In the study, the Effect of Multi-span Pit Excavation on Supporting Structure Based on the CSM Method was investigated. The study was generally successful and the following points should be noted:

Comments for author File: Comments.pdf

The English language of the study is sufficient. But someone other than the authors should do a final reading.

Author Response

Reviewers' comments I

Response Letter

Dear Assigned Editor and Reviewer:

On behalf of my co-authors, we are very grateful to you for giving us an opportunity to revise our manuscript. We appreciate you very much for your positive and constructive comments and suggestions on our manuscript entitled “Study on the Effect of Multi-span Pit Excavation on Supporting Structure Based on the CSM Method” with the reference number sustainability-2534639.

We have studied reviewers’ comments carefully and tried our best to revise our manuscript according to the comments. The following are the responses and revisions we have made in response to the reviewers' questions and suggestions on an item-by-item basis. Our response is given in normal font and changes/additions to the response letter are given in the red text. Any revisions to the manuscript have been marked up using the “Track Changes” function. Again, we are very grateful to Editor and Reviewers for reviewing the paper so carefully!

Comment No. 1: At the end of the introduction, the difference of the study from the literature should be clearly stated.

Response: Following the reviewers' suggestions, we've reordered the Introduction, added/replaced 16 references, deleted 4 references, undertaken a comprehensive and systematic review of the innovations and shortcomings of the existing literature, and summarised and presented the research in this paper. At the end of the introduction, the shortcomings of the current study, the research objectives and the purpose of the study are more clearly defined.

The modified text reads:

Introduction

The numerical simulation method offers several advantages, including strong intuitions, low costs, simple operation, strong flexibility, immediate feedback of results, and real-time monitoring of engineering progress studied the supporting system of Seattle Herald Square District, investigated the physical and mechanical indexes of CSM wall deformation, CSM wall strength, groundwater level change, and maximum lateral displacement of the supporting system in the foundation pit supporting engineering, and verified the performance of CSM wall technology. However, the authors did not deeply study the internal force change of the supporting structure. As a result, this method has been widely utilized in numerous projects. Thus, conducting such simulations holds significant importance and value as it can provide insights and improve the efficiency and safety of the excavation process.

This paper presented a numerical simulation of a multi-span foundation pit excavation project in eastern China. The goal of the study was to investigate the displacement of the supporting structure, internal force of the internal support, displacement of the ground connecting wall, and the stress law of the supporting system during the foundation pit excavation process. The study employed Midas GTS NX software to model the entire system, including the surrounding soil mass, supporting structure, and foundation pit. A total of ten working conditions were analyzed, each involving different CSM wall embedment depth and excavation span. These conditions were listed as ①-⑩: ① short ground wall equal length single span, ② short ground wall equal length two spans, ③ short ground wall equal length three spans, ④ short ground wall equal length four spans, ⑤ short ground wall equal length five spans, ⑥ long ground wall equal length single span, ⑦ long ground wall equal length two spans, ⑧ long ground wall equal length three spans, ⑨ long ground wall equal length four spans, and ⑩ long ground wall equal length five spans. The study provides relevant data support for the design and construction of similar projects, which is of great practical significance and practical value.

Comment No. 2: The layers must be clearly indicated in Figure 1.

Response: Thanks to Reviewer for reminder, we added the picture called Shematic diagram of the main structure of the pit in section 2.1 to solve the problem.

The modified text reads:

2.1 General situation of foundation pit retaining structure

This project is a multi-span foundation pit in East China. This foundation pit excavation project is constructed by open excavation, the excavation depth of the main foundation pit is about 27.2 m, and the excavation depth of the multi-span section is about 18.5 m. The open excavation area has a foundation pit breadth ranging from 53.16 m to 62.77 m. Within the foundation pit, there are five steel supports spaced at a vertical interval of 6.00 m. The first and second steel supports have a cross-sectional area of 0.11 m², the third and fourth have a cross-sectional area of 1.20 m², and the fifth has a cross-sectional area of 0.11 m².

The pit excavation project due to urbanization construction, the site has been artificially transformed, the current terrain is relatively flat, the underground soil layer from top to bottom for the miscellaneous fill, clay 1, clay 2, clay 3, silt, clay 4, the thickness of the soil layer in order of about 1.9 m, 12.0 m, 13.4 m, 15.3 m, 3 m, 34.5 m. support form for the ground connecting wall and internal support system, the thickness of the continuous underground wall is 1000mm. The thickness of diaphragm wall is 1000 mm. The soleplate is mainly located in layer ③ clay 1, while the bottom of the construction piles and the pile base are located in layer ⑤ clay 3. The general situation of foundation pit supporting structure is shown in Figure 1. The strata beneath the foundation pit enclosure in this project consist of the following layers, arranged from top to bottom: ① a layer of miscellaneous fill, ② a layer of clay 1, ③ a layer of clay 2, ④ a layer of clay 3, ⑤ a layer of sandy silt, ⑥ a layer of clay 4. The main structure of foundation pit is shown in Fig. 1.

Comment No. 3: The preferred mesh size of the model used should be given. Since the mesh size directly affects the result, has a study been done to determine the mesh size in advance?

Response: Thanks to the reviewer's comments, we have tried the grid size before during the simulation process. Both to ensure good computational speed and simulation accuracy, and finally to determine the size of each model component. In this revision, the original formulation has increased the size of the soil cell by way of example.

The modified text reads:

3.2.2 GTS NX Models

The wireframe of the model was created using CAD, and a two-dimensional model was established using finite element software MIDAS/GTS to simulate the excavation and construction process of the foundation pit. The 2D unit simulated the soil of each layer, and the inner support, uplift pile, column pile, and structural plate were simulated using a 1D linear elastic beam unit model. The pressure bar between walls was simulated by a 1D elastic truss element line model, comprising a total of 16,454 2D elements and 15,283 nodes. Among them, each the soil layer element grid size is 1.05m×0.93m. Table 2 displays the structural unit material parameters used in the model, and Figure 1 illustrates the model. The CSM wall was set 0.1m away from the supporting structure, with an embedded depth of 18.5 m for working conditions ①, ②, ③, ④, and ⑤ and 27.0 m for working conditions ⑥, ⑦, ⑧, ⑨, and ⑩. The span of soil was 37.00 m under working conditions ① and ⑥, 40.80 m under working conditions ② and ⑦, 45.15 m under working conditions ③ and ⑧, 50.07 m under working conditions ④ and ⑨, and 55.00 m under working conditions ⑤ and ⑩. Working conditions 1, 4 and 9 are selected as typical representatives, and the schematic diagram is shown in Fig. 3.

