Effects of Sample Preparation Methods on Permeability and Microstructure of Remolded Loess

Round 1

Reviewer 1 Report

The primary objective of this study is to explore the influence of different sample preparation methods on the permeability of remolded loess. A lot of experiments were conducted. I enjoy read this article. However, the draft requires some revision before being accepted. Here are some suggestions.

1. The author should pay attention to precise English writing. For example, this study focused on Heifangtai remolded loess as the research subject, The results indicate that: under both sample preparation methods, dry density remains the most influential factor affecting permeability., and so on.

2. The abstract is too long. Concise and clear it, please.

3. Please further improve the references. For example, “Wang L, Chen W, Zhang Y, Vuik C. Investigating effects of heterogeneity and fracture distribution on two-Phase flow in fractured reservoir with adaptive time strategy. Trans Porous Media.”, “Zhang Y, Zou Y, Zhang Y, et al. Experimental Study on Characteristics and Mechanisms of Matrix Pressure Transmission Near the Fracture Surface During Post-Fracturing Shut-In in Tight Oil Reservoirs[J]. Journal of Petroleum Science and Engineering, 2022, 219: 111133.”, and so on.

4. The soil was then wrapped in plastic wrap and sealed for at least 72 hours at room temperature (20°C) to ensure thorough mixing of soil and water. How to control this temperature?

5. In figure 4, explain the difference of seepage time about these lines.

6. The conclusion section are not well organized. Concise the conclusion, so that the reader can clearly know the important information in the shortest time.

minor revise

Author Response

Response to Reviewer 1’s Comments

The primary objective of this study is to explore the influence of different sample preparation methods on the permeability of remolded loess. A lot of experiments were conducted. I enjoy read this article. However, the draft requires some revision before being accepted. Here are some suggestions.

1.The author should pay attention to precise English writing. For example, this study focused on Heifangtai remolded loess as the research subject, The results indicate that: under both sample preparation methods, dry density remains the most influential factor affecting permeability., and so on.

Answer: Thank you for your suggestion. We have carefully reviewed the English writing in the new manuscript, checked the grammar and sentence structure, and made all the necessary corrections.

2. The abstract is too long. Concise and clear it, please.

Answer: Thank you for your suggestion. According to your suggestion, we have reorganized the manuscript and revised the abstract. The purpose of the new abstract is to explore the effects of sample preparation methods on the permeability and microstructure of remolded loess. Make the thesis more clear. Then the experimental design and the experimental process are briefly discussed. The results and conclusions point out that the uniformity of the sample is poor due to the pre-wetting method, and the sample has more correct large pores and obvious aggregate structure. This is the internal cause of the difference in permeability. At last, it is pointed out that when dry density is low, sample preparation method has great influence on permeability of remolded loess, but when dry density is high, the influence is small. The modified in this paper, more concise, in order to better summarized our research content and main findings. We reduced the length of the summary while ensuring that key information and core ideas were retained.

3. Please further improve the references. For example, “Wang L, Chen W, Zhang Y, Vuik C. Investigating effects of heterogeneity and fracture distribution on two-Phase flow in fractured reservoir with adaptive time strategy. Trans Porous Media.”, “Zhang Y, Zou Y, Zhang Y, et al. Experimental Study on Characteristics and Mechanisms of Matrix Pressure Transmission Near the Fracture Surface During Post-Fracturing Shut-In in Tight Oil Reservoirs[J]. Journal of Petroleum Science and Engineering, 2022, 219: 111133.”, and so on.

Answer: Thank you for your suggestion. According to your advice. Some new references have been added in the revised draft, and the newly added references are numbered 15, 16, 19,20,21 and 25 in the paper.

4. The soil was then wrapped in plastic wrap and sealed for at least 72 hours at room temperature (20°C) to ensure thorough mixing of soil and water. How to control this temperature?

Answer: Thank you for your suggestion. We put the wrapped sample into an incubator with constant temperature and humidity to ensure that the ambient temperature and humidity remain unchanged.

