Impact of Rock Fragment Shapes and Soil Cohesion on Runoff Generation and Sediment Yield of Steep Cut Slopes under Heavy Rainfall Conditions

Round 1

Reviewer 1 Report

 

1. The paper discusses the erosion processes of soil cut slopes and their impact on hydrology. The authors conducted indoor simulated rainfall experiments on a steep slope with high rainfall intensity, different rock fragment contents and roundness, and varying soil cohesion. They found that the sediment yield of the uncemented pebble slope is twice as much as that of the uncemented breccia slope. The cemented breccia slope has a smaller sediment yield due to its larger runoff rate and flow velocity. The more rounded shape and larger radius of curvature of spherical particles result in stronger erosion due to local turbulence. They also observed that rill density and cumulative sediment yield of the steep alluvial cut slope are greater than that of the steep colluvial cut slope under heavy rainfall. A manuscript has a practical application and also provides important theoretical for the next studies. The paper can be accepted for publication after providing the corrections mentioned below.

 

2. The Introduction section would benefit from an expanded literature review, specifically focusing on research conducted outside of China.

 

3. It would be beneficial for the authors to provide some contextual information on the importance of conducting this study.

 

4. Could you discuss any limitations or constraints of your research?

 

5. Important issues must be discussed in your research (indicate lines when revised):

ü  what is the relationship between rock fragment shapes and soil cohesion on runoff generation and sediment yield of steep cut slopes?

ü  how does the shape of rock fragments impact the erosion capacity of steep cut slopes under heavy rainfall conditions?

ü  what is the effect of soil cohesion on the runoff and sediment yield of steep cut slopes under heavy rainfall conditions?

ü  how does the cumulative sediment yield of steep cut slopes differ based on the rock fragment content and roundness?

ü  what are the implications of this research on managing erosion and runoff in steep cut slopes under heavy rainfall conditions?

 

6. Please provide answers for four important questions and provide lines where it is discussed:

ü  how were the different rock fragment contents and roundness levels selected for the experiments, and how were they incorporated into the soil samples?

ü  what specific measures were taken to ensure the accuracy and reliability of the data collected during the indoor simulated rainfall experiments?

ü  what methods were used to measure the various parameters of interest such as infiltration rate, runoff shear stress, runoff power, drag coefficient, Reynolds number, Froude number, and flow velocity?

 

7. Please discuss in the introduction as well as in the discussion the effect of Slope failure and coupling effect. Here consider below mentioned papers:

Boubazine, L.; Boumazbeur, A.; Hadji, R.; Fares, K. Slope failure characterization: A joint multi-geophysical and geotechnical analysis, case study of Babor Mountains range, NE Algeria. Min. Miner. Depos. 2022, 16, 65-70. https://doi.org/10.33271/mining16.04.065

Barvor, Y.J.; Bacha, S.; Qingxiang, C.; Zhao, C.S.; Mohammad, N.; Jiskani, I.M.; Khan, N.M. Research on the coupling effect of the composite slope geometrical parameters. Min. Miner. Depos. 2021, 15, 35-46. https://doi.org/10.33271/mining15.02.035

I believe they are worth considering in your paper.

 

8. Why do not all figures in colours.

 

9. Figure 14 must be discussed in more details.

 

 

10. Overall, the article is positively received, and with the incorporation of all suggested revisions, it will be recommended for publication in the journal "Sustainability."

Author Response

We would like to thank you, most sincerely, for all the effort and expertise that you have contributed to reviewing. Your valuable comments are great helpful to improve the manuscript. We have carefully considered the comments and have revised the manuscript accordingly. We hope that the revised manuscript is acceptable. Detailed responses to your comments are given below.

 

M1. The introduction section would benefit from an expanded literature review, specifically focusing on research conducted outside of China.

The literature review has been expanded to include studies conducted outside of China in Lines 32-42 (i.e., Soil erosion has been acknowledged as a severe environmental threat that not only leads soil degradation but also poses a significant and widespread risk to freshwater and oceans [1,2]. The recent United Nations report on global soil resources highlights soil erosion as a major environmental and agricultural concern worldwide. Soil erosion in modern times is the result of a combination of natural factors and human activities [3]. Over the past 1,000 years, human activities have been the primary cause of soil erosion, accounting for 10 times greater than those caused by all natural processes combined [4–6]. Through activities such as farming, grazing, deforestation, afforesta-tion, urban development, and construction projects, humans change the combination of climate, soil, vegetation, and topography, thereby weakening or intensifying soil erosion [7,8]. The estimated annual average soil erosion load worldwide in 2012 was approximately 3.59 × 1010 t [9].).

M2. It would be beneficial for the authors to provide some contextual information on the importance of conducting this study.

The information on the importance of conducting this study have been added in Lines 100-104 (i.e., Understanding the processes and influential factors of soil erosion is crucial in developing a soil erosion model that can accurately detect and predict soil loss from cut slopes. This knowledge is of utmost importance for effectively managing and reducing soil and water loss from cut slopes).

M3. Could you discuss any limitations or constraints of your research?

