Macro–Microscale Research on the Single Shear Characteristics of the Root–Loess Interface in Robinia pseudoacacia

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article is concerned with evaluating the strength of a root-less composite. The research is interesting and important from the point of view of stability of loess slopes. The paper is generally well written, some minor comments below.

1) Abstract should be shortened

2) Figures 1-5, 8-9, 12-14, 18-19 - Due to the small size not all parts are clearly visible. In Figure 2  there is additionally a double numbering (with numbers and letters) and it is not explained in the description.

3) Lines 58-68 - There is mention of preliminary studies, but it is not clear whose

4) Line 156 - It will be more informative to give the mean and standard deviation than the mean value itself

5) Table 1 - It is not clear by what methods the consistency limits were determined and on what basis the soil was classified

6) Table 2 - The arrangement of the table suggests that for a particular type of root, the test was performed at specific moisture content, pressure, etc. From the text, I understood that all these parameters were variable and tests were performed for all variants.  Please correct it, so that will be clear.

7) Section 2.3.2 and Figure 6 -  The legend for Figure 6 should be included in the figure caption (or in the pictures).

8) Table 3 - It is not clear on what basis the model parameters were determined

9) Section 3.2 - Due to soil variability, even in the case of laboratory reproduction of specimens, there may be significant differences in the obtained parameters. The accuracy of parameters and their increase reported to 2 decimal places seems unnecessary. As the angle of friction and cohesion are interrelated, it would be worthwhile to trace these relationships as well.

Comments on the Quality of English Language

The work is generally written in correct language, but due to minor errors it would be useful to perform proof reading.

Author Response

Question #1: Abstract should be shortened.

Response: Thank you for your suggestion. We have revised the abstract to make it more concise while ensuring that all key findings and contributions of the study are clearly presented. The revised version eliminates redundant details and focuses on the most essential aspects of our research.

We appreciate your valuable feedback, which has helped improve the clarity and effectiveness of our abstract.

Question #2: Figures 1-5, 8-9, 12-14, 18-19 - Due to the small size not all parts are clearly visible. In Figure 2  there is additionally a double numbering (with numbers and letters) and it is not explained in the description.

Response: Thank you for your valuable feedback. We acknowledge that the small size of Figures 1–5, 8–9, 12–14, and 18–19 may have made certain details difficult to discern. To improve clarity, we have adjusted the figure sizes and enhanced resolution where necessary.

Additionally, in Figure 2, we recognize that the dual numbering system (with numbers and letters) was not adequately explained in the description. We have now clarified this in the figure ensure proper interpretation.

Question #3: Lines 58-68 - There is mention of preliminary studies, but it is not clear whose.

Response: Thank you for your insightful comments. We acknowledge that the preliminary studies mentioned in lines 58-68 were not clearly described. To clarify this, we have revised the text to explicitly state that these studies refer to our own preliminary work.

Question #4: Line 156 - It will be more informative to give the mean and standard deviation than the mean value itself.

Response: Thank you for your valuable suggestion. We agree that providing both the mean and standard deviation offers a more comprehensive representation of the data. Previously, we included the mean to support the experimental design. However, upon your suggestion, we realize that presenting the mean in this context is not appropriate, and we have therefore decided to remove it.

Question #5: Table 1 - It is not clear by what methods the consistency limits were determined and on what basis the soil was classified.

Response: Thank you for your valuable comment. We acknowledge that the methods used to determine the consistency limits and the basis for soil classification were not clearly stated in Table 1. To address this, we have revised the manuscript by explicitly specifying the methods used to determine the consistency limits and the classification criteria This information has been added in Section 2.2 and clarified in the caption of Table 1.

Question #6: Table 2 - The arrangement of the table suggests that for a particular type of root, the test was performed at specific moisture content, pressure, etc. From the text, I understood that all these parameters were variable and tests were performed for all variants. Please correct it, so that will be clear.

Response: Thank you for pointing out the issue with Table 2. We recognize that the previous arrangement may have led to the misunderstanding that each root type was tested under fixed conditions, whereas, in reality, the tests were conducted under varying moisture content, pressure, and other parameters. To avoid this misunderstanding, we have decided to remove Table 2 and instead provide a detailed textual description of the experimental conditions in the manuscript. The experiment was designed using the controlled variable method, systematically testing different variable combinations to ensure the scientific rigor and reliability of the results.