5. In figure 4, explain the difference of seepage time about these lines.

Answer: Thank you for your suggestion, We would like to provide an explanation for the variations in seepage time observed in Figure 4. Throughout the experimental process, we simultaneously monitored the conductivity of the leachate. In test, samples with lower dry densitiy tend to exhibit higher permeability, leading to more rapid changes in the conductivity of the leachate. Conversely, samples with higher dry densitiy have lower permeability, resulting in slower changes in the conductivity of the leachate There are two criteria for the termination of the test. When the permeability coefficient value of the sample does not change or the conductivity value of the leachate remains stable, we end the permeability test of a single sample, which results in the difference in seepage time in Figure 4.

6. The conclusion section are not well organized. Concise the conclusion, so that the reader can clearly know the important information in the shortest time.

Answer: Thank you for your suggestion. Thank you for reviewing our paper and providing valuable feedback. We greatly appreciate your guidance on the organization of the conclusion section.

In the revised conclusion, we have made the following changes. Firstly, we emphasize the significant impact of sample preparation methods, initial moisture content, and dry density on the permeability of remolded loess. Secondly, we summarize the variation of loess permeability with respect to the flow time for both sample preparation methods. Additionally, we explicitly state that the leaching of soluble salts affects the changes in soil permeability, informing readers about the experimental results of our study.

We also compare the micro-pore structure of the samples prepared by different methods, highlighting that the pre-wetting method results in more large pores and noticeable aggregate structures. This internal factor contributes to the observed differences in permeability between the two sample preparation methods. Finally, based on our research findings, we propose a recommended dry density value for evaluating the influence of sample preparation methods on the permeability of remolded loess. We suggest that when the dry density is below a certain threshold, the impact of sample preparation methods on the permeability should be assessed.

The revised conclusion statement is refined, providing a concise summary of our discoveries and results. It effectively demonstrates the logical flow of the research, emphasizes the importance of the conclusions, and establishes a strong connection with the research objectives and questions addressed in the paper.

Author Response File: Author Response.docx

Reviewer 2 Report

This paper attempted tostudies the influence of different sample preparation methods on the permeability and microstructure of remolded loess, a type of soil widely distributed in China and prone to landslides due to irrigation.There are several issued need to be improved as follows:

 

·      The title of the paper is too long and vague. It should be more specific and concise, such as “Effects of Sample Preparation Methods on Permeability and Microstructure of Remolded Loess”. This title would clearly indicate the main variables and outcomes of the study, and attract more readers who are interested in loess engineering and geology.

 

·       The abstract of the paper is poorly written and does not clearly state the main objectives, methods, results and contributions of the study. It should be rewritten to provide a brief and informative summary of the paper, following the structure of introduction, methods, results, and conclusion. 

 

·       The introduction of the paper is too general and does not provide a clear background and motivation for the study. It should include a literature review of previous studies on loess permeability and sample preparation methods, as well as a clear statement of the research questions and hypotheses. Then, the introduction could review some previous studies on loess permeability and sample preparation methods, and highlight the research gaps and limitations that need to be addressed. Finally, the introduction could state the main objectives, methods, results and contributions of the study.

 

• The materials and methods section of the paper is not well organized and lacks some details. It should be divided into subsections such as sample collection, sample preparation, permeability test, electrical conductivity test, and microstructure analysis. It should also provide more information on the equipment, parameters, procedures, and quality control measures used in the experiments. Next, the section could explain how the permeability test was conducted using a constant head permeameter, including the equipment model, specifications, settings, water head, flow rate, hydraulic gradient, and Darcy’s law. The section could also mention how the water content and dry density of each sample were measured before and after the permeability test. Similarly, the section could explain how the electrical conductivity test was conducted using a four-electrode method, including the equipment model, specifications, settings, voltage, current, resistance, and Ohm’s law. The section could also mention how the water content and dry density of each sample were measured before and after the electrical conductivity test. Finally, the section could explain how the microstructure analysis was conducted using a SEM, including the equipment model, specifications, settings, sample preparation, image acquisition, and image processing. The section could also mention how the pore size distribution, connectivity, tortuosity, and surface roughness of each sample were quantified using image analysis software.

