Numerical Simulation Study of Landslide Formation Mechanism Based on Strength Parameter

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study "Numerical Simulation Study of Landslide Formation Mechanism Based on Strength Parameter" is a solid and meaningful contribution that provides useful scientific and practical insights into landslide formation mechanisms through numerical simulation and parameter inversion. The topic is relevant and well-motivated. I encourage the authors to carefully address the detailed comments and suggestions to improve clarity, strengthen the discussion of methods and results, and highlight the practical value of the study. Once these revisions are made, the paper will be suitable for publication.

1. The title is clear and reflects the main method (numerical simulation) and topic (landslide formation mechanism). The abstract includes redundant phrases. For example, “strength parameters of the sliding surface soil are the foundation… (Line 9)” could be shorter. It reads more like an introduction than an abstract, the impact or broader implications are underdeveloped. Specific numerical results are good, but the uncertainty or error range is missing. I highly recommend using shorter words and sentences, highlight the practical significance (line 20) (e.g., “These findings support improved hazard mitigation planning for similar geological settings.”).
2. In introduction literature cited is valid but not critically analysed, the gap that this paper fills are not made explicit enough. It could better explain why this particular site is important (beyond general landslide hazard). Rewrite the last two paragraphs to clearly articulate the research gap. (line 33-59).
3. In Figure 7 Rewrite x-axis as cohesion instead of chesio.
4. In the methodology of choosing numerical modelling show sensitivity of results to mesh size. Discuss model assumptions (e.g., drained vs undrained conditions). Expand on the calibration/validation of the numerical model which shows better explanation of choosing the model.
5. In results section add field measurement validation if available. Discuss how numerical results match real failure timing and extent.
6. Explain Figure 14 in the text to show the results of different landslide displacement and deformations.
7. The conclusions mostly restate results and could be strengthened by adding practical recommendations for slope design, excavation control, or monitoring to guide future engineering practice.
8. Yang Jian, 2001 (Line 34) reference is missing in the reference list. Zhang Sumin & Zhang Kuangcheng (1975) — is listed but does not appear cited in the body.
9. Zhang Xu, Zhou Shaowu, Gong Weiqiang, Pan Jinhua, Jiang Shu, Wan Liangpeng. Stability analysis of Biyouzhao landslide in Wudongde reservoir area of Jinsha River 338 [ J ].People 's Yangtze River, 2019,50 ( 01 ) : 124-129. It is also listed but not cited in the body.

Author Response

For research article

We sincerely appreciate the time and effort the reviewers have dedicated to evaluating our manuscript. Their insightful comments have significantly improved the quality of our work. Below, we provide a point-by-point response to their valuable suggestions.

Comments 1:The title is clear and reflects the main method (numerical simulation) and topic (landslide formation mechanism). The abstract includes redundant phrases. For example, “strength parameters of the sliding surface soil are the foundation… (Line 9)” could be shorter. It reads more like an introduction than an abstract, the impact or broader implications are underdeveloped. Specific numerical results are good, but the uncertainty or error range is missing. I highly recommend using shorter words and sentences, highlight the practical significance (line 20) (e.g., “These findings support improved hazard mitigation planning for similar geological settings.”).

Response 1: Modifications have been made in the manuscript

Comments 2: In introduction literature cited is valid but not critically analysed, the gap that this paper fills are not made explicit enough. It could better explain why this particular site is important (beyond general landslide hazard). Rewrite the last two paragraphs to clearly articulate the research gap. (line 33-59).

Response 2: Modifications have been made in the manuscript

Comments 3:In Figure 7 Rewrite x-axis as cohesion instead of chesio.

Response 3: Modifications have been made in the manuscript.

Comments 4:In the methodology of choosing numerical modelling show sensitivity of results to mesh size. Discuss model assumptions (e.g., drained vs undrained conditions). Expand on the calibration/validation of the numerical model which shows better explanation of choosing the model.

Response 4:Table 4 is added; The author believes that drainage conditions need not be considered; In this paper, Moore Coulomb model is used. In landslide simulation, the model is widely used to describe the mechanical behavior of sliding zone soil and most of the soil and rock mass, which can better reflect the process of plastic deformation after reaching the yield condition.