The limitations of our paper have been added in Lines 584-597 (i.e., The paper primarily focuses on the characteristics of soil erosion processes in relation to varying rock fragment shapes and soil cohesion. It aims to preliminarily explore the impact of rock fragment shapes and soil cohesion on runoff generation and sediment yield of steep cut slopes under heavy rainfall conditions. However, the mechanism by which rock fragment shape and soil cohesion affect soil erosion in steep cut slope remains unclear. Additional testing conducted at various slopes and rainfall intensities would provide further insight into the extent of the impact of rock fragment shape and soil cohesion on runoff and sediment responses in more complex conditions. These findings would be instrumental in developing the soil erosion model or relationship that is suitable for accurately quantifying soil erosion on cut slopes, considering the variability in rock fragment shapes and soil cohesion. In addition, field evaluations are warranted to determine the impact of rock fragment shapes and soil cohesion on soil erosion in the natural environment and on a larger scale. The implementation of large-scale application methods would help eliminate the effect of particle size on soil erosion responses.).

M4. Important issues must be discussed in your research (indicate lines when revised):

ü  What is the relationship between rock fragment shapes and soil cohesion on runoff generation and sediment yield of steep cut slopes?

Due to the moderate compaction, no cementation, and high roundness of alluvial accumulation between Pai Town and Songlinkou mountain road, the indoor rainfall experiment did not include slopes composed of cemented rounded gravel soil. As a result, the relationship between rock fragment shapes and soil cohesion on runoff generation and sediment yield of steep cut slopes was not extensively discussed. The study primarily focused on examining the individual effects of rock fragment shapes and soil cohesion on runoff generation and sediment yield of steep cut slopes.

ü  How does the shape of rock fragments impact the erosion capacity of steep cut slopes under heavy rainfall conditions?

The impact of rock fragments shape on the erosion capacity of steep cut slopes under heavy rainfall conditions is discussed in Lines 515-525 (i.e., The cumulative sediment yield of the URGSS and UAGSS exhibits a pattern of initial slow increase, followed by a rapid increase, and then another period of slow increase. As the rock fragment content increases, the rate of increase in cumulative sediment yield become more stable, and the initial cumulative sediment yield is slightly higher. During the initial stage of runoff generation, the cumulative sediment yield of the UAGSS is greater than that of the URGSS. However, in the later stages of the runoff generation, the cumulative sediment yield of URGSS gradually surpassed that of the UAGSS. Furthermore, it was observed that the higher the rock fragment content, the earlier the exceedance occurred. This indicates that the rock fragment content has a greater impact on the erosion capacity of rill on URGSS compared to the UAGSS. Overall, the cumulative sediment yield of the URGSS is approximately 20% higher than that of the UAGSS.), and Lines 576-583 (i.e., After the test, macroscopic erosion characteristics of the slope surface reveal that the angular gravel surface is uneven, with greater roughness. It closely adheres to the soil and is more prone to form deep and wide rills during the erosion and development of rills. The number of rills is small. Conversely, the surface of the rounded gravel is smooth, with less close adherence to the soil. Its shape is more regular, with a larger radius of curvature and greater intensity of local turbulence generated by the water flow. Therefore, it is easier to transport the soil around the rounded gravel, forming a small annular groove centered on it, and spreading over the slope, resulting in a sharp increase in sediment yield).

ü  What is the effect of soil cohesion on the runoff and sediment yield of steep cut slopes under heavy rainfall conditions?

The effect of soil cohesion on infiltration rate of steep cut slope under heavy rainfall condition is discussed in Lines 392-396 (i.e., Compared with uncemented slopes, the average infiltration rate of CAGSS decreases, and the degree of the infiltration rate change is small, but the infiltration rate is significantly reduced. For instance, when the slope with 30% rock fragment content, the infiltration rate of CAGSS is reduced by 39.4% compared to the uncemented slope. This date indicates that slopes with soil cohesion rapidly reduce the soil infiltration capacity.)

The effect of soil cohesion on flow velocity of steep cut slope under heavy rainfall condition is discussed in Lines 449-453 (i.e., the presence of soil cohesion in the CAGSS prevents the formation of rill erosion, unlike the UAGSS. Erosion on the CAGSS is limited to the areas between rills, resulting in mimimal change in shape. The surface of the CAGSS remains relatively flat, allowing for smoother water flow compared to UAGSS. Therefore, the flow velocity of the UAGSS is smaller than that of CAGSS due to energy conservation principles.)

The effect of soil cohesion on flow mode and pattern of steep cut slope under heavy rainfall condition is discussed in Lines 476-478 (i.e., slopes with soil cohesion have high shear strength, making it difficult for runoff to erode the slope to form rills. Thus, the slope remains relatively flat, and the the drag coefficient of the CAGSS is minimal), and Lines 483-486 (i.e., the effect of rock fragment shapes on Reynolds number is less significant than that of soil cohesion, indicating that the presence of cementation is the primary factor affecting the flow pattern of slope water.)

The effect of soil cohesion on sediment yield of steep cut slope under heavy rainfall condition is discussed in Lines 525-529 (i.e., On the other hand, the cumulative sediment yield of CAGSS increases slowly and steadily over time, although it remains significantly lower than that of UAGSS. Additionally, it was observed that the rock fragment content has a very slight impact on the cumulative sediment yield of the CAGSS).

In addition, relevant information is comprehensively discussed in discussion chapter as a whole in Lines 546-550 (i.e., In the case of slopes with soil cohesion rapidly reduce the soil infiltration capacity, so the CAGSS has an earlier initial runoff time and a higher runoff rate. The fixed soil grain of CAGSS improves its soil shear strength, making it less susceptible to runoff erosion [56], resulting in a much lower sediment yield than the UAGSS.).

ü  How does the cumulative sediment yield of steep cut slopes differ based on the rock fragment content and roundness?