 

·       The results and analysis section of the paper is too descriptive and does not provide enough interpretation and discussion of the data. It should use more graphs and tables to present the results, and explain the underlying mechanisms and implications of the observed trends and differences. It should also compare the results with previous studies and discuss the limitations and uncertainties of the study. Then, the section could continue to explain the results of SEM analysis,. Next, the section could compare the results with previous studies and discuss how they agree or disagree with them. Finally, the section could discuss the limitations and uncertainties of the study, such as sample size, heterogeneity, measurement error, etc., and suggest ways to overcome them in future research.

·       The conclusion of the paper is too brief and does not highlight the main findings and contributions of the study. It should summarize the main results, discuss their significance and implications for loess engineering and geology, and suggest directions for future research. Then, the conclusion could list some bullet points to summarize the main findings, such as:

o   Water content had a negative effect on both permeability and electrical conductivity of loess samples for all sample preparation methods.

o   Natural cutting had the highest permeability and electrical conductivity among all sample preparation methods, followed by wet cutting, wet tamping, and dry tamping.

o   Sample preparation methods affected the microstructure of loess samples significantly, as reflected by their pore size distribution, connectivity, tortuosity, and surface roughness.

o   Natural cutting preserved the original pore structure of loess better than the other methods, while wet tamping and dry tamping caused more soil disturbance and compaction.

o   Wetting had a similar effect on loess as tamping, while drying had a minor

 

 

This paper could be accept to publish after revise.

Author Response

Response to Reviewer 2’s Comments

This paper attempted tostudies the influence of different sample preparation methods on the permeability and microstructure of remolded loess, a type of soil widely distributed in China and prone to landslides due to irrigation.There are several issued need to be improved as follows:

1.The title of the paper is too long and vague. It should be more specific and concise, such as “Effects of Sample Preparation Methods on Permeability and Microstructure of Remolded Loess”. This title would clearly indicate the main variables and outcomes of the study, and attract more readers who are interested in loess engineering and geology.

Answer: Thank you for your suggestion. According to your suggestion, we have reviewed the title of the paper. We think the title you suggested makes the main idea of the paper more clear, which is very beneficial to improve the cognition of the paper. Can attract more readers. Thanks again for your suggestions on the thesis topic. We accepted your suggestion and revised the title of the paper to "Effects of Sample Preparation Methods on Permeability and Microstructure of Remolded loess".

2. The abstract of the paper is poorly written and does not clearly state the main objectives, methods, results and contributions of the study. It should be rewritten to provide a brief and informative summary of the paper, following the structure of introduction, methods, results, and conclusion.

Answer: Thank you for your suggestion. According to your suggestion, we have reorganized the manuscript and revised the abstract. The purpose of the new abstract is to explore the effects of sample preparation methods on the permeability and microstructure of remolded loess. Make the thesis more clear. Then the experimental design and the experimental process are briefly discussed. The results and conclusions point out that the uniformity of the sample is poor due to the pre-wetting method, and the sample has more correct large pores and obvious aggregate structure. This is the internal cause of the difference in permeability. At last, it is pointed out that when dry density is low, sample preparation method has great influence on permeability of remolded loess, but when dry density is high, the influence is small. The modified in this paper, more concise, in order to better summarized our research content and main findings. We reduced the length of the summary while ensuring that key information and core ideas were retained.

3. The introduction of the paper is too general and does not provide a clear background and motivation for the study. It should include a literature review of previous studies on loess permeability and sample preparation methods, as well as a clear statement of the research questions and hypotheses. Then, the introduction could review some previous studies on loess permeability and sample preparation methods, and highlight the research gaps and limitations that need to be addressed. Finally, the introduction could state the main objectives, methods, results and contributions of the study.

Answer: Thank you for your suggestion. Thank you for reviewing our paper and providing valuable feedback. We value your guidance on the introduction. The revised manuscript provides more specific background information in the research background of the introduction. At the beginning of the introduction, the significance of laboratory research on remodeled soil is added, and the scientific issue of the influence of laboratory samples on the hydraulic characteristics of remodeled soil is raised. Then, the previous research results are summarized from the aspects of dry density, water content and sample preparation methods. The effects of dry density and water content on pore structure and permeability of loess are also summarized. The differences of samples caused by different preparation methods were found and verified by predecessors through various means. Finally, the research objective of this research is proposed, and the methods and contents of this research are summarized.

