Load-Bearing Performance of Precast Piles with Integrated Side Drainage Channels in Coastal Soft Soil

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper studies the settlement characteristics of the new type of drainage pile based on theoretical methods, analyzes the influence of factors such as vacuum drainage consolidation time and pile length on pile bearing capacity, and conducts a comparison between theoretical and measured results. The research content is innovative and has certain practical engineering significance.

However, there are still a few shortcomings that need to be addressed:

(1) Please provide a comprehensive explanation of the "prefabricated vertical drains (PVDs)" mentioned in the text.

(2) In Case Two, only the soil layer information at the site and the bearing capacity curve of a single pile are provided, but no pictures of the on-site tests are shown. It is suggested to refer to Case One and supplement the relevant photos.

(3) Line 493: When calculating the influence of pile length on the bearing capacity of a single pile, why is the vacuum drainage time of the drainage pile set at 7 days? Is the consolidation time too short? Please comment.

(4) What is the influence law of soil shear modulus on the bearing capacity of a single pile? Please supplement the explanation.

(5) The trend chart of the bearing capacity change of single piles with different lengths of drainage piles is missing.

(6) What should be noted in the practical application of the new drainage pile technology and theory? Please supplement the explanation.

Comments on the Quality of English Language The author is recommended to improve the English writing to enhance the paper's readability.

Author Response

Comments 1: Please provide a comprehensive explanation of the "prefabricated vertical drains (PVDs)" mentioned in the text.

Response 1: Revised accordingly.

Prefabricated vertical drains (PVDs) is a common and mature soft ground reinforcement technology. And the new PDP technology combines precast pile with PVDs; as Figure 1 shows. (line120)

Comments 2: In Case Two, only the soil layer information at the site and the bearing capacity curve of a single pile are provided, but no pictures of the on-site tests are shown. It is suggested to refer to Case One and supplement the relevant photos.

Response 2: Revised accordingly. Thanks. We supplemented the relevant pictures in Case two. (line 455)

Comments 3: Line 493: When calculating the influence of pile length on the bearing capacity of a single pile, why is the vacuum drainage time of the drainage pile set at 7 days? Is the consolidation time too short? Please comment.

Response 3: Through an in-depth analysis of the relationship between time and bearing capacity, it is observed that after 7 days of drainage consolidation, the bearing capacity of a single pile increases by approximately 12.7%. This indicates a significant improvement in the pile's bearing capacity by this point. However, once the drainage consolidation period exceeds 7 days, the rate of increase in bearing capacity shows a clear slowing trend. In practical on-site construction, due to the critical consideration of the project timeline, there is often a need to improve the bearing capacity of a single pile as efficiently as possible within a relatively short time to ensure the overall progress and construction efficiency of the project. Therefore, setting the drainage consolidation period to 7 days is the most appropriate, as it effectively meets the practical need for short-term improvement in bearing capacity while aligning with the project timeline requirements.

Comments 4: What is the influence law of soil shear modulus on the bearing capacity of a single pile? Please supplement the explanation.

Response 4: The explanations are added in the text.

As the drainage consolidation progresses, the effective stress within the soil gradually increases, leading to a continuous rise in the shear modulus. Consequently, the bearing capacity of the pile is progressively enhanced. Extended drainage consolidation duration induces more pronounced enhancement in soil mechanical properties, which consequently leads to improvement in pile bearing capacity. (line 499)

Comments 5: The trend chart of the bearing capacity change of single piles with different lengths of drainage piles is missing.

Response 5: Thanks. The relevant figure is added in the text, i.e., Figure 17. (line 518)

Comments 6: What should be noted in the practical application of the new drainage pile technology and theory? Please supplement the explanation.

Response 6: The theoretical calculation process is based on ideal conditions. In practical application, there are several factors to need to be considered, such as soil layer characteristics, drainage system and drainage boundary conditions. (1) Different soil layers have significant variations in permeability, particle composition, porosity, and other properties. When applying the drainage pile theory, it is essential to accurately understand the characteristics of each soil layer to reasonably estimate the drainage effect. (2) When installing pumps, drainage pipes, and other components, it is crucial to ensure good sealing and firm connections to prevent leakage and blockages. During the operational phase, regular checks are necessary to monitor whether the pumps overheat, ensuring the drainage system functions efficiently. (3) If the groundwater supply in the area is abundant, it will increase the difficulty of drainage, potentially causing the PVD to remain submerged for extended periods, which could impair their drainage efficiency.

