Centrifuge Model Tests and Numerical Analysis of Uplift Capacity of Strip Anchors in Geogrid-Reinforced Sand
, Kanniappan Ilamparuthi 4 and Mustafa Laman 2Round 1
Reviewer 1 Report
Fantastic study and the content is need of the hour since the study deals with anchors for the foundations. Presented neatly about the content and with proper citations.
Author Response
We thank the Reviewer for the encouraging comments.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The reviewer puts forward the following suggestions for this manuscript, and requires the authors to revise it based on the reviewer's comments. Major revision is suggested. If not, please explain the reasons.
1. The summary needs to be rewritten. Usually in this part, we will use a short statement to explain what research means and analysis methods of this paper uses to show the research significance and innovation of this paper's research work.
2. In the introduction part, the author is asked to explain the logical framework of thinking in the introduction. The introduction part is short of explaining the research significance of this paper and the current research blank.
3. In the introduction part, the author needs a more detailed concluding discourse, stating what the paper has done, achieved and solved.
4. Please adjust the size and clarity of Figure 7.
5. This paper does not indicate line numbers, and does not highlight the referenced references and charts, which is very inconvenient for reviewers and readers to read the literature.
6. There are a lot of abbreviations in this article, which is very confusing to read. It is suggested to compile an abbreviation word explanation table.
7. Please explain the structural framework of this paper. The reviewer thinks that this part of work lacks discussion.
8. Please state the guiding significance of your research in the conclusion.
Author Response
Response to Reviewer 2 Comments
The reviewer puts forward the following suggestions for this manuscript, and requires the authors to revise it based on the reviewer's comments. Major revision is suggested. If not, please explain the reasons.
Point 1. The summary needs to be rewritten. Usually in this part, we will use a short statement to explain what research means and analysis methods of this paper uses to show the research significance and innovation of this paper's research work.
Response 1. According to the comments of the Reviewer, the summary section of the revised article was rewritten as follows:
Anchor-type foundations are one of the foundation types used in structures subject to tensile forces. These anchors are generally designed according to the weight of the soil on them depending on the depth they are buried and the frictional resistance obtained from the failure surfaces during failure. One method of increasing the uplift capacity of the foundation without increasing the burial depth is the use of geogrid material. In this study, the uplift capacities of strip anchor plates at different embedment depths were investigated by considering the geogrid effect placed in different combinations. The aim of the study is to investigate whether a more economical solution can be obtained by using geogrid without increasing the embedment depth of the anchor plate. Experiments were carried out using centrifugal experimental setup, which gives values closer to the real results. The tests were performed on sand of two different densities for anchor burial depths H/B=2 and H/B=5. According to the results, the uplift capacity is significantly improved when geogrid is used. As the reinforcement configuration, the use of a single geogrid layer placed just above the anchor plate with an inclination angle of 45 degrees gave more effective results than using the geogrid horizontally and vertically. In the study, up to 98% increases in uplift capacity were obtained with reinforcement. In addition, the prototype model was analyzed with a numerical program based on the finite element method, and the results were compared with the experimental results. As a result of the comparison, it was observed that the experimental and numerical results were compatible with each other. Suggestions for practice are presented using the results obtained.
Point 2. In the introduction part, the author is asked to explain the logical framework of thinking in the introduction. The introduction part is short of explaining the research significance of this paper and the current research blank.
Response 2. According to the comments of the Reviewer, in the revised article, the following section has been added to the introduction.
When the literature is evaluated, it is seen that the experimental studies on the behavior of foundations subjected to uplift force generally cover small-scale laboratory experiments and the number of studies using geogrid reinforcement is quite few. The fact that the uplift capacities of geogrid reinforced anchors have not been investigated by centrifuge tests stands out as an important shortcoming. The most important difference of this study from the studies in the literature is that the uplift capacity of anchor plates in reinforced soil is investigated by centrifuge tests. In the study, the effect of sand density on uplift capacity was investigated in both unreinforced and reinforced conditions. The experiments were carried out at two different burial depths and the optimum reinforcement arrangement was investigated by placing the geogrid in different geometric conditions in the tests. Finite element analyzes were carried out using the prototype model of the experimental setup and the analysis results were compared with the experimental results. The findings obtained from the study showed that the burial depth and sand density significantly affect the uplift capacity, the uplift capacity of the anchor plate can be increased by using geogrid reinforcement, and the uplift capacity can be increased by placing the geogrid reinforcement into the soil at different angles.
Point 3. In the introduction part, the author needs a more detailed concluding discourse, stating what the paper has done, achieved and solved.
Response 3. According to the comments of the Reviewer, in the revised article, the following section has been added to the introduction.