Comment No. 4: Higher resolution images should be used in Figures 1 and 2.

Response: Thanks to Reviewer for reminder, we have paid attention to this question and it is clearer.

Comment No. 5: The CSM narrative can be supported with a visual for better understanding by the readers (author's choice).

Response: Thanks to Reviewer for reminder, we have added a picture called Shematic diagram of the main structure of the pit in section 3.2.2 to solve the problem you mentioned.

The modified text reads:

3.2.2 GTS NX Models

The wireframe of the model was created using CAD, and a two-dimensional model was established using finite element software MIDAS/GTS to simulate the excavation and construction process of the foundation pit. The 2D unit simulated the soil of each layer, and the inner support, uplift pile, column pile, and structural plate were simulated using a 1D linear elastic beam unit model. The pressure bar between walls was simulated by a 1D elastic truss element line model, comprising a total of 16,454 2D elements and 15,283 nodes. Table 2 displays the structural unit material parameters used in the model, and Figure 1 illustrates the model. The CSM wall was set 0.1m away from the supporting structure, with an embedded depth of 18.5 m for working conditions ①, ②, ③, ④, and ⑤ and 27.0 m for working conditions ⑥, ⑦, ⑧, ⑨, and ⑩. The span of soil was 37.00 m under working conditions ① and ⑥, 40.80 m under working conditions ② and ⑦, 45.15 m under working conditions ③ and ⑧, 50.07 m under working conditions ④ and ⑨, and 55.00 m under working conditions ⑤ and ⑩. Working conditions 1, 4 and 9 are selected as typical representatives, and the schematic diagram is shown in Fig. 3.

Comment No. 6: Results should be supported with sample visuals.

Response: We are extremely grateful to Reviewer for pointing out this problem. In Section 4.4, we have better characterized the bending moment of the steel bracket in Case 1 by means of a cloud diagram.

The modified text reads:

In the excavation process, the bending moments inside the steel struts of different processes are different, but there is a maximum bending moment in all the 5 steel struts of all processes, and if this maximum bending moment is smaller than the maximum permissible bending moment, the steel struts will meet the engineering requirements. Take condition 1 as an example, we can get the bending moment cloud diagram of process 8 steel strut, as shown in Fig. 14, the maximum bending moment is considered in the calculation.

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript entitled “Study on the Effect of Multi-span Pit Excavation on Supporting Structure Based on the CSM Method “ has been investigated in detail. The topic addressed in the manuscript is interesting, however there are few issues which could be addressed by the authors:

1. Keywords should be written in alphabetical order.

2. There are no numerical results in the “Abstarct” section. Please add results to this section.

3. Authors should clearly write what the motivation of this paper is.

4. More metric may be used for comparison of results.

5. Some paragraphs are too long to read. They should be divided into two or more for comprehensibility and readability.

Author Response

Response Letter

Dear Assigned Editor and Reviewer:

Comment No. 1: At the end of the introduction, the difference of the study from the

Comment No. 1: Keywords should be written in alphabetical order.

Response: Thanks to Reviewer for reminder, we modified the keyword order.

The modified text reads:

Keywords: CSM construction method; Embedded depth; Finite element model; Foundation pit excavation; Foundation pit span

Comment No. 2: There are no numerical results in the “Abstract” section. Please add results to this section.

Response: Thanks to Reviewer for reminder. We also recognize that numerical results will play a quantitative role in the abstract to more objectively characterize the extent to which influencing factors contribute to the results. We add some numerical results in the “Abstract” section.

The modified text reads:

Abstract: The Cutter Soil Mixing (CSM) construction method is a relatively new technique developed in recent years for wall construction using double wheel milling and deep stirring equipment. In order to study the displacements and internal support stresses of the support structure during the excavation of a multi-span foundation pit based on the CSM, construction method, a two-dimensional finite element model was established using Midas GTS NX finite element software. The model was based on the multi-span foundation pit excavation project in eastern China, with steel bracing and the CSM construction method as the main support forms. Ten different working conditions were compared and analyzed to ascertain the displacements of the CSM wall and force on the support system during the foundation excavation process. The study findings demonstrate the embedment depth of the CSM wall and the span of the pit excavation influence the displacement and support stresses of the support structure. The further increases in embedment depth may be helpful in improving support result, but their effectiveness is limited. As the embedment depth increases, the internal support moment and lateral displacement of the wall increase slightly. Taking a pit with a shallow embedded CSM wall as an example, the transverse and vertical displacements increase and then decrease with a four-span pit as the limit, and the axial force and bending moment of the steel supports increase and then decrease with a two-span pit as the limit. The maximum lateral displacement value of the CSM wall at five-span is higher than the value at two-span increased by 21.14%. The study provide important reference significance for the embedment depth of diaphragm wall and pit excavation span in the subsequent excavation works of the same type of foundation pits.

Comment No. 3: Authors should clearly write what the motivation of this paper is.

Response: Thanks to the reviewer's reminder, we strongly agree with this point. In the Abstract, Introduction and Conclusion, we point out the research objectives and significance of this paper.

The modified text reads:

Abstract:

The study findings demonstrate the embedment depth of the CSM wall and the span of the pit excavation influence the displacement and support stresses of the support structure. The further increases in embedment depth may be helpful in improving support result, but their effectiveness is limited. As the embedment depth increases, the internal support moment and lateral displacement of the wall increase slightly. Taking a pit with a shallow embedded CSM wall as an example, the transverse and vertical displacements increase and then decrease with a four-span pit as the limit, and the axial force and bending moment of the steel supports increase and then decrease with a two-span pit as the limit. The maximum lateral displacement value of the CSM wall at five-span is higher than the value at two-span increased by 21.14%. The study provide important reference significance for the embedment depth of diaphragm wall and pit excavation span in the subsequent excavation works of the same type of foundation pits.

