Deformation Analysis of 50 m-Deep Cylindrical Retaining Shaft in Composite Strata

Comments 1: In the present case, the authors have provided a review article with barely 22 citations. Although MDPI may not have strictly specified the number of citations involved with a typical article, I think it's better to add more references. Moreover, the presentation can be significantly improved and extended by providing details on analyses and comparison of their own results with those discussed in the other publications by underlining the novelty of their current important work.

Response 1: Thank you for pointing this out. We agree with this comment. To construct a robust theoretical framework, the introduction section has been integrated with a comprehensive body of literature on circular shafts, encompassing methodologies such as numerical simulations, theoretical analyses, and field measurements. The literature synthesis was systematically revised to ensure a logical progression of ideas, transcending a simplistic enumeration of studies to emphasize conceptual connections and disciplinary advancements.

Furthermore, the conclusion of the introduction explicitly identifies the current limitations in field measurement research—particularly the lack of empirical data on large-magnitude groundwater drawdown effects—and articulates the novel contribution of this study: an in-depth investigation into the deformation behaviors of two adjacent circular shafts subjected to groundwater level declines exceeding 10 meters. The specific content added at the introductory conclusion is presented as follows:

In the field of in-situ measurement studies on circular shafts, current literature has predominantly focused on scenarios with minor water level fluctuations. However, the response mechanisms of circular shafts under drastic water level fluctuations remain underexplored, warranting discussions and investigations. This paper presents an in-situ measurement analysis of two unsupported cylindrical retaining shafts with identical geometric and structural configurations, both experiencing groundwater drawdown exceeding 10 meters during construction.

Comments 2: Les figures 1, 9, 10, et 13 sont petites, pour augmenter ses tailles il vaux mieux les présenter verticalement.

Response 2: Thank you for pointing this out. We agree with this comment. To enhance the clarity and readability of the figures, we have rearranged Figures 1, 9, 10, and 13 to be displayed vertically.

Comments 3: Il faut présenter les figures 11 et 12 d'une manière séparer, la même chose pour 7 et 8.

Response 3: Thank you for pointing this out. We agree with this comment. Figure 11 and Figure 12 have been presented separately. Meanwhile, Figure 7 and Figure 8 have also been presented separately.

Comments 1: The term "elevation" is not labeled in English. Furthermore, the section depicting the partition wall boundary in both supporting structure schematics is discontinuous, and the numbering in Diagram No. 1 is inconsistent.

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have translated the corresponding Chinese content into English and corrected the numbering of the diaphragm walls for Shaft No. 1. Regarding the discontinuity of the diaphragm walls, this is because the embedment depths of different wall panels vary in actual construction, resulting in non-uniform embedment depths at the bottom of the diaphragm walls.

Comments 2: The monitoring parameter "In-wall inclinometry" (Section 2) and the item "Horizontal Displacement of the Retaining Wall" (Table 2) refer to the same measurement and require unified terminology.

Response 2: Therefore, we have standardized the terminology as "In-wall inclinometry" for both "In-wall inclinometry" (Section 2) and "Horizontal Displacement of the Retaining Wall" (Table 2).

Comments 3: The rationale for the significantly different number and positioning of surface settlement monitoring points between the two compared foundation pits requires clarification.

Response 3: We agree with this comment. Therefore, Therefore, in the first paragraph of Section 3, we have supplemented the reason why the surface settlement measuring points for Shaft No. 1 are denser than those for Shaft No. 2: "Considering that the strata exposed within the excavation range of Shaft No. 1 are relatively weaker compared to those of Shaft No. 2, and given that its construction is expected to cause more disturbance to the surrounding strata, the surface settlement measuring points for Shaft No. 1 are arranged with higher density."

Comments 4: Explain the underlying mechanisms leading to the two distinct horizontal deformation patterns observed: ' middle-larger, both-ends-smaller ' or ' top-larger, bottom smaller '.

Response 4: Thank you for pointing this out. We agree with this comment. Therefore, in Item 1) of Section 4.1, we have added the following description of the potential causes for these two deformation patterns: "This occurs because the foundation pit is subjected to inward-directed soil and water pressures. Additionally, the displacement at the bottom is relatively restrained due to the rock socketing effect of the base slab."

Comments 5: The date selected for the "last condition" in Figure 4 appears inconsistent with the working conditions shown for the other data points.

