Coupled Effect of Wet-Dry Cycles and Rainfall on Highway Slope Made of Yazoo Clay
Round 1
Reviewer 1 Report
General comments:
The paper titled “Coupled Effect of Wet-Dry Cycles and Rainfall on Highway Slope made of Yazoo Clay” deals with swelling/shrinkage behaviour of Yazoo clay and the impact of wetting/drying cycles on the slope stability. The present manuscript is in an early stage and more a geoengineering report of an engineering office than a scientific study without any scientific issue. The impact of wetting/drying cycles on shrinkage/swelling behaviour of mineral substrates is well-known and new information are totally missing.
Abstract:
The results section in the abstract could be more compact, may underpinned with values.
1. Introduction:
The introduction should supply sufficient background information to understand the results of the present study. The introduction of the present study is of poor structure and must be shortened considering the key information: clay – underground movement – wetting/drying – shrinkage/swelling. Information about Plaxis 2D are totally missing, why Plaxis 2D?
Line 36-43: What is Yazoo clay and why is the clay used for highway slopes? Is it a regional problem? Environmental and monetary extent of the problem?
Line 41: Type and amount of clay, clay mineralogy, thus, 1:1 layer kaolinite with less pronounced swelling and shrinkage behaviour than 2:1 layer montmorillonite
Line 55-58: If considering the phenomenon of swelling/shrinkage should be more complex discussed, additional and actual literature is missing:
Hartge, K.H.; Horn, R. In Essential Soil Physics - An introduction to soil processes, structure, and mechanics; Horton, R., Horn, R., Bachmann, J., Peth, S. Eds.; Schweizerbart Science Publishers, Stuttgart, Germany, 2016.
Line 63-65: There are some more or less actual papers considering the swelling/shrinkage behavior of clay materials:
Widomski, M. Stepniewski, W., Horn, R., Bieganowski, A., Gazda, L., Franus, M., Pawłowska, M. (2015). Shrink-swell potential, hydraulic conductivity and geotechnical properties of clay materials for landfill liner construction**. International Agrophysics. 29. 365-375. 10.1515/intag-2015-0043.
Beck-Broichsitter, S., Gerke, H., Horn, R. (2018). Suitability of Boulder Marl and Marsh Clay as Sealing Substrates for Landfill Capping Systems—A Practical Comparison. Geosciences. 8. 356. 10.3390/geosciences8100356.
Huang, C.; Shao, M.; Tan, W. Soil shrinkage and hydrostructural characteristics of three swelling soils inShaanxi, China. J. Soils Sediments 2011,11, 474–481.
Line 77-79: The composition of the clay should be added into a Table as part of the result section.
2. Methodology
The experiment and the components are not clear and should be illustrated more clearly. Why the authors did measured the shear strength of dry soil samples? In reality, the clay as slope material will never reach this condition in practise! The investigations and therefore the boundary conditions are unrealistic. Vertical stress and/or shear movement considering pore water pressure > 0 also impacts the deformation behaviour and particle movement of the slope. Additionally, soil water retention curves (constrained or unconstrained van Genuchten unimodal or bimodal approach?) and shrinkage curves including the shrinkage behaviour (structural, proportional…) are essential and missing. Mechanical and/or hydraulic stresses are essential describing deformation processes and the shrinkage/swelling behaviour of clay substrates.
The theoretical and mathematical background for the experiment (Mohr Coulomb, Atterberg limits?) and the used software (Plaxis 2D) is totally missing in methodology considering Line 364-398. SEM? What technique, resolution?
Localizing soil deformation and measure deformation rates photographs were taken at defined time steps during the experiments including image analysis?
Line 149: A general overview about the problem setting/study side is missing. Readers from other scientific disciplines struggling with slope structures of highways. This is very important to introduce into the problem (picture could also be a part of the introduction).
Line 153: The material was homogenized and lost its initial structure, also possible organic carbon?!
Line 155-157: The authors should show or describe the results of the Proctor compaction test (results). This is needful to understand the experiment.
Line 167: Temperature in degrees?
Line 187: Figure 1, the pictures are of minor quality and (a-d) must be better explained.
3. Results
The discussion is missing and should be mentioned.
Line 214: Figure 2, mins?
Line 227: Void ratio and porosity in which unit? Figure 3, use the linear regression for both parameters.
Line 238-240: The porosity is increasing through cracking while the cohesion is decreasing and therefore the slope stability. Are that realistic field conditions
Line 251-254: This information should be a part of the methodology.
Line 268-296: Information about cohesion, shear strength and Atterberg limits of the Yazoo clay should be added into a Table, but Table 3 is inadequate and should be structured.
Line 309: What is a slope ratio of 3H? The boundary conditions for Plaxis 2D should be mentioned in the methodology. A good example is the following paper:
Baba, H. O., Peth, S. 2012. Large scale soil box test to investigate soil deformation and creep movement on slopes by Particle Image Velocimetry (PIV), Soil & Tillage Research, 125, 38-43, doi:10.1016/j.still.2012.05.021.