Introduction

Through laboratory tests, Rabbani. et al. [22] studied that the tensile strength of the treated soft clay can be increased by 35 times by using CSM method and A mixture of Air Cooled Blast Furnace Slag (ACBFS) and Industrial Hydrated Lime (IHL) as chemical stabilizer, which is obviously higher than using chemical stabilizer alone. Russell et al [23] added polypropylene fibres to hydraulic soil mixes to investigate the ability of the fibres to improve the flexural properties of walls.

In engineering applications, Gomes. et al. [11] listed successful application cases of CSM technology in foundation pit support and foundation treatment in Portugal, and proposed the design and implementation standards of CSM technology through two-dimensional finite element simulation. However, the model was not extended to three-dimensional calculation. Leach. et al. [12] investigated the CSM plate by combining simulation and monitoring in an example of a shaft with IPE300 steel placed on the inner surface of CSM plate as support and an average excavation depth of 18 meters. Although the authors achieved good results, they concluded that the method could only be applied in a small range. At present, the use of CSM walls in China is relatively scarce, and there is a lack of sufficient studies on numerical simulation regarding this type of structure. Therefore, conducting such simulations holds immense importance and value as they provide valuable insights and opportunities to enhance the efficiency and safety of the excavation process.

The numerical simulation method offers several advantages, including strong intuitions, low costs, simple operation, strong flexibility, immediate feedback of results, and real-time monitoring of engineering progress [24-27]. Consequently, both local and international scholars have used numerical simulation to gain a deeper understanding of the deformation characteristics and stress patterns of foundations. This research has produced some results [28-32]. Compared with the engineering application, the numerical simulation study of foundation excavation using CSM construction method lags behind. In the deep foundation pit of the Suning Square project in Nanchang, Jiangxi Province, Theunissen and Fraser [33] evaluated the acceptable level of lateral displacements of the CSM walls by simulating the strut loads and wall stiffnesses of the support system that were known. Lindquist. et al. [13] studied the supporting system of Seattle Herald Square District, investigated the physical and mechanical indexes of CSM wall deformation, CSM wall strength, groundwater level change, and maximum lateral displacement of the supporting system in the foundation pit supporting engineering, and verified the performance of CSM wall technology. However, the authors did not deeply study the internal force change of the supporting structure. As a result, this method has been widely utilized in numerous projects. Thus, conducting such simulations holds significant importance and value as it can provide insights and improve the efficiency and safety of the excavation process.

Conclusion

The GTS NX finite element simulation software is employed, taking the foundation pit project in eastern China as a reference case. The objective is to assess the impact of CSM walls and internal support systems and provide valuable insights for optimizing the design of similar pit excavation projects in the future. The research compares ten different working conditions to determine the displacements of the CSM wall and the forces exerted on the support system during the foundation excavation process. Two factors were investigated in this study, namely pit span and CSM wall burial depth. The effect of different pit spans on the behavior and performance of the CSM wall system was investigated for single, two, three, four and five span pits. The conclusions are as follows.

Comment No.4: More metric may be used for comparison of results.

Response: Thanks to Reviewer's reminder, In the comparative analysis, we tried to improve the description of the indicators and the degree of influence of objective representational factors. These indicators are reflected in both the abstract and the result analysis, so they are not listed.

Comment No.5: Some paragraphs are too long to read. They should be divided into two or more for comprehensibility and readability.

Response: We sincerely appreciate the valuable comments. We fully respect the reading habits of the readers and carry out a comprehensive revision of the paper to ensure the logical flow of the article, concise description of the paragraph content and clear expression.

In order to make the article readable and tightly organized, we carefully read through the whole article several times, and modified the abstract, introduction, conclusion, references, misspellings and other improper points. We sincerely thank the editor and all reviewers for their valuable feedback that we have used to improve the quality of our manuscript. Once again, thank you very much for your comments and suggestions. Correspondence should be directed to Guoqing Cai at the following address:

Institution and address: School of Civil Engineering, Beijing Jiaotong University, Haidian, Beijing 100044, China

Telephone: +86 010 51683462

Email: [email protected]

Thanks very much for your attention to our paper. Very sincerely yours,

Jian Wu, Ye-peng Shan, De-jun Liu, Yan-lin Su, Hua-xiong Wang, Guo-qing Cai*

Author Response File: Author Response.docx

Reviewer 3 Report

Authors carried out extensive research on Study on the Effect of Multi-span Pit Excavation on Supporting Structure Based on the CSM Method

1) Begin the abstract with a background summary/problem of research

2) Provide recommendation for future use or application of your research in the abstract

3) There is need to update the review of previous studies section, as few literatures were only considered

4) The research gap, research significance and objectives were not clear at the end of the introduction section

5) Section 2.1, provide the photos of the foundations

6) Section 3.1, based on what do you based your assumptions and how did you validate them, what are the references considered?

7) How were your models validated?

8) Merge your results and discussions together not separately presented

9) Rewrite all your conclusions

10) Check for grammatical errors

need to check for grammatical errors

Author Response

Response Letter

Dear Assigned Editor and Reviewer:

Comment No. 1: Begin the abstract with a background summary/problem of research.

Comment No. 2: Provide recommendation for future use or application of your research in the abstract.

Response: Thanks to Reviewer for reminder, we have mainly rewritten the background summary/problem of the abstract. This background summary/problem will help the reader get involved in the research more quickly. We make some suggestions for research at the end of the summary.

The modified text reads:

Comment No. 3: There is need to update the review of previous studies section, as few literatures were only considered

Comment No. 4: The research gap, research significance and objectives were not clear at the end of the introduction section

Response: Thanks to Reviewer for reminder, We are acutely aware that the original introductory section has fewer references and lacks a systematic summary, Therefore, the introduction has been rearranged, 16 references have been added/replaced, 4 references have been deleted, and a comprehensive and systematic review of the innovations and shortcomings of the existing literature has been carried out to summarise and introduce the research of this paper. At the end of the introduction, the current research deficiencies, research objectives and research aims are more clearly identified.