Response 5: Thank you for pointing this out. For clarification, the inclinometry curve of the "last condition" is intended to demonstrate the final state of the wall's horizontal deformation. The two shafts stabilized in different states, hence the corresponding dates of their final states differ.

Comments 6: The 224 and 225 lines state most maximum displacements occur within H-20 to H+10, which aligns with Shaft No. 1 data (red). However, Shaft No. 2 data (blue) predominantly fall within H+20 to H-10, contradicting the stated range.

Response 6: Thank you for pointing this out. In response to the comment, we have revised the depth of the maximum horizontal displacement of the wall to H + 20 to H - 20, highlighting the commonality between the two shafts. Furthermore, in the last paragraph of Section 4.1, we have added a description of the differences in the depth of the maximum horizontal displacement between the two shafts to enhance the rigor of the expression: "(Shaft No. 1 is primarily situated between H - 20 and H + 10, whereas Shaft No. 2 is predominantly located between H + 20 and H - 10.)"

Comments 7: The description of groundwater level change stages focuses solely on Shaft No. 1 and omits a comparative analysis distinguishing the two stable stages between the shafts.

Response 7: Thank you for pointing this out. Since the water levels outside the two shafts showed little difference during the stable stage, Section 4.2, Item 1) has already provided a unified description of the stable stage for both shafts. The description of water levels in this section focuses on the subsequent stage of drastic fluctuations, which is the core focus of this study.

Comments 8: There are some details in the paper: (1) Figure 7, Figure 11 and Figure 14 lack legends; (2) Figure 10 can not be clear about the specific meaning.

Response 8: Thank you for pointing this out. We agree with this comment. Therefore, we have added the legends for Figure 7, Figure 11, and Figure 14. The specific meanings in Figure 10 have been explained at the beginning of Section 4.3 and in the legend of Figure 10. The text primarily illustrates the relationship between surface settlement data and groundwater levels. Considering space constraints, the surface settlement data for individual shafts are uniformly plotted in one figure.

Comments 1: Instruments used should be labeled with the model and manufacturer.

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, Therefore, we have supplemented Table 2 with as much information as possible regarding the model numbers and manufacturers of the instruments.

Comments 2: In the Introduction section, the limitations of current research on ultra-deep and large-diameter cylindrical foundation pits should be added.

Response 2: Thank you for pointing this out. We agree with this comment. Therefore, we have supplemented the conclusion of the introduction with the limitations of current field measurement studies and the innovative points of this paper—investigating the deformation patterns of two circular shafts subjected to groundwater level drawdown exceeding 10 meters. The added content is as follows:

In the field of in-situ measurement studies on circular shafts, current literature has predominantly focused on scenarios with minor water level fluctuations. However, the response mechanisms of circular shafts under drastic water level fluctuations remain underexplored, warranting discussions and investigations. This paper presents an in-situ measurement analysis of two unsupported cylindrical retaining shafts with identical geometric and structural configurations, both experiencing groundwater drawdown exceeding 10 meters during construction.

Comments 3: In the introduction part of the data is too simple; it is suggested to add a simulation or a theoretical analysis. The current manuscript is more like an experimental report. And add an explanation of Figure 15.

Response 3: Thank you for pointing this out. We agree with this comment. To construct a robust theoretical framework, the introduction section has been integrated with a comprehensive body of literature on circular shafts, encompassing methodologies such as numerical simulations, theoretical analyses, and field measurements. The literature synthesis was systematically revised to ensure a logical progression of ideas, transcending a simplistic enumeration of studies to emphasize conceptual connections and disciplinary advancements.

Furthermore, the conclusion of the introduction explicitly identifies the current limitations in field measurement research—particularly the lack of empirical data on large-magnitude groundwater drawdown effects—and articulates the novel contribution of this study: an in-depth investigation into the deformation behaviors of two adjacent circular shafts subjected to groundwater level declines exceeding 10 meters. The specific content added at the introductory conclusion is presented as follows:

In the field of in-situ measurement studies on circular shafts, current literature has predominantly focused on scenarios with minor water level fluctuations. However, the response mechanisms of circular shafts under drastic water level fluctuations remain underexplored, warranting discussions and investigations. This paper presents an in-situ measurement analysis of two unsupported cylindrical retaining shafts with identical geometric and structural configurations, both experiencing groundwater drawdown exceeding 10 meters during construction.

The detailed description of Figure 15 has already been provided at the conclusion of Section 4.4.

Comments 4: Some formatting issues (including but not limited to).

①Page1 ，“urations of retaining structures[1-3]。” Chinese punctuation exists.

(ii) The vertical coordinate in Figure 1 is in Chinese and should be revised. The (b) scale of Figure 1 (a) should be the same.

③Page 3, Line 122, “structures are graphically illustrated in Figure Figure 2.” There's an extra “Figure”.

④The various symbols of Figures 7, 8, and 14 have no corresponding explanation.

⑤Chinese is also present in Figure 13.

⑥Page 5， Line 144 “2. Monitoring Point Deployment Scheme” The serial number is incorrect; it should read “3.”

Response 4: We sincerely appreciate the reviewer's valuable comments on the formatting issues. The corresponding revisions are made as follows:

① Modified the Chinese punctuation marks to English ones on the first page.

② Standardized the scale of the two images in Figure 1.

③ Removed the redundant word "Figure" where applicable.

④ Added the legends for Figures 7, 8, and 14.

⑤ Translated the Chinese descriptions to English in Figure 13.

⑥ Adjusted the numbering of the titles in the text to ensure they are arranged in the correct order.

Comments 1: The title should be as concise as possible and to the point, mentioning only key parameters. For instance, is it really necessary to indicate the 50 m depth of the shaft in the title? I believe this can generally be referred to as a deep shaft instead. Furthermore, although the shaft is constructed for a railway tunnel, mentioning the railway service is not a key or necessary parameter for this shaft project. Rather, it can be noted in the Keywords.

Response 1: Thank you for the invaluable suggestions regarding the title. In response, we have made the following revisions: Since there are few studies on 50m-deep circular foundation pits, this burial depth highlights a distinctive feature of the research object in this paper. Additionally, this depth represents a commonality in the dimensions of the two shafts, hence the element "50m" was not removed from the title. Meanwhile, as "Intercity Railway Tunnel" is not a key focus of this study, it has been omitted from the original title.

The final title is: Deformation Analysis of 50m-deep Cylindrical Retaining Shaft in Composite Strata.

Comments 2: The affiliations need to be in order and should be rearranged by switching the 2 and 3 affiliations.

Response 2: Thank you for pointing this out. We agree with this comment. Therefore, we have switched the 2 and 3 affiliations.

Comments 3: The abstract appears to be disconnected in line 14. In that line, you begin discussing the focus of the project on shaft displacement monitoring, which suggests that this should be mentioned in relation to cylindrical shaft behaviour between lines 12 and 14. Additionally, it requires a better justification for why the displacement types mentioned are chosen for this project.

Response 3: Thank you for pointing this out. We agree with this comment. Therefore, we have added a transition sentence in the second sentence of the abstract to explain why deformation monitoring data were chosen as the research focus of this paper.

Comments 4: In the abstract, the main findings haven't been properly discussed; a critical discussion is required.

Response 4: Thank you for pointing this out. In response to the reviewer's comments, the abstract has been revised to follow the logical flow of "research background - research methods and content - research conclusions - suggestions - summary", with the main arguments thoroughly discussed.

Comments 5: In the abstract, are lines 22 to 28 general suggestions or your contributions? If they are suggestions, they should be mentioned concisely here and be proportionate to the results you mentioned; as it stands, they are longer than your main findings. However, if they are results, they need to be quantified for better understanding.

Response 5: Thank you for pointing this out. The content from lines 22 to 28 is not entirely suggestions; it includes hypotheses on the causes of the structure's outward deformation toward the foundation pit based on the monitoring data, as well as proposed construction and design recommendations. Given that both shafts experienced groundwater seepage, and the monitoring data showed significant changes in wall and stratum deformations, the abstract concludes with targeted construction and design suggestions to ensure the research findings better serve practical engineering. Additionally, the two sentences presenting suggestions have been merged and simplified.

Comments 6: What is the novelty and main contribution of this research? This needs to be clearly noted in the abstract and the introduction section.

