Numerical techniques for design calculations of longitudinal bending in buried steel pipes subjected to lateral Earth movements

This paper presents simplified finite-element analysis procedures based on geometrical nonlinearity and ductile Mohr–Coulomb–Davis plasticity for analysis of bending behaviour of steel pipes subjected to lateral soil loading. A simple, and easy to implement, user-defined subroutine to represent soil stiffness using the Janbu model is also presented and discussed. The development of a three-dimensional (3D) finite-element model is presented, and its evaluation against experimental measurements is discussed. Data are presented for different burial depths of the pipe, including soil loading on the pipe as well as 3D responses, longitudinal bending deflections and pressure distribution along the pipe. It was shown that numerical analyses which include soil modulus dependency on confining pressure lead to effective 3D calculations of pulling forces, bending moments along the pipeline and flexural deformations, based on measured soil parameters. The 3D analysis model requires the use of lower order (linear displacement) elements, which overestimated peak mobilized load. However, those 3D calculations effectively provided the progress of both the load–deflection and longitudinal bending response of the steel pipe at embedment ratios up to 5 where most energy pipelines are buried.


Comments to the Author(s)
The paper needs substantial improvement in terms of writing, analysis and presentation before publishing. Some points to consider are as below. Subroutine incorporated modelling shows improvement in prediction of pipe response. But, the paper needs improvement by highlighting the its main contribution and significance.
• Please highlight the significance of research work (such as need of incorporating stress dependent E value) • Line 46 p.1; it would be appropriate to use third person language in the manuscript • Line 35 p.2: Please add more description of the tests; such as soil condition, soil type, etc • Line 18 page4; cohesion of 1kpa can be excessive for dry sand. Please verify the selection • Line 21 page4; please provide reference for dilation angle use • Fig.5; large mesh sensitivity can be observed. Please define the mesh size in fine, medium and coarse mesh. Also, provide number of elements in each approach • Section 4.5; please compare the model prediction of load-displacement curve with the experiments • Please also compare peak load/(soil unit weight x height x diameter x length) as the guidelines are based on this scale • Results and discussion section has not been written well. It needs improvement in terms of presentation and rigorous analysis. • Would pipe pulling load same as pipe lateral load? • It is clear from literature that plane strain and structured elements are the most suitable element type for this problem (lateral pipeline analysis). I am not sure why authors want to present this parametric study on element types? It appears not significant to present in the paper • Why there is a substantial difference between tests and 3-D numerical model predictions in Fig  14 • Even with Janbu's incorporation, there is substantial difference in peak load and mobilization in Fig. 17. Please discuss • It would be useful to propose analytical model for bending moment based on the numerical predictions using janbu's stress dependent formulation Decision letter (RSOS-181550.R0)

07-Mar-2019
Dear Dr Almahakeri, The editors assigned to your paper ("NUMERICAL TECHNIQUES FOR DESIGN CALCULATIONS OF LONGITUDINAL BENDING IN BURIED STEEL PIPES SUBJECTED TO LATERAL EARTH MOVEMENTS") have now received comments from reviewers. We would like you to revise your paper in accordance with the referee and Associate Editor suggestions which can be found below (not including confidential reports to the Editor). Please note this decision does not guarantee eventual acceptance.
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We suggest the following format: AB carried out the molecular lab work, participated in data analysis, carried out sequence alignments, participated in the design of the study and drafted the manuscript; CD carried out the statistical analyses; EF collected field data; GH conceived of the study, designed the study, coordinated the study and helped draft the manuscript. All authors gave final approval for publication.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch.
Kind regards, Andrew Dunn Royal Society Open Science Editorial Office Royal Society Open Science openscience@royalsociety.org on behalf of Prof R. Kerry Rowe (Subject Editor) openscience@royalsociety.org Associate Editor's comments: Please accept our apologies for the delay in completing review of your manuscript: we struggled to recruit suitable referees as rapidly as we (and, no doubt, you) had hoped. Nevertheless, we have now secured the commentary of three reviewers. As you will see, there are a number of matters that need to be addressed before the manuscript may be considered further. Please incorporate the changes requested by the reviewers and, if you do not do so, provide full rebuttals for any absences --if you are unable to satisfy the reviewers that the paper is ready for acceptance post-revision, we will not be able to consider it further for publication. Best of luck and we'll look forward to receiving your revision shortly.

