Study on the Strength and Deformation Characteristics of Coarse-Grained Soil under End-Restraint and End-Free (Microfriction) Conditions

Round 1

Reviewer 1 Report

This manuscript investigated the influence of the end restraint on the stress – strain characteristics of coarse-grained soil.

The paper is recommended for publication; however, a minor revision is requested addressing the following concerns:

Test equipment:

1- How do you calibrate your setup? Please add the calibration procedure in this section.

2- Figure 2: Please mention the dimensions of Load-transfer plate in the figure.

Triaxial testing procedure:

3- Please mention Standard number for the conducted test.

4- Figure 4: Please mention the dimensions of specimen in the figure.

Test results and discussion:

5- Table 2: The error bars should be provided for the values of this table.

References:

 

Recheck the reference format carefully to make sure it is consistent with the journal.

Author Response

Dear reviewer,

Many thanks for the insightful comments and suggestions from you and the reviewers. Accordingly, I have made revision to incorporate the comments on an item by item basis, and improved the English expressions in the revised manuscript. The following are the answers and revisions that I have been done in response to the reviewers' questions and suggestions.

Test equipment:

1.How do you calibrate your setup? Please add the calibration procedure in this section.

Thanks for the reviewer’s helpful advice and recommendations.The paper with the title “Development and preliminary application of a microfriction load-transfer plate for triaxial tests in geotechnical engineering” written by Wang Yanli et al. has been published in Chinese Journal of Geotechnical Engineering.The device is calibrated in the paper. Given the length of the paper, the calibration procedure is not added in this paper.

2.Figure 2: Please mention the dimensions of Load-transfer plate in the figure.

Thanks for the reviewer’s helpful advice and recommendations. Load transfer plate is a three-dimensional view, it is not convenient to mark the size, it is a diameter of 300 mm, 60 mm thick disk, which has been introduced in the article.

Triaxial testing procedure:

1.Please mention Standard number for the conducted test.

The Test Regulations for Coarse-Grained Soils of Hydropower Engineering (DL/T5356-2006 ) of China is was adopted in the paper. “T5356-2006” is deleted.

2.Figure 4: Please mention the dimensions of specimen in the figure.

The specimen is a three-dimensional view, it is not convenient to mark the size. The remolded soil samples were prepared by a multilayer wet stamping method with dimensions of 300 mm (diameter) × 600 mm (height) has been introduced in the article.

Test results and discussion:

1.Table 2: The error bars should be provided for the values of this table.

The error bars has been provided for the values of Table 2.

References:

Recheck the reference format carefully to make sure it is consistent with the journal.

The reference format has been carefully rechecked to make sure it is consistent with the journal in the revised paper.

Reviewer 2 Report

The subject matter covered in the publication "Study on the end constraint effect in the triaxial test of 3 coarse-grained soils" fits perfectly into the contemporary topics related to broadly understood construction, including the analysis of dam stability. The presented literature aims to introduce the reader to the topic and to define the problem correctly. The authors found room for their research; the proposed studies were properly designed, the analysis of the results is accurate, and the conclusions are correctly defined. The title of the publication corresponds with its content, and the language used in the publication is clear and easy to understand.

The authors overlooked a few editorial errors in their work, such as: a single letter at the end of the text, lack of centering for the figures, and the value and unit should be in the same line.

After making the corrections, I recommend the article for publication.

Author Response

Thanks for the reviewer’s helpful advice and recommendations. A few editorial errors in the work have been modified in the revised paper, such as: a single letter at the end of the text, lack of centering for the figures, and the value and unit should be in the same line.

Reviewer 3 Report

The paper begins by clearly stating the objective of the study, but it could benefit from a brief introduction to contextualize the reader. For instance, explaining why studying the behavior of this coarse-grained soil is significant in the field of geotechnical engineering would be helpful.

The paper is well-structured, following a logical sequence of events, which is positive.  

The results are mentioned, but it would be beneficial to include a brief interpretation of these results. For example, why is the behavior of the soil under low stresses significant, and what are the implications in the field of geotechnical engineering?

In summary, the paper presents interesting experimental research, but some improvements can be made to make it more informative and engaging for the reader. By clarifying terminology, including visual data, and deepening the interpretation of results, you can enhance the impact of your paper.

I hereby accept this paper for publication.

Author Response

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled “Study on the strength and deformation characteristics of the coarse-grained soil under end-restraint and end-free (microfriction) conditions” (ID: applsci-2629477).Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction including visual data, and deepening the interpretation of results.

