Effect of the Surface Roughness on the Shear Strength of Granular Materials in Ring Shear Tests
Round 1
Reviewer 1 Report
I am pleased that the questions were carefully answered by authors, and the suggestions were all considered by the authors according to the feedback.
Author Response
We thank the reviewer for the comment.
Reviewer 2 Report
In this paper an interesting topic is nice and potential.
In general the paper is well done and well structured.
I have only a minor comment.
Before the publication I suggest to check English and grammar.
Author Response
English has been corrected by commercial editing service from Springer Nature and Editage Servcie.
Reviewer 3 Report
The title and the introductory part of the paper may be misleading. It may seem like the paper deals with the surface roughness of the particles rather than the roughness of the interface. Although the authors mentioned about this, but it is a bit too late in the introduction. The introduction part should also be improved and be made more coherent and relevant to the purpose of the study.
What was the reason for selecting aquarium gravel here? There is no mention of the moisture content used for the testing. The results may be significantly affected depending on the degree of saturation. The study was conducted only on one kind of material. There is no mention of any replication either. Replicate testing and tests on different materials (with different particle sizes and angularites for example) may affect some of the findings and explanations provided here. Explanations provided in some cases are not very clear, especially in section 3.3.
Thus, this reviewer recommends the following:
Modification of the title and introduction
Replicate testing
Testing with different moisture contents (to see the difference between drained and undrained conditions)
Testing at least one more material with very different properties (crushed rock gravel for example)
Improving the explanations.
Some English proof-reading.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 3 Report
Even though I would have expected some improvement and modification of the paper to make it more interesting and reliable, I don't see any major problem in publishing the paper in its current form either. Thus now it's up to the editors to make the decision.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
GENERAL COMMENT
The paper investigates the effect of surface roughness on the shear strength of granular materials. The manuscript is well written and well structured. Minor suggestions are provided in the following.
SPECIFIC COMMENTS
· Figure 1d: please modify the figure accordingly to the displayed measures (Douter, Dinnner, w, and h are not clearly indicated in the figure).
· Line 113: this sentence “In the perfect plastic, it may be considered a yield strength (i.e., a constant stress obtained after failure)” is confusing, please reformulate.
· Figure 3: how many nominally identical tests did the authors conduct? Are these data average values, or the curves of a representative test?
· Figure 4: for clarity, it would be better to include the shear velocities also in the graphs.
· Figure 5: again, are the plotted data average values? If a certain repeatability was considered, please declare it and present the results scatter. If only one test was carried out, please clearly state it in the text.
· Figure 6: the color of the “rough” curve displayed in the legend does not correspond to the color shown in the figures. For better inspection of the results, please also explore the possibility to include in the graphs a zoom of the grain size region of greater interest.
· Please clearly state the novelty of this contribution (in the introduction and/or in the conclusions sections).
Reviewer 2 Report
The present study deals with the examination of the surface roughness on the shear strength of gravels in the ring shear test. The topi is interesting and the paper is well written.
Some additional points to address are the following:
1) The bibliography should be improved. See for example:
- Sandeep, C., & Senetakis, K. (2018). Effect of Young’s modulus and surface roughness on the inter-particle friction of granular materials. Materials, 11(2), 217.
- Samanta, M., Punetha, P., & Sharma, M. (2018). Effect of roughness on interface shear behavior of sand with steel and concrete surface. Geomechanics and Engineering, 14(4), 387-398.
The paper can be accepted after minor revision.
Reviewer 3 Report
1 | Can you cite some of the applications of surface roughness in your introduction so that the focus of your paper is more on surface roughness and not about grain crushing, shear velocity, and drainage? The reason is that most of these finding especially grain crushing, shear velocity, and drainage, have been previously concluded by the previous papers of the authors.
This gives the question, how do you choose the dimensions and spacing of the saw-like surfaces (especially depending on the size of the granular material) and why is this an important aspect in ring shear testing? In fact, other authors have stated that reduced wall friction will result in lower residual strength and a better agreement with field case histories. Rough surface can result in overestimated shear strengths but may be significant if the slip surface falls between two non-homogeneous materials. |
2 | In line 138, why did you say that a limited range of shear velocities were used due to unnecessary water leakage? In your other paper (“Shear and viscous characteristics of gravels in ring shear tests”) you were able to conclude that at shear velocities less than 1 mm/sec, strain hardening occurs but at shear velocities greater than 1/mm, strain softening occurs for the same gravel material and the same test apparatus. Meanwhile in line 76, you mentioned that grain crushing was more influential than the effect of surface roughness on the shear stress and shear zone for shear velocities larger than 1mm/sec, and this is one of the reasons why you didn’t want to use shear velocities greater than 1 mm/sec. But then in lines 67-68, you then mentioned that shear zone formation is beyond the scope of the study even though you used shear velocities less than 1 mm/sec. This has to be clarified especially since there was only a small difference in the grain size distribution of the samples after grain crushing for the smooth and rough tests. Hence, the results of the test showed that that the surface roughness only affected the shear strength for specific shear velocities, and did not affect the grain size distribution and the shear strength for different drainage conditions.
