Design of Tunnel Initial Support in Silty Clay Stratum Based on the Convergence-Confinement Method
Round 1
Reviewer 1 Report
In this manuscript, the stress release law during tunnel excavation in silty clay strata has been studied based on the convergence-confinement method and field test data. The stress release law of the surrounding rock under support was analysed using the displacement back analysis method. The safety factor of the support scheme and optimized supporting time under different subgrade conditions in silty clay stratum were evaluated. This study is of novelty, and its object is a topic of great interest to the actual construction process and the research results can produce effective guidance for construction.
Before it can be accepted for publication, the following issues should be addressed:
Major issues:
1. This paper focuses on silty clay stratum under different water content conditions. What is the mechanism by which the variation in water content affects the mechanical parameters? Please provide a brief additional explanation.
2. Which monitoring section does the field value of steel grid stress in Figure 7 come from? Additional explanation is needed to ensure the validity of comparative data analysis.
Minor issues:
1. The font size of some paragraphs is inconsistent, such as the title of Figure 1. Please check the whole manuscript carefully.
2. The title of the image is not standardized, the first letter of the secondary title should be lowercase.
3. Does “u1” in Eq. 15 and Eq. 26 represent the same physical quantity? Please provide additional explanation.
4. The sentence on page no. 13, lines 391-393 need to be rewritten for better understanding.
Author Response
Major issues:
Point 1: This paper focuses on silty clay stratum under different water content conditions. What is the mechanism by which the variation in water content affects the mechanical parameters? Please provide a brief additional explanation.
Response 1: Thank you for your valuable comments. A description of the mechanism of the water content effect on the mechanical properties of silty clay has been added in the revised manuscript, and the relevant references are cited; see lines 66-71, page 2.
Point 2: Which monitoring section does the field value of steel grid stress in Figure 7 come from? Additional explanation is needed to ensure the validity of comparative data analysis.
Response 2: Thank you for your valuable comments. The field measured values of the steel grid stress in Figure 7 come from test section ④, as explained in the revised manuscript. The theoretical calculation values are calculated using Equation 28, see lines 372-374, page 12.
Minor issues:
Point 1: The font size of some paragraphs is inconsistent, such as the title of Figure 1. Please check the whole manuscript carefully.
Response 1: Thank you for your valuable comments. We have revised the caption font size in Figure 1 and carefully checked the caption form of all figures in the revised manuscript.
Point 2: The title of the image is not standardized, the first letter of the secondary title should be lowercase.
Response 2: Thank you for your valuable comments. We have checked and revised the titles of all figures.
Point 3: Does “u1” in Eq. 15 and Eq. 26 represent the same physical quantity? Please provide additional explanation.
Response 3: Thank you so much for your valuable comments!
We apologize for the error in Eq. 26, u1 in Eq. 26 should be changed to ul. u1 in Eq. 15 is the convergence displacement when the supporting structure has not yet played its role, while ul in Eq. 26 indicates the radial deformation of the supporting structure. This has been corrected in the revised manuscript, see lines 343-344, page 11.
Point 4: The sentence on page no. 13, lines 391-393 need to be rewritten for better understanding.
Response 4: Thank you for your valuable comments. This sentence has been rewritten in the revised manuscript, see lines 412-413, page 13.
Reviewer 2 Report
This paper is rich in workload, complete in data and well written, which is of great significance to on-site engineering practice. However, this paper does not fit the scope of the Sustainability, the content of the paper is more consistent with the journals related to geotechnical engineering.
Author Response
Response to Reviewer 2 Comments
Point 1: This paper is rich in workload, complete in data and well written, which is of great significance to on-site engineering practice. However, this paper does not fit the scope of the Sustainability, the content of the paper is more consistent with the journals related to geotechnical engineering.
Response 1: Thank you for your affirmation of our research work.
The construction of urban rail transit is the development and utilization of underground space resources. Therefore, the construction process should minimize the impact on the surrounding environment. Exploring the scientific and effective excavation and support scheme is a scientific exploration for the sustainable development strategy of underground space resources development.
In addition, the monitoring and measurement data in this study effectively feed into the stability analysis of the rock surrounding the tunnel and the optimization of the support design scheme, which reflects the sustainability of the monitoring and measurement technology. Therefore, we believe that our research work is in line with the scope of the Sustainability. Thank you again for your recognition and support of our work.
