Flexible Pile Group Interaction Factors under Arbitrary Lateral Loading in Sand

Round 1

Reviewer 1 Report

General comment:

This article provides interesting findings about the influence of arbitrary lateral loading on the “pile interaction factors” obtained through numerical experiments using Plaxis 3D. The numerical simulations were carefully done, and the publication of this article will merit the readers of the journal of Marine Science and Engineering to be sure. But if the reviewer has to say something, the authors had better consider if there would be so much difference in the “pile group response” from what we can expect from the available theory and knowledge.

 

Individual comments

Lines 273 to 274 on Page 7:

According to [73], pile-soil separation will occur near the top of the pile, no deeper than 20% of pile length (depending on the pile and soil stiffness).

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The reviewer does not think that authors can say “no deeper than 20% of the pile length” for sure (Please remember that we often use short piles).

As the authors wrote, piles grouped together are indeed flexible in the sense that they are not deformed over their entire length L, instead piles deformations can be negligible beneath an active length La. This La is proportional to the fourth root of EI/G, where EI is the pile group’s overall bending stiffness and G. For example, Konagai et al. (2003) showed that the behavior of grouped piles can be well described in terms of two bending stiffness parameters EI_sway and EI_rock for sway and rocking motions (see below).

Konagai K., Yin Y., MURONO Y., Single beam analogy for describing soil-pile group interaction, Soil Dynamics and Earthquake Engineering, 23(3), 213-221, 2003.

https://www.sciencedirect.com/science/article/abs/pii/S0267726102002129

As long as the authors limit the discussion to this particular case described in this article, the authors can set the model boundaries substantially far through a trial and error. But the reviewer thinks that the distance will probably depends on the active pile length. So, if any consideration is given to this, this section would be more attractive.

 

5. Results and discussion:

The findings given in this chapter are really important and interesting. However, piles are assumed to be linear and elastic in this article. So, if the reviewer has to say something, the reviewer wonders if there would be so much difference in the “pile group response” from what we can expect from the available theory and knowledge. As the reviewer wrote above, the overall “pile group response” can be well described in terms of two bending stiffness parameters EI_sway and EI_rock for sway and rocking motions, and particularly EI_rock can vary as the horizontal loading direction changes. 

Figures 11 to 17:

Readers of this article may not be sure which color (in gray scale) is which pile.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The organization and proofreading are required for the whole manuscript.

Author Response

The authors thank the Reviewer for his effort to review the manuscript and provide useful comments. We have addressed these comments, as detailed below.

Point 1: 


Extensive editing of English language and style required.  The organization and proofreading are required for the whole manuscript.

Response 1: Authors accept this comment. The proof read has been done and the changes are applied throughout the whole manuscript.

 

The authors sincerely appreciate your constructive comments. We believe  that  these  have helped to improve the quality of the paper.

Reviewer 3 Report

The authors present a well written manuscript numerically studying the influence of load application angle on the individual pile response of piles within a group configuration. The manuscript has many sections that are explained in much more detail than necessary (e.g., the very extensive literature references) but are informative however. Other section could benefit from some improvements, particularly with respect to the presentation of technical results and mechanisms.

Some critical comments are summarized below:

1. The introduction needs an English check, the rest of the manuscript reads well. 
2. The authors provide no loading protocol or any description on how lateral loads were applied. The experiment used for validation was a centrifuge experiment. Do the authors also use ground motions as their input loading? Please add this information.
3. Little explanation is provided on the mechanisms observed in Figures 11 forward. Can the authors provide a more detailed description of WHY the piles behaved the way they do? Perhaps support this with a Figure or Schematic (e.g., describe the soil movement etc).
4. It looks like the moments are not really influenced by the loading angle, which is expected given the typical circumferential reinforcement symmetry of the piles. It would be worth stating that, or elaborating on this observation in general.
5. This reviewer would recommend expressing comparisons quantitatively (e.g., 50% less, or "only 10% more, etc), instead of using general descriptions like "was found to be less than, or more than"
6. Since the readers will not necessarily be familiar with the Kothaus experiment, it is unclear whether the sand in the experiment was dry, moist, saturated and and where loading was applied. Similarly, this is not clear in the FEM studies. Table 2 implies that the sand was dry. If this is the case, how is this research applicable to the Journal of Marine Science, where piles are embedded in wet and saturated materials (i.e., below sea-level)? Shouldn't the authors have considered the impact of water within the soil layer and above the soil layer - unless the reviewer is mistaken about the focus of the Journal.
7. What about the pile shear? The authors describe which fitting technique worked best to get shear profiles but don't show any shear profiles in the manuscript. Can those be added? 
8. Also, when calculating the interaction factor, what lateral pile force was used here as reference? The pile head force, correct? Can the authors please add how this force was extracted from the FEM, since the loading application was not clear?
9. The pile cap assumption is somewhat hard to follow. The authors state that large cap sizes are unrealistic, however, in common practice, all pile groups are connected by a pile cap that provides some sort of fixity, unless the pile extends into a bridge pier or column and can be assumed free head. The configuration depicted by the authors would indicate some level of fixity but not a complete fixity? What in-situ configuration would the FEM model actually reflect? It is therefore not clear what practical case is represented with the FEM model.
10. Please add gridlines to the Figures 11 and forward. It is hard to read the values with the limited tick marks.
11. Figure 8 can be removed, it does not add any value to the paper. Similarly Figure 7 could be omitted as the description is enough. Instead shear forces in the piles should be presented.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf