Study on the Characteristics and Mechanism of Shield Tunnel Mud Cake Disintegration in Complex Red-Bed Geology
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript "Study on the characteristics and mechanism of mud cake disintegration in complex red-bed geological shield tunnel " presents a novel experimental apparatus and dispersant formulation for studying mud cake disintegration in red-bed shield tunnels. The introduction of a new experimental apparatus enhances data quality and reliability, strengthening the research foundation. Furthermore, the successful identification and implementation of a 10% oxalic acid dispersant formulation for red-bed formations demonstrate the approach's practical applicability. The successful application of the Haizhu Bay Tunnel project demonstrates the approach's potential value—however, limitations in generalizability and a lack of in-depth mechanistic exploration warrant further development before publication.
-The study's focus on red-bed geology limits the generalizability of the findings to other tunnel environments. Has a similar methodology been used in other geologies? Can the method be modified for different geologies?
-While threshold concentrations for dispersants are established, a deeper exploration into the mechanisms governing these thresholds is necessary for a more comprehensive understanding.
-Although the paper acknowledges the need for further investigation, a more detailed roadmap for addressing the complexities and inherent variability encountered in diverse tunnel geologies would strengthen the overall impact.
In consideration of the general limitations previously outlined, this study presents a study with a narrow focus. Nevertheless, the novel techniques and methodologies introduced by this study serve to underscore the significance of the research. It is appropriate to publish the draft after the author has made minor revisions to address the above concerns.
Author Response
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Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsStudy on the characteristics and mechanism of mud cake disintegration in complex red-bed geological shield tunnel is very interesting paper. Some improvement is required!
Page 1. The geology of complex red-bed, characterized by its high viscosity and water content (what is a value of water content?)
Page 1: mud cake (from which process? Which elements and compounds? Origin?)
Page 1: Ultimately, the engineering application of a 10% oxalic acid solution, which proved effective in disintegrating the mud cake (which chemical process?), significantly enhanced the excavation efficiency in the Haizhu Bay Tunnel project.
Page 2. Anagnostou et al. [13] studied the effects of adding dispersants (which type of dispersants?)
Page 2: complex environment and construction difficulties (which type of environmental problem)
Page 6: which can accurately record the dynamic process of mud cake disintegration (which conditions?)
Page 9: The comparison presented in Figure 7b indicates that the PW-T5 sample took the longest time (10 min? 2 hour?..) to disintegrate, although the process was relatively smooth, requiring more materials (100 g? 1kg?)
Page 9: Please to inject an unit for concentration at Figure 9.b (g/l? or %?)
Page 10: Please to inject an unit for concentration at Figure 11.b (g/l? or %?)
Page 11: Please to inject an unit for concentration at Figure 13.b (g/l? or %?)
Page 13: Can we put Concentration insead solution at x-axis in Figure 17.
General questions:
Is mud cake a silica gel material?
Is desintegration with oxalic acid one chemical or physical process? If it is chemical process, can you write some chemical equations?
Author Response
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Reviewer 3 Report
Comments and Suggestions for AuthorsTitle: “Study on the characteristics and mechanism of mud cake disintegration in complex red-bed geological shield tunnel “
In this work the authors presented an improved disintegration experiment instrument to study the disintegration characteristics of mud cake from the red-bed geology under different dispersant solutions, proposing a dispersant formulation suitable for the red-bed geology of the Haizhu Bay Tunnel project.
General comment: This work seems to be interesting. Nevertheless, it should be reworked and revised to improve its impact and quality. More specifically, the following major points should be reworked:
The main structure of the work should be reworked to insert the standard section :
“Introduction”
“Materials and Methods”
“Results”
“Discussion”
“Conclusions”
As a consequence, the current structure of the main text should be changed accordingly.
In particular,
Figure 1: the caption of this figure should be improved. Within the map the scale is currently lacking. Please rework.
Lines: “The geology of the tunnel mainly consists of gravel sand, medium sand, silty clay,
and complete, strong, medium, and slight weathering muddy siltstone. Muddy siltstone,
which forms a significant portion of the geology as depicted in Figure 2, has a silt con-
tent of about 25% to 50% and a clay content of 50% to 75%, making clay its predominant
material. This composition significantly increases the risk of mud cake formation during
shield tunneling”
and figure 2
Figure 2. Longitudinal geological section.
