Deformation and Force Analysis of Wood-Piled Island Cofferdam Based on Equivalent Bending Stiffness Principle

Round 1

Reviewer 1 Report

This manuscript investigates the deformation and force behavior of wood-piled island cofferdam by using the finite difference method. A detailed parametric analysis has been performed to capture the effects of pile length, dam width, tension bar interval, and pile interval. Overall, the paper is well-written, and the findings are interesting to both researchers and practicing engineers.  The revision should consider the specific comments listed below.

(1)   The title of this manuscript may be better revised to be “…Based on Equivalent Bending Stiffness Principle”.

(2)   In this study, the independent wood piles are equivalent to sheet piles. Please elaborate the merit and demerit of this equivalence? Is the deviation of results from the actual ones acceptable?

(3)   The Mohr-Coulomb (MC) model is used to simulate the constitutive behavior of silt and clay. However, the behavior of silt and clay is characterized by nonlinearity and plasticity, which has not been considered by the MC model. In this case, a more sophisticated advanced constitutive model is recommended to be used for simulating the behavior of silt and clay.  

(4)   Where are the material parameters summarized in Table from? Please give an explanation.

(5)   Please supplement a unit for the legend of the horizontal displacement contours in Fig. 9.

(6)   The use of wording for one thing should be consistent within the entire manuscript. For example, the phrases “wood-pile cofferdam”, “wood pile cofferdam”, and “wooden pile cofferdam” need to be unified.  

Author Response

Response to Reviewer Comments

Dear Reviewer 1,

Thank you for your constructive comments on our manuscript. These comments are valuable and helpful for revising and improving our paper. We have carefully considered the comments and some necessary corrections have been made. We have addressed and responded to all comments of the reviewers in a point-by-point fashion and highlighted major changes in main text with red color (“Track Changes” function). Please refer to the revised manuscript for details.

Comment 1. The title of this manuscript may be better revised to be “…Based on Equivalent Bending Stiffness Principle”.

Thank you for raising the wonderful suggestion about the article title. The "Equivalent Bending Stiffness Principle" is a more appropriate expression. After careful consideration, we have adopted your valuable suggestion for revising the title.

Comment 2. In this study, the independent wood piles are equivalent to sheet piles. Please elaborate the merit and demerit of this equivalence? Is the deviation of results from the actual ones acceptable?

Thank you for the comment. The wood piles are independently inserted in the riverbed and connected by the surrounding wood piles purlins. In this study, these independent wood piles were equivalent to continuous and homogeneous sheet pile material, which may deviate from the actual situation. Although this equivalent accuracy needs to be further verified, it is conducive to the simplification of numerical modeling and facilitates the parametric analysis of the wood-piled structure. Therefore, it can be considered that this is a relatively appropriate and reasonable simplification. According to the feedback from the construction site, the wood-piled cofferdam performed well during the entire cofferdam construction and service period, and no visible lateral deformation and leakage were observed. Certainly, further verification of the proposed research by monitoring data in the field and centrifuge model test results is required. These issues will be addressed in future research work to extend the versatility and application of the proposed wood-piled island cofferdam by building sophisticated numerical models.

Comment 3. The Mohr-Coulomb (MC) model is used to simulate the constitutive behavior of silt and clay. However, the behavior of silt and clay is characterized by nonlinearity and plasticity, which has not been considered by the MC model. In this case, a more sophisticated advanced constitutive model is recommended to be used for simulating the behavior of silt and clay. 

Thank you for your constructive comments about the choose of soil constitutive model. We noted the choice of constitutive model before modeling and carefully considered this problem. Unfortunately, the types of soil parameters recorded in the geological survey report are very limited, which forced us to choose the Mohr-Coulomb constitutive model with fewer soil parameters. The Mohr-Coulomb constitutive model has wide applicability in underground engineering, and the calculation results between Mohr-Coulomb and other nonlinear models are acceptable based on previous experience.

Comment 4. Where are the material parameters summarized in Table from? Please give an explanation.

Firstly, the parameters of silt and clay come from the geological exploration report of the project. As for the parameters of the solidified soil and the backfilling soil, they were measured by experiments on site. The most important wood pile parameters in this study are based on the values measured in the laboratory by Qiu et al.[1], and some reductions are made on this basis. The specific flexural stiffness value of wood piles has been explained in section 4.1 ‘Although wood is an anisotropic material, in order to facilitate modeling, it was simplified as an isotropic material, taking the flexural modulus of the wood piles as the overall elastic modulus’ and Section 4.3 ‘According to the bending strength of the wood pile calculated by Qiu et al.[1]…’. The parameters of other materials were valued according to industry specifications.

Comment 5. Please supplement a unit for the legend of the horizontal displacement contours in Fig. 9.

In the revised manuscript, we add the unit for the legend of the horizontal displacement contours in Fig. 9. as the reviewer pointed out, thank you very much for your careful reading and detailed comments.

Comment 6. The use of wording for one thing should be consistent within the entire manuscript. For example, the phrases “wood-pile cofferdam”, “wood pile cofferdam”, and “wooden pile cofferdam” need to be unified.  

Thank you for your constructive suggestion on our manuscript. We have unified the expression about the cofferdam form. Specifically, the cofferdam-related expression has been unified as "wood-piled cofferdam" and "sheet-pile cofferdam".