Reviewer 3 Report
In the draft, the convergence-confinement method is used to analyse the safety of tunnels during excavation and support under different subgrade surrounding rock conditions in silty clay strata. However, the following issues need to be clarified.
1. In Section 1, Lines 60-61, “but not for silty clay strata which are widely distributed in urban residential areas.” This statement is reasonable?
2. In Section 3.1, Line 130, “The self-weight of the computing medium is neglected”. Please clarify why the self-weight is neglected.
3. Fig. 3, ground reaction curves are from the project in this article?
4. Please check the English writing.
Author Response
Response to Reviewer 3 Comments
Point 1: In Section 1, Lines 60-61, “but not for silty clay strata which are widely distributed in urban residential areas.” This statement is reasonable?
Response 1: Thank you for your valuable comments. We have rewritten the statement in the revised manuscript, see lines 64-66, page 2.
Point 2: In Section 3.1, Line 130, “The self-weight of the computing medium is neglected”. Please clarify why the self-weight is neglected.
Response 2: Thank you for your meaningful questions. We have adjusted the presentation in the revised manuscript.
The self-weight of the soil body has been considered in the process of ground stress calculation, and the deformation of the surrounding rock is the macroscopic expression of soil stress release. The effect of soil self-weight on the deformation can be basically ignored in the plane strain model. In addition, the calculation formula will be greatly simplified by neglecting the self-weight of the soil.
Point 3: Fig. 3, ground reaction curves are from the project in this article?
Response 3: The GRC in Figure 3 reflect the calculated results for the three different subgrades of silty clay in this study, and the soil parameters are from Table 1. The relevant expressions have been added in the revised manuscript, see lines 191-193, page 5.
Point 4: Please check the English writing.
Response 4: Thank you for your valuable comments. We have carefully checked the English expressions in the manuscript and corrected some English writing.
Reviewer 4 Report
This article is a fine submission on studying the stress release of the tunnel in the Harbin Metro project. Whereas, there are a number of issues identified for the authors to revise the manuscript.
1) Why convergence-confinement method is best suited for the study needs to be analyzed in the introduction;
2) Since Harbin is in a low temperature zone and it is very cold in winter, the freezing impact of the silty soil needs to be included in the study;
3)Reference needs to be added for equations that are not derived in the study, such as Eqs. 5, 17-20, etc.
Author Response
Response to Reviewer 4 Comments
Point 1: Why convergence-confinement method is best suited for the study needs to be analyzed in the introduction.
Response 1: Thank you for your valuable comments.
The CCM specifies the demand for support by the convergence of the surrounding rock. In addition, it can effectively reflect the constraint characteristics of the support pressure on the surrounding rock and take into account the spatial constraint of the tunnel face on the convergence of the surrounding rock. Therefore, this method has unique advantages in the evaluation of the surrounding rock stability, the optimal design of the support structure, and the selection of the support timing.
It is because of the above advantages of the CCM that this method is chosen in this study. We have provided an additional explanation in the introduction, see lines 46-51 and 77-85, page 2.
Point 2: Since Harbin is in a low temperature zone and it is very cold in winter, the freezing impact of the silty soil needs to be included in the study.
Response 2: Thank you for your valuable comments.
The burial depth of the tunnel in this project exceeded the thickness of the frozen soil. We have provided an additional explanation in lines 91-93, page 2.
Point 3: Reference needs to be added for equations that are not derived in the study, such as Eqs. 5, 17-20, etc.
Response 3: Thank you for your reminder. Eq. 5 references Ref. 41, for which additional clarification has been made, see line 164, page 5.
Eqs. 17-20 refer to Ref. 47, which has been explained in the revised manuscript, see lines 323-324, page 10.
Other Eqs. are also described in the content to account for citation.
Reviewer 5 Report
Reviewers' comments:
This paper presents a design of tunnel initial support in silty clay stratum using the convergence-confinement method. It is an interesting paper; however, in my opinion, the paper can be accepted for publication after considering the following revisions as follows:
1. Please clarify the relevance or novelty and contributions of this work. Please explain why the present study is more important compared to existing works in this direction. To capture the interest of readers, the main contribution and advantages of this work should be indicated.
2. The construction status of silty clay tunnels under different water contents using the existing excavation and support scheme are illustrated in Figure 1 (a) to Figure 1 (c). The description of the response of surrounding rock during excavation in silty clay stratum under different water content should be provided.
3. Table 1 lists the parameters of silty clay in different subgrade. How to obtain these parameters?
4. All the symbols in Equation (1) must be clearly defined. Furthermore, the symbols depicted in the equations should be consistent in the content.