Comments to Author:
Reviewers' Comments to Author: Reviewer: 1 Comments to the Author(s) This paper provides numerical results from the analysis of pipes pulled horizontally through sand. The flow in the manuscript is weak in places and important information required in a paper focusing on modeling is missing. There is a disproportionate emphasis at the beginning on the experimental programme that had been carried out previously and published elsewhere. Given the large end displacements, up to 30 mm, progressive failure would be expected, which cannot be properly accommodated by the constitutive model. Some specifics include: 1. The English must be improved. In some places it is awkward, there are spelling mistakes and inappropriate words or grammatical tense are used. Take for example, the third sentence in the introduction. Soil instability may be considered a soil failure but soil creep is a mechanism. Also referring to 5 lines down from the top of page 2 the word focused should probably be replaced by focusing. On page 2, line 30: analyses is spelt incorrectly. 2. Figure 9 appears to be referred to before Figure 8. 3. It is clear from the introduction that the paper focuses on analysis, yet section 2 provides a disproportionate amount of information on the "Testing Program". From a numerical analysis point of view, it would have been sufficient to show the basic layout of the test being analyzed (not the facility) and the properties of the soil, including a figure of a typical stress-strain response of the sand. Had the sand been dense, it would probably have undergone post-peak softening that would have included shear banding. For such a case a constant dilation angle would have been inappropriate and local progressive failure would have taken place before the peak load would have been reached that reflects a macro-scale measure. The reviewer is aware that only the behavior up to peak was of interest. 4. The reviewer appreciates that a commercial code was used and that low-order elements are favoured for problems involving contact and large displacements. Were the stress and strain rate measures objective? Also, the 3-D 8-node element is known to have problems if bending modes are present, say adjacent to the pipe. Was selective (not reduced) integration used to improve the performance of the 8-node element? 5. Page 6, line 58: What does the quadrilateral element response have to do with the triangular element response? In section 4.2 it was made clear that the 2-D, 6-node triangular element was used. There are ways of predicting softer responses with 3-node triangular elements. 6. Page 7, Line 39: Should likely be referring to Figure 12 not 11. 7. Section 5.5: Just because ASCE charts go up to a friction angle of 45, is not a good reason to use the residual strength for carrying out the analysis.

Reviewer: 2
Comments to the Author(s) This paper presents experimental data and numerical simulations of tests investigating the behavior of buried steel pipelines subjected to lateral earth movement. The presented experimental data are useful for understanding pipeline behavior and for future numerical model calibration by other researchers. The presented numerical modeling, including the Janbu expression for the elastic modulus distribution with depth, is based on rather simple, standard procedures. The conclusions derived from the comparisons of the experimental measurements and the numerical results seem to be reasonable. Therefore, this reviewer recommends publication of the article.

Reviewer: 3
Comments to the Author(s) The paper needs substantial improvement in terms of writing, analysis and presentation before publishing. Some points to consider are as below. Subroutine incorporated modelling shows improvement in prediction of pipe response. But, the paper needs improvement by highlighting the its main contribution and significance.
• Please highlight the significance of research work (such as need of incorporating stress dependent E value) • Line 46 p.1; it would be appropriate to use third person language in the manuscript • Line 35 p.2: Please add more description of the tests; such as soil condition, soil type, etc • Line 18 page4; cohesion of 1kpa can be excessive for dry sand. Please verify the selection • Line 21 page4; please provide reference for dilation angle use • Fig.5; large mesh sensitivity can be observed. Please define the mesh size in fine, medium and coarse mesh. Also, provide number of elements in each approach • Section 4.5; please compare the model prediction of load-displacement curve with the experiments • Please also compare peak load/(soil unit weight x height x diameter x length) as the guidelines are based on this scale • Results and discussion section has not been written well. It needs improvement in terms of presentation and rigorous analysis. • Would pipe pulling load same as pipe lateral load? • It is clear from literature that plane strain and structured elements are the most suitable element type for this problem (lateral pipeline analysis). I am not sure why authors want to present this parametric study on element types? It appears not significant to present in the paper • Why there is a substantial difference between tests and 3-D numerical model predictions in Fig  14 • Even with Janbu's incorporation, there is substantial difference in peak load and mobilization in Fig. 17

Do you have any ethical concerns with this paper? No
Have you any concerns about statistical analyses in this paper? No

Recommendation?
Accept with minor revision (please list in comments)