The relevant information is discussed in Lines 515-525 (i.e., The cumulative sediment yield of the URGSS and UAGSS exhibits a pattern of initial slow increase, followed by a rapid increase, and then another period of slow increase. As the rock fragment content increases, the rate of increase in cumulative sediment yield become more stable, and the initial cumulative sediment yield is slightly higher. During the initial stage of runoff generation, the cumulative sediment yield of the UAGSS is greater than that of the URGSS. However, in the later stages of the runoff generation, the cumulative sediment yield of URGSS gradually surpassed that of the UAGSS. Furthermore, it was observed that the higher the rock fragment content, the earlier the exceedance occurred. This indicates that the rock fragment content has a greater impact on the erosion capacity of rill on URGSS compared to the UAGSS. Overall, the cumulative sediment yield of the URGSS is approximately 20% higher than that of the UAGSS.)

ü  What are the implications of this research on managing erosion and runoff in steep cut slopes under heavy rainfall conditions?

The implications of this research on managing erosion and runoff in steep cut slopes under heavy rainfall conditions is discussed in Lines 97-104 (i.e., the objectives of the study were: (1) to examine hydrodynamic properties such as infiltration rate, runoff rate, flow velocity, flow mode, and pattern under different rock fragment shapes and soil cohesion; (2) to evaluate the effects of rock fragment shapes and soil cohesion on the sediment yield. Understanding the processes and influential factors of soil erosion plays a pivotal role in establishing a soil erosion model that can accurately detect and predict soil loss. This knowledge is of utmost importance for effectively managing and reducing soil and water loss from cut slopes.).

M6. Please provide answers for four important questions and provide lines where it is discussed:

ü  How were the different rock fragment contents and roundness levels selected for the experiments, and how were they incorporated into the soil samples?

The selection of different rock fragment contents for the experiments is based on the information provided in Lines 216-218 (i.e., According to the particle analysis of the cut slope along the Pai–Mo road, the average mass of the 2–60 mm rock fragment group was about 40%. The rock fragment content of the test slope was set to 3 gradients based on the mass ratio of 30%, 40%, and 50%.).

The selection of rock fragment roundness level is based on the information provided in Lines 221-229 (i.e., To investigate the impact of rock fragment shapes on runoff generation and sediment yield of cut slopes, we prepared the uncemented rounded gravel soil slope (URGSS) and uncemented angular gravel soil slope (UAGSS) by mixing commercial rounded and angular gravels, respectively. Based on the Krumbein [45] and Krumbein–Sloss [46] charts, the rounded gravels have rounded to well-rounded shapes with round-ness values 0.7 ≤ R ≤ 0.9, and they are of medium sphericity with values 0.5 ≤ S ≤ 0.7. Conversely, the commercial angular gravels have angular to very angular shapes with roundness values 0.1 ≤ R ≤ 0.3, and they are also of medium sphericity with values 0.5 ≤ S ≤ 0.7.).

The information regarding the incorporation of rock fragments of different sizes, ranging from 2 to 60 mm, into the fine-grained particle (grains sizes < 2mm), is provided in Lines 235-247 (i.e., In addition, to eliminate potential interference, the sand and fine–grained particle (grains sizes < 2mm) for all test samples were exclusively collected from the alluvial at K2+814 m of Pai–Mo road, which is located within the plateau temperate semi–humid climate zone. The soil has a bulk density of 1.2 g/cm3, a natural moisture content of approximately 11%, a sand content of 55%, a powder content of 17%, and a clay content of 28%. According to the soil texture classification standard of the US Ministry of Agriculture, the soil texture is sandy clay loam, and its mechanical composition is mainly sand. After being naturally air–dried, the soil was sieved through a 2 mm sieve. Subsequently, a mass ratio of 70% sand and fine–grained particle (grains sizes < 2mm) mixed with 30% rock fragments of different sizes range 2–60 mm. Similarly, 60% sand and fine–grained particle (grains sizes < 2mm) mixed with 40% rock fragments of different sizes range 2–60 mm. Lastly, 50% sand and fine–grained particle (grains sizes < 2mm) mixed with 50% rock fragments of different sizes range 2–60 mm.).

ü  What specific measures were taken to ensure the accuracy and reliability of the data collected during the indoor simulated rainfall experiments?

We took rigorous measures to ensure the accuracy and reliability of the data collected during the indoor simulated rainfall experiments, e.g., 1) to investigate the impact of rock fragment shapes on runoff generation and sediment yield of cut slopes, we prepared the uncemented rounded gravel soil slope (URGSS) and uncemented angular gravel soil slope (UAGSS) by mixing commercial rounded and angular gravels, respectively (Lines 221-224); 2) to eliminate potential interference, the sand and fine–grained particle (grains sizes < 2mm) for all test samples were exclusively collected from the alluvial at K2+814 m of Pai–Mo road (Lines 235-237); 3) To ensure the quality of sample preparation, digital image processing technology is used to control the variation in rock fragment–specific surface area and spatial arrangement among URGSS, UAGSS and CAGSS. The test was conducted when the difference is less than 3% (Table 3), and the spatial arrangement characteristics were similar (Lines 264-267); 4) The rainfall intensity in the four corners and center of the soil trough is measured using a rain gauge to calculate the average rainfall intensity and uniformity, ensuring that it meets the design requirements (Lines 274-276); 5) The sample is lightly sprinkled with a sprinkler kettle until the drainage hole begins to seep. After this, the rainfall test is conducted by allowing the sample to stand for 12 hours, ensuring that the soil moisture content and water distribution remain relatively consistent for each test (Lines 277-280); 6) The rainfall continues for 30 minutes after a steady runoff is observed on the slope. Following the initial runoff generation, sediment runoff samples are collected at 2-minute intervals using collecting flasks. KMnO4 solution is released from the top of the soil tank, and the time it takes to descend through the bottom of the trough is recorded to determine the water flow velocity (Lines 283-288). 7) After the slope generates runoff, a 30-minute period is dedicated to surface runoff and sediment collection. The time is carefully recorded using a stopwatch. Samples are collected at intervals of 2 minutes, and the mass of sediment-containing runoff is measured using a highly precise electronic scale with an accuracy of 0.1 g. Subsequently, the collected sample is allowed to stand for 8 hours, facilitating the natural stratification of sediment and water. After this process, the supernatant is carefully poured out, and the wet sediment is extracted and placed into an aluminum box. In order to accurately quantify the sediment, it is subjected to a drying process in an oven at 105 °C for a duration of 8 hours (Lines 289-297).