Reviewer 4 Report

1) The article needs grammatical and syntax improvements. The linguist level of this article does not meet the requirements.

2) Title

The title is probably the most crucial section of the whole paper. The title immediately clues the reader and the reviewers into what your point is and why it’s important. The title is not informative, specific, and understandable. The authors should modify the title.

3) Abstract

The abstract requires significant revision to improve the quality of the manuscript.

4) Introduction

4-1) In the introduction section, the literature review part is generally not well organized. The introduction needs to be revised.

4-2) The theoretical, analytical, and standard approaches should be discussed.

5) Large-scale triaxial test with different end restraint conditions

5-1) This section needs to be reformatted as it contained apart of the results.

5-2) The authors should explain better the reason of performing these experimental studies.

6) The following paragraphs (sentences) are unclear:

6-1) The interface was sacrificed to ensure close contact between the layers. After the preparation of the last layer of the sample was completed, the surface was flattened, and filter paper and a sample cap were added to the upper part. The rubber membrane was tightened up and down, the forming cylinder was removed after vacuuming, and a pressure chamber was installed. For the end-free (microfriction) test, after the preparation of the final layer of the sample was completed, first, a cap-shaped rubber cap was placed on the top of the sample and tied with the rubber film of the sample. The lateral upper part was provided with an exhaust hole, which was connected to the drainage hole at the bottom of the test instrument to provide drainage. After vacuuming, the forming cylinder was removed, the sample was lifted, the microfriction load-transmitting plate was placed on the bottom of the sample, the microfriction load-transmitting plate and loading plate were placed on the upper part of the sample, and finally, the pressure chamber was installed, as shown in Figure 4.

6-2) Figure 9 and Figure 10 show the curves of the tangent deformation modulus, tangent volume modulus, and axial strain under fixed confining pressures. The tangent deformation modulus and tangent volume modulus of the rockfill materials decreased with the increase in the axial strain at the initial stage of shear. At the same time, the end constraint increased the tangent deformation modulus and decreased the tangent volume modulus, and the effect decreased with the increase in the strain and confining pressure. This was due to the shear shrinkage of the rockfill materials during the shear process.

7- Research significance

The purpose of the study is not mentioned in the abstract and introduction. What is the purpose of the study and the contribution of the results to the literature? Also, the significance of the study must be described in a separate section after the introduction.

8- The authors only hardly discuss results. Please discuss your results more deeply.

9- Conclusion

Limited new knowledge can be found in the conclusion part. The conclusion section needs to be re-written.

Minor editing of English language required

Author Response

Manuscript ID: applsci-2629477

Title: Study on the strength and deformation characteristics of the coarse-grained soil under end-restraint and end-free (microfriction) conditions

Dear Reviewer:

Thank you for the comments concerning our manuscript entitled “Study on the strength and deformation characteristics of the coarse-grained soil under end-restraint and end-free (microfriction) conditions” (ID: applsci-2629477).Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval.

Sincerely,

Yanli Wang (Corresponding author)

 

Answers to reviewers:

Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Question: 1) The article needs grammatical and syntax improvements. The linguist level of this article does not meet the requirements.

Authors’ response:

We tried our best to improve the manuscript and made some changes to the manuscript. These changes will not influence the content and framework of the paper. And here we did not list the changes but marked in the revised paper. We appreciate for Reviewers’ warm work earnestly and hope that the correction will meet with approval.

2) Title

Question: The title is probably the most crucial section of the whole paper. The title immediately clues the reader and the reviewers into what your point is and why it’s important. The title is not informative, specific, and understandable. The authors should modify the title.

Authors’ response:

Thanks for the reviewer’s helpful advice and recommendations. According to the associate reviewers’ comments, we have made modifications to the title and supplemented extra information to make our title convincing.The new title is”Study on the strength and deformation characteristics of the coarse-grained soil under end-restraint and end-free (microfriction) conditions”.

3) Abstract

Question: The abstract requires significant revision to improve the quality of the manuscript.

Authors’ response:

Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript. We have made modifications to the abstract.