The modified text reads:

Introduction

In recent years, the continuous development of urban underground space has led to a number of challenges to engineering brought about by the deformation of supporting structures in foundation pits [1-6]. The CSM method combines the undisturbed soil mixing method with the double wheel milling groove method and can be adapted to a variety of environments. Despite its many advantages, such as seepage prevention, soil retaining, foundation engineering, and geological improvement [7-12]. The CSM approach for excavating multi-span foundation pits offers several benefits, including high construction efficiency, suitability for complex site conditions, precise verticality control, effective anti-seepage measures, low soil replacement rates, and environmentally-friendly practices[13-20]. The quality of the deep foundation pit wall is raised to a new level by using the CSM construction method with new materials. Li. et al. [21] adopted the SC50 CSM cement mixing pile machine to construct equal thick soil cement mixing walls as the anti-seepage reinforcement curtain and conducted three non-position test wall tests on-site, proving the anti-seepage property of CSM wall in the excavation of deep foundation pits. Through laboratory tests, Rabbani. et al. [22] studied that the tensile strength of the treated soft clay can be increased by 35 times by using CSM method and A mixture of Air Cooled Blast Furnace Slag (ACBFS) and Industrial Hydrated Lime (IHL) as chemical stabilizer, which is obviously higher than using chemical stabilizer alone. Russell et al [23] added polypropylene fibres to hydraulic soil mixes to investigate the ability of the fibres to improve the flexural properties of walls.

The numerical simulation method offers several advantages, including strong intuitions, low costs, simple operation, strong flexibility, immediate feedback of results, and real-time monitoring of engineering progress [24-27]. Consequently, both local and international scholars have used numerical simulation to gain a deeper understanding of the deformation characteristics and stress patterns of foundations. This research has produced some results [28-32]. Compared with the engineering application, the numerical simulation study of foundation excavation using CSM construction method lags behind. In the deep foundation pit of the Suning Square project in Nanchang, Jiangxi Province, Theunissen and Fraser [33] evaluated the acceptable level of lateral displacements of the CSM walls by simulating the strut loads and wall stiffnesses of the support system that were known. Lindquist. et al. [13] studied the supporting system of Seattle Herald Square District, investigated the physical and mechanical indexes of CSM wall deformation, CSM wall strength, groundwater level change, and maximum lateral displacement of the supporting system in the foundation pit supporting engineering, and verified the performance of CSM wall technology. However, the authors did not deeply study the internal force change of the supporting structure. As a result, this method has been widely utilized in numerous projects. Thus, conducting such simulations holds significant importance and value as it can provide insights and improve the efficiency and safety of the excavation process.

Comment No. 5: Section 2.1, provide the photos of the foundations

Response: Thanks to the suggestion of the reviewer, the description of the position of the support structure of the mine in relation to the ground has been added to the original project summary.

Comment No. 6: Section 3.1, based on what do you based your assumptions and how did you validate them, what are the references considered?

Response: When carrying out a study of the displacement and internal forces of foundation support structures, a research hypothesis is a speculation or assumption about the research problem, which is usually a hypothetical statement about the expected results. In this paper, we refer to many references when making these assumptions, and the research assumptions are clear, specific and verifiable. When performing the numerical simulation analysis, we use measured data to compare with the numerical simulation results to calibrate the accuracy of the numerical model results used to test or support the research hypotheses.

Comment No. 7: How were your models validated?

Response: Thanks to the reviewer's reminder, we have added more specific information in Section 2, Engineering Overview, and added the comparison curve between numerical simulation data and measured data in Section 2, Numerical Modelling, to verify the accuracy of the model's prediction results.

The modified text reads:

2.2 Monitoring program

The monitoring items of this project mainly include the horizontal/vertical displacement of CSM wall and vertical displacement of the top of column post. The area shown in Fig. 2 is arranged with 7 CSM wall horizontal/vertical displacements (Ld) and 6 column vertical displacement monitoring points (L). The monitoring frequency was determined according to the actual situation of the project before excavation of the pit, and the monitoring frequency was adjusted according to the change of data during the construction process.

3.4 Validation of model results

In order to ensure the accuracy and reliability of the numerical finite element simulation calculation results, the pit CSM wall horizontal displacement monitoring data were extracted and compared with the Midas GTS NX simulation results, and the results are shown in Fig. 6. The simulation results were slightly smaller than the measured data, and the maximum horizontal displacements of the CSMs in the one-span pits were more consistent with the average errors of Ld 2 and Ld 6, which were 14 % and 14 %, respectively. The average errors of lateral displacement and Ld2 and Ld6 are 14% and 14% respectively, which are in good agreement, and the finite element numerical model can be considered more reliable.

Comment No. 8: Merge your results and discussions together not separately presented

Comment No. 9: Rewrite all your conclusions

Response: Thanks for the reviewer's reminding, we have re-integrated the discussion and conclusion, and the conclusion will be more concise and smooth.

Conclusion

According to the comparison between the field measured data and the numerical simulation, the maximum lateral displacement of the side wall of the foundation pit increases gradually with the excavation of the foundation pit, and the lateral displacement tends to be stable gradually at the later stage of excavation. The maximum lateral displacement of the CSM wall is only 4 mm, and the perpendicularity and displacement of the wall are controlled at a safe level.
Once embedment depth has been reached, further increases in embedment depth may be helpful in improving cavity containment, but their effectiveness is limited. As the embedment depth increases, the internal support moment and lateral displacement of the wall increase slightly. To achieve optimal design and ensure safety, the depth of the CSM wall embedment should be fully considered during the design stage of the foundation pit.
As the span of the excavation increases, the pressure of the soil on the CSM wall increases, the axial force of the steel column increases continuously, and the values of the lateral displacement of the CSM wall, the vertical displacement and the bending moments of the steel column first increase and then decrease. The most unfavourable value is in this area of the pit span, so it should be fully considered in the pit design.

Comment No. 10: Check for grammatical errors

Response: We thank the reviewers for reminding us that there are indeed some grammatical errors in our paper, and that these errors may affect the readers' understanding and evaluation of the paper. Therefore, we are carefully checking the grammatical errors in the paper and correcting them in this revision. At the same time, we conduct a comprehensive self-examination of the paper, fully consider the reading habits of the readers, and correct the expressions that are not clear enough.