Reviewer 2 Report

Comments and Suggestions for Authors

In the article 'Load Bearing Performance of Precast Pills with Integrated Side Drainage Channels in Coastal Soft Soil', the shear displacement method of PDP is combined with the consolidation theory of soft soil foundation. A calculation model for the load settlement behavior of PDP was developed by considering the influence of vacuum induced soil consolidation, and a method for analyzing the load transfer mechanism of PDP was established. This model can accurately calculate the bearing capacity of PDP. I found it suitable for publication in Sustainability, but it must be modified by the author. The specific opinions are as follows:

1. The propagation phenomenon of shear strain and shear stress in the annular soil around the pile in Figure 3 is not clear enough and needs to be strengthened; The r1 in line 209 'Where rm representatives the extent of the sheet zone and r1 representatives the influence range of consolidation' is not shown in the figure. The 398th line describes' The two piles were spaced 5 meters apart. 'However, this data is not present in Figure 9. It is recommended to highlight these details in the figure.
2. The format of paragraphs in lines 313 and 317 should be adjusted. It is suggested to check whether the full text format and the reference format are consistent.
3. No description of Figure 10 found throughout.
4. Fig. 11 shows the comparison of Q-S curves between measurement and theoretical value for case one. The authors did not analyze the data How did they get The findings demonstrated that the trend of the measured curve aligned closely with that of the theoretical curve. Please explain why. The same is true for Figure 12.
5. It is suggested that the author check whether the full text references are cited.
6. The research significance of this paper can be more fully explained.

Comments on the Quality of English Language

The English could be improved to more clearly express the research.

Author Response

Comments 1: The propagation phenomenon of shear strain and shear stress in the annular soil around the pile in Figure 3 is not clear enough and needs to be strengthened; The r1 in line 209 'Where rm representatives the extent of the sheet zone and r1 representatives the influence range of consolidation' is not shown in the figure. The 398th line describes' The two piles were spaced 5 meters apart. 'However, this data is not present in Figure 9. It is recommended to highlight these details in the figure.

Response 1: Thanks. The modifications has been made in Figure 3 and Figure 9. (line220 and line416)

Comments 2: The format of paragraphs in lines 313 and 317 should be adjusted. It is suggested to check whether the full text format and the reference format are consistent.

Response 2: Revised accordingly.

Comments 3: No description of Figure 10 found throughout.

Response 3: Thank you for pointing this out. We have added explanations in the text.

The static load tests are shown in Figure 10. The slow-maintained load method was employed for the testing, which involves applying the load in incremental stages. The next stage of loading was initiated only after the stability criteria for the current stage were satisfied. The test was concluded once the specified termination conditions were met. During the static load test, the load was applied in increments of 45kN, representing 1/10 of the estimated ultimate bearing capacity. (line423)

 

Comments 4: Fig. 11 shows the comparison of Q-S curves between measurement and theoretical value for case one. The authors did not analyze the data How did they get The findings demonstrated that the trend of the measured curve aligned closely with that of the theoretical curve. Please explain why. The same is true for Figure 12.

Response 4: The parameters such as soil permeability coefficient and compression modulus provided in the geological survey report have a certain range. During numerical simulation calculations, some parameters were selected through inversion analysis. Therefore, the theoretical curve is close to the measured curve.

Comments 5: It is suggested that the author check whether the full text references are cited.

Response 5: The full text references have been checked and all references have been cited. Thanks.

Comments 6: The research significance of this paper can be more fully explained.

Response 6: This paper derives an innovative computational model for pile bearing capacity by synthesizing the shear displacement method with the load transfer method, explicitly accounting for vacuum-induced drainage consolidation effects. The proposed methodology demonstrates enhanced practical applicability in engineering practice. This research provides theoretical support for developing novel drainage pile technologies in coastal regions, while advancing the adoption of green low-carbon pile foundation in coastal engineering practices.

We have provided corresponding supplementary explanations in the revised manuscript．(line551)

Reviewer 3 Report

Comments and Suggestions for Authors

This paper focuses on a novel pile foundation technology in deep soft soil areas through theoretical investigations. The primary innovation lies in the application of the shear displacement method to deduce the bearing capacity calculation formula of the new pile technology, and the influence of drainage consolidation on soil parameters and side friction resistance of piles are considered. The proposed method was verified through two engineering cases, and a detailed parameter analysis of the theoretical method was carried out. The research demonstrates significant theoretical and practical relevance for optimizing pile design in soft soil area.

The following suggestions are made for further improvement.

