Review Reports

Round 1

Reviewer 1 Report

This paper proposed a numerical model for the simulation of pipe-soil interaction under seismic loading. The distribution of the liquefaction potential of soil around the pipelines and the corresponding effect on the uplift resistance as well as the upheaval buckling behaviors of pipelines were discussed via a parametric study. The paper is generally presented in a good structure. However, some of the simulated results do not seem to be convicing. Besides, the language needs to be greatly improved. Thus, it cannot be recommended for publication in the present form. Detailed comments are as follows:

 

1. The abstract should be shortened largely, with an emphasis on the contribution and innovation of this paper.

 

2. Many grammatical mistakes are noticed (e.g. Lines 115-116, 142, 200, 208, 296-297, 301, 364, 412-413, 447). Please take substantial efforts to polish the language.

 

2. The mesh of soil surrounding the pipe is rather coarse. Please discuss on mesh sensitivity of the present model.

 

3. The liquefaction potential is usually evaluated using the ratio of excess pore pressure to initial vertical effective stress u_e/σ’_v0. However, the authors proposed their own criterion based on a user-defined parameter r_u=1-σ_v/σ_v0, in which the overburden stress rather than soil effective stress is used. Please justify.

 

4. The negative pore pressure ratio reaches -1.5 in Figs. 4-6. Please elaborate on this in more detail.

 

5. It is mentioned that the soil is simulated using the PM4Sand model in seismic loading period and HSS model in post-earthquake period. Tables 1-2 show that the strength and stiffness parameters (e.g. shear modulus and friction angle) of these two models are different. Please elaborate on how the variation of stiffness and strength parameters are considered during earthquake-induced liquefaction.

 

6. Fig. 7 shows that at f = 1 Hz the pipe with deeper embedment sinks at significantly higher rate. This is somewhat counter-intuitive and a detailed discussion is needed.

 

7. A lot of plots need to be modified, and presented in a professional format.

 

8. At the presence of liquefaction under sesmic loading, very large displacement / deformation is highly likely to occur. Is it possible to consider this effect in the present model? See some analyses of pipe-soil interaction problems using large displacement / deformation techniques (e.g. Quantifying Residual Resistance of Light Pipelines during Large-Amplitude Lateral Displacement Using Sequential Limit Analysis; Finite element algorithms for dynamic analysis of geotechnical problems; “Finite element modeling ofpartially embedded pipelines in clay seabed using Coupled Eulerian– Lagrangian method)

Author Response

Annotation

We thank the reviewer for the very detailed check. This is much appreciated. All the comments are addressed in the newly revised manuscript and we believe the revised version is considered suitable for publication. On marked and another unmarked manuscript are submitted. In the marked manuscript, the changes incorporated as per the suggestion of the Reviewer 1 are highlighted as green; while the changes suggested by the Reviewer 2 are highlighted as yellow.

Reviewer 1.

This paper proposed a numerical model for the simulation of pipe-soil interaction under seismic loading. The distribution of the liquefaction potential of soil around the pipelines and the corresponding effect on the uplift resistance as well as the upheaval buckling behaviors of pipelines were discussed via a parametric study. The paper is generally presented in a good structure. However, some of the simulated results do not seem to be convincing. Besides, the language needs to be greatly improved. Thus, it cannot be recommended for publication in the present form. Detailed comments are as follows:

1. The abstract should be shortened largely, with an emphasis on the contribution and innovation of this paper.

 

Reply:

The authors are thankful to the reviewer for the suggestion.

The abstract is shortened, and the contribution and novelty of the article is emphasized as per the suggestion. Thus, the word number of the abstract is reduced from 363 to 323. Please check.

 

2. Many grammatical mistakes are noticed (e.g. Lines 115-116, 142, 200, 208, 296-297, 301, 364, 412-413, 447). Please take substantial efforts to polish the language.

 

Reply:

The authors are thankful to the reviewer for the suggestion.

The above lines are grammatically corrected and rephrased in some cases to enhance clarity.

 

3. The mesh of soil surrounding the pipe is rather coarse. Please discuss on mesh sensitivity of the present model.

 

Reply:

The authors are thankful for the comment.

In the current model a relative element size of 1.33 is considered, which resulted the soil body to be discretized into 687 elements and 6102 nodes, as discussed in section 3.1.

The mesh size used in this study is decided by a mesh convergence study with different mesh sizes. It is observed that the current mesh size caused very little sacrifice of accuracy of the result while reducing a considerable extent of computational cost.

The above clarification is also added in Section 3.1.

 

4. The liquefaction potential is usually evaluated using the ratio of excess pore pressure to initial vertical effective stress u_e/σ_v0’. However, the authors proposed their own criterion based on a user-defined parameter r_u =1-(σ_v /σ_v0) , in which the overburden stress rather than soil effective stress is used. Please justify.

 

Reply:

The authors are thankful for the opportunity to explain the doubt.