For triaxial compression testing in geotechnical engineering, large-scale triaxial shear tests of coarse-grained soil were performed under end-restraint and end-free (microfriction) conditions utilizing a large-scale triaxial shear apparatus and a self-developed microfriction load-transfer plate. Under end-restraint and end-free (microfriction) circumstances, the strength and deformation characteristics of the coarse-grained soil were investigated. Analysis was done on how the end restraint affected the stress-strain characteristics of the coarse-grained soil. The findings demonstrated that the coarse-grained soil's stress-strain curves under end-restraint and end-free (microfriction) conditions displayed both softening under low confining pressures and hardening under high confining pressures. The stress-strain curve's tendency to soften under low confining pressures was more pronounced under end-free (microfriction) conditions. Due to the influence of end constraint, the peak strength of the coarse-grained soil increased under the same confining pressure, although this increase was less than 10% if the samples had the typical height-to-diameter ratio of 2 in the drained triaxial test. Both times, the coarse-grained soils first displayed volumetric contraction under low confining pressures, followed by volumetric dilation, and both times they displayed volumetric dilation under high confining pressures. The volumetric contraction tendency of the coarse-grained soil was more pronounced in the first stages of shearing when low confining pressures were present. As the shear increases, it becomes more obvious that the coarse-grained soil has a tendency to dilate under end-free (microfriction) circumstances. Throughout the shearing operation, the coarse-grained soil exhibited a high propensity toward shear contraction. The coarse-grained soil's strength values were not greatly impacted by the end limitation, but the deformation parameters were. Under the end-restraint conditions, the deformation parameter increased significantly while the strength parameter index only little changed.

4) Introduction

Question: 4-1) In the introduction section, the literature review part is generally not well organized. The introduction needs to be revised.

Authors’ response:

Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript. We have made modifications to the introduction.

Question: 4-2) The theoretical, analytical, and standard approaches should be discussed.

Authors’ response:

Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript. We have added the theoretical, analytical, and standard approaches discuss in the introduction.

5) Large-scale triaxial test with different end restraint conditions

Question: 5-1) This section needs to be reformatted as it contained a part of the results.

Authors’ response:

The authors are grateful for the comments. We have reformatted this section and deleted the result part.

Question: 5-2) The authors should explain better the reason of performing these experimental studies.

Authors’ response:

The authors are grateful for the comments. The purpose of performing these experimental studies would provide a theoretical foundation and scientific basis for the safety and stability analysis of high earth-rockfill dams. The significance of the study was described in a separate section in the end of the introduction.

6) The following paragraphs (sentences) are unclear:

Question: 6-1) The interface was sacrificed to ensure close contact between the layers. After the preparation of the last layer of the sample was completed, the surface was flattened, and filter paper and a sample cap were added to the upper part. The rubber membrane was tightened up and down, the forming cylinder was removed after vacuuming, and a pressure chamber was installed. For the end-free (microfriction) test, after the preparation of the final layer of the sample was completed, first, a cap-shaped rubber cap was placed on the top of the sample and tied with the rubber film of the sample. The lateral upper part was provided with an exhaust hole, which was connected to the drainage hole at the bottom of the test instrument to provide drainage. After vacuuming, the forming cylinder was removed, the sample was lifted, the microfriction load-transmitting plate was placed on the bottom of the sample, the microfriction load-transmitting plate and loading plate were placed on the upper part of the sample, and finally, the pressure chamber was installed, as shown in Figure 4.

Authors’ response:

Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript. We have made modifications as follows.

In order to guarantee close contact between the layers, the interface was compromised. After the last layer of the sample had been prepared, the surface was flattened, and the upper portion was then covered with filter paper and a sample cap. After vacuuming the forming cylinder and tightening the rubber membrane up and down, a pressure chamber was added. After the preparation of the final layer of the sample was finished, a cap-shaped rubber cap was initially placed on top of the sample and fastened with the rubber film of the sample for the end-free (microfriction) test. The test instrument's lateral top half had an exhaust hole that was connected to the drainage hole at the bottom to provide drainage. As shown in Figure 4, after vacuuming, the forming cylinder was removed, the sample was lifted, the microfriction load-transmitting plate was positioned on the sample's bottom, the microfriction load-transmitting plate and loading plate were positioned on the sample's upper portion, and finally, the pressure chamber was installed.

Question: 6-2) Figure 9 and Figure 10 show the curves of the tangent deformation modulus, tangent volume modulus, and axial strain under fixed confining pressures. The tangent deformation modulus and tangent volume modulus of the rockfill materials decreased with the increase in the axial strain at the initial stage of shear. At the same time, the end constraint increased the tangent deformation modulus and decreased the tangent volume modulus, and the effect decreased with the increase in the strain and confining pressure. This was due to the shear shrinkage of the rockfill materials during the shear process.

