Numerical Study on Pile Group Effect and Carrying Capacity of Four-Barreled Suction Pile Foundation under V-H-M Combined Loading Conditions

Round 1

Reviewer 1 Report

The following comments have to be addressed to improve the quality of the manuscript

1.      In title and throughout the manuscript, the author mentioned about “carrying capacity”. What does carrying capacity means? Vertical or lateral? It has to be more specific than general.

2.      Abstract contains redundant information which needs to be eliminated and should be presented in concise form.

3.      Line 13: Expanded forms along with abbreviation (V-H-M) should be provided at the first occurrence.

4.      Line 15: “It is assumed that the Young’s modulus and undrained shear strength of the clayed soil increase linearly with soil depth”. The sentence seems unnecessary in the abstract.

5.      Line 16, “pile length-diameter aspect ratio”. It seems unclear.

6.      Introduction, Line 48 and 52: Avoid using the word scholars. Instead prefer ‘researchers’.

7.      Line 72: “There are few studies on the pile group effect of the four-barreled 72 suction pile foundation”. Mention the studies described as few in this context and explain more about what they explored or studied.

8.      Line 83: “…. D had no effect on the standardized carrying capacity”. However, D refers to Diameter (as per Figure 1) which has major impact on the load carrying capacity. A clear explanation is demanded to understand the context.  Also provide the expanded forms along with abbreviation (D) should be provided at the first occurrence.

9.      Line 91: “Constrain the three degrees of freedom of the soil bottom boundary and the two horizontal degrees of freedom of the side boundary”. The sentence is unclear.

10.   Line 93: C3D8R is brick element. What is its relevance in pile foundation?

11.   Figure 1: “Geometry of four-barreled suction pile foundation and definition of loads: (a) side view;(b) top view”. However, figure (a) does not provide any side view as mentioned.

12.   Figure 2: “Element meshing: (a) global view; (b) top view; (c) side view”. Title of (a) seems irrelevant.

13.   Line 105: What is the rationale behind the selection of the idealizations? In general, soil which is confined in all directions exhibit a bilinear or trilinear stress-strain relationship and there will not be any plastic behavior.

14.   Section 3: Title of section 3 and subsection 3.1 should have ‘load carrying capacity’ rather than carrying capacity.

15.   Line 152: ‘RP’. The abbreviation should be provided at the first instance always.

16.   Figure 5: Ideally, an interaction envelope should include three planes so that it provides a complete solution for any load combinations possible. The representation is incomplete and is to be modified into a three-dimensional one.

17.   Line 164 to 169: Use simple sentences.

18.   Section 4.1: Why the effect of increasing aspect ratio of the piles did not have any marginal effect of the axial capacity which is wrong? Please specify.

19.   Line 190: “When the S/D ratios is less than 2, the E_V varies from 0.96-1. When the S/D ratios is greater than 2, the E_V is 1”. Explain the phenomena behind this using existing literature.

20.   Figure 17: Three dimensional interaction envelope should be provided.

21.   Section 6: Conclusion should provide more insights on the quantitative findings from the research.

22.   Line 361: The length of this specific conclusion should be reduced

23.   Section 6: Beyond the findings from the study, a general recommendation by the author should be provided at the end of conclusion.

 

24.   References: More references should be included.

Author Response

Response to Reviewer 1 Comments

Point 1: In title and throughout the manuscript, the author mentioned about “carrying capacity”. What does carrying capacity means? Vertical or lateral? It has to be more specific than general.

Response 1: The carrying capacity mentioned here takes into account the coupling of loads in multiple directions, not simply referring to the bearing capacity in a certain direction, so we believe that this expression is more appropriate.

Point 2: Abstract contains redundant information which needs to be eliminated and should be presented in concise form.

Response 2: We have made corresponding revisions.

Point : Line 13: Expanded forms along with abbreviation (V-H-M) should be provided at the first occurrence.

Response 3: We have made corresponding revisions.

Point 4: Line 15: “It is assumed that the Young’s modulus and undrained shear strength of the clayed soil increase linearly with soil depth”. The sentence seems unnecessary in the abstract.

Response 4: The undrained shear strength and elastic modulus of actual seabed foundation increase with depth, but may not increase linearly. In order to simulate, it is assumed that the undrained shear strength increases linearly with depth.

Point 5: Line 16, “pile length-diameter aspect ratio”. It seems unclear.

Response 5: We have made corresponding revisions, and revise as “embedment depth”.

Point 6: Introduction, Line 48 and 52: Avoid using the word scholars. Instead prefer ‘researchers’.

Response 6: We have made corresponding revisions.

Point 7: Line 72: “There are few studies on the pile group effect of the four-barreled 72 suction pile foundation”. Mention the studies described as few in this context and explain more about what they explored or studied.

Response 7: We have made corresponding revisions.