4. The materials and methods section of the paper is not well organized and lacks some details. It should be divided into subsections such as sample collection, sample preparation, permeability test, electrical conductivity test, and microstructure analysis. It should also provide more information on the equipment, parameters, procedures, and quality control measures used in the experiments. Next, the section could explain how the permeability test was conducted using a constant head permeameter, including the equipment model, specifications, settings, water head, flow rate, hydraulic gradient, and Darcy’s law. The section could also mention how the water content and dry density of each sample were measured before and after the permeability test. Similarly, the section could explain how the electrical conductivity test was conducted using a four-electrode method, including the equipment model, specifications, settings, voltage, current, resistance, and Ohm’s law. The section could also mention how the water content and dry density of each sample were measured before and after the electrical conductivity test. Finally, the section could explain how the microstructure analysis was conducted using a SEM, including the equipment model, specifications, settings, sample preparation, image acquisition, and image processing. The section could also mention how the pore size distribution, connectivity, tortuosity, and surface roughness of each sample were quantified using image analysis software.

Answer: Thank you for your suggestion. Based on your input, we have made some improvements to the Materials and Methods section. In the revised manuscript, we have included a subsection specifically dedicated to the micro test analysis. This subsection provides an overview of the general process of micro test analysis, covering steps such as sample selection, curing, polishing, profiling, and other relevant procedures. We have also included details regarding the selection of magnification for the stereo mirror and polarizing microscope.

Furthermore, the Materials and Methods section has been restructured into five sections: sample characteristics, experimental design, sample preparation, permeability coefficient test, and microstructure test. This revised organization aims to enhance the clarity and coherence of the section, allowing readers to easily navigate through the different aspects of the research methodology.

5. The results and analysis section of the paper is too descriptive and does not provide enough interpretation and discussion of the data. It should use more graphs and tables to present the results, and explain the underlying mechanisms and implications of the observed trends and differences. It should also compare the results with previous studies and discuss the limitations and uncertainties of the study. Then, the section could continue to explain the results of SEM analysis,. Next, the section could compare the results with previous studies and discuss how they agree or disagree with them. Finally, the section could discuss the limitations and uncertainties of the study, such as sample size, heterogeneity, measurement error, etc., and suggest ways to overcome them in future research.

Answer: Thank you for your suggestion. Thank you for your valuable feedback on our paper. We appreciate your input on the results and discussion section. In the revised manuscript, we have made further additions to the chapter discussing the impact of sample preparation methods on permeability.

Specifically, we have provided a more detailed analysis of the variations in surface porosity of the samples under different dry densities for both sample preparation methods. This analysis is visually presented in Figure 12. We have discussed the reduction in surface porosity observed in the experiments and explored the changes in surface density, structural looseness, and different bonding mechanisms of water and soil particles under different sample preparation methods.

Furthermore, we have included an expanded discussion on the microstructural features of the samples observed under a polarizing microscope. We have analyzed the particle morphology distribution, contact relationships among skeleton particles, pore structure of the samples, and degree of consolidation from four aspects. The results are summarized in Table 4, and additional descriptions and analyses of pore characteristics under polarized microscopy have been included in the revised manuscript.

6. The conclusion of the paper is too brief and does not highlight the main findings and contributions of the study. It should summarize the main results, discuss their significance and implications for loess engineering and geology, and suggest directions for future research. Then, the conclusion could list some bullet points to summarize the main findings, such as:

o   Water content had a negative effect on both permeability and electrical conductivity of loess samples for all sample preparation methods.

o   Natural cutting had the highest permeability and electrical conductivity among all sample preparation methods, followed by wet cutting, wet tamping, and dry tamping.

o   Sample preparation methods affected the microstructure of loess samples significantly, as reflected by their pore size distribution, connectivity, tortuosity, and surface roughness.

o   Natural cutting preserved the original pore structure of loess better than the other methods, while wet tamping and dry tamping caused more soil disturbance and compaction.

o   Wetting had a similar effect on loess as tamping, while drying had a minor

Answer: Thank you for your suggestion. Thank you for reviewing our paper and providing valuable feedback. We greatly appreciate your guidance on the organization of the conclusion section.