Question #7: Section 2.3.2 and Figure 6 -  The legend for Figure 6 should be included in the figure caption (or in the pictures).

Response: Thank you for your helpful suggestion. We have revised Figure 6 by including the legend in the figure caption. This adjustment enhances clarity and ensures that readers can easily interpret the figure.

Question #8: Table 3 - It is not clear on what basis the model parameters were determined.

Response: Thank you for your valuable comment. We appreciate your concern regarding the determination of model parameters in Table 3. The determination of model parameters is based on fitting the stress-strain curves derived from experimental data. Specifically, to ensure consistency between the simulated and experimentally measured stress-strain curves, we continuously adjust the parameters listed in Table 3 until the two curves closely align, thereby establishing the final parameter values. To enhance readability and comprehension, we have explicitly outlined the parameter determination process in Section 2.3.2 of the manuscript.

Question #9: Section 3.2 - Due to soil variability, even in the case of laboratory reproduction of specimens, there may be significant differences in the obtained parameters. The accuracy of parameters and their increase reported to 2 decimal places seems unnecessary. As the angle of friction and cohesion are interrelated, it would be worthwhile to trace these relationships as well.

Response: Thank you for your valuable comments. We appreciate your insights and have carefully considered your suggestions:

Parameter Precision: We acknowledge that reporting parameters to two decimal places may not be necessary. To improve readability and align with practical significance, we have adjusted the reported values to one decimal place.

Friction Angle and Cohesion Relationship: We appreciate this insightful suggestion. According to the Mohr-Coulomb criterion, there is a certain relationship between soil cohesion (C) and internal friction angle (ϕ). Cohesion (C) represents the contribution of cementation or suction between soil particles to shear strength and is influenced by cementation effects, water content, and fine particle content. In contrast, the internal friction angle (ϕ) reflects the friction and interlocking between particles, which depends on particle arrangement, density, and mineral composition. In non-cohesive soils, cohesion is close to zero, and shear strength is primarily determined by the internal friction angle. In this study, the tested soil is remolded loess, which has weaker structural integrity compared to undisturbed soil. To further investigate the relationship between cohesion and internal friction angle, We are currently testing the strength of undisturbed soil containing roots, followed by CT scanning of the tested samples. The results will be published in future studies.

Question #10: The work is generally written in correct language, but due to minor errors it would be useful to perform proof reading.

Response: Thank you for your suggestion. We have carefully proofread the manuscript and corrected minor language errors to improve clarity and readability. Additionally, we have ensured consistency in terminology and phrasing throughout the text.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the manuscript, the Authors undertook to assess the influence of the root system of the tree species "Robinia pseudoacacia" on the stability of a slope built of mineral formations of loess origin. For this purpose, they performed shear strength tests taking into account the influence of loess moisture and different root contents in the soil sample in a direct shear apparatus constructed for this purpose by the Authors, consisting of 9 frames.

The manuscript is interesting, the discussion of the research results and observations is well conducted. The graphic presentation of the research results is appropriate.

In general, the conclusions are consistent with the aim and scope of the work and refer to the obtained research results.

Comments:
- unify the name of the tree whose roots were used in the research - for example, in line 117 there is the name "Locust", and in line 190 - "Acacia", and in the title of the article "Robinia pseudacacia";
- is the "China honey Locust" the same tree species as the "Locust" - lines 148 to 151;
- in my opinion that the term "ring" does not fit the construction of the apparatus, they were definitely not rings, but frames;
- were the test samples formed, if so, what scheme was adopted in adding the roots, which were certainly of different lengths and thicknesses;
- how was the "Bend radius" of the root determined - see application (1), lines 669-679, is it really "bend radious" that was the basis for dividing the roots into three groups;
- I propose replacing the term "indoor" with "laboratory";
- please comment on what the term "fractal dimesion of the loess failure surface" means - line 401;
- please comment on lines 563-565 - I do not understand what "force chains" the Authors are writing about;
- in my opinion, the applications require rethinking or rephrasing in English, for example in application (3) does the root-soil interface increase the shear strength of the soil sample? In my opinion, these are parameters describing this interface;
 - please comment on what the "biting physical mechanism" means in the case of the conducted research - application (4) - line 690-692;
- what are the indications for further research;
- can the Authors indicate what effects can be obtained in numerical calculations of slope stability after taking into account the influence of the root system;
- what practical advice can be drawn from the conducted laboratory tests;

Comments on the Quality of English Language

The article is written in fairly good English.
However, in my opinion, the article should undergo linguistic correction.