ü  What methods were used to measure the various parameters of interest such as infiltration rate, runoff shear stress, runoff power, drag coefficient, Reynolds number, Froude number, and flow velocity?

The total mass of muddy water containing sediment and the dry weight of sediment are directly collected at 2-minute intervals, as mentioned in Lines 290-292. This data enables us to calculate the runoff generation ( ) using equation (1). Subsequently, the infiltration rate can be determined by applying equation (4).

The flow velocity is measured using the dye KMnO4 tracer method, which is the maximum flow rate of the surface layer.

The runoff shear stress, runoff power, Reynolds number, Froude number, and drag coefficient are calculated by the equation (7), (8), (9), (10), and (11), respectively.

M7. Please discuss in the introduction as well as in the discussion the effect of Slope failure and coupling effect. Here consider below mentioned papers:

Boubazine, L.; Boumazbeur, A.; Hadji, R.; Fares, K. Slope failure characterization: A joint multi-geophysical and geotechnical analysis, case study of Babor Mountains range, NE Algeria. Min. Miner. Depos. 2022, 16, 65-70. https://doi.org/10.33271/mining16.04.065

Barvor, Y.J.; Bacha, S.; Qingxiang, C.; Zhao, C.S.; Mohammad, N.; Jiskani, I.M.; Khan, N.M. Research on the coupling effect of the composite slope geometrical parameters. Min. Miner. Depos. 2021, 15, 35-46. https://doi.org/10.33271/mining15.02.035

I believe they are worth considering in your paper.

Thank you for your valuable comment and paper sharing. Rainfall is widely recognized as the primary cause of soil erosion and slope failure. The rainfall intensity, soil properties, location of the ground water table, and the slope geometry (angle, height) play a significant role in the rainfall-induced soil erosion and slope failure. In addition, the process usually initiates with the infiltration of rainfall into the soil, which subsequently leads to the generation of runoff and the sediment yield. Ultimately, these cumulative effects can contribute to slope failure over time. It is indeed a continuous and interconnected process. However, it is equally important to acknowledge that it is also a progressive process. And, the main focus of the study is on investigating the characteristics of soil erosion processes in relation to different rock fragment shapes and soil cohesion. Rainfall-induced slope failure is not the subject of the study. Therefore, in order to maintain the primary theme and focus of the study, we decided not to include discussions pertaining to rainfall-induced slope failure. We hope that this explanation is acceptable.

M8. Why do not all figures in colours.

All figures have been updated with colors.

M9. Figure 14 must be discussed in more details.

We have added a more detailed discussion about Figure 14 in Lines 515-529. we have rewritten the corresponding sentence to provide a clearer explanation. (i.e., The cumulative sediment yield of the URGSS and UAGSS exhibits a pattern of initial slow increase, followed by a rapid increase, and then another period of slow increase. As the rock fragment content increases, the rate of increase in cumulative sediment yield become more stable, and the initial cumulative sediment yield is slightly higher. During the initial stage of runoff generation, the cumulative sediment yield of the UAGSS is greater than that of the URGSS. However, in the later stages of the runoff generation, the cumulative sediment yield of URGSS gradually surpassed that of the UAGSS. Furthermore, it was observed that the higher the rock fragment content, the earlier the exceedance occurred. This indicates that the rock fragment content has a greater impact on the erosion capacity of rill on URGSS compared to the UAGSS. Overall, the cumulative sediment yield of the URGSS is approximately 20% higher than that of the UAGSS. On the other hand, the cumulative sediment yield of CAGSS in-creases slowly and steadily over time, although it remains significantly lower than that of UAGSS. Additionally, it was observed that the rock fragment content has a very slight impact on the cumulative sediment yield of the CAGSS (Figure 14)).

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript aims to examine the hydrodynamic properties under different forms of rock fragments and soil cohesion, evaluate their effects on sediment production; and to determine the soil erosion risk of the steep slope of the road cut composed of several Quaternary sediments in an area of high rainfall intensity. 

The text is well presented and contextualized, and the results are well discussed. It would be very interesting if evaluations were carried out with other slope ranges and precipitation intensity.