Response 6: hank you for pointing this out. We agree with this comment. Therefore, we have supplemented the conclusion of the introduction with the limitations of current field measurement studies and the innovative points of this paper—investigating the deformation patterns of two circular shafts subjected to groundwater level drawdown exceeding 10 meters. The added content is as follows:

In the field of in-situ measurement studies on circular shafts, current literature has predominantly focused on scenarios with minor water level fluctuations. However, the response mechanisms of circular shafts under drastic water level fluctuations remain underexplored, warranting discussions and investigations. This paper presents an in-situ measurement analysis of two unsupported cylindrical retaining shafts with identical geometric and structural configurations, both experiencing groundwater drawdown exceeding 10 meters during construction.

Comments 7: In line 66, the authors Wu, Y. X. et al. are mentioned twice.

Response 7: Thank you for pointing this out. We agree with this comment. Accordingly, we have corrected the redundant expressions at the corresponding locations.

Comments 8: In regard to the research by Wu, Y. X. et al. in line 66, you noted that they categorised the drawdown process into four distinct stages. This appears to be an incomplete discussion, as after mentioning “ … four distinct stages”, it is expected that you will discuss these stages. If you prefer not to do so, please consider rewriting the sentence.

Response 8: Thank you for pointing this out. We agree with this comment. Therefore, we revised the wording of this reference citation and relocated it to the second-to-last paragraph of the introduction.

Comments 9: A reference is required for the sentence between 69 and 71.

Response 9: Thank you for pointing this out. We agree with this comment. Therefore, we have added references at the corresponding locations.

Comments 10: Thank you for the informative introduction. However, it appears that the literature is presented consecutively without proper reasoning regarding how they relate to the current research and how this research will address their gaps. It is recommended to improve this aspect.er.

Response 10: Thank you for pointing this out. We agree with this comment. Therefore, we have supplemented the conclusion of the introduction with the limitations of current field measurement studies and the innovative points of this paper—investigating the deformation patterns of two circular shafts subjected to groundwater level drawdown exceeding 10 meters. The added content is as follows:

In the field of in-situ measurement studies on circular shafts, current literature has predominantly focused on scenarios with minor water level fluctuations. However, the response mechanisms of circular shafts under drastic water level fluctuations remain underexplored, warranting discussions and investigations. This paper presents an in-situ measurement analysis of two unsupported cylindrical retaining shafts with identical geometric and structural configurations, both experiencing groundwater drawdown exceeding 10 meters during construction.

Comments 11: Line 122, Figure is mentioned twice.

Response 11: Thank you for pointing this out. We agree with this comment. Therefore, we corrected the redundant mentions of "Figure" in the manuscript.

Comments 12: What is the purpose of Table 1, discussing the construction timeline of each layer? If there is a scientific reason, it needs to be outlined properly, unless I don’t see its contribution.

Response 12: Thank you for pointing this out. In the analysis of field monitoring data, presenting the construction timeline is indispensable. As stated, the monitoring frequency for all instruments was once a day. Figures 9, 10, and 13 plot monitoring data against construction days, enabling readers to visually track the trend of monitoring data over time (in days). Table 2 previews the time nodes of each construction phase to provide readers with an initial understanding of the project timeline.

Comments 13: In Table 2, the monitoring frequency for the inclinometer is mentioned, but not for the others. This needs justification.

Response 13: Thank you for pointing this out. The monitoring frequency for all items is once a day, as specified in Table 2.

Comments 14: In Figure 4:

①The horizontal axes represent the horizontal deformation in each subfigure. Please provide the title for this axis. Additionally, correct the unit; it should be millimetre, not metre.

②The figure has not been discussed properly, with details remaining vague, which makes it hard for the reader to understand. For example, there are 9 data points in each subfigure for different excavation depths. How can the excavation depth of 13.6 m provide information at deeper depths up to nearly 50 metres? Or why the at positions 2 and 4 the depth is shorter? The shaft 2 is 51.3 meters, how you have data at the depth of 55 meters only at the position of 3?

③You mentioned that deformations are moderate at around 15 mm, while in Shaft No. 2, in positions 1, 2, and 6, they reached 60 and 80 mm.

④The figure shows that while Shaft No. 1 mainly exhibits negative deformation, Shaft No. 2 presents a combination of deformations, including a fully positive deformation in position 4. A critical discussion is required.

⑤Is there a reason for the specific dates mentioned for Shafts No. 1 and 2? What do these dates refer to, and why have they been compared with the depth data?

Response 14: We sincerely appreciate the numerous improvement suggestions for Figure 4. The presentation and discussion of Figure 4 have been revised as follows, accompanied by detailed explanations:

①The horizontal axis title unit was changed to "mm," and a title was added and positioned at the far right for optimal visualization.