5. In Equation (11), two fitting parameters are required to evaluate the longitudinal displacement value at different times during tunnel excavation. How to obtain these fitting parameter? The selection of the fitting algorithm must be detailed and justified.
6. The comparative analysis of vault displacement obtained by theoretical calculation and field monitoring is demonstrated in Figure 5. It appears that the theoretical calculation values may not be consistent with the variation law of vault displacement in practical engineering. Please explain the source of measurement error and properly describe the results in the examples.
7. Please provide the equation for calculating the SSE as shown in Table 2.
8. The theory or methodology of the MATLAB fitting tool must be provided. Please give a reference to the fitting formula as depicted in Equations (13), (14) and (15).
9. Please provide a figure with a schematic diagram.
10. Please connect the significant results of the main points in the “Discussion “section. Even if the findings were explained in the numerical experiments, it is necessary to describe a more robust discussion of the achieved results, in order to better explain the strengths of the proposed method respect to other approaches and its possible limits. The discussion should be inserted in a “Discussion” section, before “Conclusion” section. Please briefly add future perspectives and further applied applications of this specific research work in the discussion section.
Author Response
Response to Reviewer 5 Comments
Point 1: Please clarify the relevance or novelty and contributions of this work. Please explain why the present study is more important compared to existing works in this direction. To capture the interest of readers, the main contribution and advantages of this work should be indicated.
Response 1: Thank you for your valuable comments.
In this study, the stress release law of tunnel excavation in silty clay strata was inferred based on field monitoring data. The deformation law of three different subgrades of silty clay strata was clarified. The optimal time of the initial support application was determined by a comprehensive analysis of the ground reaction curve and the support characteristic curve. Finally, the support scheme was optimized for tunnels in different subgrades of silty clay strata by introducing the concept of the safety factor.
We summarize the main work of this study in the last part of the introduction, while the conclusion mainly summarizes the contributions of this study, see lines 77-85, page 2.
Point 2: The construction status of silty clay tunnels under different water contents using the existing excavation and support scheme are illustrated in Figure 1 (a) to Figure 1 (c). The description of the response of surrounding rock during excavation in silty clay stratum under different water content should be provided.
Response 2: Thank you for your valuable comments.
We have added the response of surrounding rock during excavation in silty clay stratum under different water content in the revised manuscript, see lines 106-113, page 3.
Point 3: Table 1 lists the parameters of silty clay in different subgrade. How to obtain these parameters?
Response 3: Thank you for your question. It is indeed true that the soil parameters are important for the accuracy of the convergence calculation results of the surrounding rock, and we have also explained in detail the testing and selection process of the soil parameters in our previous study (Ref. 35). This paper was not focused on the soil parameters study, so we give the list of parameters directly, and the previous research papers were cited. See lines 117-120, page 3.
Point 4: All the symbols in Equation (1) must be clearly defined. Furthermore, the symbols depicted in the equations should be consistent in the content.
Response 4: Thank you for your valuable suggestions. We have clarified the meaning of all symbols in Eq. 1 and the explanation of their meaning has been added in the content, see lines 150-154, page 4.
We have also checked the explanation of the symbols in the other equations in the content and have revised them all in the revised manuscript.
Point 5: In Equation (11), two fitting parameters are required to evaluate the longitudinal displacement value at different times during tunnel excavation. How to obtain these fitting parameter? The selection of the fitting algorithm must be detailed and justified.
Response 5: Thank you for your valuable comments. In the fitting process here, we have clarified the specific form of the fitting formula and only need to determine the parameters in the fitting formula, so we use equation 11 as a custom function and carry out the fitting work directly using MATLAB curve fitter. The fitting process mainly relies on the existing toolbox of MATLAB, and fitting algorithms are not our results. We have provided an additional explanation in the revised manuscript (see lines 221-224, pages 6-7).
Point 6: The comparative analysis of vault displacement obtained by theoretical calculation and field monitoring is demonstrated in Figure 5. It appears that the theoretical calculation values may not be consistent with the variation law of vault displacement in practical engineering. Please explain the source of measurement error and properly describe the results in the examples.
Response 6: Thank you for your valuable comments.
There are obvious fluctuations in the measured data, mainly considering the influence of different support stages, especially the advanced support measures on the vault settlement. The advanced support structure can form a scaffolding effect in front of the tunnel face, so the influence on the vault settlement is complicated. The stress release of the surrounding rock is an irreversible process, so the vault settlement characterizing the stress release should also be monotonically increasing. There is good agreement between the measured data and theoretical results in Figure 5 in terms of the overall trend.