1. In the construction site schematic diagram of precast drainage pile (Figure 1), please clearly label the key equipment and components in the illustration to facilitate readers' understanding of the innovative technology. (line127)
2. Regarding Equation (9) inthe manuscript, please provide additional explanation on how drainage consolidation affects the shear modulus of surrounding soil. (line196)
3. The information conveyed in Figure 3 lacks clarity and requires further refinement. Additionally, "Within the influence area of the PDP, …… the settlement magnitude changed from the initial z2 to z1." please supplement the explanation of the physical significance of z1 and z2. (line215)
4. Given identical drainage durations, the bearing capacity improvements observed in precast drainage piles of varying lengths demonstrate comparable magnitudes. Please elaborate on the underlying reasons for this phenomenon.
5. In the example calculation analysis, the bearing capacity of a single pile increased by 29.6% after 28 days of drainage. Please discuss the feasibility of achieving such improvement in practical engineering applications and provide additional clarification if possible.

Author Response

Comments 1: In the construction site schematic diagram of precast drainage pile (Figure 1), please clearly label the key equipment and components in the illustration to facilitate readers' understanding of the innovative technology. (line 127)

Response 1: Revised accordingly. The main equipment and components were added in Figure 1. (line130)

Comments 2: Regarding Equation (9) in the manuscript, please provide additional explanation on how drainage consolidation affects the shear modulus of surrounding soil. (line 196)

Response 2: Supplementary explanations were made as required. (line 189)

“During the consolidation and drainage process, the soil tends to become more compact and stable, with its shear strength increasing. Meanwhile, according to the Mohr-Coulomb law, as the effective stress rises, the strength of the soil also improves.”

Comments 3: The information conveyed in Figure 3 lacks clarity and requires further refinement. Additionally, "Within the influence area of the PDP, …… the settlement magnitude changed from the initial z2 to z1." please supplement the explanation of the physical significance of z1 and z2.

Response 3: Revised accordingly for Figure 3. And the physical meaning of z1 and z2 are added in the revised manuscript. (line213 and line 221)

“The coordinated deformation relationship between the PDP and the surrounding soil is shown in Figure 3, where r_m represents the extent of the shear zone; r₁ represents the influence range of consolidation; z₁ represents the pile settlement induced solely by shear action; z₂ represents the pile settlement under combined effects of shear force and drainage consolidation. Under the load applied at the pile top, the soil surrounding the pile underwent shear deformation and settled to z₂. Within the influence area of the PDP, the soil underwent consolidation, resulting in altered soil properties. Consequently, the settlement magnitude changed from the initial z₂ to z₁.”

Comments 4: Given identical drainage durations, the bearing capacity improvements observed in precast drainage piles of varying lengths demonstrate comparable magnitudes. Please elaborate on the underlying reasons for this phenomenon.

Response 4: The pile length is not the key factor affecting the improvement of single pile bearing capacity through drainage consolidation. The main reasons for this come from two aspects: the constitutive relationship of the soil adopts a linear relationship; and the variation of soil strength with depth was not taken into account. In practical engineering, the mechanical properties of soil are complex, and the distribution of soil softness and hardness is uneven, and the influence of pile length may vary.

It has been revised in the manuscript. (line 527)

Comments 5: In the example calculation analysis, the bearing capacity of a single pile increased by 29.6% after 28 days of drainage. Please discuss the feasibility of achieving such improvement in practical engineering applications and provide additional clarification if possible.

Response 5: In an ideal state, the bearing capacity of a single pile increases by 29.6% after 28 days of drainage consolidation. There are multiple factors that affect the improvement of single pile bearing capacity through drainage consolidation. (1) It is related to the degree of vacuum. The transmission process of vacuum negative pressure in the foundation is relatively complex, and this article assumes 90 kPa, which may be higher than the actual situation. (2) It is closely related to the permeability of soil. If the permeability of the on-site foundation is high, the improvement effect is significant; otherwise, the improvement effect is poor. (3) Related to drainage boundary conditions. If the groundwater source is continuously replenished, it will affect the increase in the bearing capacity of the pile. The above conditions will affect the actual pumping and drainage efficiency, and need to be analyzed in conjunction with geological conditions and construction plans. The discussion has been added in the revised paper. (line 505)

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thanks for the revisions and reply.

Comments on the Quality of English Language

The English language quality of the manuscript is generally good, with clear and concise writing that effectively communicates the research. However, there are a few minor issues that could be improved, such as occasional awkward phrasing and inconsistent use of terminology. Addressing these will further enhance the clarity and readability of the paper.