Authors’ response:

Thank you again for your positive comments and valuable suggestions to improve the quality of our manuscript. We have made modifications as follows.

The tangent deformation modulus, tangent volume modulus, and axial strain curves for given confining pressures are shown in Figures 9 and 10. With an increase in axial strain at the beginning of shear, the tangent deformation modulus and tangent volume modulus of the rockfill materials declined. The end constraint simultaneously reduced the tangent volume modulus and increased the tangent deformation modulus, and the impact waned as the strain and confining pressure increased.

7- Research significance

Question: The purpose of the study is not mentioned in the abstract and introduction. What is the purpose of the study and the contribution of the results to the literature? Also, the significance of the study must be described in a separate section after the introduction.

Authors’ response:

The authors would like to thank the reviewers for the thorough review, which helped improve the manuscript significantly. The manuscript was revised based on their comments. The significance of the study was described in a separate section in the end of the introduction.

In conclusion, there will be significant mistakes when using data from traditional triaxial tests to estimate the stress and deformation of high earth-rock fill dams. In order to successfully address the end restraint problem of triaxial tests and precisely determine soil mechanical characteristics, geotechnical micro friction triaxial test technology must be adopted. In this paper the strength and deformation characteristics of coarse-grained soil under normal end-restraint and end-free (microfriction) conditions were studied. The influence of the end restraint on the stress–strain characteristics of coarse-grained soil was analyzed. The results provide a theoretical foundation and scientific basis for the safety and stability analysis of high earth-rockfill dams.

Question: 8- The authors only hardly discuss results. Please discuss your results more deeply.

Authors’ response:

The authors are grateful for the suggestion. And here we did not list the changes but marked in the revised paper. We appreciate for Reviewers’ warm work earnestly and hope that the correction will meet with approval.

9- Conclusion

Question: Limited new knowledge can be found in the conclusion part. The conclusion section needs to be re-written.

Authors’ response:

The authors are grateful for the suggestion. We have re-writted the conclusion as follows.

Using a large-scale high-pressure triaxial shear apparatus and a self-designed microfriction load-transfer plate for triaxial compression tests in geotechnical engineering, large-scale triaxial shear tests of coarse-grained soil samples with restraint end and free end (microfriction) were conducted. Under typical end-restraint and end-free (microfriction) soil conditions, the strength and deformation characteristics of coarse-grained soil were investigated. Analysis was done on how the end restraint affected the stress and strain properties of coarse-grained soil. These are the conclusions:

(1) The stress-strain relationship curves of the coarse-grained soil had the same properties under the end-restraint and end-free (microfriction) circumstances. With regard to dense coarse-grained soils, the deviator stress-strain curves of the specimen with a restraint end showed strain-softening behavior under a smaller confining pressure and strain-hardening behavior under a larger confining pressure. When subjected to a modest confining pressure, the deviator stress-strain curve of the specimen with the free end showed a more pronounced propensity to soften than the specimen with the restraint end.

(2) The volumetric strain behaviors of the coarse-grained soils were consistent both in the end-restraint and end-free (microfriction) regimes. Under a low confining pressure, the coarse-grained soils first exhibited volumetric contraction, followed by volumetric dilation, and both exhibited volumetric contraction under a higher confining pressure. The tendency of the coarse-grained soil's volumetric shrinkage at a low confining pressure was more pronounced in the initial stages of shearing. With the emergence of shearing, the volumetric dilation tendency of the coarse-grained soil under free end (microfriction) conditions became more pronounced. When confining pressures were higher, the specimen with the restraint end's volumetric strain was consistently greater than the specimen with the free end, which displayed a marked tendency for volumetric contraction throughout the whole shearing process.

(3) The end restraint had little effect on the strength parameters of the coarse-grained soil and had a greater impact on the deformation parameters. When the Duncan–Chang E-B and E-μ models were used for fitting, compared with the end-free (microfriction) model, the linear strength indices c and φ and the nonlinear strength indices φ0 and Δφ slightly increased. The deformation parameter indicators K and Kb increased significantly, indicating that the end restraint had a higher effect than the end free on the deformation properties of the coarse-grained soil.

(4) It can be seen that the end restraint restricted the radial deformation of the sample's end and that the radial deformation of the sample's middle portion was significantly larger than that of the sample, indicating bulging, by comparing the deformations of the samples with restraint ends and free ends after the test. The microfriction-affected samples had substantially more consistent distribution.