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Article
Peer-Review Record

Impact of Piping Erosion Process on the Temporal–Spatial Mechanisms of Soil

Water 2022, 14(18), 2841; https://doi.org/10.3390/w14182841
by Qiong Xiao
Reviewer 1: Anonymous
Reviewer 2:
Water 2022, 14(18), 2841; https://doi.org/10.3390/w14182841
Submission received: 20 July 2022 / Revised: 9 September 2022 / Accepted: 10 September 2022 / Published: 12 September 2022
(This article belongs to the Special Issue Rainfall and Water Flow-Induced Soil Erosion)

Round 1

Reviewer 1 Report

The article is very interesting and fits into the journal area. This work investigates the seepage impact on the internal heterogeneity of granular systems and examining the mechanical behaviour of eroded soil matrix at different locations of embankments to give some insights into the design of practical infrastructures.

 

Please correct or complete:

·        Line 33: the meaning of ICOLD

·        Line 95: the meaning of LAMMPS

·        Line 147: “The wall, with a dimension of 0.01 m in the x-direction” - dimension 0.01 m is not in concordance with figure 1

·        Figure 1: it was RVE 1, RVE 2 and RVE 3 and different designations were used along the text

·        Line 189: missing a space in the text: Figure5

·        Line 316: “and the temporal eroded specimen at t=0.1 s and t=0.2 s”

Comments for author File: Comments.pdf

Author Response

We thank the referee for the careful and insightful review of our manuscript. Here are the detailed revisions based on the comments and concerns.

  • Line 33: Add the complete spelling of ICOLD
  •  Line 95: Add the complete spelling of LAMMPS
  •  Line 147: The dimension is modified
  • Figure 1: The designations are modified as RVE_C, RVE_D, RVE_U
  • Line 189 and Line 316: Address the missing space

Reviewer 2 Report

The authors focus on the potential for seepage to increase the risk of dam failure. They simulate the transport of water and a bimodal mixture of fine (0.25 mm) and coarse (1 mm) sand below a no-flow barrier and present a weighted clustering coefficient to improve predictions of the reduction of peak shear strength as erosion of fines from the matrix progresses.

The authors do a fine job setting up and executing their numerical model and interpreting the results but this reviewer finds the transferability to real-world dam risk to be limited for the following reasons:

1     Model domain: The active model, both temporally (0.01, 0.1, and 0.2 seconds), and spatially (5 cm x 8 cm ), is extremely limited. Model runs do not continue through steady state and do not encompass the dimensions of piping and tunnel enlargement leading to dam failure.

2      Dam failure: As described by Foster et al. [2000], dam failure is primarily a result of two events: dam overtopping or failure of gates; and piping that progresses through three stages. The three stages of piping described by Foster: (1) initiation through an unprotected exit point; (2) backward erosion and tunnel enlargement; and (3) Dam breach as settlement leads to overtopping, collapse of tunnel, or toe unraveling. The simulations in this manuscript address only the first 0.2 seconds of stage (1) and use a model configuration of a vertical no-flow barrier in unconsolidated earthfill with the bottom of the corewall in the foundation; described as zone type 9 -  “Earthfill with corewall” by Foster et al. Only two percent of the 11,192 dams in the database were of this type and failures attributable to erosion of the foundation under that corewall  accounted for only 2 of 136 dam failures in the database. When we add the model configuration of bimodal well-sorted sands for the embankment fill, there were no failures.

3      Fill texture and charge: In future work the authors may consider adding a variety of scenarios including varying degrees of sorting and sediment materials. The results show the lower conductivity of the finer fill. They also cite Bendahmane et al. [2011] who found decreasing permeability (lower K) with increasing Kaolin. Kaolin is a 1:1 clay that is unlike 1:2 clays like montmorillinite and smectite that have significant shrink swell potential. Foster also mentions that the percentage of dispersive soils in the embankment are directly correlated with the potential for dam failure as piping would be accelerated.

All in all, the research is well presented with minor improvements in English translation needed. One main clarification of translation would be for the term ‘hydrologic condition’ which could refer to the heads, gradients, velocities, densities, or viscosities.

Thank you for the opportunity to review this research, and best wishes for success in your future research. I include more detailed comments in the attached PDF.

Comments for author File: Comments.pdf

Author Response

We thank the referee for the careful and insightful review of our manuscript.

#The authors focus on the potential for seepage to increase the risk of dam failure. They simulate the transport of water and a bimodal mixture of fine (0.25 mm) and coarse (1 mm) sand below a no-flow barrier and present a weighted clustering coefficient to improve predictions of the reduction of peak shear strength as erosion of fines from the matrix progresses.
The authors do a fine job setting up and executing their numerical model and interpreting the results but this reviewer finds the transferability to real-world dam risk to be limited for the following reasons:
1 Model domain: The active model, both temporally (0.01, 0.1, and 0.2 seconds), and spatially (5 cm x 8 cm ), is extremely limited. Model runs do not continue through steady state and do not encompass the dimensions of piping and tunnel enlargement leading to dam failure.
2 Dam failure: As described by Foster et al. [2000], dam failure is primarily a result of two events: dam overtopping or failure of gates; and piping that progresses through three stages. The three stages of piping described by Foster: (1) initiation through an unprotected exit point; (2) backward erosion and tunnel enlargement; and (3) Dam breach as settlement leads to overtopping, collapse of tunnel, or toe unraveling. The simulations in this manuscript address only the first 0.2 seconds of stage (1) and use a model configuration of a vertical no-flow barrier in unconsolidated earthfill with the bottom of the corewall in the foundation; described as zone type 9 - “Earthfill with corewall” by Foster et al. Only two percent of the 11,192 dams in the database were of this type and failures attributable to erosion of the foundation under that corewall accounted for only 2 of 136 dam failures in the database. When we add the model configuration of bimodal well-sorted sands for the embankment fill, there were no failures.
3 Fill texture and charge: In future work the authors may consider adding a variety of scenarios including varying degrees of sorting and sediment materials. The results show the lower conductivity of the finer fill. They also cite Bendahmane et al. [2011] who found decreasing permeability (lower K) with increasing Kaolin. Kaolin is a 1:1 clay that is unlike 1:2 clays like montmorillinite and smectite that have significant shrink swell potential. Foster also mentions that the percentage of dispersive soils in the embankment are directly correlated with the potential for dam failure as piping would be accelerated.

We agree that the problem raised by the referee could be seen as a major concern and should be devoted to more attention in future work. As the referee mentioned, dam risk is a complicated condition in the real world. This study attempts to investigate the impact of a hydraulic head on the transferability of the fine particles and the mechanisms of the prediction of peak shear strength using a simple small-scale numerical model. Extensive works can be conducted in the future concerning different sediment materials and the execution of GPU to simulate a large-scale configuration.

#All in all, the research is well presented with minor improvements in English translation needed. One main clarification of translation would be for the term ‘hydrologic condition’ which could refer to the heads, gradients, velocities, densities, or viscosities.
Thank you for the opportunity to review this research, and best wishes for success in your future research. I include more detailed comments in the attached PDF.

We have been able to incorporate changes to reflect most of the suggestions. The vocabulary like ‘hydraulic condition’ and ‘seepage’ has been replaced with ‘hydraulic head’ and ‘piping’ to clarify more clearly. Detailed changes and comments can be tracked in the modified manuscript. 


Thank you for the effort and expertise that you contributed towards reviewing the manuscript, which has certainly contributed to improving the quality. We include some replies to the detailed comments in the attached PDF.

Author Response File: Author Response.pdf

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