The most important difference of this study from the studies in the literature is that the uplift capacity of anchor plates in reinforced soil is investigated by centrifuge tests. In the study, the effect of sand density on uplift capacity was investigated in both unreinforced and reinforced conditions. The experiments were carried out at two different burial depths and the optimum reinforcement arrangement was investigated by placing the geogrid in different geometric conditions in the tests. Finite element analyzes were carried out using the prototype model of the experimental setup and the analysis results were compared with the experimental results. The findings obtained from the study showed that the burial depth and sand density significantly affect the uplift capacity, the uplift capacity of the anchor plate can be increased by using geogrid reinforcement, and the uplift capacity can be increased by placing the geogrid reinforcement into the soil at different angles.
Point 4. Please adjust the size and clarity of Figure 7.
Response 4. According to the comments of the Reviewer, Figure 7 is arranged as follows.
Figure 7. Variation of NUR – α for geogrid reinforcement
Point 5. This paper does not indicate line numbers, and does not highlight the referenced references and charts, which is very inconvenient for reviewers and readers to read the literature.
Response 5. As the reviewer noted, line numbers have been added to the article. The representation of references and tables in the text is arranged according to the format of the journal.
Point 6. There are a lot of abbreviations in this article, which is very confusing to read. It is suggested to compile an abbreviation word explanation table.
Response 6. According to the valuable suggestion, we have made a list of abbreviations at the (see below). Other symbols are explained in the paragraph in which the symbol is mentioned in the article.
Abbreviations
|
Abbreviation |
Full name |
|
N |
gravity acceleration factor |
|
BP |
width of the prototype anchor plate |
|
BM |
width of the model anchor plate |
|
LP |
length of the prototype anchor plate |
|
LM |
length of the model anchor plate |
|
tP |
thickness of the prototype anchor plate |
|
tM |
thickness of the model anchor plate |
|
QUP |
prototype uplift force |
|
QUM |
model uplift force |
Point 7. Please explain the structural framework of this paper. The reviewer thinks that this part of work lacks discussion.
Response 7. Based on the Reviewer’s comment, the following paragraph has been added to the end of the introduction.
The structural framework of this article is as follows. Chapter 2 introduces the centrifuge experimental setup and presents the experimental program and the results of the experiments with and without reinforcement. Chapter 3 describes the results of the finite element analysis performed using the prototype model. Comparison and discussion of the experimental and numerical results obtained are presented in Chapter 4. Chapter 5 draws the conclusion.
Point 8. Please state the guiding significance of your research in the conclusion.
Response 8. Based on the Reviewer’s comment, the following paragraph has been added to the conclusions chapter.
The fact that the study was carried out with the centrifuge technique is thought to contribute to obtaining results closer to the actual uplift capacity values of the anchor plates. In addition, the study provides preliminary evidence that the uplift capacity of the anchor plates can be further improved by placing the geogrid layers at different angles.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript focuses on the uplift capacity of the strip anchors. Especially, factors such as embedment depths and geogrid are investigated through both experiments and numerical simulations with different combinations of the influencing parameters. Based on the results, a reinforcement configuration is recommended with a more effective uplift capacity. The topic of the manuscript falls into the scope of the journal and is of practical importance in the field of geotechnics. Interesting results are presented in the manuscript. Questions exist and revisions are needed in several locations of the paper. The detailed comments are listed below:
1. Line 235: it is recommended to include a figure of the nova curtain net geogrid. Please discuss what is the possible influence for different types of geogrids on the uplift capacity of the strip anchors?
2. In the tests, three configurations of the geogrid are used: inclination of 0°, 45° and 90°. Were these inclinations also in accordance with the actual practice of geotechnics?
3. In reference [7], several embedment ratios are used, of which only the values of 2 and 5 are investigated in this manuscript. On what basis are they chosen? Please provide descriptions.
4. Line 331: “Figure 3b” should be Figure 4b? Please also check typos throughout the manuscript.
5. Line 333: please discuss why post-peak reductions in uplift capacity were only observed at deeper burying depth? Is there a critical depth where this reduction in uplift capacity occurs?
6. What is the constitutive model used for the anchor plate? Please also provide the data for the parameters for the anchor plate. Is the anchor plate and geogrid modeled as separate model parts in contact with the soil material? What is the contact condition between the anchor plate (and geogrid) and the soil in the numerical model?
7. The information of the dimensions and boundary conditions are needed in Fig. 10 and 11. Please also illustrate the modeled geogrid in the Figures.
8. According to Table 5, the value of Qu descends as the meshing is finer. More detailed explanations are needed for why mesh density level of “fine mesh” is chosen in the numerical simulations.
