings and future directions that need to be overcome in this study.