Analysis of a Landslide on a Railway Track Using Laser Scanning and FEM Numerical Modelling
Round 1
Reviewer 1 Report
The authors have performed analysis on a failed soil mass along a railway route using morphology derived from laser scanning, geotechnical analysis of the constituting soil material, and 3-dimensional finite element analysis. The analysis is a conventional work and a general practice in the slope stability analysis routine nowadays. However, as the study is on a railway track, it holds high social significance. The study has conducted a nice finite element simulation of the failed region but lacks its interpretation and discussion part of the FEM. As the study is on a railway track, a comprehensive geotechnical analysis was expected to describe the grain size, composition, Atterberg limits, etc. with a subsequent adequate discussion of each material property with respect to the stability. However, the conducted geotechnical analysis is sufficient for finite element analysis.
Below are a few specific observations and suggestions for the authors:
Line 18, 19: The authors use the term irrigation throughout the manuscript. I am not clear from the manuscript whether the water saturation is due to an artificial system or just natural rainfall. This needs to be clarified.
The following statements in the introduction need to be supported by suitable references.
Line 45-46:
“Frequent fluctuations in the groundwater level (alternating irrigation and drying) contribute to a reduction in soil strength, which facilitates the movement of ground layers”
Line 49-51:
“In cohesive soils which have humidity close to the liquidity limit, the cohesion force disappears almost completely. As a consequence, the low cohesion of deeper layers may contribute to the movements of larger masses of soils.
Line 53: in this line, “Other natural factors are, for example:….” Other natural factors for what? Please clarify
Line 78: in this line, “The analyzed region was under the influence of all glaciations in Poland”. Please mention the period of glaciation with suitable references.
Line 198. Figure 12: The caption should mention the entity that is represented by the 3D color map and a brief relevance. Also, quantitative water content of the material whose properties were considered for modeling would be appreciated.
Similarly, brief information indicating the relevance of highlighted features is necessary for the caption of figure 13.
Line 201: mention the full form of the acronym IL at least once in the manuscript.
Line 219: The term dusty soil is not an appropriate geological or geotechnical description of the soil type. Consider naming based on the composition or grain-size distribution.
Line 220, 221, 222: The statement is superficial. Consider discussing the fact in more detail with the quantitative value of plasticity and liquidity of the material and suitable references.
Line 228: good and bad climatic conditions are too general. Consider pointing out the specific conditions.
Line 234: The FoS does not indicate the morphological and all geological conditions rather it is an estimation based on several parameters including the above two.
Again as the FoS in the finite element method is very sensitive to several material parameters which in turn are best represented by a range of values than a single deterministic value, it is not always appropriate to perform all the interpretations based on FoS value. Hence, the authors are recommended to make interpretations based on stress, strain, and other derivatives from FEM analysis along with the FoS value.
The authors have mixed the discussion and conclusion of the work. It is necessary to rearrange these two portions to impart clarity and better understanding to the readers' minds.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Analysis of the Causes of a Landslide on the Railway Route Using Laser Scanning and FEM Numerical Modelling
The article presents AN analysis of the causes of a landslide BY using laser scanning and FEM numerical modelling on a specific railway route. The landslide was formed in the area of Poland known as the Polish Low. This area is not considered to be prone to the formation of land movements. Much more dangerous areas from this point of view are found in the south of Poland. In the north, however, landslides are rare and usually occur on slopes next to rivers. In this case, specific conditions for the activation of mass movements of soil occurred. The analysed landslide damaged the railway tracks and caused significant material losses. In determining the causes of this landslide, remote sensing with LIDAR aerial technique and measurements with a terrestrial laser scanner were used. The surface of the area before and after the landslide was reconstructed. A 3D model of the landslide was created based on geotechnical studies and FEM modelling was performed in MIDAS. This paper discusses the results of the many methods that enabled assessment of the causes of the analysed landslide. This analysis concludes that the main reason for the landslide was the irrigation of the ground in the trackbed and the unfavorable morphology of the area on which the railway embankment was located.