We have provided an additional explanation in the revised manuscript (see lines 307-313, page 9).
Point 7: Please provide the equation for calculating the SSE as shown in Table 2.
Response 7: Thank you for your comments.
SSE means the sum of squares due to error (definition with reference to statistics). This statistical parameter is calculated as the sum of squares of the errors between the fitted data and the corresponding points of the original data and is calculated as follows:
The closer the SSE is to zero, the better the fit is.
Point 8: The theory or methodology of the MATLAB fitting tool must be provided. Please give a reference to the fitting formula as depicted in Equations (13), (14) and (15).
Response 8: Thank you for your comments.
As with Eq. 11, the fitting of Eq. 13, 14, and 15 apply the curve fitting toolbox in MATLAB, and each equation is fitted separately as a custom function. The use of the fitting tool can be found in https://ww2.mathworks.cn/help/curvefit/index.html?s_tid=CRUX_lftnav
It should be noted that Eqs. 14 and 15 are not obtained by fitting but indirectly through the theoretical derivation with the fitting results of Eq. 13.
Point 9: Please provide a figure with a schematic diagram.
Response 9: Thank you for your comments.
Indeed, scientific fitting tools guarantee the validity of research results. As a mature data analysis software, MATLAB is powerful in data fitting. However, the fitting principle is not the focus of our attention in this paper, and the fitting process is only a direct use of the original fitting tool (Curve Fitting Toolbox), so we do not explain much about the fitting process in the text.
Point 10: Please connect the significant results of the main points in the “Discussion “section. Even if the findings were explained in the numerical experiments, it is necessary to describe a more robust discussion of the achieved results, in order to better explain the strengths of the proposed method respect to other approaches and its possible limits. The discussion should be inserted in a “Discussion” section, before “Conclusion” section. Please briefly add future perspectives and further applied applications of this specific research work in the discussion section.
Response 10: Thank you for your comments.
We outline the advantages of this method and the close relationship between this method and the monitoring and measurement technology in the discussion section. As an effective application of the monitoring and measurement technique, this study also fully demonstrates the sustainability of the monitoring technique. The discussion section can be found in lines 502-523, page 16.
Reviewer 6 Report
The topic of this research is initial support design based on the convergence confinement method. The advantage of the work is the fact that the stress release law during tunnel excavation in silty clay strata has been studied combined with field test data. In particular, a detailed analysis of the longitudinal displacement profile was carried out in conjunction with the support application time. The research results are of great guidance for engineering construction.
The stress release ratio of the silty clay stratum was analysed based on field monitoring data in this study. What are the macroscopic characteristics of the stress release process in the soil mass? Is the inversion result based on the field monitoring data unique? Please provide an appropriate explanation.
The presentation of scientific notation in Table 2, Table 3 and Table 5 is recommended to be standardized and uniform. The presentation of the vertical coordinates in Figure 9 is recommended to be standard.
Author Response
Response to Reviewer 6 Comments
Point 1: The stress release ratio of the silty clay stratum was analysed based on field monitoring data in this study. What are the macroscopic characteristics of the stress release process in the soil mass? Is the inversion result based on the field monitoring data unique? Please provide an appropriate explanation.
Response 1: Thank you for your valuable comments.
The macroscopic characteristics of stress release during tunnel excavation are the displacement and the displacement increment of the surrounding rock. Generally, the greater the stress release ratio is, the greater the displacement and the displacement increment of the surrounding rock (see lines 300-301, page 9). After the support action is applied, the rate of surrounding rock deformation can be effectively controlled even if the stress release rate is large. If not, the timing of the support needs to be advanced to complete an effective support at a smaller stress release ratio.
The inversion results in this paper not only rely on the field monitoring data but also consider the theoretical analysis results and then comprehensively compare the stress release law with and without support conditions.
Point 2: The presentation of scientific notation in Table 2, Table 3 and Table 5 is recommended to be standardized and uniform. The presentation of the vertical coordinates in Figure 9 is recommended to be standard.
Response 2: Thank you for your valuable comments.
We have modified the scientific notation in the tables and content. We revised the representation of the vertical coordinates in Figure 9.
Round 2
Reviewer 2 Report
the revision can be accepted
Reviewer 3 Report
It can be accepted in present form.