Line 313: The fitting parameter (α, n) should be added to the text.
Line 323: The effect of cracking on soil hydraulic permeability is well-known. The homogenized material will reach the proportional shrinkage phase with the beginning of the dehydration, thus, large cracks and therefore preferential flow at early dehydration stage should be assumed. The K-values are not constant considering the concept of pre-compression and pre-shrinkage stress as described in f.e.:
Alaoui, A., Lipiec, J., Gerke, H.H. A review of the changes in the soil pore system due to soil deformation: A hydrodynamic perspective. Soil Tillage Res. 2011, 115–116, 1–15.
Beck-Broichsitter, S., Gerke, H.H., Horn, R. 2018c. Effect of compaction on soil physical properties of differently textured landfill liner materials. Geosciences, 9(1). doi: 10.3390/geosciences9010001.
Line 363-398: Variations of pressure heads and water contents considering the number of wetting/drying cycles should be added.
Line 405: Figure 7, the graphs are of minor quality and should be improved. Scales and units are missing. Phi-C?
Line 417: Figure 8, the graphs are of minor quality and should be improved. Scales and units are missing.
Line 431: Figure 9 is totally unclear and units are also missing.
4. Conclusion
The experiment conditions, especially the shear strength measurements assume special conditions (dry soil samples). Thus, the results have no generality, especially under variable-saturated soil conditions in the field.
Line 447: Unit of the void ratio? Changes on porosity are missing?
Line 450-452: Decreasing cohesion decreases the slope stability as function of porosity and void ratio.
Line 453-454: Is the Plaxis 2D software adequate?
References
The references in the text do not correspond to the “author’s guideline” of the journal. The references should be formatted uniformly. The correct journal title abbreviations are also missing (f.e., Engineering Geology = Eng. Geol.).
Author Response
Please check our responses in the attached file.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The figure shouldn’t include the student images. Need to change.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Authors,
This paper describes the effect of and wetting-drying cycles on the mechanical behaviour of Yazoo clay. The experimental results are then used to support 2D Plaxis numerical simulations to analyse the effect of wetting-drying cycles on the stability of a slope. The work is original, but the discussion of results is rather weak and sometimes confusing. The paper could be eventually considered for publication only after the Authors have considered the following major comments.
1. The Authors use sometimes Imperial Units and some other time SI Units. It is strongly suggested to use SI units.
2. The introduction section is not well structured and sometimes it is hard to understand the link between the literature and present study and the originality of the present work is not highlighted at all. In the Results section (Page 10/20 Lines 268-274), the Authors include a paragraph that should be moved to the Introduction. The Authors are encouraged to revise the structure of the Introduction.
3. Page 2/20 Lines 70-78. The Authors describe extensively the geology of the region where Yazoo clay is abundant. This paragraph should be supported by a map to help the reader locating the specific area that the Authors are describing.
4. Page 2/20 Lines 87. “35%” instead of “35”
5. Page 4/20 Line 150. Meaning of acronym CH?
6. Page 4/20 Line 156. It would be better to specify which size corresponds to the #40 U.S. sieve.
7. Page 4/20 Line 165. The Authors should comment on the fact that putting an aluminum foil between the sample and the porous stone could affect the drainage of water.
8. Page 4/20 Lines 168-170. The Authors state that soil samples were dipped in water for 24 hours during saturation. How is it possible to adopt this saturation method without destroying the soil samples?
9. Pages 5-6 Table. The Authors state that they measured undrained cohesion but then they present results in terms of effective cohesion and friction angle. Can the Authors clarify this point?
10. Page 6. How the wetting and drying cycles were conducted? This is rather important information and it is missing from the methodology section.
11. Page 6/20 Lines 194-196. The Authors state that they measured horizontal load, but they did not present any results from these measurements. This is very interesting information and not very common. The authors are invited to include these data in the paper.
12. Pages 6-7 Figure 2. Deformation is presented in millimeters while in the text (Page 6 Lines 201/204) it is defined as a ratio between two lengths.
13. Page 7/20 Line 217-220. This sentence should be rephrased as it is not clear how swelling can produce a decrease in void ratio. Also, this sentence seems to contradict what is represented in Figure 2.
14. Why did the Authors consider only seven wetting and drying cycles? What would have happened with subsequent cycles?
15. Page 8/20. There is no need for presenting void ratio and porosity as the two parameters are dependent.
16. Page 10/20. The authors neglect that the Mohr-Coulomb envelopes depend on suction. It is, in fact, more realistic that the shift of the straight lines is generated by changes in suction (Consider Equation 1 in Page 14/20) rather than changes in effective cohesion and friction angle! The Authors never mention suction when discussing experimental results but then they extensively use suction to describe the numerical simulations. This is a weak point on this work and the Authors are invited to comment.