Institution and address: School of Civil Engineering, Beijing Jiaotong University, Haidian, Beijing 100044, China

Telephone: +86 010 51683462

Email: [email protected]

Thanks very much for your attention to our paper. Very sincerely yours,

Jian Wu, Ye-peng Shan, De-jun Liu, Yan-lin Su, Hua-xiong Wang, Guo-qing Cai*

Author Response File: Author Response.docx

Reviewer 4 Report

The paper presents the results of a parametric study using numerical simulation of displacements and internal stresses of the support structure during the excavation of foundation pit based on the Cutter Soil Mixing (CSM). For constitutive behavior of the soil, the Modified Mohr-Coulomb material model has been adopted into to two-dimensional finite element model using Midas GTS NX 11 finite element software. The study findings demonstrate the substantial influence of the pre-burial depth of the CSM wall and the excavation span of the pit on the displacements and support stresses of the support structure.

Dear authors,

together with this note, a PDF file with the coloured lines and notes with remarks and suggestions to improve your manusript is sent. The main areas to address are as follows:

1. The parameters of the soil material model should be introduced into the manuscript. As the paper deals solely with the numerical modeling using FEM, the in-depth description of the numerical (computational, FEM, Midas/gts) model is essential. Therefore, the presentation of the used values of the material model parameters for Modified Mohr-Coulomb (MMC) constitutive model would be very welcomed. Together with other main settings and boundary conditions, these informations are necessary for proper understanding and reproductibility of the computational model.

2. Clarification and reasoning for some conlusions in corresponding sections should be improved. Reformulation or clarification according the presented data using proper metric and/or specific values or mathematical expression are recommended.

3. Example schematic labeled Figures of the model/situation/condition would be welcomed.

4. Minor editing issues.

Sincerely

Reviewer

Comments for author File: Comments.pdf

Author Response

Response Letter

Dear Assigned Editor and Reviewer:

We have studied reviewers’ comments carefully and tried our best to revise our manuscript according to the comments. The following are the responses and revisions we have made in response to the reviewers' questions and suggestions on an item-by-item basis. Our response is given in normal font and changes/additions to the response letter are given in the red text. Again, we are very grateful to Editor and Reviewers for reviewing the paper so carefully!

Comment No. 1: The parameters of the soil material model should be introduced into the manuscript. As the paper deals solely with the numerical modeling using FEM, the in-depth description of the numerical (computational, FEM, Midas/gts) model is essential. Therefore, the presentation of the used values of the material model parameters for Modified Mohr-Coulomb (MMC) constitutive model would be very welcomed. Together with other main settings and boundary conditions, these informations are necessary for proper understanding and reproductibility of the computational model.

Response: Thank you for your attention to the selection of models in this paper and your suggestions to improve the quality of the paper. It is true that some of the model parameters were omitted from the original article, and we have focused on adding the parameter determination and selection of the MMC model in 3.2.

The modified text reads:

3.2 Model overview

3.2.1 Constitutive model

This study adopted the Modified Mohr-Coulomb constitutive model (MMC) as the basic model and established a two-dimensional finite element model based on the project’s geological conditions and the surrounding environment. The Modified Mohr-Coulomb model is an extension of the Mohr-Coulomb model and is commonly used for silty or sandy soils. It is a composite material model that combines nonlinear elastic and plastic models to describe the soil behavior [38-39]. Parameters of each soil layer in the foundation pit are shown in Table 1.

Table 1. Physical and mechanical properties of soils

Number	Stratum	Initial void ratio e₀	Poisson's ratio v	Volumetric weight γ (kN∙m^-3)	Elasticity modulus (MPa)	Internal friction angle φ (°)	Cohesion c (kPa)	Secant modulus (MPa)	Tangent modulus (MPa)	Unloading elastic modulus (MPa)
①	Miscellaneous fill	0.7	0.4	18.4	21.00	8.0	10.0	2500	2500	7500
②	Clay 1	0.9	0.3	18.9	24.70	18.0	14.0	3100	3100	9300
③	Clay 2	0.6	0.3	20.2	23.44	20.8	13.0	3100	3100	9300
④	Clay 3	0.7	0.3	20.0	28.50	22.6	14.6	3100	3100	9300
⑤	Sandy silt	0.6	0.3	20.2	22.68	32.4	6.6	3700	3700	11100
⑥	Clay 4	0.8	0.3	20.1	25.82	18.9	24.0	3100	3100	9300

Comment No. 2: Clarification and reasoning for some conlusions in corresponding sections should be improved. Reformulation or clarification according the presented data using proper metric and/or specific values or mathematical expression are recommended.

Response: We have added the suggested content to the manuscripton [insert the exact location where the change can be found inthe revised manuscript].

Comment No. 3: Example schematic labeled Figures of the model/ situation/ condition would be welcomed.

Response: We have added the necessary supplements and explanations to all the diagrams to make them easier for readers to understand. We have labelled the soil layer information on the original basis of Fig. 1 and labelled the internal structure. Fig. 3 is expanded to show the construction model under different working conditions.

The modified text reads:

Project Overview

2.1 General situation of foundation pit retaining structure

3.2.2 GTS NX Models

The wireframe of the model was created using CAD, and a two-dimensional model was established using finite element software MIDAS/GTS to simulate the excavation and construction process of the foundation pit. The 2D unit simulated the soil of each layer, and the inner support, uplift pile, column pile, and structural plate were simulated using a 1D linear elastic beam unit model. The pressure bar between walls was simulated by a 1D elastic truss element line model, comprising a total of 16,454 2D elements and 15,283 nodes. Table 2 displays the structural unit material parameters used in the model, and Figure 1 illustrates the model. The CSM wall was set 0.1m away from the supporting structure, with an embedded depth of 18.5 m for working conditions ①, ②, ③, ④, and ⑤ and 27.0 m for working conditions ⑥, ⑦, ⑧, ⑨, and ⑩. The span of soil was 37.00 m under working conditions ① and ⑥, 40.80 m under working conditions ② and ⑦, 45.15 m under working conditions ③ and ⑧, 50.07 m under working conditions ④ and ⑨, and 55.00 m under working conditions ⑤ and ⑩. Working conditions 1, 4 and 9 are selected as typical representatives, and the schematic diagram is shown in Fig. 3.

Comment No. 4: Minor editing issues.

Response: We tried our best to improve the manuscript and made some changes to the manuscript. These changes will not influence the content and framework of the paper. And here we did not list the changes but marked in red in the revised paper. We appreciate for Editors/Reviewers’ warm work earnestly and hope that the correction will meet with approval.

Institution and address: School of Civil Engineering, Beijing Jiaotong University, Haidian, Beijing 100044, China

Telephone: +86 010 51683462

Email: [email protected]

Thanks very much for your attention to our paper. Very sincerely yours,

Jian Wu, Ye-peng Shan, De-jun Liu, Yan-lin Su, Hua-xiong Wang, Guo-qing Cai*

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The study may be published after modifications. Thank you for your responses

Author Response

Response Letter

Dear Assigned Editor and Reviewer:

On behalf of all the contributing authors, I would like to express our sincere appreciations again of your letter and reviewers’ constructive comments concerning our article entitled “Study on the Effect of Multi-span Pit Excavation on Supporting Structure Based on the CSM Method” with the reference number sustainability-2534639. These comments are all valuable and helpful for improving our article.

According to reviewers’ comments and our re-examination of the manuscript, we made a lot of modifications to the manuscript to make the logic of the manuscript smoother. In this revised version, our changes to the manuscript are marked in blue to distinguish them from the first revision, which was marked in red. We have included some of the important changes at the bottom of the letter for you and Assigned Editor to review. Again, we are very grateful to Editor and Reviewers for reviewing the paper so carefully!

Modification 1. Monitor project and engineering background profiles for clarification and reformulation.

The modified text reads:

2.2 Monitoring program

The monitoring items of this project mainly include the horizontal/vertical displacement of CSM wall and vertical displacement of the top of column post. The area shown in Figure. 2 is arranged with 7 lateral/vertical displacements measurement control points of CSM wall (Md) and 6 vertical displacement measurement control points of column (V). The monitoring frequency was determined according to the actual situation of the project before excavation of the pit, and the monitoring frequency was adjusted according to the change of data during the construction process.

Modification 2. In the original text, multiple expressions of "+" and "-" are distributed throughout each section, leading to separation and disunity of meaning. In this revision, more attention is paid to readers' reading habits and conventional rules, and detailed descriptions are made in the analysis of displacement, axial force and bending moment to express specific meaning.

The modified text reads:

3.4 Validation of model results

In order to ensure the accuracy and reliability of the numerical finite element simulation calculation results, the pit CSM wall lateral displacement monitoring data were extracted and compared with the Midas GTS NX simulation results, and the results are shown in Figure. 6. The displacement of the CSM wall is indicated as “+” and “-” for the direction towards and outside the pit, respectively. As can be seen in Figure 6, the lateral displacement of the top of the CSM wall developed continuously as the excavation depth increased during excavating the foundation pit. From the pit excavation to the completion stage, the displacement of the top of the CSM wall towards the outside of the pit gradually increases and tends to be stable, and the maximum displacement is -4.06 mm. The simulation results are slightly larger than the measured data, and the maximum lateral displacements of the CSM in the single-span pits have a smaller average error of 21 % and 14 % with respect to Md 2 and Md 6, respectively. Simulation values agree well with monitoring data, and it is reasonable to assume that finite element model results can basically accurately reflect CSM wall displacement and deformation law, and changing law of other influences.

4.2 CSM wall vertical displacement

To analyze the maximum vertical displacement of CSM wall unit nodes for various embedment depths under working condition ①, we selected fifteen processes and calculated the simulated values of the vertical upward and downward displacement of the CSM wall support structure. The results are shown in Figure. 9. The displacement of CSM wall "+" and "-" represent vertical downward and upward displacement respectively.

4.4 Bending moment of internal support

Bending moment analyses of steel braced unit nodes were carried out for 15 different processes in Table 1 for different burial depths of the CSM wall under working condition ①. Two bending moments were selected for numerical analysis, and the simulated values of the process steel support axial force are presented in Figure. 13. The moment of the external force on the beam on the left side of the section towards the center of the section is a positive bending moment when turning clockwise and a negative bending moment when turning anticlockwise. As can be seen from the figure, the bending moment of the steel column removal stage is generally larger than that of the steel column construction stage. When the last steel support is installed, although the bending moment value of the steel support is reduced, the direction is deflected, which easily causes the instability of the steel support.

Modification 3. This alteration enhances control and safety levels with regard to displacement, consequently assessing the safety of foundation pit engineering.

The modified text reads:

3.4 Validation of model results

Excessive lateral displacement can seriously compromise the safety of the project as the displacement of the top of the CSM wall directly affects the deformation of the surrounding ground outside the pit. According to the study of Zhang et al. [39] on the limit displacement of the retaining wall under the limit equilibrium state, for the clay layer, the maximum lateral displacement limit of the retaining wall towards the inside of the pit is basically in the range of 0.002~0.005 H (H is the height of the rigid support structure above the ground), and the maximum lateral displacement limit of the retaining wall towards the ground is about 10 times of the maximum lateral displacement of the retaining wall towards the inside of the pit [40]. The excavation depth of this pit is H = 27.2 m, and the maximum lateral displacement towards the soil is 4.06 mm, which is much smaller than the lower limit of allowable displacement.

Modification 4. Minor editing issues

Reorganize and improve the abstract and keywords.
Re-examine the data in this article.
We have restructured certain paragraphs, streamlining and condensing content found in graphs and tables to align with reader preferences for ease of consideration.
Reformat Table 1 for aesthetic purposes.
Check for syntax and change bugs
The format of references is unified and standardized.

Institution and address: School of Civil Engineering, Beijing Jiaotong University, Haidian, Beijing 100044, China

Telephone: +86 010 51683462

Email: [email protected]

Thanks very much for your attention to our paper. Very sincerely yours,

Jian Wu, Ye-peng Shan, De-jun Liu, Yan-lin Su, Hua-xiong Wang, Guo-qing Cai*

Author Response File: Author Response.pdf

Reviewer 3 Report

All comments addressed

Author Response

Response Letter

Dear Assigned Editor and Reviewer:

On behalf of all the contributing authors, I would like to express our sincere appreciations again of your letter and reviewers’ instant feedback concerning our article entitled “Study on the Effect of Multi-span Pit Excavation on Supporting Structure Based on the CSM Method” with the reference number sustainability-2534639. These comments are all valuable and helpful for improving our article.

Modification 1. Monitor project and engineering background profiles for clarification and reformulation.