Author Response

We greatly appreciate your suggestion. However, it is important to note that the paper primarily focuses on the characteristics of soil erosion processes in relation to varying rock fragment shapes and soil cohesion. The main objective is to preliminarily explore the impact of rock fragment shapes and soil cohesion on runoff generation and sediment yield of steep cut slopes under heavy rainfall conditions. In order to provide a comprehensive understanding, we have added a section in revision to highlight the limitations of our study. The details can be found in lines (i.e., However, the mechanism by which rock fragment shape and soil cohesion affect soil erosion in steep cut slope remains unclear. Additional testing conducted at various slopes and rainfall intensities would provide further insight into the extent of the im-pact of rock fragment shape and soil cohesion on runoff and sediment responses in more complex conditions. These findings would be instrumental in developing the soil erosion model or relationship that is suitable for accurately quantifying soil erosion on cut slopes, considering the variability in rock fragment shapes and soil cohesion. In addition, field evaluations are warranted to determine the impact of rock fragment shapes and soil cohesion on soil erosion in the natural environment and on a larger scale. The implementation of large-scale application methods would help eliminate the effect of particle size on soil erosion responses.).
We hope that the revised manuscript is acceptable.
Thanks again for your contribution.

Author Response File: Author Response.docx

Reviewer 3 Report

Review of the manuscript “Impact of rock fragment shapes and soil cohesion on runoff generation and sediment yield of steep cut slopes under heavy rainfall conditions”

General comments

On this manuscript are exposed the results of an experimental investigation carried out in the laboratory with a material constituted from the mixture of solid particles of natural soil mixed in different proportions, with and without the addition of siliceous cement. The particles have different degrees of roundness, the influence of which is being studied.

The work is interesting and contains an experimentation work that I consider suitable for publication. But some improvements should be made.

The work is well written, it is generally clear on its approach, and reaches a series of conclusions supported - for the most part - in the experimentation carried out.

The text is easy to read and is correctly arranged. A certificate is provided that the text was “edited for proper English language, grammar, punctuation, spelling, and overall style by one or more of the highly qualified native English speaking editors at Dr. Transpro”.

Being the study of the impact of fragments shapes the main purpose of the manuscript, one of the weaknesses of the work is the way in which these rock fragments are defined or characterized. It is understood from the text that the authors experimented with samples with two types of roundness, called pebbles and breccia. Although the terms used are “graphic”, I consider they are not adequate, since the shape of a rock fragment can be better defined using the terms “Very Angular, Sub angular, sub rounded, rounded, very rounded...”, or considering some of the parameters usually used. Some ideas can be found in the following references:

Ersoy, A., Waller, M.D., 1995. Textural characterisation of rocks. Eng. Geol. 39, 123–136. https://doi.org/10.1016/0013-7952(95)00005-Z

Nie, Z., Fang, C., Gong, J., Yin, Z.-Y., 2020. Exploring the effect of particle shape caused by erosion on the shear behaviour of granular materials via the DEM. Int. J. Solids Struct. 202, 1–11. https://doi.org/10.1016/j.ijsolstr.2020.05.004

The Ersoy and Waller (1995) can be easily obtained with applying the digital image analisis software used by the authors. I consider a better definition of the fragments shape should be included in some way for being able to compare the results.

On the other hand, in the first sections of the work, the context of a large area in which an important infrastructure has been built it is exposed. The authors mentioned that they have described and identified a total of 78 cut slopes, including some general data of them on Table 1.  Adding to this, it is said that one of the objectives is “to determine the risk of soil erosion from the step  shapes…” (lines 88-92). From my point of view, on the results and on the final conclussions, this is not treated and therefore, I would eliminate it from the text. A potential reader would expect to find a final zoning, or an experimentation clearly based on the reproduction on a laboratory scale of the inventoried cut slopes.

 

 

 

Introduction

Lines 87-92: the objectives are listed. The first and the second seem appropriate to the content, but not the third one, since there is no clear approximation in the work to determine the risk of erosion as such. One would expect some kind of quantification or at least qualification of the slopes studied based on erosion potential, but this is not done. Personally, I think that this third idea should be removed.

 

Materials and Methods

The context of the provenance of the studied materials, the type of deposits to which they correspond, and the slopes are also described.

Line 111: I think it is more extended to indicate 8,8% instead of 88.01 ؉

Figure 2. It should be interesting to delimitate the five locations indicated in Table 1, maybe with arrows or similar, and also adding same test to indicate the more abundant deposits on each area (moraine, terraces…)

Line 158, the slope ratio 1:0.75 or 1:1.5. It should be recommended to add, may be in brackets, (H:V)(meaning horizontal:vertical)

In Table 1:

o   Distance/km: It is not clear what it means. May be better “Distance (km)”

o   Falling gradient: I don´t understand this information. Consider to adopt the indications on my previous comment about this.

Líneas 167-168. It seems some editing minor error exist. Would be better to write “VI terraces which were excavated…”

Lines165-185: It is not clear if these data have been obtained within the framework of this study or not, nor is any reference provided if they come from previous works.

Line 175: Macadam soil layer. It is meaning an artificial soil, is it not? At least it is in some parts of the world. The same term is used in Line 183 referring to grain size. With the size idea, it is more properly the use of “cobbles”.

Lines 175 and 177 are apparently intended to reflect the granulometric distribution. The same occurs between lines 183 and 185, when describing the colluvial deposits. If they are available, it would be more appropriate to present the standard granulometric curve or curves for each deposit. This is especially relevant if you want to extrapolate the results obtained in the experimentation with those cut slopes identified.

2.3 Experimental equipment and materials

Line 198. The effective area of ​​2 x 2 is mentioned. It is not clear what it refers to, in view of the diagram. Could it be explained a little bit more or add some indications on Figure 5.

Line 209: Two decimal places are given for the sand content; I think for this data it is more appropriate to give a whole number (55%).