This article presents an interesting case study. I can recommend this for publication once the following suggestions are considered:
· The abstract shows a lack of structure and presents some inconsistencies. The authors should be more concise on the message and the aims they want to show. In addition, I have observed some typos or not well-expressed sentences. Just, a few examples here are shown. In the first sentence: “The article presents AN analysis of the causes of a landslide BY using laser scanning and FEM numerical modeling on a specific railway route.” Just few lines ahead, What is the purpose behind this argument? -> “Much more dangerous areas from this point of view are found in the south of Poland.” Also in the abstract, the authors argue: “… analyzed landslide. This analysis…” -> Please avoid reiterations.
· In the introduction, the authors start like this: “Determining the causes of a landslide that poses a threat to transport infrastructure is a very complicated task. Each case of landslide must be analysed separately. Generalising the causes of landslides may lead to incorrect conclusions. Firstly, the randomness and unpredictability of such events should be emphasised. Secondly, the causes are natural in most cases [1−8]. In Poland – due to the natural morphology of the ground – there are many landslides, especially in the transport corridors [9, 10]. Monitoring of the ground is used quite frequently to reduce the risk of landslides. One of the monitoring methods is the remote sensing technique. A terrestrial laser scanner gives good results in monitoring earth structures, particularly railway and road embankments [11−18].” Several points to point out. In the first 4 sentences, even it is “a very complicated task” you should introduce in some way for readers. It is very vague the introduction in this way. After that, what happened in Poland must be introduced properly in a second paragraph. What do you mean by “many landslides”. Can you introduce official stats related to this? In fact, you introduce more or less what happens in Poland at the end of the introduction. Why there? Please try to be more coherent with the structure. Also at the beginning, the methods used for detection and monitoring of these landslides need to be presented in the next paragraph with much more detail.
· I am trying to look for the parameters used by the LiDAR device for this research. According to the authors in lines 185-186, “The table below summarises the parameters used in the model. The land model from the LIDAR [24] was used for calculations of the slope prior to the landslide.“ But I do not see any table below. Some paragraphs before the authors argue “Measurements were made with a RIEGL VZ-400 laser scanner. The measurement points are located at distances no greater than 400 m apart. The vertical resolution of the measurements is about 5 mm. The measurements were made in several locations. Each measurement produced clouds of points in 3D with an accuracy of approx. 2−5 mm. Each measuring point was marked out by GPS. The point cloud was developed in the RiSCAN 107 PRO (2009) as a result of submitting four scans. The point cloud is oriented in the local coordinate system. In the RiSCAN PRO program, the vegetation was removed within the analyzed area. A differential model from two measurements obtained using the RiSCAN PRO program.” My question at this point is what is the real importance of the point density in the results if we consider the heterogeneity of the ground. Some studies discuss these aspects related to Airborne light detection and ranging (LiDAR) point density analysis and the empirical variation in LiDAR point density over different land covers. I would recommend you to add a brief discussion about this topic because you limited the presentation of your LIDAR campaign.
· ”Figure 1 is not well introduced in the caption. I can imagine the landslides are located in the red spots, but that means the large area is located in the south. In addition, I am missing a graphical scale on this map. This also applies to the following figures such the numbers 9 and 10, for example.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The measurement technique is to be detailed.
A measurement uncertainty study is to be performed.
The measurements were performed in 2020, why the paper is submitted after 2 years?
The numerical method is to be detailed. What is the used method? What are the solved equations? What is the convergence criterion? What are the initial and boundary conditions? What are the used assumptions.
A validation/verification of the numerical model is to be performed.
A grid dependency test is to be performed.
The authors concluded that ‘’ The geological structure indicates the possibility of rainwater filtration through the aquatic layer beneath the base of the embankment, which irrigated the layers of dusty and sandy layers resulting in a rapid reduction in their strength capacity’’ practically what are the solutions against this problem.
Author Response
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Author Response File: Author Response.pdf