Therefore, other aspects or conditions of the test results need to be well explained for readers to have more knowledge about the behavior of the gravel material. |
3 | In order to provide a better explanation, the authors should include in the introduction a background on the common behavior of materials in ring shear tests. The behavior of some materials in ring shear tests in different conditions (shear velocity, drainage condition, etc) such as the stress-strain graph, effect of normal stress, shear stress-shear velocity, and others that have been already concluded by previous studies. |
4 | What is the purpose of not applying normal stress? Can you cite some applications? Generally, three or more normal stresses are applied to a test specimen to determine the failure envelope. |
5 | Why don’t you make a drawing of the test apparatus with the dimensions (Figure 1d) by annotation not by just putting the dimensions so that the readers can understand better? |
6 | Maybe you could put some arrows on the stress-time graph what is happening to the specimen such as, strain hardening, yield, ultimate strength, residual strength, etc. It’s difficult to distinguish. Furthermore, some samples in the smooth ring shear almost exhibited a perfectly plastic behavior namely Fig. 4c and 4e. |
7 | You should explain a little bit about ring shear apparatus, how it works, its development, and applications, its advantages and disadvantages. |
8 | Make a summary or table of the properties of the gravel. |
9 | In lines 109-111 and line 161 and 162, why did you mention shear stress and shear strain relationship when none of your graphs show the same relationship? Most of your figures are shear stress-time relationship. |
10 | Errors and grammar need to be slightly improved.
For example: Line 59 – “is common to examine” “to is commonly used to examine” Line 61 – “to measure” to “that allows the measurement of the shear stress” Lines 64-65 – “with the maximum outer diameter of 250 mm.” to “with the maximum outer diameter at 250 mm.” or “with a maximum outer diameter of 250 mm.” Line 75 – “normal shear stress”? Lines 74-76 – Change the statement so that it states why shear velocities greater than 1 mm weren’t used Lines 94-94 – Suggestion: “The dimensions of the rough surface are fixed. The thickness, width, and height are 5 mm, 3 mm, and 22 mm, respectively, for the lower ring, and 5 mm, 3mm, and 26 mm, respectively for the upper ring.” Line 96 – 32 inner rough surface? Lines 169-171 - “the difference varies from . . .“, “increased 10 fold” |
Comments for author File: Comments.pdf
Reviewer 4 Report
· General: Shear velocity can be easily confused with Shear wave velocity. I recommend using “Shear Rate” Instead of “Shear Velocity”
· Lines 74-76: The authors recommended the upper limit of the shear rate is 1 mm/s because of grain crushing. How about the lower limit at 0.01 mm/s? For studying the effect of shear rate, it is essential to cover the rate difference of one hundred times. Is there constraint from the apparatus limiting the slow shear rate?
· Lines 116 – 118: Are the results compatible with the framework of critical state soil mechanic (Schofield and Wroth, 1968)?
Schofield, A. N., and Wroth, C. P. (1968), Critical State Soil Mechanics, McGraw-Hill, p. 310, ISBN 978-0641940484
· Figures 3 and 4: It is recommended to use shear strain instead of time in the x-axis
· The effect of shear rate in determining the shear strength of granular soil is a controversial topic. There are many past studies in evaluating the potential of soil liquefaction cover this topic. Some studies (Chang et al., 1982; Dash and Sitharam, 2016; and Zhang and Li, 1992) concluded shear strength of sand decrease with increasing shear rate. Some studies (Wong et al., 1975; Riemer et al., 1996; and Kwan and Huaz, 2018) concluded that the rate effect is negligible. The effect of shear rate is one of the main conclusions in this paper. The authors should discuss the finding from the past studies and explain why their result (shear strength increase with shear rate) is different from the results reported in the literature.
Chang, N. Y., Hsieh, N. P., Samuelson, D. L., and Horita, M. (1982). “Effect of Frequency on Liquefaction Potential of Saturated Monterey No.0 Sand.” Computational methods and experimental measurements: proceedings of the international conference, Washington, D.C., 433–446.
Dash, H. K., and Sitharam, T. G. (2016). "Effect of frequency of cyclic loading on liquefaction and dynamic properties of saturated sand." International Journal of Geotechnical Engineering, 10(5), 487-492.
Zhang, X., and Li, Y. (1992). "Sand Behaviour under Irregular Loading." Tenth World Conference Earthquake Engineering, Madrid, Spain, 1413-1416.
Wong, R. T., Seed, H. B., and Chan, C. K. (1975). "Cyclic Loading Liquefaction of Gravelly Soils." Journal of geotechnical engineering Division, 101(6), 571-583.
Riemer, M. F., Gookin, W. B., Bray, J. D., and Arango, I. (1994). Effects of loading frequency and control on the Liquefaction Behavior of Clean Sands. Geotechnical Engineering Rep. No. UCB/GT/94-07, UC Berkeley, CA.
Kwan W.S., Huaz J. Effects of Irregular Loading on Sand Responses Before and After Liquefaction Initiation. Proceedings of the 11th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Los Angeles, CA. 2018.
· Line 166: “For convenience, the value (peak shear strength) at the end of the test was selected..” Define “end of the test” with a unified level of shear strain. In figure 5, I see tests end at different times: 3000 sec, 2250 sec, and 1000 sec. The authors mentioned the tested materials are strain hardening; therefore, it is crucial to define the peak shear strength at a particular shear strain level.