Comments 5:In results section add field measurement validation if available. Discuss how numerical results match real failure timing and extent.

Response 5: Modifications have been made in the manuscript. (line 304)

Comments 6:Explain Figure 14 in the text to show the results of different landslide displacement and deformations.

Response 6: Figure 14 in the text should be figure 13, which is the author's annotation error. The explanation has been marked red in the text(line 271)

Comments 7:The conclusions mostly restate results and could be strengthened by adding practical recommendations for slope design, excavation control, or monitoring to guide future engineering practice.

Response 7: Added a conclusion(line 313)

Comments 8:Yang Jian, 2001 (Line 34) reference is missing in the reference list. Zhang Sumin & Zhang Kuangcheng (1975) — is listed but does not appear cited in the body.

Response 8: Deleted

Comments 9: Zhang Xu, Zhou Shaowu, Gong Weiqiang, Pan Jinhua, Jiang Shu, Wan Liangpeng. Stability analysis of Biyouzhao landslide in Wudongde reservoir area of Jinsha River 338 [ J ].People 's Yangtze River, 2019,50 ( 01 ) : 124-129. It is also listed but not cited in the body.

Response 9: Deleted

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript entitled “Numerical Simulation Study of Landslide Formation Mechanism Based on Strength Parameter” investigates four small-scale landslides in Diebu County, Gansu Province, China, using a combination of field investigation, parameter back analysis, and numerical simulation. While the topic is relevant and the case study is of practical interest for slope stability assessment, I find that the current version of the manuscript needs substantial improvement before it can be considered for publication.

First, the most significant issue is that the novelty of this study is not clearly demonstrated. The manuscript applies existing methods, such as the transfer coefficient method for parameter inversion and FLAC3D numerical simulation with the Mohr–Coulomb model. However, these approaches have already been widely used in similar studies. The authors should clarify which aspects of their work are new compared to these prior studies and explain what advances in knowledge this particular case contributes. Simply showing that the numerical results match the observed field conditions does not, in itself, establish sufficient scientific novelty.

Secondly, the practical usefulness of the findings is not sufficiently discussed. Although the authors have obtained shear strength parameters through inversion and have analyzed the effect of slope toe excavation on landslide stability, they do not adequately explain how these findings could be applied to design, construction planning, or landslide disaster prevention. The manuscript would benefit greatly from a dedicated section that discusses how these results can guide local engineering practice or hazard mitigation.

Furthermore, I am concerned that the reproducibility of the study is limited due to a lack of detailed explanation of key procedures. In particular, the theoretical basis and calculation process for the parameter inversion should be described in more detail. For example, it remains unclear why six sets of cohesion and friction angle values were selected for four landslides, and how the final optimal parameter set was determined. In addition, the stability calculation methods, the boundary conditions used in the numerical models, the meshing approach, and the model validation steps are only briefly mentioned. To ensure that other researchers can replicate the analysis, it is essential to provide sufficient equations, methodological flowcharts, and conceptual diagrams where appropriate.

The figures and tables also require improvement. In line with MDPI guidelines, figures should include clear scale bars, north arrows, and slope gradients for each landslide cross-section where relevant. Figure captions should be more descriptive so that each figure is understandable on its own, even without referring to the main text. For complex results, such as deformation or shear strain distributions, it would help to add annotations that clearly highlight key findings.

Overall, I believe that this manuscript contains valuable field data and shows the authors’ efforts to combine investigation and simulation; however, in its current form, it remains at the level of a technical report that merely confirms observed phenomena rather than a scientific paper that advances theory or practice. It is therefore critical for the authors to strengthen the explanations of the underlying methods, clarify the contribution relative to existing research, and provide concrete implications for practice.

 

Comments:

(1) Figures 2 and 3

Add a scale bar to show the length. Also, in accordance with the MDPI guidelines, please provide an explanation of the differences between the figures so that they can be understood by reading the captions alone.

(2) Table 1

Many technical properties are unfamiliar to readers, such as "sliding mass strike." To help readers understand each parameter, we recommend adding conceptual diagrams.

(3) Line 143 and Table 2

The theory behind reproducing the inverse analysis and the procedure for determining the parameters are necessary. The reviewer could not understand why six common C and φ values were selected for the four different slopes. The procedure and theory must be explained in a way that allows any reader to correctly understand and reproduce them.

