Investigation on the Triaxial Mechanical Characteristics of Cement-Treated Subgrade Soil Admixed with Polypropylene Fiber

Round 1

Reviewer 1 Report

In this manuscript, the authors make great efforts to investigate the effect of polypropylene fibers on the brittle failure of cement-treated subgrade soil by doing triaxial tests.

The introduction including the literature review is too short and the authors should more clearly state what the aim of the current paper is and why this research is needed. The information given in the current introduction is very limited and does not well explain the current state-of-the-art. For the cited literature more information should be given.

The paper is presenting an interesting analysis. However, the whole paper is written more as a report than as a scientific paper.

The author state at the beginning that their research will “provide a reference for the application of PCS in practical engineering problems”. However, the whole study is based on a set of small specimens where the large particles have been removed as well as impurities such as stones. The authors do not provide any discussion on the impact of these components in real applications.

Furthermore, the authors do not specify if the whole study is based on single results where each triaxial test is leading to one specific curve presented in Fig.4. (and following) or if these curves represent an average of several tests.

The authors should explain why for all the tests the load-strain behavior was only analyzed for a maximum strain of 10%. For the different fiber contents the behavior after the ultimate load is changing and of particular interest. However, the authors seem not take into consideration these differences.

The main objective of the current paper is to take the effect of confinement into account and thus, the confining pressure has been varied. However, the authors do not explain why they did chose the analyzed confining pressures and do also not relate the chosen confinement pressures to possible confining pressure in soil structures.

The author states in the last paragraph before the conclusion that “Compared to 6‰ PCS sample, when the fiber content is 10‰, the failure angel increases by 11%, but is still less than that of 0‰ PCS sample and the modification effects does not improve with the increase in fiber content. The main reason is that when the fiber content is too large, it is easy for the fibers to overlap and accumulate in the soil, the soil cannot be compacted well and the fibers cannot connect well.” This assumption was not supported by any analysis of the authors. Furthermore, related to this finding the question raises what would be the effect of large particles or even stones in the mixture. This should be further analyzed.

The paper needs still major improvements and should be further completed by additional tests. Therefore, for the moment the paper cannot be recommended for publication.

 

Some detailed comments:

Line 92 and following: Please give some more information about e.g. the geotechnical test specifications, the temperature, humidity etc.

Fig. 1.: This figure is not needed and should be taken out.

Tab. 1.: For some properties the unit is missing and for the density the unit (g x cm3) is wrong. Also the separation of the text and the unit by a “/” is not appropriate.

Fig. 2.: This figure is not really showing the fibers

Fig. 4. and following: The authors should indicate the fiber content in each diagram

Line 141 and following: the chapter on the strength curves should be further developed and further explanations should be given.

Author Response

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Author Response File: Author Response.doc

Reviewer 2 Report

The paper presents an experimental investigation on the effect of polypropylene fiber and confinement on the mechanical properties of cement-treated subgrade soil. Test results presented in this study is interested to researcher and engineer. However, some parts of the manuscript should be revised before considering for publication.

Some comments are made as bellows:

Fig. 1 is not necessary and should be removed. The English writing need to be improved by a native speaker, since some sentences and phrases were found to be awkward, for example: “Fig. 2 Polypropylene fibers under in this study” should be revised as “Fig. 2 Polypropylene fibers used in this study”; “peak strain” may be “strain at peak stress”, etc. The authors are strongly recommended to provide which standard(s) they used to perform this experiment? If not, they need to explain what references they used for the sample preparation procedure, etc. Discussion presented in Section 3 and 4 should be improved since it lacks the explanation for the phenomenon they observed from test results. Any theoretical or previous evidences that can support their results?  Conclusion no.1: “…and the stress first increases and then decreases with the increase in axial strain with a significant peak value.” should be removed.

Author Response

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Author Response File: Author Response.doc

Reviewer 3 Report

The topic falls within the scope of the journal.

It is well written in general; nonetheless, an additional check to correct minor typos, words repetitions and such would be recommended.

Quality of figures is generally poor. These can be improved taking care of they look in B&W as well.

The experimental campaign is interesting, but complementing the numbers with physical and material observations/interpretations is lacking.

I attach a pdf with many comments. In case of resubmission please provide an answer to all of them (better if it is directly on the same file)

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.doc

Round 2

Reviewer 2 Report

The explanation in the last paragraph of Section 3 is still not satisfactory. The authors said “When the fiber content is 6‰, the modification effect of fiber on cement soil samples is the best. The reason is that, within a certain range of fiber content, as the fiber content increases, the fiber can play a better pore filling effect.” My question are:

How about in case of the fiber content of 10‰? What is the “certain range” of fiber content?

Please revise!

Author Response

Thank you very much for your effort on reviewing our manuscript with No. applsci-606132. Following your valuable comments, the draft has been revised thoroughly. Point-to-point responses to your comments are attached. In addition, a clean copy and track changes copy of the revised draft were also attached for your reference.

Yours

Wei Wang

Author Response File: Author Response.pdf

Reviewer 3 Report

please check English again

I attach a pdf with comments

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

I do not find any change in the revised version regarding my comments.

Second round comments:

The explanation in the last paragraph of Section 3 is still not satisfactory. The authors said “When the fiber content is 6‰, the modification effect of fiber on cement soil samples is the best. The reason is that, within a certain range of fiber content, as the fiber content increases, the fiber can play a better pore filling effect.” My question are:

How about in case of the fiber content of 10‰? What is the “certain range” of fiber content?

Please revise!

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 4

Reviewer 2 Report

The revised version and the response letter now satisfy me, therefore it can be published.