Design and Application of an In Situ Test Device for Rheological Characteristic Measurements of Liquefied Submarine Sediments

Round 1

Reviewer 1 Report

General comments:

• The manuscript is very unclear about the differences of fluid and soil mechanics. From the current state of the texts and some misleading conclusions, the reader must assume the authors themselves are not aware of the differences. Therefore, precise definitions are required for the fluid mechanical and soil mechanical terms used and in which cases which ones are applied. Additionally, a definition for the term “liquified sediment” is needed for understanding the procedures. Provided that there is no contact between soil particles (and hence no soil structure) “liquified sediments” corresponds to a suspension, which implies that all soil mechanical conventions, procedures and parameters are not applicable. In contrast: Provided that “liquified sediments” corresponds to a soil which is fluid according to Atterberg, it is implied that all fluid mechanical conventions, procedures and parameters are not applicable.
• Not all literature sources are named in the Reference section.
• The knowledge transfer from the literature to the research question is poor. The appropriateness of the references needs to be checked.
• The title should be adapted in the sediment description. See comment for section 3 regarding submarine sediments.

Introduction:

• Scientific correctness requires to be explicit about descriptions. Formulations like “turbidity currents etc. marine geohazards” should be avoided.
• There usually is no prevention of geohazards but only better understanding and an early warning that is aimed for.
• Submarine landsliding is a topic usually encountered in deeper waters. Please elaborate the relevance for this nearshore site.
• The named test methods (e.g. CPT) do not test rheological parameters.
• The shear rate is not a material parameter.
• Explain how and why the shear column theory can be applied to the problem at hand.
• 5m are not deepwater conditions. Please be precise and clear about the boundary conditions in your tests.

Section 2: Design of the in situ test device

• Why is the probe left in the soil for stabilization? If the soil is not liquified the procedure will not change the structure destruction upon insertion. Give details on the procedure, e.g. the duration of stabilization.
• It is assumed the soil is not liquified as the soil structure still is destroyed during the testing procedure – a better definition and description is required.
• The test procedure is not described, e.g. what shear rate is applied. Please complement.
• The formulas and picture deliver that the device is an in situ vane shear test. Please elaborate. Vane shear tests are not conclusive for suspensions.
• Please give a literature source for your formulas.

Section 3: Application of the in situ test device

• From the description of the sediments properties they would be defined as sediments of terrigenous origin. It Is necessary to elaborate on this as the term “submarine sediment” usually refers to deep sea contexts where other geological boundary conditions prevail. The term “submarine” should be omitted for this application site, as this is a fluvially dominated shelf sea environment with shallow water depths.
• An explanation for the choice of the test site is lacking. Please add the water depths in which you tested and the exact soil conditions.
• Why is there simulated wave loading? Is this not a natural environment?
• An explanation for the choice of test procedure is missing. Why is the given timing chosen?
• Again, it is not clear whether a suspension or a soil is looked at.
• The term viscosity is introduced here and used interchangeably with shear stress. This is not comparable and therefore incorrect.

Section 4: Verify the accuracy of the in situ test device

• Terms like “soft characteristics” are introduced here. This is not geotechnical of fluid mechanical terminology and requires explanation. If this results from language difficulties please consider editing the paper with respect to the correct English technical terms.
• For the evaluation of test data the procedure should be explained, e.g. how many tests were conducted from which the mean values are displayed.
• An explanation is lacking for the sample preparation method. Why was the sample dried? The corresponding loss of organic matter will influence the rheological properties.
• Again, it is not clear whether a suspension or a soil is looked at. Rheometer tests are not conclusive for soil.
• The test procedure for the laboratory tests is not described, e.g. what shear rate is applied.
• State all units for the soil parameters introduced in the table.
• Why is the given timing chosen?

Section 5: Discussion

• One test each (lab and in situ) Is not a sufficient data base to conclude the general applicability of the device.
• The discussion does not provide any new insights and does not clarify how the developed device is an asset and contributes to the scientific community (plenty of in situ vane shear tests have been conducted and published already).
• The shortcomings of the study are not addressed.
• The in situ test is a soil mechanical test while the lab test is a fluid mechanical test. The obtained results cannot be compared due to the definition of the boundary conditions during testing. Please elaborate on why you consider a comparison valid.

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

An interesting article describing a new instrument for remote measurement of the properties of liquid surface sediments on the sea floor. The article presents new data for measuring the rheological characteristics of soils using new, original equipment. The article is well written and illustrated. The material is presented fully. I believe that the material presented in the article will arouse great interest among potential readers. There are minor editorial comments, including the spelling Non-Newton fluid or non-Newtonian fluid, clay silt or clayey silt. The year is not specified in the link Horng et al. (page 7, Discussion). In general, an interesting scientific and methodological publication with a presentation of new, original data. It is recommended for publication after minor edits in the text.