②The circular foundation pit utilizes a quasi-circular diaphragm wall composed of 24 segments, with a rock-socketed depth of approximately 3–5 m (i.e., the wall bottom is 3–5 m below the excavation surface). Inclinometers embedded within the wall measure horizontal deformation via buried inclinometer tubing, enabling the capture of wall displacements at deeper layers during all excavation stages. It should be noted that embedment depths vary among wall segments—for instance, the wall at Shaft No. 2, Position 3 extends to 55 m, while others are shallower (see Figure 1 for depth variations). In addition, installation errors of ±1–2 m in inclinometer tubing contribute to depth inconsistencies. For Shaft No. 2, Position 3, inclinometer tubing damage below 30 m rendered displacement measurement unfeasible, thus only wall deformation data from 0–30 m depth are provided.

③The 15-mm deformation described in the text corresponds to the wall deformation during the 0–40 m soil layer excavation stage (as explicitly stated in the manuscript). The 60-mm and 80-mm wall deformations raised in the review represent deformations occurring during subsequent construction phases.

④The outward deformation of Shaft No. 1 toward the pit exterior is discussed in the conclusion section, while the diverse deformation patterns of Shaft No. 2 are addressed in Section 4.1, Item 5. The entirely inward deformation at Position 4 is attributed to surcharge loads imposed at the pit edge.

⑤The specific dates specified for Shafts No. 1 and No. 2 denote post-excavation construction milestones, intended to illustrate the impact of subsequent works on wall horizontal deformation. This aspect is elaborated in Section 4.1, Item 4.

Comments 15: Provide the displacement unit for Figures 5 and 6.

Response 15: Thank you for pointing this out. We agree with this comment. Therefore, we added the unit "(unit: mm)" to the titles of Figures 5 and 6.

Comments 16: In Figures 7 and 8, The displacement unit cannot be metres. The legend is missing.

Response 16: Thank you for pointing this out. We agree with this comment. Therefore, we converted the displacement units to millimeters and added legends to Figures 7 and 8.

Comments 17: In Figure 9:

Place the title of the axis for the vertical axis in the correct position.

The horizontal line is provided based on the date of excavation; it is suggested that depth information also be given so that the reader can easily understand at which depth the shafts experience greater variation in groundwater.

Response 17: Thank you for pointing this out. We agree with this comment. Therefore, Therefore, we corrected the vertical axis title position in Figure 9. The original figure already includes markers for "excavation depth," allowing readers to correlate construction progress and time nodes with the horizontal axis dates.

Comments 18: In Figure 11, the Legend is missing.

Response 18: Thank you for pointing this out. We agree with this comment. Therefore, we added a legend to Figure 11.

Comments 19: In most of the figures where you provide subfigures, a comparison between them is expected. This is particularly relevant for Shaft No. 1 and 2 in your figures. Additionally, the scales in the figures differ. They need to be in a similar scale to facilitate a comparison.

Response 19: 

Regarding the horizontal displacement monitoring data of the walls for the two shafts, considering the significant differences in the values of shaft horizontal displacement and surface settlement, using the same scale would result in overly dense distribution of data points or curves for one shaft, which is inconvenient for presentation. Thus, different scales are adopted for different measuring points to facilitate readers in clearly understanding the horizontal deformation of the wall at different construction stages.

However, we have also made efforts to enable better comparison of data between the two shafts. For example, for the horizontal displacement data of Shaft No. 1 and Shaft No. 2:

For Shaft No. 1, the horizontal coordinate range for points 03, 04, and 05 (with relatively small displacement) was adjusted to -20 mm to +10 mm, and the range for points 01, 02, and 06 (with larger displacement) was adjusted to -80 mm to +20 mm.

For Shaft No. 2, the horizontal coordinate range for points 01, 02, and 05 (with relatively small displacement) was adjusted to -20 mm to +20 mm, and the range for points 01, 02, and 06 (with larger displacement) was adjusted to -40 mm to +400 mm.

The vertical coordinate range for wall vertical displacement was unified as -60 mm to +15 mm.

Comments 20: The displacement unit cannot be metres in Figure 14.

Response 20: Thank you for pointing this out. We agree with this comment. Therefore, have changed the unit in Figure 14 to mm.