Point 8: Line 83: “…. D had no effect on the standardized carrying capacity”. However, D refers to Diameter (as per Figure 1) which has major impact on the load carrying capacity. A clear explanation is demanded to understand the context.  Also provide the expanded forms along with abbreviation (D) should be provided at the first occurrence.

Response 8: The original expression is wrong, should be ' normalized bearing capacity ', that is, the influence of diameter on bearing capacity is normalized. And abbreviation D has been described in the text.

Point 9: Line 91: “Constrain the three degrees of freedom of the soil bottom boundary and the two horizontal degrees of freedom of the side boundary”. The sentence is unclear.

Response 9: We have made corresponding revisions and add a reference literature

Point 10: Line 93: C3D8R is brick element. What is its relevance in pile foundation?

Response 10: The hexahedral eight-node linear reduced integral element C3D8R has the following advantages: it is not easy to occur shear self-locking phenomenon under bending load; the results of displacement are more accurate; when the mesh is distorted, the accuracy of the analysis is not greatly affected.

Point 11: Figure 1: “Geometry of four-barreled suction pile foundation and definition of loads: (a) side view;(b) top view”. However, figure (a) does not provide any side view as mentioned.

Response 11: We have made corresponding revisions and revise as “oblique upper view”.

Point 12: Figure 2: “Element meshing: (a) global view; (b) top view; (c) side view”. Title of (a) seems irrelevant.

Response 12: We have made corresponding revisions and revise as “typical 3D mesh”.

Point 13: Line 105: What is the rationale behind the selection of the idealizations? In general, soil which is confined in all directions exhibit a bilinear or trilinear stress-strain relationship and there will not be any plastic behavior.

Response 13: In the finite element foundation simulation, we generally constrain the horizontal and vertical displacements of the bottom surface of the foundation, and constrain the horizontal displacement on the side to simulate the semi-infinite foundation in the actual situation. The Tresca yield criterion with associated flow rule was appropriate and it was adopted by many researchers.

Point 14: Section 3: Title of section 3 and subsection 3.1 should have ‘load carrying capacity’ rather than carrying capacity.

Response 14: We have made corresponding revisions.

Point 15: Line 152: ‘RP’. The abbreviation should be provided at the first instance always.

Response 15: We have made corresponding revisions.

Point 16: Figure 5: Ideally, an interaction envelope should include three planes so that it provides a complete solution for any load combinations possible. The representation is incomplete and is to be modified into a three-dimensional one.

Response 16: Figure 5 shows a schematic diagram of a two-dimensional h-m failure envelope obtained using the fixed displacement ratio method. The so-called fixed displacement ratio method refers to taking the ratio of displacement increments in both directions as a constant for displacement-controlled loading until the load components in both directions reach the limit value. At this time, the loading path converges to a certain point on the envelope, and the third load component remains unchanged during this process.

Point 17: Line 164 to 169: Use simple sentences.

Response 17: We have made corresponding revisions.

Point 18: Section 4.1: Why the effect of increasing aspect ratio of the piles did not have any marginal effect of the axial capacity which is wrong? Please specify.

Response 18: The original text does not say that the increase of pile length-diameter ratio has little effect on the vertical bearing capacity, but that the increase of pile length-diameter ratio has a significant effect on the vertical bearing capacity. With the increase of pile spacing, the pile group effect gradually weakens until it disappears. Therefore, the vertical bearing capacity no longer increases with the increase of pile spacing. Please review in detail.

Point 19: Line 190: “When the S/D ratios is less than 2, the E_V varies from 0.96-1. When the S/D ratios is greater than 2, the E_V is 1”. Explain the phenomena behind this using existing literature.

Response 19: The explanation of this phenomenon is shown in Figure 7 and the next paragraph.

Point 20: Figure 17: Three dimensional interaction envelope should be provided.

Response 20: We have made corresponding revisions.

Point 21: Section 6: Conclusion should provide more insights on the quantitative findings from the research.

Response 21: We have made corresponding revisions.

Point 22: Line 361: The length of this specific conclusion should be reduced

Response 122We have made corresponding revisions.

Point 23: Section 6: Beyond the findings from the study, a general recommendation by the author should be provided at the end of conclusion.

Response 23: We have made corresponding revisions.

Point 24: References: More references should be included.

Response 24: We have made corresponding revisions.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments

 

This study presents the numerical modeling on carrying capacity of barreled suction pile foundation in clays by considering V-H-M loading conditions.

 

1.     Abstract does not highlight novelty, please revise it.

2.     Introduction is very short and not provide the true picture of this study. Moreover, scope of this study is not clear, and discuss the contribution of this study exhaustively. 