*) The colours of Figures 2 should be explained through a legend. Please rework.
Paragraphs: “3. Design of Experiments, 3.1. Materials,3.1.1. Sample of Mud Cake”
*) These sections should be changed according to the previous comments.
Lines:” 3.1.2. Dispersant
1. Sodium Silicate
Sodium silicate produced by Wuxi Yatai United Chemical Co., Ltd. was selected
(Figure 5a), with a Na2O content of 19.3 ~ 22.8%. It is a grayish-white powder that dis-
solves in water to form an alkaline solution.
2. Oxalic Acid
The dispersant oxalic acid selected comes from Wuxi Yatai United Chemical Co.,
Ltd., with a content of C2H2O4 of 99.5%, which is colorless crystal and acidic after dis-
solving in water (Figure 5b).
3. Sodium Hexametaphosphate
Produced by Wuxi Yatai United Chemical Co., Ltd., it has a P2O5 content of 65 ~
70%, is a white powder (Figure 5c), and becomes alkaline after dissolving in water.”
*) This section should be changed. Please rework and improve the clarity and the structure.
3.2. Specimens
3.3. Experiment Method
4. Experiment Results
*) This section should be improved and the main text should be rewritten. All the captions of figures 7,8,9,10,11,12,13, 14 should be reworked to insert more information.
Section : “5. Analysis and Discussion”
*) This section should be the “Discussion”.
5.2. Mechanism Analysis of Dispersant and Coatings 2024, 14, x FOR PEER REVIEW 12 of 17
As shown by the experiment, as the thickness of the mud cake increases, the FDA of
the mud cake gradually decreases and the time for complete disintegration becomes
longer. This may be due to the fact that as the thickness of the mud cake increases, the
distance for internal water diffusion becomes longer, leading to a slower disintegration
process.
5.2. Mechanism Analysis of Dispersant
The experimental results indicate that the dispersant has a certain disintegrating ef-
fect on the mud cake. When soil particles in the mud cake are placed in a dispersant so-
lution, ionic dissociation occurs between the surface minerals of the particles and the
dispersant, forming a layer of negatively charged soil particles (NCSP) on the surface of
the particles as shown in Figure 15. To maintain overall electrical neutrality, NCSP ad-
sorbs cations from the dispersant solution, forming a compact stern layer around the soil
particles. Additionally, there exists a charge-balanced transition solution region between
the stern layer and the dispersant solution, which is referred to as the diffusion layer
[26].
The stern layer and the diffusion layer jointly form a hydrated film around the soil
particles. The zeta potential, which is the potential difference between the NCSP and the
boundary of the diffusion layer, determines the thickness of this hydrated film. The
thickness of the hydrated film directly affects the spacing between soil particles, thereby
influencing the bonding between them. A thicker hydrated film results in a greater spac-
ing between soil particles and a weaker bond among them. This makes it difficult for soil
particles to aggregate and adhere, thus achieving the purpose of mud cake disintegra-
tion.
Figure 15. Gouy-Chapman-Stern double layer model.
*) Not sure that this section should be inserted within the “Discussion”. Perhaps, it should be inserted within the “Methods” section.
5.4. Recommended Optimal Dispersant Concentration
*) This section should be moved and presented within the “Results” section (if Figure 16 is novel with respect those of the results section) and discussed here.
Figure 19. Changes in excavation parameters before and after injection.
and
lines:” After the dispersant was injected, the torque of the shield machine decreased from
10.72 kNm at Ring 180 to 7.98 kNm at Ring 184, and the tunneling speed increased from
8.25 mm/min at Ring 180 to 12.79 mm/min at Ring 181. The injection of the dispersant
solution significantly improved the tunneling performance of the shield machine. This
indicates that the 10% oxalic acid solution has an excellent dispersing effect on the mud
cake in red-bed geology, enhancing the tunneling efficiency of the shield machine. At
the same time, it also verifies the reliability of the results from laboratory experiments”
*) This is one of the main results of the work and should be moved in the “Results” section and only commented here.
7. Conclusion and Suggestions
*) This section should be improved. Please rework and avoid lists.
References
*) Please add more and not only regional references, to support the novelty of the work.