In the revised conclusion, we have made the following changes. Firstly, we emphasize the significant impact of sample preparation methods, initial moisture content, and dry density on the permeability of remolded loess. Secondly, we summarize the variation of loess permeability with respect to the flow time for both sample preparation methods. Additionally, we explicitly state that the leaching of soluble salts affects the changes in soil permeability, informing readers about the experimental results of our study.

We also compare the micro-pore structure of the samples prepared by different methods, highlighting that the pre-wetting method results in more large pores and noticeable aggregate structures. This internal factor contributes to the observed differences in permeability between the two sample preparation methods. Finally, based on our research findings, we propose a recommended dry density value for evaluating the influence of sample preparation methods on the permeability of remolded loess. We suggest that when the dry density is below a certain threshold, the impact of sample preparation methods on the permeability should be assessed.

The revised conclusion statement is refined, providing a concise summary of our discoveries and results. It effectively demonstrates the logical flow of the research, emphasizes the importance of the conclusions, and establishes a strong connection with the research objectives and questions addressed in the paper.

 

Author Response File: Author Response.docx

Reviewer 3 Report

The Authors explored the influence of sample preparation methods on the permeability of remolded loess focusing on Heifangtai soil. Some major revisions are required

1. What is the relevancy of the soil used in the Authors' study with other regions in the world.

2. What is the influence of variability of soil sample on the results of study?

3. Some recent study should be added in the literature review. Please add the following literature review in the revised manuscript

- https://doi.org/10.1680/jenge.17.00008

- https://doi.org/10.1680/jgeot.15.P.270

- https://doi.org/10.1631/jzus.A1900589

- DOI: 10.1520/GTJ20190237

3. What is the originality of the study?

4. It seems only one type of soil used in the study. How about the other soil types? Is the results of study applicable for other studies?

5. Figure 2 needs to be improved in term of resolution

6. Provide scale in Figurer 12.

7. Provide more explanation for Figure 12. It is not really clear the function of so many figures in Figure 12

8. Provide scale in Figure 13.

9. More discussion on Figure 13

10. Conclusions should be revised to address the objective of study

Moderate English revision

Author Response

Response to Reviewer 3’s Comments

The Authors explored the influence of sample preparation methods on the permeability of remolded loess focusing on Heifangtai soil. Some major revisions are required

1.What is the relevancy of the soil used in the Authors' study with other regions in the world

Answer: Thank you for your suggestion. The selected study area for this research is representative of the soil in the Loess Plateau region of China. It is a terrace platform of the Yellow River and became a gathering place for immigrants from the reservoir area in the late 20th century. In order to improve agricultural productivity, local farmers have practiced extensive irrigation by extracting water from the Yellow River, resulting in a long-term rise in the groundwater level and intense regional hydrological cycles. This has made the area a hotspot for current research.

With the development of the Loess Plateau region, soil reshaping has become a major focus of research. Permeability, as one of the fundamental properties of loess soil, has a significant impact on its stability. However, there is a lack of research on the influence of sampling methods on the study of permeability in reshaped soil. Therefore, we believe that such research is necessary. Due to limitations in scope, we have only focused on studying one type of soil. In future studies, we plan to include comparative research between loess soil and other soil types.

2. What is the influence of variability of soil sample on the results of study?

Answer: Thank you for your feedback. Variation in samples is inevitable during the research process, and we can only minimize the impact of sample variation on the study results to the best of our ability. Here are the approaches we have taken to reduce this influence:

1.During the mixing process of water and soil, we spray water onto the soil surface and let it settle without artificial stirring to prevent soil aggregation.

2.During the compaction process, we maintain a consistent pressure on the sample using a hydraulic jack for a specific duration, avoiding inconsistent sample volumes caused by soil rebound.

3.Throughout the experiment, we ensure consistent initial and final hydraulic heads to prevent variations in test results due to different water levels.

Some recent study should be added in the literature review. Please add the following literature review in the revised manuscript

- https://doi.org/10.1680/jenge.17.00008、 https://doi.org/10.1680/jgeot.15.P.270、 https://doi.org/10.1631/jzus.A1900589、 DOI: 10.1520/GTJ20190237

Answer: Thank you for your suggestion. According to your advice. Some new references have been added in the revised draft, and the newly added references are numbered 15, 16, 19,20,21 and 25 in the paper.