3.      The literature can be reorganized; to strengthen the literature review, the following contributions along some other latest studies must be discussed and cited in this study;

https://doi.org/10.1016/j.compgeo.2019.103160

4.     For ease of reader add a flowchart describing the methodology of this study

5.     Quality of Figs. 7, 9, 11, and 13 is not good, maintain size of all figs and legends and respective legends.

6.     Elaborate the boundary conditions of your model in detail, in Section 2.1.

7.      Some parts of conclusion section are redundant, remove them.

Comments for author File: Comments.docx

Author Response

Response to Reviewer 2 Comments

 

Point 1: Abstract does not highlight novelty, please revise it.

Response 1: We have made corresponding revisions.

Point 2: Introduction is very short and not provide the true picture of this study. Moreover, scope of this study is not clear, and discuss the contribution of this study exhaustively. 

Response 2: We have made corresponding revisions.

Point 3: The literature can be reorganized; to strengthen the literature review, the following contributions along some other latest studies must be discussed and cited in this study;

https://doi.org/10.1016/j.compgeo.2019.103160

https://doi.org/10.1016/j.undsp.2021.04.004

https://doi.org/10.1080/1064119X.2019.1576244

Response 3: Thank you very much for the reviewer 's reference suggestions, and we have cited relevant literature in this article.

Point 4: For ease of reader add a flowchart describing the methodology of this study

Response 4: In order to facilitate the readers ' reading, we have added a paragraph to explain the framework of the article.

Point 5: Quality of Figs. 7, 9, 11, and 13 is not good, maintain size of all figs and legends and respective legends.

Response 5: We have made the corresponding replacement and modification in the text.

Point 6: Elaborate the boundary conditions of your model in detail, in Section 2.1.

Response 6: We have made corresponding revisions.

Point 7: Some parts of conclusion section are redundant, remove them.

Response 7: We have made corresponding revisions.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The efforts made by the author(s) in improving the quality of the manuscript based on the comments provided are highly appreciated. However, a few of the most important comments provided in the last review were not fully addressed. Hence, for accepting the manuscript in the further level of review, the following comments have to be addressed.

·        Line 108 of the manuscript states that “The first-order, eight-node linear brick, reduced integration element C3D8R was used to model the soil [21-23]”.  As mentioned by the referred literature [21] and [22], either the C3D8P or COH3D8P elements can be used for modeling soil or the soil mass should be modeled as a single layer of infinite elements (CIN3D8). The use of C3D8R can be inappropriate for modeling soil as it does not account for soil pore pressure. Moreover, the study does not consider the interface modeling between the soil and pile which is very essential for understanding the slip and interfacial shear transfer. Considering these observations, the accuracy of the developed FE model is questionable.

 

·        In conclusion, the Inclusion of quantitative findings from the research has not been carried out effectively. The general summary/recommendations based on the study have not been included in the conclusion even after mentioning them in the first review comments.

Author Response

 

Response to Reviewer 1 Comments

Point 1: Line 108 of the manuscript states that “The first-order, eight-node linear brick, reduced integration element C3D8R was used to model the soil [21-23]”.  As mentioned by the referred literature [21] and [22], either the C3D8P or COH3D8P elements can be used for modeling soil or the soil mass should be modeled as a single layer of infinite elements (CIN3D8). The use of C3D8R can be inappropriate for modeling soil as it does not account for soil pore pressure. Moreover, the study does not consider the interface modeling between the soil and pile which is very essential for understanding the slip and interfacial shear transfer. Considering these observations, the accuracy of the developed FE model is questionable.

 

Response 1: Firstly, the original text in referred literature [22] is “The pile mass and soil mass were dispersed using continuum solid elements using mainly 8-noded hexahedral elements ( C3D8R ) along with a small number of 6-noded wedge elements ( C3D6 ). The outer layer of the soil mass was modeled using a single layer of solid infinite elements ( CIN3D8 ).” That is, the 8-noded hexahedral elements ( C3D8R ) is mainly used, and the use of the single layer of infinite elements (CIN3D8) is just for the outer layer of the soil mass to improve calculation accuracy. And we cited more references in the article. So we believe that the use of C3D8R is appropriate.

Secondly, the research in this paper focuses on the bearing capacity of the foundation under undrained conditions of clay foundation, and the pore pressure is not considered. The C3D8P [21] just considers the degree of freedom of pore pressure on the basis of the C3D8 element.

Finally, the pile-soil interface model used in this study is introduced in lines 134-139 of the article. And the validation of the FE model is described in Section 2.2.

 

Point 2: In conclusion, the inclusion of quantitative findings from the research has not been carried out effectively. The general summary/recommendations based on the study have not been included in the conclusion even after mentioning them in the first review comments.

Response 2: We have added as much quantitative description of the conclusions as possible and given general recommendations.

 

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript can be accepted in current form because all suggestions are entertained well. 

Author Response

Thank you very much for reviewing.

Author Response File: Author Response.docx