Author Response

Thanks for your encouragement. We have checked the entire manuscript carefully to avoid the spelling mistakes. Also, we refined the language with the aid of the MDPI Language Editing Service. In the revised manuscript, the Non-Newton fluid have been changed into non-Newtonian fluid. Horng et al. should be Horng et al. (2010, 2011).

Reviewer 3 Report

Overall comments:

The manuscript is reasonably well written and generally understandable, with mostly minor grammatical errors scattered throughout. The primary innovation is the development of a modified vane shear test instrument that allows for much greater shear rates in liquefied sediments and is thus better suited for estimating rheology of bed materials in those types of environments (e.g., Yellow River). The validation of the device is rather limited (one location, three times of measurement for both field and lab), but it does qualitatively demonstrate the instrument performance.  The field work seems like it may have been poorly planned, as one measurement was interrupted by a flood tide.  Why was this event not anticipated?

I feel that this paper should ultimately be accepted for publication, following moderate revision to clarify and resolve a few questions and issues described below.

----------------------------------------------------------------

Specific comments and corrections:

Line numbers:  If possible, please number your lines.  It is generally much more convenient for reviewers when authors include line numbers in their submission.  As the authors did not include line numbers this time, I will be somewhat less precise in identifying the article text associated with the comments below. I apologize if this causes any confusion about my suggestions.  

Page 1, paragraph 2, line 7: Do you mean "further" instead of "furth"?

Page 2, line 10:  I would suggest that you be less absolute about your verification of these results.  After all, you get different results in the lab and field, and you end up needing to justify/explain this difference.  Instead of "verify the accuracy of the in situ data", perhaps you could say "qualitatively verify the trends shown in the in situ data", or something similar?

Section 2, paragraph 2, line 5-6: I am not familiar with the expression "destroy the sediments".  Is this a common expression?  If not, I would suggest using a different word than "destroy", for example "disturb" or "agitate".

Page 2, equations (1)-(3): Please provide a reference for these equations or describe how they were derived.  On the line before the equations, the word should be "follows" instead of "flows".

Section 3.1, paragraph 1, last 4 lines:  Why did you only choose one site?  Is this representative of the whole area?  Did you investigate other possible sites and compare them to this one?  Please clarify what you did to exert "simulated wave loading" in the sediment.  Also, I don't think that you should say here that the test was conducted at 120 minutes, since you did not conduct such a test for this field site.

Section 3.2, paragraph 1, line 2:  Can you clarify further why you were unable to get the 120min data?  Couldn't you have anticipated the flood tide and begun your data acquisition 30-60min earlier?  If this was simply due to bad planning on your part, you probably shouldn't even mention it at all in the article.  If there is a different reason, you should state it clearly in this paragraph.

Section 3.2, paragraph 1, line 11:  Suggest using "destruction", "dissolution", "collapse", or "disappearance" instead of "destroy".

Figure 3, top panel: The lines are hard to distinguish on the left side of this panel.  Is there any way that you can expand the horizontal axis of this figure or zoom in on the left side?

Section 4.1, paragraph 1, lines 8-9:  Why do you remove the shell fragments in the lab when they remained in place in the field?  Could this significantly affect your results?  Could you comment on what fraction of the overall volume the shell fragments were?  If you expect that the effects of these fragments on results (other than potentially breaking your instrument) would be minimal, you should probably note that here. 

Section 4.2, paragraph 1, lines 4-5:  A bit unclear.  If I understand your intent correctly, perhaps this might be better phrased as "For any given shear rate, the shear stress increases with the consolidation time".

Page 8, first four lines:  You need to explain this more clearly and completely.  If rapid consolidation is a property of the sediment in the field, why would it not be the same in the lab when you use the same sediment?  Perhaps you should give this a different name than "sediment properties"?  At the least, you should clarify why consolidation rates would be different in lab versus field (or provide references that confirm and explain this).  Are you suggesting that hydrodynamic properties of the study area were different from those in the lab and thus made the sediment behavior different?

Section 5.2:  Have you actually created and tested this version of the instrument, or is this section entirely hypothetical?  If this version does not yet even exist, I'm not sure that this section (and Figure 5, where the water level is far too low!) adds much to the paper.  If you want to indicate that your instrument has the potential to be used in deep water, you could probably do so in just one or two sentences, inserted into the Conclusions section. 

 

 

Author Response

Please see the attachment

Author Response File: Author Response.docx