Line 206-215: some data is given on the material collected in the field, which comes from a cut slope of alluvial nature. Then, some data are indicated. From my point of view, being results, they should be place at the beginning of Results Chapter. In any case, the type of tests done, and the laboratory standards followed should be indicated. On the other hand, it seems that the particles of grain size < 2mm have been excluded for preparing the soils to be tested. It is said that this fraction was reserved for later use. I guess grain sizes were fractionated, and then, this < 2mm material separated were used as follows:

·        30 % rock fragments of different sizes + 70 % of grains sizes < 2mm

·        40 % rock fragments of different sizes + 60 % of grains sizes < 2mm

·        50 % rock fragments of different sizes + 50 % of grains sizes < 2mm

Wether or not my interpretation is right, please consider the modification of the text to clarity this circumstance.

Line 224-225: Concerning the information about the mix of different particle sizes, I recommend to add, if possible, the granulometric curve of the materials.

Lines 227-229: It is said the cohesion has been changed adding cement with different mass fractions, but these masses are not expecified. They should be included, as it is expected that after reading the methodology, all the experimentation should be able to be reproduced in another laboratories. In the current state, this is not possible.

Table 2. If the sample used came from an alluvial cut-slope, how it was created the Breccia testing material? According to Line 224, it seems that some fragments were crushed for being use as the rock fragments for the Breccia. Why was not chosen the option of sampling some moraine cut slopes, as the one in Figure 4 (center) or Figure 4 (right).

Also in this table 2, I recommend changing the caption of column 5: Slope gradient (°); and column 6: Rainfall intensity (mm·h^-1).

Line 326: Drag coefficient (as appears in Table 5) or or Darcy-Weisbach friction coefficient.

Results and analysis

In Figures 9, 10, 11, 12, 13 and 14, use for the vertical axis the corresponding parameter abbreviation (Q);(V). It turns to be more easily comprehended.

I do recommend to include the circularity of the rock fragments, using the same digital image analysis approach.

Line 423-428: Please, check the punctuation.

Line 429-430: Please, check the punctuation.  Is a “uncemented slope, the erosion of…”.

Conclussions

Lines 577-581: The first conclusion could be a conclusion of a manuscript where descriptions of different cut slopes were exposed, but this is not the case. It should be very interesting to link laboratory with field observations, but this is not in the manuscript as its current state. I recommend to avoid this first point.

Author Response

We very much appreciate that you read our original manuscript carefully and your insightful and very detailed comments. We have carefully considered the comments and have revised the manuscript accordingly. Your insightful comments help us to improve the manuscript greatly. We hope that the revised manuscript is acceptable. Detailed responses to your comments are given below.

 

M1. Being the study of the impact of fragments shapes the main purpose of the manuscript, one of the weaknesses of the work is the way in which these rock fragments are defined or characterized. It is understood from the text that the authors experimented with samples with two types of roundness, called pebbles and breccia. Although the terms used are “graphic”, I consider they are not adequate, since the shape of a rock fragment can be better defined using the terms “Very Angular, Sub angular, sub rounded, rounded, very rounded...”, or considering some of the parameters usually used. 

Ersoy, A., Waller, M.D., 1995. Textural characterization of rocks. Eng. Geol. 39, 123–136. https://doi.org/10.1016/0013-7952(95)00005-Z

Nie, Z., Fang, C., Gong, J., Yin, Z.-Y., 2020. Exploring the effect of particle shape caused by erosion on the shear behaviour of granular materials via the DEM. Int. J. Solids Struct. 202, 1–11. https://doi.org/10.1016/j.ijsolstr.2020.05.004

The Ersoy and Waller (1995) can be easily obtained with applying the digital image analisis software used by the authors. I consider a better definition of the fragments shape should be included in some way for being able to compare the results.

Thank you for your valuable comment and paper sharing. Based on the Krumbein (1941) and Krumbein and Sloss (1951) charts, the description of particle roundness has been revised to distinguish between rounded gravel and angular gravel, respectively, instead of pebbles and breccia.

Please refer to the relevant revisions mentioned in Lines 176-195 (i.e., The area between Pai Town and Songlinkou mountain road (altitude 2950–3280 m) comprises the Brahmaputra V and VI. terraces which were excavated from Pleistocene alluvial accumulation. Field sieving tests were conducted to characterize the particle size distribution. This sub–rounded to rounded cobbles soil with boulder, gravel, and sand has moderate relative compaction, no cementation, and high roundness, with boulder group (>200 mm), cobble group (60–200 mm), gravel group (2–60 mm), sand group (0.075–2 mm), and fine–grained group (< 0.075 mm) in a ratio of 25:15:27:30:3. The Duoxiongla Tunnel’s sides have a significant number of moraine accumulation layers with considerable thickness, primarily containing sub–round to sub–angular cobbles with extremely low clay content. The lithology of the rock fragment is mainly gneiss, and has medium roundness, with boulder group (> 200 mm), cobble group (60–200 mm), gravel group (2–60 mm), sand group (0.075–2 mm), and fine–grained group (< 0.075 mm) in a ratio of 28:20:24:25:3. Due to the age and long–term consolidation of moraine accumulation layer, the cohesion of these layers is high, with dense structure and strong erosion resistance, which results in no apparent fine trench erosion on the excavation slope. Colluvial deposits are widely distributed on different sections of the Pai–Mo road contain mainly sub–angular to angular cobble soil layer has loose structure, no cementation, low roundness, with boulder group (>200 mm), cobble group (60–200 mm), gravel group (2–60 mm), sand group (0.075–2 mm), and fine–grained group (< 0.075 mm) in a ratio of 25:20:22:28:5 (Figure 4).), and Lines 221-229 (i.e., Therefore, to investigate the impact of rock fragment shapes on runoff generation and sediment yield of cut slopes, we prepared the uncemented rounded gravel soil slope (URGSS) and uncemented angular gravel soil slope (UAGSS) by mixing commercial rounded and angular gravels, respectively. Based on the Krumbein [45] and Krumbein–Sloss [46] charts, the rounded gravels have rounded to well-rounded shapes with roundness values 0.7 ≤ R ≤ 0.9, and they are of medium sphericity with values 0.5 ≤ S ≤ 0.7. Conversely, the commercial angular gravels have angular to very angular shapes with roundness values 0.1 ≤ R ≤ 0.3, and they are also of medium sphericity with values 0.5 ≤ S ≤ 0.7.).