The modified text reads:

2.2 Monitoring program

The modified text reads:

3.4 Validation of model results

4.2 CSM wall vertical displacement

4.4 Bending moment of internal support

Modification 3. This alteration enhances control and safety levels with regard to displacement, consequently assessing the safety of foundation pit engineering.

The modified text reads:

3.4 Validation of model results

Modification 4. Minor editing issues

Reorganize and improve the abstract and keywords.
Re-examine the data in this article.
We have restructured certain paragraphs, streamlining and condensing content found in graphs and tables to align with reader preferences for ease of consideration.
Reformat Table 1 for aesthetic purposes.
Check for syntax and change bugs
The format of references is unified and standardized.

Institution and address: School of Civil Engineering, Beijing Jiaotong University, Haidian, Beijing 100044, China

Telephone: +86 010 51683462

Email: [email protected]

Thanks very much for your attention to our paper. Very sincerely yours,

Jian Wu, Ye-peng Shan, De-jun Liu, Yan-lin Su, Hua-xiong Wang, Guo-qing Cai*

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear authors,

your paper was significantly improved in the required areas, mainly in the description of the methods, presentation of the input values and conlusions based on the results.

There are some issues remaining to be addressed which are yellow coloured on the corresponding lines with notes inserted in the included pdf file.

1. Presented conclusions should be partially improved, particularly in point (1)

2. Results presented in Chapter 4.1 is inconsistent in sing convention used.

3. Minor editing issues

Sincerely

Reviewer

Comments for author File: Comments.pdf

Author Response

Response Letter

Dear Assigned Editor and Reviewer:

According to reviewers’ comments and our re-examination of the manuscript, we made a lot of modifications to the manuscript to make the logic of the manuscript smoother. In this revised version, our changes to the manuscript are marked in blue to distinguish them from the first revision, which was marked in red. Except for grammar and minor questions, point-by-point responses to key and core questions for reviewers are listed at the bottom of the letter. Again, we are very grateful to Editor and Reviewers for reviewing the paper so carefully!

Comment No. 1: Section 2.1, 1. First sentence reformulation would be welcomed. It should be clear, what "project" is talked about.

Suggestion: The aim of this paper is to model the multi-span foundation excavation project in East China. The foundation pit.

Adding reference to this project would be welcomed at this point.

Response: Thank you for your attention to the foundation pit engineering in this paper and your suggestions to improve the quality of the paper. Enhancing the quality of engineering information will facilitate readers' comprehension of the intricate inherent to foundation pit excavation. Currently, the pertinent scientific research manuscript for this project remains unpublished, lagging in tandem with the construction timeline. As the inaugural material introducing this foundation pit project, this manuscript stands poised to offer a valuable reference point for forthcoming research endeavors. We extend a warm welcome to the submission of more exemplary manuscripts, poised to augment and refine the research associated with this project in the time ahead.

Comment No. 2: Section 2.2, Clarification or reformulation would be welcomed according the Figure 2: monitoring items. horizontal/vertical sensors, gauges, measurement control points.

Response: We have added the necessary supplements and explanations to all the diagrams to make them easier for readers to understand.

Taking Figure 2 as an example, the revised text is as follows:

2.2 Monitoring program

Comment No. 3: Section 4.1, "+" or "-" notation should be set accordingly for the whole chapter to be consistent in the text/figures/tables. Please, see the chapter 4.2, which is written consistently.

Response: Thank you for your guidance and help. In the original text, multiple expressions of "+" and "-" are distributed throughout each section, leading to separation and disunity of meaning. In this revision, more attention is paid to readers' reading habits and conventional rules, and detailed descriptions are made in the analysis of displacement, axial force and bending moment to express specific meaning.

The modified text reads:

3.4 Validation of model results

4.2 CSM wall vertical displacement

4.4 Bending moment of internal support

Comment No. 4: Section 4.1, Results presented in Chapter 4.1 is inconsistent in sing convention used.

Response: We have re-written this part according to the Reviewer’s suggestion. We assessed the validity of numerical models using actual engineering data. This phenomenon was analyzed in light of project measurements and other pertinent references.

The modified text reads:

After conducting numerical simulations of ten different working conditions and comparing the results using Figure. 8, and the conclusions are as follows:

The embedment depth of the CSM wall plays a vital role in the pit enclosure design process. Several factors such as construction difficulty, pit construction cost, and groundwater infiltration during precipitation excavation make it a crucial consideration for actual projects. The maximum lateral displacement at a depth of 27.0 m is about 6.8% larger than that at a depth of 18.5 m. The reason is that the smaller embedment depth does not have enough stiffness to resist the lateral earth pressure, and the tendency of deflection in the pit is intensified, resulting in the convergence of the top of the wall towards the inner side of the pit and the small lateral displacement.

Comment No. 5: Section 5, Max lateral displacement of 4 mm is the result of the field measured data and is not the results of this paper (FEM simulation). Why is this number important to mention in the conclusion, what is its relevance etc.

Response: We have re-written this part according to the Reviewer’s suggestion. The model presented in this paper is rooted in and dedicated to practical engineering, with a keen focus on the deformation of the CSM wall. The factual horizontal displacement of the CSM wall bears a direct correlation to the safety of the foundation pit and the stability of the stratum, thus rendering the actual displacement value of paramount significance. Moreover, the engineering monitoring data stand as invaluable and cherished resources, serving to validate the accuracy of the finite element model and ascertain its compatibility with the actual project. As such, the discussion of lateral displacement values finds its place in the concluding remarks of this manuscript.

The modified text reads:

Measured field data indicate that the maximum lateral displacement of the side wall of the foundation pit increases gradually with the excavation of the foundation pit, and the lateral displacement tends to be stable gradually at the later stage of excavation. The apex of the CSM wall exhibits a maximum lateral displacement toward the ground of merely 4.06 mm, which is less than the lower limit of allowable displacement. This outcome substantiates the efficacy of this technology in delivering robust foundation pit support. Moreover, the simulation results underscore their precision and reliability, as evidenced by the commendable concurrence between on-site measurements and the numerical data.

Comment No. 6: Section 5, Term perpendicularity is not mention in the whole manuscript, why it is important, what are the references etc?

- controlling and safe levels of the displacement are not mention in the paper content. what are its conditions, references etc?