References

[1] Qiu Ling; Sheng Weigao; Wang Shanshan Experimental Study on Material Mechanical Properties of Wood Pile. Engineering and Testing 2013, 53, 24–26(in Chinese).

Reviewer 2 Report

The manuscript presents an original study related to a cofferdam constructed with the use of wooden piles. Scientific quality of the study does not raise concern and there is some practical potential in it. Overall, the paper is already well prepared, but some issues requite addressing prior to publication:

- General comments - Was this design used in practice? If so, were there any measurements taken for validation?

- Line 53: Please avoid contractions (informal language) like "shouldn't". Use full version, e.g. "should not".

- Line 201 - Table 1: Cohesion/Pa - It would be better to present it in kPa. This is a standard for this unit in geotechnical engineering.

- Line 210 - "Solidified soil" is mentioned here. However, it is mentioned later that grouting took place than this description occurs, which is confusing for the reader.

- Line 213-214: More problematic is the fact that adjacent elements do not interact with each other, so in the direction along the wall the stiffness is much lower.

- Line 384-385: Should it not be related to height as a dimensionless factors? Surely, the 2.5 m is only applicable for this exact particular case.

- Line 502: Some leftover text from the draft?

- Conclusions: Conclusions are very brief. If this should be more than just a description of a case study, it should be highlighted if those conclusions are applicable only to this case or can they be generalized to similar cases?

- Lines 600-609: Leftover from a template?

Author Response

Response to Reviewer Comments

Dear Reviewer 2,

Thank you for your constructive comments on our manuscript. These comments are valuable and helpful for revising and improving our paper. We have carefully considered the comments and some necessary corrections have been made. We have addressed and responded to all comments of the reviewers in a point-by-point fashion and highlighted major changes in main text with red color (“Track Changes” function). Please refer to the revised manuscript for details.

Comment 1. General comments - Was this design used in practice? If so, were there any measurements taken for validation?

Thank you for your favorable comments. As the reviewer pointed out, measurements in the deformation of this cofferdam are warranted to elucidate the stability of the wood-piled cofferdam. The reviewer’s comments on in this study are most insightful. Unfortunately, due to the COVID19 pandemic in China, which disrupts our measurements schedule in terms of the travel control by our school and government, all students and researchers, we could not leave Hefei for on-site deformation monitoring. According to the feedback from the construction site, the wood-piled cofferdam performed well during the entire cofferdam construction and service period, and no visible lateral deformation and leakage were observed. Many thanks for understanding. We thank you again for your constructive comments.

Comment 2. Line 53: Please avoid contractions (informal language) like "shouldn't". Use full version, e.g. "should not".

Thank you very much for pointing out this inappropriate formulation, and we have corrected the errors above.

Comment 3. Line 201 - Table 1: Cohesion/Pa - It would be better to present it in kPa. This is a standard for this unit in geotechnical engineering.

We have changed the unit of Cohesion in Table 1 to kPa. Thanks for your valuable comments.

Comment 4. Line 210 - "Solidified soil" is mentioned here. However, it is mentioned later that grouting took place than this description occurs, which is confusing for the reader.

Thank you for your constructive comments. The "solidified soil" mentioned in the text refers to the reinforcement of the original silty riverbed by means of grouting. In the numerical model, the step of grouting reinforcement was realized by modifying the soil parameters at a specific depth of 2.0m below the riverbed. In order to further clarify the correspondence between construction steps and numerical simulations, we have supplemented the corresponding content in Table 2.

Comment 5. Line 213-214: More problematic is the fact that adjacent elements do not interact with each other, so in the direction along the wall the stiffness is much lower.

Thank you very much for your careful reading and favorable comments. As reviewer concerned, the wood piles are independently inserted in the riverbed and connected by the surrounding wood piles purlins. However, in this study, these independent wood piles were equivalent to continuous and homogeneous sheet pile material, which may deviate from the actual situation. We have actively investigated other ways for numerical analysis, but due to the complexity of the modelling, we had not found a better way to model the wood piles. Therefore, in order to press closer to the actual stress and deformation of the wood pile cofferdam, we have to take a simplification as shown in the study. In addition, we took the flexural modulus of the wood piles as the overall elastic modulus, and a reasonable reduction of the flexural modulus was carried out on this basis.

Comment 6. Line 384-385: Should it not be related to height as a dimensionless factors? Surely, the 2.5 m is only applicable for this exact particular case.

Thank you for your constructive comments. The univariate parameter analysis in this study has certain limitations, as far as possible we could acquire the effect of one single parameter change on the overall structure. In light of your wonderful suggestion, large quantities of orthogonal experiments will be performed in the future to address the optimal parameter combination in different wood-piled cofferdam structures.

Comment 7. Line 502: Some leftover text from the draft?

We have removed words that are not relevant to the content of the article.

Comment 8. Conclusions: Conclusions are very brief. If this should be more than just a description of a case study, it should be highlighted if those conclusions are applicable only to this case or can they be generalized to similar cases?

Thank you for your constructive comments. We supplemented the Conclusion section of the article, focusing on the suitability of cofferdam structures. In addition, we have added a separate paragraph describing the deficiency in the study and the focus of future research.

Comment 9. Lines 600-609: Leftover from a template?

Appendix A and B were not involved in the manuscript, perhaps they were added by the editor to remind the writers.