In addition, all the relevant description in tables and figures have been thoroughly revised.

 

Krumbein W.C. Measurement and Geological Significance of Shape and Roundness of Sedimentary Particles. SEPM JSR. 1941, 11(2), 64-72.

Krumbein, W.C. and Sloss, L.L. Stratigraphy and sedimentation. Soil Sci. 1951, 71, 401.

M1. Lines 87-92: the objectives are listed. The first and the second seem appropriate to the content, but not the third one, since there is no clear approximation in the work to determine the risk of erosion as such. One would expect some kind of quantification or at least qualification of the slopes studied based on erosion potential, but this is not done. Personally, I think that this third idea should be removed.

We agree with your suggestion and the third objective has been removed in the revision.

M2. Line 111: I think it is more extended to indicate 8,8% instead of 88.01 ‰.

Have revised.

M3. Figure 2. It should be interesting to delimitate the five locations indicated in Table 1, maybe with arrows or similar, and also adding same test to indicate the more abundant deposits on each area (moraine, terraces…)

The location of “Beibeng” has been added in the Figure 2. The remaining four locations mentioned in Table 1 were already present in the initial Figure 2.

The distribution characteristics of different deposits are illustrated in Lines 176-178, 183-184, 191-192. The area between Pai Town and Songlinkou mountain (altitude 2950–3280 m) comprises primarily of alluvial accumulation. Moraine accumulation are predominantly distributed on both sides of the Duoxiongla Tunnel at higher altitude. However, colluvial deposits are widely distributed on different sections of the Pai–Mo road. Due to these variations, it is challenging to accurately depict them in Figure 2, and it may make the figure difficult to interpret.

M4. Line 158, the slope ratio 1:0.75 or 1:1.5. It should be recommended to add, may be in brackets, (H:V)(meaning horizontal:vertical)

Have revised.

M5. Distance/km: It is not clear what it means. May be better “Distance (km)”.

Have revised.

M6. Falling gradient: I don´t understand this information. Consider to adopt the indications on my previous comment about this.

Have revised.

M7. Lines 167-168. It seems some editing minor error exist. Would be better to write “VI terraces which were excavated…”

Have revised.

M8. Lines165-185: It is not clear if these data have been obtained within the framework of this study or not, nor is any reference provided if they come from previous works.

These data were obtained through field sieving tests. Relevant information has been added in Line 179. (i.e., Field sieving tests were conducted to characterize the particle size distribution.)

M9. Line 175: Macadam soil layer. It is meaning an artificial soil, is it not? At least it is in some parts of the world. The same term is used in Line 183 referring to grain size. With the size idea, it is more properly the use of “cobbles”.

Have revised.

M10. Lines 175 and 177 are apparently intended to reflect the granulometric distribution. The same occurs between lines 183 and 185, when describing the colluvial deposits. If they are available, it would be more appropriate to present the standard granulometric curve or curves for each deposit. This is especially relevant if you want to extrapolate the results obtained in the experimentation with those cut slopes identified.

The paper primarily focuses on the characteristics of soil erosion processes in relation to varying rock fragment shapes and soil cohesion. It aims to preliminarily explore the impact of rock fragment shapes and soil cohesion on runoff generation and sediment yield of steep cut slopes under heavy rainfall conditions. The manuscript also presents the mass ratio of different particle groups, as described in the Lines 179-195. Therefore, considering the limitations of space and the fact that this paper does not specifically address strict similarity ratios, we have chosen not to include granulometric curve for each deposit. We hope that this explanation is acceptable.

M11. Line 198. The effective area of ​​2 x 2 is mentioned. It is not clear what it refers to, in view of the diagram. Could it be explained a little bit more or add some indications on Figure 5.

The indication has been added in Figure 5, and corresponding sentence has been revised to “The effective rainfall area has a diameter of 2 m”.

M12. Line 209: Two decimal places are given for the sand content; I think for this data it is more appropriate to give a whole number (55%).

Have revised.

M13. Line 206-215: some data is given on the material collected in the field, which comes from a cut slope of alluvial nature. Then, some data are indicated. From my point of view, being results, they should be place at the beginning of Results Chapter. In any case, the type of tests done, and the laboratory standards followed should be indicated. On the other hand, it seems that the particles of grain size < 2mm have been excluded for preparing the soils to be tested. It is said that this fraction was reserved for later use. I guess grain sizes were fractionated, and then, this < 2mm material separated were used as follows:

30 % rock fragments of different sizes + 70 % of grains sizes < 2mm

40 % rock fragments of different sizes + 60 % of grains sizes < 2mm

50 % rock fragments of different sizes + 50 % of grains sizes < 2mm

Wether or not my interpretation is right, please consider the modification of the text to clarity this circumstance.