The user-defined state parameter, pore-pressure ratio (r_u) is widely used in various research-works including Boulanger and Ziotopoulou., (2015)., to understand the liquefaction potential within a soil body and the same relation as the manuscript (r_u =1-σ_v /σ_v0) is used by the researchers. Moreover, the above expression is predefined in the PM4Sand constitutive model used in the finite element package PLAXIS 2D and not set by the author.

 

Furthermore, r_u is given as:

r_u =1-(σ_v /σ_v0) = (σ_v0 - σ_v)/ σ_v0

For undrained condition and very short duration of loading, the change in vertical stress (σ_v0 - σ_v) is due to the change in pore-pressure (u_e). Thus, the r_u defined in the current study (1-(σ_v /σ_v0)) is only a different representation of the suggested r_u (u_e/σ_v0’) and they will yield similar results.

 

σ_v0 and σ_v are revised in the manuscript as ‘initial vertical stress at the beginning of a phase’ and ‘vertical stress’, respectively. Please see, sub-section 4.1. in the manuscript.

 

Reference.: Boulanger, R. W.; Ziotopoulou, K. PM4Sand (version 3): A sand plasticity model for earthquake engineering applications. Report No. UCD/CGM-15/01, March 2015, Boulanger Ziotopoulou PM4Sand Model CGM-15-01 2015, 112pp.

 

5. The negative pore pressure ratio reaches -1.5 in Figs. 4-6. Please elaborate on this in more detail.

 

Reply:

The authors are thankful for the comment.

There are few regions within soil body where negative pore pressure ratio is reached. The reason of such negative pore water pressure ratio can be attributed to the dilation of the soil mass under the influence of the dynamic loading. A similar kind of dilation behavior of Nevada sand under dynamic loading was also observed by Dinesh et al. (2022). However, the variation of pore water pressure within the soil body was not included in their study.

The above phenomenon is already discussed in the manuscript. Please see Line no: 451 of section 4.1.

 

Reference.: Dinesh, N.; Banerjee, S.; Rajagopal, K. Performance evaluation of PM4Sand model for simulation of the liquefaction remedial measures for embankment. Soil Dynamics and Earthquake Engineering 2022, 152, 107042.

 

6. It is mentioned that the soil is simulated using the PM4Sand model in seismic loading period and HSS model in post-earthquake period. Tables 1-2 show that the strength and stiffness parameters (e.g. shear modulus and friction angle) of these two models are different. Please elaborate on how the variation of stiffness and strength parameters are considered during earthquake-induced liquefaction.

 

Reply:

The authors are thankful for the opportunity to clarify the doubt.

In the current study, PM4Sand model is used to simulate the dynamic stage as it has excellent capability to analyze the triggering of liquefaction and the resulting deformations in the soil for plane strain conditions (Dinesh et al., 2022) However, PM4Sand model produce less accurate results under static loading conditions (Vilhar and Brinkgreve., 2018). Thus, it is advised in the PLAXIS 2D manual (Vilhar and Brinkgreve., 2018) to model the static stages (Initial phase, Installation, and Post-earthquake) using some other material models (in this study, the HSS model) and to change the material model into PM4Sand model during the earthquake stage.

The stress states and displacements of a soil volume in a particular stage is calculated as per the defined stiffness and strength parameters of that stage. However, at the beginning of each stage of calculation, the internal variables are initialized as per the stress state of the previous stage; hence, the internal variables in ‘Earthquake stage’ are initialized as per the calculation of the ‘Installation stage’ and the change in material model and stiffness and strength parameters have negligible effect on the results (Vilhar and Brinkgreve., 2018).

The above statement is added in the manuscript in the 3.2. Material modelling, subsection. Please check.

Reference: Vilhar, G., and Ronald Brinkgreve. Plaxis the PM4Sand model 2018.

 

7. 7 shows that at f = 1 Hz the pipe with deeper embedment sinks at significantly higher rate. This is somewhat counter-intuitive and a detailed discussion is needed.

 

Reply:

The authors are thankful for the comment.

From Figure 4 it can be observed that at a given duration (30 sec), a soil body is more liquefied under 1 Hz seismic signal in comparison to the 3 Hz signal. Thus, it is understandable that for lower frequency (1Hz) the soil body reaches higher liquefaction potential at a faster rate. Moreover, the sinking of the pipeline can be explained from the readjustment properties of soil particles under vertical overburden stress. In case of 1Hz seismic frequency and deeper embedment depth (10D), the combined pipe soil weight is very high, moreover the soil body becomes liquefied at a very short duration of the seismic event. Thus the combined effect of the signal frequency and the pipe-soil weight, a very rapid sinking of the pipeline is observed in case of the said situation.

Few sentences, describing the reason of rapid pipe-sinking are added in Section 4.2 of the manuscript.