Response: We have refined the articulation of this segment, delved into the ultimate displacement of foundation pit support in Section 3.4 pertaining to engineering monitoring, and included two additional references. Theoretically, the discussion extends to the limiting threshold of foundation pit support, furnishing a valuable reference for engineering construction.

The modified text reads:

3.4 Validation of model results

Comment No. 7: Minor editing issues

Response: We made the following improvements

Reorganize and improve the abstract and keywords.
Re-examine the data in this article.
We have restructured certain paragraphs, streamlining and condensing content found in graphs and tables to align with reader preferences for ease of consideration.
Reformat Table 1 for aesthetic purposes.
Check for syntax and change bugs
The format of references is unified and standardized.

Institution and address: School of Civil Engineering, Beijing Jiaotong University, Haidian, Beijing 100044, China

Telephone: +86 010 51683462

Email: [email protected]

Thanks very much for your attention to our paper. Very sincerely yours,

Jian Wu, Ye-peng Shan, De-jun Liu, Yan-lin Su, Hua-xiong Wang, Guo-qing Cai*

Author Response File: Author Response.pdf

Round 3

Reviewer 4 Report

Dear Authors,

only a couple of minor corrections would be welcomed before publishing your article. Three notes on the corresponding lines (2 sentences reformulation on lines 106-109, reference no. 37 missing in the text) are included into the inlucluded pdf file.

Sincerely

Reviewer

Comments for author File: Comments.pdf

Author Response

Response Letter

Dear Assigned Editor and Reviewer:

I hope this message finds you well. On behalf of the authors of the paper entitled “Study on the Effect of Multi-span Pit Excavation on Supporting Structure Based on the CSM Method” with the reference number sustainability-2534639. I would like to extend our heartfelt gratitude for your invaluable assistance and meticulous review of our manuscript.

Your guidance and insightful recommendations have been instrumental in enhancing the quality and rigor of our research. Your meticulous scrutiny and constructive suggestions have undoubtedly contributed to refining the clarity and precision of our work. Your dedication to the peer review process plays a pivotal role in advancing the standards of scientific discourse, and we are truly grateful for your commitment to scholarly excellence.

According to your comments, we have revised the manuscript accordingly. In this revised version, our changes to the manuscript are marked in green. The revised paragraphs have presented to you for your review. Again, we are very grateful to Editor and Reviewers for reviewing the paper so carefully!

Comment No. 1: Before processing your manuscript further, it would be greatly appreciated. if you could describe, in detail, how your research contributes to sustainability.

Response: The Cutter Soil Mixing (CSM) method stands as an innovative deep-mixing construction technique, which forms a continuous underground wall of equal thickness by cutting the in-situ soil at the construction site and mixing it with cement slurry and other solidifying agents. It is suitable for embankment reinforcement and seepage control treatment of various complex geological conditions such as gravel and soft rock, deep foundation pit enclosure, etc. It is more advantageous for the drop bottom stop curtain in the area of high pressurized water. Compared with the traditional diaphragm wall, this technology is low-carbon and environmentally friendly, with high wall quality and fast construction speed, which is generally recognized by the society. This technology has certain demonstration and guiding significance for the sustainable development of multi-span foundation pit projects. The nexus between the CSM wall and sustainability has been elucidated within the abstract and introduction of the manuscript.

Comment No. 2: Please let us know if all the figures and tables in your manuscript have been submitted for publication for the first time or can be used without any copyright constraints. If this is not the case, please provide copyright permissions where they are necessary. If you adapt or use only a part of a figure or table published in a non-open access resource, copyright permission is still needed. Copyright permissions can usually be obtained via an online form or by e-mailing the copyright holder, and it is the authors’ responsibility to obtain them.

Response: We guarantee that all diagrams in this manuscript are submitted for publication for the first time and can be used without any copyright restrictions.

Comment No. 3: Section 2.1,

The meaning of these two sentences doesn`t pair with each other well and their meaning is not clear.
The verb in this sentence is probably missing.

Response: We have complied with your suggestion and made further adjustments to the paragraph.

The modified text reads:

The site of the project has been artificially transformed due to urbanization construction, resulting in a relatively flat site. Utilizing the project site exploration report, the rock and soil layers have been categorized into six layers, which are the miscellaneous fill, clay 1, clay 2, clay 3, silt, clay 4 from the surface to the bottom. These layers exhibit varying thicknesses of approximately 1.9 m, 12.0 m, 4.7 m, 23.9 m, 3 m, 34.5 m, respectively. The support form is the ground connecting wall and internal support system, and the thickness of the continuous underground wall is 1000 mm.

Comment No. 4: Section 3.2.1, Reference 37 missing in the text.

Response: Owing to our inadvertence, Document reference [37] has been misplaced, resulting in bewilderment for both you and our readership. We kindly beseech your understanding in this matter. Reference [37] describes the simulation study of deformation characteristics of soil layer and diaphragm walls during deep foundation pit excavation, in which some characteristics of the Modified Mohr-Coulomb constitutive model (MMC) were mentioned. Therefore, we included the reference [37] to the description of this model.

The modified text reads:

3.2.1 Constitutive model

This study adopted the Modified Mohr-Coulomb constitutive model (MMC) as the basic model and established a two-dimensional finite element model based on the project’s geological conditions and the surrounding environment. The Modified Mohr-Coulomb model is an extension of the Mohr-Coulomb model and is commonly used for silty or sandy soils. It is a composite material model that combines nonlinear elastic and plastic models to describe the soil behavior [37-39]. Parameters of each soil layer in the foundation pit are shown in Table 1.

Once again, we express our deepest appreciation for your valuable contribution to our work. We look forward to the opportunity of incorporating your feedback into our research. Thank you for your dedication to advancing the field of Multi-span Pit Excavation, and for your support in helping us contribute to the body of knowledge in our discipline. Correspondence should be directed to Guoqing Cai at the following address:

Institution and address: School of Civil Engineering, Beijing Jiaotong University, Haidian, Beijing 100044, China

Telephone: +86 010 51683462

Email: [email protected]

Thanks very much for your attention to our paper.

Very sincerely yours,

Jian Wu, Ye-peng Shan, De-jun Liu, Yan-lin Su, Hua-xiong Wang, Guo-qing Cai*

Author Response File: Author Response.pdf

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Study on the Effect of Multi-span Pit Excavation on Supporting Structures Based on the Cutter Soil Mixing Method

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