(4) Line 146

Need references regarding the unbalanced thrust transfer coefficient mode. In addition, recommend that simplified explanation to the model are added for readers to understand how to estimate stability under given the soil strength parameters.

(5) Table 3

There are several types of stability calculations used to determine the safety factor. You will need to explain which theory you applied and how you solved the problem.

(6) Figure 7

I understand the concept, but I am unsure about the purpose and validity of sensitivity analysis. If evaluations have been performed using a similar method, references should be provided.

(7) Line 187 and Table 4

It is essential to explain the theoretical model used by FLAC3D. Please refer to the writing style of previous papers that used numerical simulations. Although the calculation parameters in Table 4 are written as having been obtained from previous research or laboratory tests, without a detailed explanation, it is difficult to determine whether the values given are appropriate. Since these settings affect the simulation results on which this paper is based, it is necessary not only to cite the references, but also to carefully explain them in the text. Additionally, it is necessary to explain what “epsilon” represents in the table.

(8) Format for references

Please format your reference list and in-text citations according to MDPI guidelines or those used in previous Applied Science publications.

Author Response

The attached drawings can be viewed in the document.

Comments : (1) Figures 2 and 3

Add a scale bar to show the length. Also, in accordance with the MDPI guidelines, please provide an explanation of the differences between the figures so that they can be understood by reading the captions alone.

Response 1: Modifications have been made in the manuscript.

Comments : (2) Table 1

Many technical properties are unfamiliar to readers, such as "sliding mass strike." To help readers understand each parameter, we recommend adding conceptual diagrams.

Response 2: Deleted

Comments : (3) Line 143 and Table 2

The theory behind reproducing the inverse analysis and the procedure for determining the parameters are necessary. The reviewer could not understand why six common C and φ values were selected for the four different slopes. The procedure and theory must be explained in a way that allows any reader to correctly understand and reproduce them.

Response 3: To solve the two unknowns C and φ, two independent equations are needed. Therefore, if there are multiple landslides, it is necessary to solve a group of C and φ with the equations of two landslides by "pairwise combination". So there are six groups of parameters.

Comments : (4) Line 146

Need references regarding the unbalanced thrust transfer coefficient mode. In addition, recommend that simplified explanation to the model are added for readers to understand how to estimate stability under given the soil strength parameters.

Response 4: Based on the number of pages, I will explain the relevant opinions here and will not show them in the article:

Back-analysis of shear strength parameters of the slip zone soil refers to the process of establishing a limit equilibrium equation for landslide stability calculation based on the geometric boundary conditions of the landslide, the physical parameters of the sliding mass, and the stability coefficient. Using limit equilibrium theory, the shear strength parameters (cohesion c and internal friction angle φ) of the landslide are solved.

The transfer coefficient method, also known as the unbalanced thrust force method, is widely used due to its simplicity in calculation and its ability to provide design thrust forces for landslide stabilization.

According to (GB50021-2001), with a stability coefficient of 1.0, the back-calculation of shear strength parameters (c, φ) for the slip zone soil is performed using the transfer coefficient method (unbalanced thrust force method), with the formula given  please see attachment.

Comments : (5) Table 3

There are several types of stability calculations used to determine the safety factor. You will need to explain which theory you applied and how you solved the problem.

Response 5: Based on the number of pages, I will explain the relevant opinions here and will not show them in the article: In FLAC3D, the safety factor is determined by SRM strength reduction method: first set the initial shear strength parameters, then gradually reduce these parameters, and repeatedly calculate each change to gradually increase the reduction factor. This process continues until the slope reaches the critical state. At this time, the reduction factor obtained is the safety factor FS. The calculation formula of strength reduction method please see attachment.

Comments : (6) Figure 7

I understand the concept, but I am unsure about the purpose and validity of sensitivity analysis. If evaluations have been performed using a similar method, references should be provided.