Comments to the Author(s)
Authors have adequately addressed my first round comments and hence I suggest accepting. However, the structure and presentation of the manuscript can be improved. The reviewers and Subject Editor have recommended publication, but also suggest some minor revisions to your manuscript. Therefore, I invite you to respond to the comments and revise your manuscript.
• Ethics statement If your study uses humans or animals please include details of the ethical approval received, including the name of the committee that granted approval. For human studies please also detail whether informed consent was obtained. For field studies on animals please include details of all permissions, licences and/or approvals granted to carry out the fieldwork.
• Data accessibility It is a condition of publication that all supporting data are made available either as supplementary information or preferably in a suitable permanent repository. The data accessibility section should state where the article's supporting data can be accessed. This section should also include details, where possible of where to access other relevant research materials such as statistical tools, protocols, software etc can be accessed. If the data has been deposited in an external repository this section should list the database, accession number and link to the DOI for all data from the article that has been made publicly available. Data sets that have been deposited in an external repository and have a DOI should also be appropriately cited in the manuscript and included in the reference list.
If you wish to submit your supporting data or code to Dryad (http://datadryad.org/), or modify your current submission to dryad, please use the following link: http://datadryad.org/submit?journalID=RSOS&manu=RSOS-181550.R1 • Competing interests Please declare any financial or non-financial competing interests, or state that you have no competing interests.
• Authors' contributions All submissions, other than those with a single author, must include an Authors' Contributions section which individually lists the specific contribution of each author. The list of Authors should meet all of the following criteria; 1) substantial contributions to conception and design, or acquisition of data, or analysis and interpretation of data; 2) drafting the article or revising it critically for important intellectual content; and 3) final approval of the version to be published.
All contributors who do not meet all of these criteria should be included in the acknowledgements.
We suggest the following format: AB carried out the molecular lab work, participated in data analysis, carried out sequence alignments, participated in the design of the study and drafted the manuscript; CD carried out the statistical analyses; EF collected field data; GH conceived of the study, designed the study, coordinated the study and helped draft the manuscript. All authors gave final approval for publication.
• Acknowledgements Please acknowledge anyone who contributed to the study but did not meet the authorship criteria.
• Funding statement Please list the source of funding for each author.
Please note that we cannot publish your manuscript without these end statements included. We have included a screenshot example of the end statements for reference. If you feel that a given heading is not relevant to your paper, please nevertheless include the heading and explicitly state that it is not relevant to your work.
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Once again, thank you for submitting your manuscript to Royal Society Open Science and I look forward to receiving your revision. If you have any questions at all, please do not hesitate to get in touch.
Kind regards, Andrew Dunn Royal Society Open Science Editorial Office Royal Society Open Science openscience@royalsociety.org on behalf of Prof R. Kerry Rowe (Subject Editor) openscience@royalsociety.org Associate Editor Comments to Author: The reviewer considers the paper to be scientifically sound and ready for publication, but you should take another look at the paper's presentation before resubmitting, as it appears additional work to improve the clarity of presentation might be possible. Nevertheless, congratulations on this outcome! Reviewer comments to Author: Reviewer: 3 Comments to the Author(s) Authors have adequately addressed my first round comments and hence I suggest accepting. However, the structure and presentation of the manuscript can be improved. You can expect to receive a proof of your article in the near future. Please contact the editorial office (openscience_proofs@royalsociety.org and openscience@royalsociety.org) to let us know if you are likely to be away from e-mail contact. Due to rapid publication and an extremely tight schedule, if comments are not received, your paper may experience a delay in publication.

Author's Response to Decision
Royal Society Open Science operates under a continuous publication model (http://bit.ly/cpFAQ). Your article will be published straight into the next open issue and this will be the final version of the paper. As such, it can be cited immediately by other researchers. As the issue version of your paper will be the only version to be published I would advise you to check your proofs thoroughly as changes cannot be made once the paper is published. This paper provides numerical results from the analysis of pipes pulled horizontally through sand. The 4 flow in the manuscript is weak in places and important information required in a paper focusing on 5 modeling is missing. There is a disproportionate emphasis at the beginning on the experimental 6 programme that had been carried out previously and published elsewhere. Given the large end 7 displacements, up to 30 mm, progressive failure would be expected, which cannot be properly 8 accommodated by the constitutive model. Some specifics include:

9
The English must be improved. In some places it is awkward, there are spelling mistakes and 10 inappropriate words or grammatical tense are used. Take for example, the third sentence in the 11 introduction. "Soil instability may be considered a soil failure but soil creep is a mechanism".

29
** "focused" has been changed to "focusing".   The explanation was provided in the original manuscript (now lines 371-376) 288 289 13. Even with Janbu's incorporation, there is substantial difference in peak load and mobilization in 290 Fig. 17. Please discuss 291 Figure 17 is the comparison between the calculated load-displacement curve 292 using Janbu model and the one using uniform soil modulus. The Janbu model 293 curve (shown in Figure 17) was first introduced and discussed in an earlier 294 section. It was also compared to experimental data (Figure 9). It is worth 295 noting also that peak loading was determined using the Y u discussed in 296 section 4.5. and hence, Janbu model showed very good agreement at the burial 297 test illustrated in Figure 17.