17. Page 12/20 Line 332. The Authors mention vertical permeability and then they assume Kx=Ky= 0.034 cm/sec. What does this mean? Are both horizontal and vertical permeability assumed to be equal?
18. How the Authors fixed the permeability value and the position of the groundwater table?
19. Some Figures (e.g. Figure 6e) report some arrows on the toe of the slope but these are not explained in the text.
20. Page 14/20 Lines 371-373. How the soil deformations were calculated? Which model and which soil parameters were used?
21. Page 14/20 Equation1. The values of "fib" are not given in Table 3.
Author Response
Please check the responses in the attached file.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors improved the quality of the manuscript. However, there are still missing information and inconsistencies in material and method, results and discussion part. Therefore, a mayor revision is needed.
Add the content of the supplementary file to the manuscript. It is extremely hard and time consuming to read and compare two manuscripts. There are still many ininconsistencies considering abbreviations (i.e. hr, h, hrs......what does it mean 'hours').
Abstract
Line 18: Mississippi? Area? USA? Clearer explanation
Line 19: The first two sentences indicate the following question? What is the hypotheses?
Line 22: Plaxis 2D? 3D? Company…..?
Line 32: 2hr?
Line 33: Conclusion is missing, most people only read the abstract.
There are still elements of material and methods in the results and discussion part andit is still confusing. Thus, the authors should handle with the standard manuscript preparation guidelines as mentioned in the first review.
Figure 7: Water content on y-line, matric suction on x-line, why the water content in g/g, not volumetric? Van Genuchten formula should be part of the material and methods.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The Authors have addressed all comments in a satisfactory way. A minor issue is that Figure 1 was not visible in the paper downloaded from the Journal website. The Authors are therefore invited to make sure that all figures are visible in the final manuscript. Except for this very minor comment, the quality of the revised paper has remarkably improved and hence it can be published in this form.
Author Response
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Round 3
Reviewer 1 Report
Essential elements of scientific work like objectives and hypothesis are still missing. Therefore, the manuscript can only be accepted after major revision.
Abstract
Line 21-23: Objective of the study?
Introduction
I’m still reaching for a) clear objectives and b) hypothesis, otherwise, it is still a report and not a scientific work. As mentioned several times before, objectives and hypothesis are the fundament of science.
Line 42: The introduction should start with a bride motivating statement in case of one or two sentences to introduce your work well. Even if your results are quite good, interesting results can come across as boring.
Yazoo clay is important for infrastructure (i.e. highway slopes). The main problems are shrinkage/swelling…………..this is the foundation of your research!
Line 56-69: This part is unclear und should be shortened. Problem: shrinkage/swelling…..why!
Methodology
Line 90-91: Results from Proctor test?
Figure 2: (c) is still of minor quality.
Line 135: drained shear strength (water content? Or matric potential?)
Line 137: The unimodal or bimodal (?) van Genuchten (1980) approach was used to fit the measured soil water retention data (nearly-saturated, -xx hPa, -xxxhPa…………….). What kind of program did the authors used for fitting? Hydrus?
Line 141: h=pressure head?
Figure 3: r² between measured and fitted data is missing! Fitted with which Ks value? Matric suction of 100 kPa = 1000 hPa, where are the data in the nearly-saturated range (i.e. 6kPa, 30kPa)? The fitting curve is not optimal, especially in the range of 100kPa matric suction.
Figure 4: What is drying and what is the wetting cycle in (a), (b), (c)? It is not clear and should be marked.
Figure 5: In Figure 7, you show linear regression and in Figure 5 polynomial regression. Why? Authors should also show the linear regression. Void ratio in which unit? There is also no significant differences between 3, 5, and 7 cycles. Thus, homogenized Yazoo clay reached its new pre-shrinkage stage.
Line 197-199: This is material and method.
Table 5: All initial parameters used for modelling should be presented in Table 5 (including the saturated hydraulic conductivities).
Line 273: kv is much higher than kh due to the cracking, but the cracking process is not only isotropic, while further crack generations in horizontal direction are also possible resulting in an increase of kh.
Line 274: desiccation crack is ‘preferential flow path’, how strong is the clay cracking or what is the assumed diameter of the cracks? Picture?
Line 301-316: This is also material and methods.
Line 319: Formula 3 should be part of material and methods.
Figure 8: The initial phase shows matric suction of nearly 30kPa or rather 300hPa. Is it the suction or rather stress or the pore water pressure on the first layer? It is confusing.
Figure 9-10: What does the different colours mean? Units
Figure 11: The authors can put the factor of safety into a Table. Standard deviations? What does the factor of safety mean? Is 1.7 or 1.2 good (stable slope) or not? The authors should explain it. What is the critical shear stress for the slopes?
Conclusion
The conclusion must be more precisely structured.
The aim of the study was………
The results show….. as hypothesized or not hypothesized before.
Author Response
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