Author Response

Question #1: unify the name of the tree whose roots were used in the research - for example, in line 117 there is the name "Locust", and in line 190 - "Acacia", and in the title of the article "Robinia pseudacacia".

Response: Thank you for your valuable comment. We have carefully reviewed the manuscript and unified the name of the tree species throughout the text. The correct and consistent name, Robinia pseudoacacia, has been used in all instances to avoid confusion.

Question #2: is the "China honey Locust" the same tree species as the "Locust" - lines 148 to 151.

Response: Thank you for your question. The "China honey locust" and "Locust" refer to different species. The term "Locust" in our manuscript specifically refers to Robinia pseudoacacia (Black Locust), while "China honey locust" usually refers to Gleditsia sinensis. To avoid any confusion, we have revised the manuscript to ensure that only Robinia pseudoacacia is referenced consistently throughout the text.

Question #3: in my opinion that the term "ring" does not fit the construction of the apparatus, they were definitely not rings, but frames.

Response: Thank you for your insightful comment. We agree that the term "ring" is not the most accurate description of the apparatus components. To better reflect their actual construction, we have replaced "rings" with "frames" throughout the manuscript. This revision ensures greater clarity and accuracy in describing the experimental setup.

Question #4: were the test samples formed, if so, what scheme was adopted in adding the roots, which were certainly of different lengths and thicknesses.

Response: Thank you for your insightful question. The test samples were prepared using a tamping method within a layered ring framework to ensure uniform compaction. During the sample preparation process, we followed a standardized experimental scheme, maintaining consistent parameters such as soil moisture content, load, root content, and root type.

To address the variability in root length and thickness, we carefully selected and pre-divided root samples to ensure uniformity before adding them to the specimens. Roots were incorporated using a layered compaction method, where pre-sorted roots with controlled length and thickness were evenly distributed within the designated soil layers to achieve the target root content. The detailed sample preparation process is described in Section 2.3.1, and an illustration can be found in Figure 5.

Question #5: how was the "Bend radius" of the root determined - see application (1), lines 669-679, is it really "bend radious" that was the basis for dividing the roots into three groups.

Response: Thank you for your thoughtful question. The term "bend radius" was used to describe the curvature characteristics of the roots, but we acknowledge that further clarification may be needed. The classification of roots into three groups was based on their curvature, specifically considering the ratio of root arc length to chord length rather than a strict mathematical definition of "bend radius". The specific classification method is mentioned in section 2.2 of the text. This classification method is a fusion of our classification method using curvature and the previous method of diameter classification. In addition, we reconsidered the term “bending radius” and replaced it with a more appropriate descriptor in a later study.

Question #6: I propose replacing the term "indoor" with "laboratory".

Response: Thank you for your suggestion. We agree that "laboratory" is a more precise term than "indoor" in the context of our study. We have revised the manuscript accordingly, replacing "indoor" with "laboratory" throughout the text to enhance clarity and accuracy.

Question #7: please comment on what the term "fractal dimesion of the loess failure surface" means - line 401.

Response: Thank you for your question. The term "fractal dimension of the loess failure surface" refers to the quantitative characterization of the complexity and irregularity of the failure surface in loess. In our study, we use fractal dimension as a metric to describe how the failure surface exhibits self-similarity at different scales, capturing its roughness and geometric complexity. A higher fractal dimension indicates a more irregular and rough failure surface, while a lower value suggests a smoother surface.

Question #8: please comment on lines 563-565 - I do not understand what "force chains" the Authors are writing about.