Yes, your interpretation is correct. Based on your insightful and detailed suggesting, we have merged section 2.3 (experimental equipment and material) and section 2.4 (experimental design). Furthermore, we have revised corresponding sentence and added relevant information in Lines 235-247 (i.e. In addition, to eliminate potential interference, the sand and fine–grained particle (grains sizes < 2mm) for all test samples were exclusively collected from the alluvial at K2+814 m of Pai–Mo road, which is located within the plateau temperate semi–humid climate zone. The soil has a bulk density of 1.2 g/cm3, a natural moisture content of approximately 11%, a sand content of 55%, a powder content of 17%, and a clay con-tent of 28%. According to the soil texture classification standard of the US Ministry of Agriculture, the soil texture is sandy clay loam, and its mechanical composition is mainly sand. After being naturally air–dried, the soil was sieved through a 2 mm sieve. Subsequently, a mass ratio of 70% sand and fine–grained particle (grains sizes < 2mm) mixed with 30% rock fragments of different sizes range 2–60 mm. Similarly, 60% sand and fine–grained particle (grains sizes < 2mm) mixed with 40% rock fragments of different sizes range 2–60 mm. Lastly, 50% sand and fine–grained particle (grains sizes < 2mm) mixed with 50% rock fragments of different sizes range 2–60 mm.)

M14. Line 224-225: Concerning the information about the mix of different particle sizes, I recommend to add, if possible, the granulometric curve of the materials.

The manuscript includes the mass ratio of different rock fragment sizes, as described in the Lines 230-231. Similarly, for the same reasons as M10, we have decided not to include granulometric curve of the experimental materials.

M15. Lines 227-229: It is said the cohesion has been changed adding cement with different mass fractions, but these masses are not expecified. They should be included, as it is expected that after reading the methodology, all the experimentation should be able to be reproduced in another laboratories. In the current state, this is not possible.

Have revised. Please refer to Lines 231-234 (i.e., Furthermore, to investigate the impact of soil cohesion on runoff generation and sediment yield of cut slopes, we prepared the cemented angular gravel soil slope (CAGSS) by incorporating a 4% mass of cement. The CAGSS sample was prepared using 42.5 ordinary silicate cement and tested after 24 hours of curing.)

M16. Table 2. If the sample used came from an alluvial cut-slope, how it was created the Breccia testing material? According to Line 224, it seems that some fragments were crushed for being use as the rock fragments for the Breccia. Why was not chosen the option of sampling some moraine cut slopes, as the one in Figure 4 (center) or Figure 4 (right).

Relevant explanation has been added in Lines 235-238 (i.e., to eliminate potential interference, the sand and fine–grained particle (grains sizes < 2mm) for all test samples were exclusively collected from the alluvial at K2+814 m of Pai–Mo road, which is located within the plateau temperate semi–humid climate zone.)

M17. Also in this table 2, I recommend changing the caption of column 5: Slope gradient (°); and column 6: Rainfall intensity (mm·h-1).

Have revised.

M18. Line 326: Drag coefficient (as appears in Table 5) or Darcy-Weisbach friction coefficient.

We have made the revision to replace the term “Darcy-Weisbach friction coefficient” with “drag coefficient” in Line 352.

M19. In Figures 9, 10, 11, 12, 13 and 14, use for the vertical axis the corresponding parameter abbreviation (Q);(V). It turns to be more easily comprehended.

Have revised

M20. Line 423-428: Please, check the punctuation.

We have revised the corresponding sentence in Lines 440-448 (i.e. Therefore, the process of change in the URGSS and UAGSS can be roughly divided into two stages: (1) The stage of significant fluctuations occurs in the initial stage of rainfall runoff, characterized by a decrease in flow velocity accompanied by violent fluctuations; (2) The stage of gradual decline occurs in the later stage of rainfall runoff, where the fluctuation amplitude of flow velocity significantly reduces and shows a slow downward trend (as shown in Figure 11). This is because during the initial stage of rainfall, the slope surface is relatively smooth, resulting in less resistance to the thin-layer water flow on the slope surface and higher flow velocity.)

M21. Line 429-430: Please, check the punctuation.  Is a “uncemented slope, the erosion of…”.

We have revised the corresponding sentence in Lines 449-453 (i.e. However, the presence of soil cohesion in the CAGSS prevents the formation of rill erosion, unlike the UAGSS. Erosion on the CAGSS is limited to the areas between rills, resulting in mimimal change in shape. The surface of the CAGSS remains relatively flat, allowing for smoother water flow compared to UAGSS. Therefore, the flow velocity of the UAGSS is smaller than that of CAGSS due to energy conservation principles.)

M22. Lines 577-581: The first conclusion could be a conclusion of a manuscript where descriptions of different cut slopes were exposed, but this is not the case. It should be very interesting to link laboratory with field observations, but this is not in the manuscript as its current state. I recommend to avoid this first point.

Relevant information has been revised in Lines 604-607 (i.e., The steep URGSS develops numerous small annular rills around rounded gravels under high rainfall intensity. In contrast, the UAGSS composed of angular gravels has fewer rills. However, the CAGSS is not eroded under high rainfall intensity, with only raindrop splashing and erosion between rills occurring.).

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Revision is acceptable.

At the same time, most comments are discussed in the author's reply but not within the paper.

Grammar must be improved.

Reviewer 3 Report

Dear authors, thank you for your detailed explanations. From my point of view, your manuscript is very interesting. Congratulations for your work.