Comments on the Quality of English Language
The quality of language should be improved
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsTitle: “Study on the characteristics and mechanism of mud cake disintegration in complex red-bed geological shield tunnel “
In this work the authors presented an improved disintegration experiment instrument to study the disintegration characteristics of mud cake from the red-bed geology under different dispersant solutions, proposing a dispersant formulation suitable for the red-bed geology of the Haizhu Bay Tunnel project.
General comment: The authors revised their work. Nevertheless, some issues should be still improved, as reported below:
Lines: “.1. Project Overview 80
The Haizhu Bay Tunnel in Guangzhou spans between Haizhu District and Panyu 81
District. It begins on the north side of Nanzou Road, extending southward beneath the 82
Zhujiang Lijiao Waterway, Luoxi Island, and the Sanzhixiang Waterway, to conclude at 83
Nanpu Avenue (Figure 1). With a total length of 2,077 meters, the tunnel comprises two 84
tunnels running east and west, each with a diameter of 14.5 meters. This structure is not 85
only the largest diameter shield river-crossing tunnel in Guangzhou but also ranks 86
among the most challenging shield tunnels to construct in China due to its complex geo- 87
logical conditions and construction difficulties. The geology of the tunnel mainly consists of gravel sand, medium sand, silty clay, 91
and complete, strong, medium, and slight weathering muddy siltstone. Muddy siltstone, 92
which forms a significant portion of the geology as depicted in Figure 2, has a silt con- 93
tent of about 25% to 50% and a clay content of 50% to 75%, making clay its predominant 94
material. This composition significantly increases the risk of mud cake formation during 95
shield tunneling.
Figure 1. Geographical location of Haizhu Bay Tunnel. 90
The geology of the tunnel mainly consists of gravel sand, medium sand, silty clay, 91
and complete, strong, medium, and slight weathering muddy siltstone. Muddy siltstone, 92
which forms a significant portion of the geology as depicted in Figure 2, has a silt con- 93
tent of about 25% to 50% and a clay content of 50% to 75%, making clay its predominant 94
material. This composition significantly increases the risk of mud cake formation during 95
shield tunneling. 96
Figure 2. Longitudinal geological section. 98
For the east and west lines, the tunnel employs super-large diameter slurry- 99
balanced shield machines, named "Discovery" for the west and "Pathfinder" for the east. 100
The "Discovery" features a pressurized cutterhead with an opening rate of about 35%, 101
whereas the "Pathfinder" has a normal pressure cutterhead with an opening rate of 102
about 30%. Both shield machines have a cutterhead diameter of 15.07 meters (Figure 3), 103
and their relatively small opening rates can hinder the flow of excavated soil and mud. 104
This can easily result in the formation of mud cake on the face of the cutter heads
*) These lines should be moved to the "Introduction" section, since they introduced the whole work and do not present Methods or Marterials. Please rework and reorganize the section "Materials and Methods".
Section "3. Results"
*) Please rename the subsections according to the real content of these sections. For instance the name"3.1. Pure Water" is not meaningful since in this section the authors presented the "disintegration results for mud cake samples with thicknesses of 1 cm, 3 cm, and 5 cm in pure water". As a consequence, this title should be renamed "Disintegration of mud cake samples in pure water". Following this example the authors should rename all the subsections in this section accordingly.
Section ."4. Discussion
4.1. Thickness of Mud Cake
4.2. Mechanism Analysis of Dispersant"
*) The Discussion section should be used to discuss the novelty of the work with respect to the previous state of the art. As already said, the reviewer is not sure that the discussion of the "Mechanism Analysis of Dispersant" should be inserted here. For sure, this should be not the only "focus" of the discussion. Please rework and complete this section with the presentation of the novely of this work and with the improved performance of the framework proposed by the authors.
section "Conclusions"
*) As already said, the use of lists is not the best way to organize this section, even if some literature works use this strategy. Perhaps, the authors could provide a more elegant section.
Reference
*) As aready said, the authors should provide not only regional references, but they should insert more international references to better present the current state of the art.
Comments on the Quality of English Language
The authors should further improve the quality of the language. For instace avoiding the repetitions of words.. "e.g., When....when......when.... " etc.
Author Response
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Author Response File: Author Response.pdf