Response 6: As for the sensitivity of uncertain factors, the sensitivity coefficient method is a common method for analyzing uncertain factors. The sensitive factors that have an important impact on the target benefit index are found out one by one from multiple uncertain factors, which are expressed by the sensitivity coefficient E. The sensitivity coefficient method takes a set of benchmark parameters as the standard, and changes one of them on this basis, while the other parameters remain unchanged to calculate the corresponding target physical quantity value. The sensitivity of shear strength parameters to each landslide safety factor is determined according to the variation range of landslide safety factor under the unit variation range of shear strength parameters c and φ of soil in four landslide sliding zones.

Comments : (7) Line 187 and Table 4

It is essential to explain the theoretical model used by FLAC3D. Please refer to the writing style of previous papers that used numerical simulations. Although the calculation parameters in Table 4 are written as having been obtained from previous research or laboratory tests, without a detailed explanation, it is difficult to determine whether the values given are appropriate. Since these settings affect the simulation results on which this paper is based, it is necessary not only to cite the references, but also to carefully explain them in the text. Additionally, it is necessary to explain what “epsilon” represents in the table.

Response 7: In this paper, Moore Coulomb model is used. In landslide simulation, the model is widely used to describe the mechanical behavior of sliding zone soil and most of the soil and rock mass, which can better reflect the process of plastic deformation after reaching the yield condition; epsilon is Poisson's ratio.

For more please see attachment.

Comments : (8) Format for references

Please format your reference list and in-text citations according to MDPI guidelines or those used in previous Applied Science publications.

Response 8: Modifications have been made in the manuscript.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Revision to peer review results is a process designed to make a submitted manuscript clearer and more accessible to the readers—not for the reviewers. Therefore, responses to reviewer comments should be reflected in the revised manuscript itself. By doing so, the manuscript will be more comprehensible and engaging to a broader audience.

The followings need to be revised.

Previous Comment 3
Your response to the reviewer is excellent. Since this explanation improves the readers' understanding, it should be incorporated into the main text. For instance, regarding Lines 151–152:
Old: "Six sets of strength parameters for the slip zone soils were obtained through pairwise equation solving. (Table 2)"
New (suggested): "To solve for the two unknowns, cohesion (c) and internal friction angle (φ), two independent equations are required. Therefore, in the case of multiple landslides, a ‘pairwise combination’ of the equations from two landslides is used to solve for each (c, φ) pair. In this study, 4C2 = 4×3/2 = 6 sets of parameters were derived."

Previous Comment 4
Similarly, please do not limit your explanation to reviewers; it should be included in the text to enhance readability for all readers. In Applied Sciences, omitting important explanations for space limitations is not an acceptable reason. For example, regarding Lines 135–137:
Old: "In accordance with the Geotechnical Investigation Code (GB50021-2001, 2009 Edition) issued by the Ministry of Construction of China, the stability coefficient was set as 1.0 for inversion calculation of shear strength parameters using the transfer coefficient method."
New (suggested): "Using the limit equilibrium method, the shear strength parameters (cohesion c and internal friction angle φ) of the landslide slip zone were determined. This method is widely used because it simplifies calculations and enables the estimation of the thrust force required for stabilization. According to GB50021-2001, when the safety factor is 1.0, the shear strength parameters (c, φ) are back-calculated using the transfer coefficient method (unbalanced thrust force method), as expressed by the following equation:"

The equation in the attachment should be added to the next revision manuscript to enhance the readability for any readers.

Previous Comment 5
Likewise, a description of the theoretical background embedded in FLAC3D is essential. Without such explanation, the manuscript would only be useful to FLAC3D users and lack broader scientific value. Please respond to the reviewer comment with the aim of improving reader readability. For instance, regarding Lines 193–195:
Old: "Based on the current topographic data and historical imagery, the pre-landslide geomorphology was reconstructed, and three-dimensional geological models of the four landslides were established using FLAC3D (Figure 8) for numerical simulations."
New (suggested): "FLAC3D adopts the Mohr–Coulomb model, which is widely used to simulate the mechanical behavior of slip zone soils and most soil/rock masses in landslide studies. This model accurately captures the process of plastic deformation. The safety factor (FS) is determined using the Strength Reduction Method (SRM). Initially, shear strength parameters are assigned, and then progressively reduced through iterative calculation until the slope reaches a critical state. The reduction factor at this point is defined as the safety factor."

