Experimental Study on the Influence of Slurry Concentration and Standing Time on the Friction Characteristics of a Steel Pipe-Soil Interface

Round 1

Reviewer 1 Report

The authors carried out lab tests to study the friction between steel pipe-soil interfaces.

However, I have several questions regarding the experiments:

1, how useful the experimental conclusions can be? 

first of all, it is a steel plate, not a pipe. The friction is related to the contact area which is related to the geometry. I understand that experiments with a plate is easier to control and sound more general, but this also put a question mark on your results when implementing them in real engineering? How useful those numbers could be?

2, why the normal load is always 100kPa?

the normal load would influence the forming of the contact interface, especially for the study of the standing time......If you change the normal load, all the reported numbers might also change. Therefore, the authors should at least test different normal loads.

3, I would rather treat the manuscript as an experimental report. Simply because the authors cannot really explain the physics behind the phonomenon. For example, 

When the concentration is less than or equal to 20%, the peak shear stress and friction coefficient first decrease and then increase with the increase of concentration

but why??? The author should study the property of the 'material' under different contractions, and explain why there is a trend like this. Not just simply report the experimental results, since if there is no correct 'physics' behind the phenomenon, no one is able to evaluate how useful/correct these experiments are.

I think this study has several flaws...simply because I do not see anything physical and applicable. As I said, all these reported numbers are useless, no one can really learn anything from them for use in real engineering. Unless the authors would explain why there is a trend like that, that would be useful for the instruction of the real engineering problems. 

 

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

This paper presents that the friction characteristics of steel pipe-soil interface under different slurry concentration and slurry standing time were studied through the direct shear tests. The purpose of the research is clear, the writing is standardized, and it has an engineering value. I would suggest a revision for this paper before it can be accepted for publication. The detailed comments listed below can be useful for the authors in improving their manuscript.

1. In the introduction, the source of Fig. 1 should be given.
2. What is the ratio of the size of the test sample to the engineering prototype? Because the shape of the pipe has been simplified. Even if the shear speed is the same, the shear rate is different. The reviewer believes that the shear rate should be consistent. Please elaborate on how to ensure the similarity between the test model and the engineering prototype.
3. A real picture of the laboratory should be added, including the sample size.
4. The undrained shear strength of sampleshas a significant effect on pipe-soil interaction. This paper does not mention the strength of samples. Is there any corresponding experimental data?
5. According to paststudies (e.g., 1. Scour below pipes in waves; 2. Effect of pipeline surface roughness on peak impact forces caused by hydrodynamic submarine mudflow), pipe surface roughness also has a significant influence. How does the authors consider the influence of this important factor?
6. Parallel tests should be mentioned to demonstrate the stability of the instrumentation and sample preparation.
7. Whether the relationship between shear stress and shear strain (and shear rate) can be given in the figure is more meaningful for establishing corresponding constitutive model.
8. According to figure 6, the sample is limited in the rigid ring. How to consider this boundary effect? How to consider the difference between the test and the actual project?
9. In the discussion section, it is suggested to add an analysis of the study results in terms of mechanism. Also, comparison with past studies is suggested.
10. "With the increase of the concentration of compound bentonite slurry, the slurry changes from liquid state to semi-solid state, and its main function changes from lubrication and drag reduction to supporting soil." in the conclusion should be removed, which is not the conclusion.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

thanks for authors' reply, I have no further questions or comments.

Reviewer 2 Report

I suggest accepting this version.