3. What is the originality of the study?

Answer: Thank you for your suggestion. Geotechnical testing is an essential means of studying soil mechanics and is crucial for engineering practices. The results of laboratory tests on reshaped soil play a key role in engineering applications. Currently, both domestic and international specifications, guidelines, and various reference standards do not provide clear requirements for the sampling method of reshaped soil. However, an increasing number of researchers have recognized that different sampling methods can affect the homogeneity of specimens. As a result, studies have been conducted to investigate the influence of sampling methods on the permeability of reshaped soil, aiming to provide assistance for future research in this field

4. It seems only one type of soil used in the study. How about the other soil types? Is the results of study applicable for other studies?

Answer: Thank you for your suggestion. In this study, only one kind of soil was indeed used. The research area chosen in this study is the northwest of the Loess Plateau in China, which is a typical accumulation area of irrigation-induced landslides. Seepage has great influence on the stability of loess tableland. Therefore, we selected the loess in this area to study. For other types of soil, whether the research is suitable for other studies will also be our later research goals, and perhaps we will continue to share and discuss the new research results with you in the near future

5. Figure 2 needs to be improved in term of resolution.

Answer: Thanks for your suggestions. I have modified Fig.2 according to your suggestions, and the number of sample photos has been reduced to make them clearer. The text in the image has been re-edited and the font size has been increased to make it more eye-catching.

6. Provide scale in Figurer 12.

Answer: Thank you for your suggestion. I have modified Figure 12 according to your suggestion. A clearer scale was added. Since more discussion has been added to this chapter, it is named Figure 13 in the new manuscript.

7. Provide more explanation for Figure 12. It is not really clear the function of so many figures in Figure 12

Answer: Thanks for your suggestion. Based on your suggestions, I have made partial adjustments to Figure 12. In the revised manuscript, I have made layout modifications to the figure and added a new chart illustrating the variation of specimen porosity with dry density under different sampling methods. This new chart clearly demonstrates the relationship between specimen porosity and dry density for both sampling methods. Furthermore, additional discussions regarding the pore distribution characteristics of the specimens under different sampling methods have been included after the figure.

8. Provide scale in Figure 13.

Answer: Thank you for your suggestion. I have modified figure 13 according to your suggestion. A clearer scale was added. In the new manuscript it is named Figure 14.

9. More discussion on Figure 13

Answer: Thank you for your suggestion. According to your suggestions, we have made further revisions to the manuscript. In the revised version, we have provided additional discussions for Figure 13. We have elaborated on the microstructural characteristics of the specimens under the two sampling methods, including particle morphology distribution, contact relationships between skeleton particles, specimen pore structure, and degree of consolidation. The summarized results are presented in Table 4. Furthermore, the new manuscript includes more detailed analysis and descriptions of pore characteristics under polarized light microscopy.

10. Conclusions should be revised to address the objective of study.

Answer: Thank you for your suggestion. Thank you for reviewing our paper and providing valuable feedback. We greatly appreciate your guidance on the organization of the conclusion section.

In the revised conclusion, we have made the following changes. Firstly, we emphasize the significant impact of sample preparation methods, initial moisture content, and dry density on the permeability of remolded loess. Secondly, we summarize the variation of loess permeability with respect to the flow time for both sample preparation methods. Additionally, we explicitly state that the leaching of soluble salts affects the changes in soil permeability, informing readers about the experimental results of our study.

We also compare the micro-pore structure of the samples prepared by different methods, highlighting that the pre-wetting method results in more large pores and noticeable aggregate structures. This internal factor contributes to the observed differences in permeability between the two sample preparation methods. Finally, based on our research findings, we propose a recommended dry density value for evaluating the influence of sample preparation methods on the permeability of remolded loess. We suggest that when the dry density is below a certain threshold, the impact of sample preparation methods on the permeability should be assessed.

The revised conclusion statement is refined, providing a concise summary of our discoveries and results. It effectively demonstrates the logical flow of the research, emphasizes the importance of the conclusions, and establishes a strong connection with the research objectives and questions addressed in the paper.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Meet the journal publish requirments.

Reviewer 3 Report

The authors have addressed the comments from Reviewers

English is ok