Response: Thank you for your question. The term "force chains" in lines 563–565 refers to the network of contact forces transmitted through soil particles, particularly in the presence of plant roots. In soil-root interaction studies, force chains describe how stress is distributed within the soil matrix, where roots act as reinforcing elements that alter stress paths and load transfer mechanisms. These chains are especially relevant in understanding the mechanical stabilization effects of roots within the loess.

Question #9: in my opinion, the applications require rethinking or rephrasing in English, for example in application (3) does the root-soil interface increase the shear strength of the soil sample? In my opinion, these are parameters describing this interface.

Response: Thank you for your valuable feedback. We acknowledge the need to refine the wording in the applications for better clarity in English. Specifically, in application (3), we agree that the root-soil interface itself does not directly increase the shear strength of the soil sample; rather, it is the parameters describing this interface (such as adhesion and friction) that influence shear strength.

To address this, we have carefully revised the text to ensure that the relationship between the root-soil interface and shear strength is accurately conveyed. We appreciate your insightful comment and have improved the phrasing accordingly.

Question #10: please comment on what the "biting physical mechanism" means in the case of the conducted research - application (4) - line 690-692.

Response: Thank you for your question. The term "biting physical mechanism" in lines 690–692 refers to the mechanical interlocking effect between soil particles and roots at the root-soil interface. In the context of our research, this mechanism describes how roots penetrate and engage with soil particles, creating an interlocking structure that enhances soil cohesion and resistance to shear forces. The interaction between the root surface and soil particles leads to an increase in friction and adhesion, which contributes to overall soil reinforcement.

To improve clarity, we have revised the text to provide a more precise explanation of this concept. We appreciate your valuable feedback.

Question #11: what are the indications for further research.

Response: Thank you for your comment. We acknowledge that the phrase regarding further research may have been unclear or unnecessary in the context of our study. To avoid potential misinterpretations, we have removed this expression from the manuscript and ensured that our conclusions focus solely on the findings of the present study.

We appreciate your valuable feedback, which has helped us improve the clarity and precision of our manuscript.

Question #12: can the Authors indicate what effects can be obtained in numerical calculations of slope stability after taking into account the influence of the root system.

Response: Thank you for your insightful question. The numerical calculations of slope stability that incorporate the influence of the root system can yield the following effects:

Increased Shear Strength – Root reinforcement enhances the soil’s shear strength parameters, particularly by increasing cohesion, thereby improving overall slope stability.

Redistribution of Stress and Strain – The presence of roots alters the internal stress distribution within the slope, leading to a more uniform load-bearing capacity and reducing localized stress concentrations.

Reduction in Factor of Safety (FoS) Variability – Incorporating root reinforcement generally results in a higher and more stable FoS, with its effectiveness dependent on root density, spatial distribution, and mechanical properties.

Mitigation of Shallow Slope Failures – Root systems play a crucial role in near-surface stability by forming an interlocking network that resists shallow sliding, particularly in loess slopes.

These effects are an integral part of our ongoing research, and we are currently conducting further investigations to quantify and model these influences more precisely.In addition, the corresponding content has been added to the section 3.4 part of the manuscript.

Question #13: what practical advice can be drawn from the conducted laboratory tests.

Response: Thank you for your valuable question. Based on the conducted laboratory tests, the following practical advice can be drawn:

Root Selection for Slope Stabilization – The study highlights that Robinia pseudoacacia roots significantly enhance soil shear strength. This suggests that selecting plant species with similar root architecture and mechanical properties can be effective for bioengineering applications.

Optimized Root System Density and Distribution – The results indicate that a well-distributed root network improves soil stability. Thus, afforestation or bioengineering projects should aim for an optimal planting density to maximize reinforcement effects.

To ensure these insights are clearly conveyed, we have revised the discussion/conclusion section accordingly. We appreciate your suggestion, which has helped refine the practical relevance of our study.

Question #14: The article is written in fairly good English. However, in my opinion, the article should undergo linguistic correction.

Response: Thank you for your feedback. We appreciate your recognition of the overall quality of the English in our article. To further improve clarity and readability, we have carefully reviewed the manuscript and made necessary linguistic corrections. Additionally, we have sought professional language editing to ensure the text meets the highest linguistic standards.

Author Response File: Author Response.docx