Previous Comment 6
This comment is not requesting a description of the methodology but is pointing out the need to clarify the objective and validity of the sensitivity analysis. For example, regarding Lines 173–175:
Old: "Based on the calculated results from Table 4, the sensitivity analysis of the influence of cohesion (c) and internal friction angle (φ) on landslide stability is presented in Figure 7."
New (suggested): "Based on the calculated results, Figure 7 presents a summary of the influence of strength parameters (cohesion c and internal friction angle φ) on the safety factor of the slope."

Previous Comment 7
There is still no explanation of the parameter ε in Table 5. A clear explanation of parameters is essential for readers. Also, while the values in Table 5 are cited from reference [21], this reference could not be found on the publisher's website. Please revise the citation with the correct bibliographic information.

Other Minor Revisions
(a) In Table 1, Line 3:
Change "trailing edge Width (m)" → "trailing edge width (m)"
(b) In Talbe 1, Line 5:
Please add the unit for “distance from road surface height.”
(c) In Lines 178–179:
Old: "The results indicate that the average sensitivity factors of strength parameters c and φ for the four landslides are 28% and 23.6%, respectively."
This appears to be reversed. To be consistent with the subsequent description, it should read:
Corrected: "The results indicate that the average sensitivity factors of strength parameters c and φ for the four landslides are 23.6% and 28%, respectively."
(d) Line 208:
Correction: "Table 4" → "Table 5"
(e) In the Conclusion section:
The first item is labeled "(1)" twice. Please remove one of them.

Comments for author File: Comments.pdf

Author Response

For research article

We sincerely appreciate the time and effort the reviewers have dedicated to evaluating our manuscript. Their insightful comments have significantly improved the quality of our work. Below, we provide a point-by-point response to their valuable suggestions.

Comments 1: Previous Comment 3

Your response to the reviewer is excellent. Since this explanation improves the readers' understanding, it should be incorporated into the main text. For instance, regarding Lines 151–152:

Response 1: Modifications have been made in the manuscript

Comments 2: Previous Comment 4
Similarly, please do not limit your explanation to reviewers; it should be included in the text to enhance readability for all readers. In Applied Sciences, omitting important explanations for space limitations is not an acceptable reason. For example, regarding Lines 135–137:

Response 2: Modifications have been made in the manuscript

Comments 3: Previous Comment 5
Likewise, a description of the theoretical background embedded in FLAC3D is essential. Without such explanation, the manuscript would only be useful to FLAC3D users and lack broader scientific value. Please respond to the reviewer comment with the aim of improving reader readability. For instance, regarding Lines 193–195:

Response 3: Modifications have been made in the manuscript

Comments 4: Previous Comment 6
This comment is not requesting a description of the methodology but is pointing out the need to clarify the objective and validity of the sensitivity analysis. For example, regarding Lines 173–175:

Response 4: Modifications have been made in the manuscript

Comments 5: Previous Comment 7
There is still no explanation of the parameter ε in Table 5. A clear explanation of parameters is essential for readers. Also, while the values in Table 5 are cited from reference [21], this reference could not be found on the publisher's website. Please revise the citation with the correct bibliographic information.

Response 5: ε is Poisson's ratio; The Chinese citation format of document 21 is:

Wang Chunlei, Zhao Huai, Ma Fuchun, et al. Research on the Deformation and Failure Mechanism of the No. 2 Blackduo Landslide in Diebu County [J]. Safety and Environmental Engineering, 2013, 20(03): 22-26.

Comments 6: Other Minor Revisions
(a) In Table 1, Line 3:
Change "trailing edge Width (m)" → "trailing edge width (m)"
(b) In Talbe 1, Line 5:
Please add the unit for “distance from road surface height.”
(c) In Lines 178–179:
Old: "The results indicate that the average sensitivity factors of strength parameters c and φ for the four landslides are 28% and 23.6%, respectively."
This appears to be reversed. To be consistent with the subsequent description, it should read:
Corrected: "The results indicate that the average sensitivity factors of strength parameters c and φ for the four landslides are 23.6% and 28%, respectively."
(d) Line 208:
Correction: "Table 4" → "Table 5"
(e) In the Conclusion section:
The first item is labeled "(1)" twice. Please remove one of them.

Response 6: Modifications have been made in the manuscript

 

 

Author Response File: Author Response.pdf