 

8. A lot of plots need to be modified and presented in a professional format.

 

Reply:

The authors are thankful to the reviewer for the suggestion.

The following changes have been done to present the plots more professionally.

• The legends are added in Figure 4,5 and 6.
• The font size of the Figure 7 is increased for better visibility.
• The format of legend is changed in Figure 10.

 

9. At the presence of liquefaction under seismic loading, very large displacement / deformation is highly likely to occur. Is it possible to consider this effect in the present model? See some analyses of pipe-soil interaction problems using large displacement / deformation techniques (e.g. Quantifying Residual Resistance of Light Pipelines during Large-Amplitude Lateral Displacement Using Sequential Limit Analysis; Finite element algorithms for dynamic analysis of geotechnical problems; “Finite element modeling of partially embedded pipelines in clay seabed using Coupled Eulerian– Lagrangian method)

 

Reply:

The authors are thankful to the reviewer for the suggestion.

However, the current analyses were performed using a small strain finite element (SSFE) package called PLAXIS 2D and it is not possible to simulate large displacement problems using the current package. However, study of pipe-soil interaction problems using large displacement / deformation techniques can be performed in future studies.

The mentioned articles are added in the conclusion section as future scope.

 

Author Response File: Author Response.docx

Reviewer 2 Report

This is an interesting work, and efforts are done on this work. There are some minor suggestions and questions for consideration.

1.        “The study of thermal…of the pipeline [35]” In this paragraph, there are many reference lumps, they should be cited separately, to show the difference of each, and to show the key features of each reference. Meanwhile, the dot at the end of this paragraph is missing.

2.        Any assumptions of this study should be mentioned in the problem description, better in a way of list.

3.        How to choose dimensions of the boundaries, how is the test performed?

4.        How to determine the maximum and minimum void ratios?

5.        In Figure 4, the meaning of the colored bar should be presented next to the bar. Same issue for figure 5 and 6.

 

Author Response

Annotation

We thank the reviewer for the very detailed check. This is much appreciated. All the comments are addressed in the newly revised manuscript and we believe the revised version is considered suitable for publication. On marked and another unmarked manuscript are submitted. In the marked manuscript, the changes incorporated as per the suggestion of the Reviewer 1 are highlighted as green; while the changes suggested by the Reviewer 2 are highlighted as yellow.

Reviewer 2.

This is an interesting work, and efforts are done on this work. There are some minor suggestions and questions for consideration.

1. “The study of thermal…of the pipeline [35]” In this paragraph, there are many reference lumps, they should be cited separately, to show the difference of each, and to show the key features of each reference. Meanwhile, the dot at the end of this paragraph is missing.

 

Reply:

The authors are thankful to the reviewer for the suggestion.

In the introduction section several references are used combinedly to describe different facts and phenomenon regarding pipeline upheaval displacement. However, the number of such lumps are reduced as per the suggestion. Moreover, the discussions on several key references are further added separately in the manuscript. Please check the ‘Introduction’ section.

The dot at the end of this paragraph is added.

2. Any assumptions of this study should be mentioned in the problem description, better in a way of list.

 

Reply:

The authors are thankful to the reviewer for the suggestion.

The assumptions were mentioned at the end of the ‘Problem Statement’. Moreover, one more assumption is added, and the assumptions are arranged in a way of list as suggested.

 

3. How to choose dimensions of the boundaries, how is the test performed?

 

Reply:

The authors are thankful to the comment.

A boundary optimization study is performed in the static condition to decide the boundary dimensions.

Several trial numerical analyses (uplift test of pipeline) with different boundary sizes are performed and the minimum boundary dimension for which the boundary conditions did not interfere with the result (failure mechanism and uplift capacity) is considered as the required boundary dimension.

The above clarification is added in the manuscript at section 3.1.

 

4. How to determine the maximum and minimum void ratios?

 

Reply:

The authors are thankful to the reviewer for the comment.

The maximum and minimum void ratios are the void ratios corresponding to the minimum and maximum relative density of sand, respectively. However, in the current study, the maximum and minimum void ratios of the Nevada sand are considered by consulting previous literatures (Dinesh et al., 2022; 1.   Vilhar and Brinkgreve., 2018).

 

Reference:

1. Vilhar, G., and Ronald Brinkgreve. Plaxis the PM4Sand model 2018.
2. Dinesh, N.; Banerjee, S.; Rajagopal, K. Performance evaluation of PM4Sand model for simulation of the liquefaction remedial measures for embankment. Soil Dynamics and Earthquake Engineering 2022, 152, 107042.

 

 

5. In Figure 4, the meaning of the colored bar should be presented next to the bar. Same issue for figure 5 and 6.

 

Reply:

The authors are thankful to the reviewer for the suggestions.

The colored bars represent the pore pressure ratio within the soil volume. The meaning of the colored bar is added at the top of the bars, as legend, for figures 4,5 and 6.

 

Author Response File: Author Response.docx