9. What is the innovation of this manuscript as compared with the previous studies, such as references [5], [7] [12] and [26].
10. The conclusions indicate that the inclination angle of 45 degrees for the geogrid gave a better result. Please discuss the applicability of the findings in the geotechnical constructions. What are the limitations of the investigation work of this manuscript?
Author Response
Response to Reviewer 3 Comments
The manuscript focuses on the uplift capacity of the strip anchors. Especially, factors such as embedment depths and geogrid are investigated through both experiments and numerical simulations with different combinations of the influencing parameters. Based on the results, a reinforcement configuration is recommended with a more effective uplift capacity. The topic of the manuscript falls into the scope of the journal and is of practical importance in the field of geotechnics. Interesting results are presented in the manuscript. Questions exist and revisions are needed in several locations of the paper. The detailed comments are listed below:
Point 1. Line 235: it is recommended to include a figure of the nova curtain net geogrid. Please discuss what is the possible influence for different types of geogrids on the uplift capacity of the strip anchors?
Response 1. With the recommendation of the Reviewer, the picture of the reinforcement material used in the experiments was added to the revised article.
Figure 4. Geogrid reinforcement used in centrifuge tests
In this study, experiments were carried out using a single type of geogrid reinforcement. Therefore, no research has been conducted on the effect of the tensile capacity of the geogrid reinforcement on the uplift capacity. However, as it is known, depending on the increase in the tensile capacity of the geogrid reinforcement, a slight increase in the uplift capacity is expected. According to the results obtained from a study on reinforced slopes conducted by the authors Keskin and Laman in 2014, (Keskin, M. S., Laman, M. (2014). Experimental and numerical studies of strip footings on geogrid-reinforced sand slope. Arabian Journal for Science and Engineering, 39, 1607-1619) it was observed that the bearing capacity increased by around 5% due to the increase in the tensile capacity of the geogrid reinforcement. However, it was observed that the amount of increase was more limited in numerical analysis. The reviewer is right in suggesting that this effect be discussed. It is necessary to examine this effect in future studies.
Point 2. In the tests, three configurations of the geogrid are used: inclination of 0°, 45° and 90°. Were these inclinations also in accordance with the actual practice of geotechnics?
Response 2. Thanks for this comment of Reviewer. In geotechnical engineering, in the construction of such structures, backfilling is done after excavation and foundation construction. Giving the desired slope and placing the geogrid can be done in practice during the filling or in the excavation made before the construction of the building. Selvadurai (1990 and 1993) presents the method of geogrid placement in detail in his studies:
Point 3. In reference [7], several embedment ratios are used, of which only the values of 2 and 5 are investigated in this manuscript. On what basis are they chosen? Please provide descriptions.
Response 3. Reviewer is right. Anchor plates are called shallow and deeper anchors according to their embedment depth. In the studies by Das (1978), anchors buried deeper than H/B=5 are called deep anchors. In this study, considering the difficulty of centrifugation experiments, tests were carried out at depths of 2 and 5, since the behavior of surface anchors was investigated.
Point 4. Line 331: “Figure 3b” should be Figure 4b? Please also check typos throughout the manuscript.
Response 4. Thank you for the Reviewer’s correction. Figure 3b has been corrected as Figure 4b. Typo and grammatical errors in the revised article were carefully checked and necessary corrections were made.
Point 5. Line 333: please discuss why post-peak reductions in uplift capacity were only observed at deeper burying depth? Is there a critical depth where this reduction in uplift capacity occurs?
Response 5. As mentioned in the Reviewer’s point 3, anchor plates are called shallow and deeper anchors according to their embedment depth. Anchors buried deeper than H/B=5 are called deep anchors. Ppost-peak decreases in uplift capacity were observed at depth close to this limit. It also becomes more pronounced in dense sand.
Point 6. What is the constitutive model used for the anchor plate? Please also provide the data for the parameters for the anchor plate. Is the anchor plate and geogrid modeled as separate model parts in contact with the soil material? What is the contact condition between the anchor plate (and geogrid) and the soil in the numerical model?
Response 6. The following paragraph has been added to the revised article with the recommendation of the Reviewer.
In the numerical analysis, a rigid beam element of the strip anchor plate is modeled. The modulus of elasticity of the steel material was used as the stiffness values, EA and EI. Soil/structure interface behavior in PLAXIS can be modeled using parameters generated using the Rint interaction coefficient. In this study, fully rough interface conditions, Rint = 1 are assumed.
Point 7. The information of the dimensions and boundary conditions are needed in Fig. 10 and 11. Please also illustrate the modeled geogrid in the Figures.
Response 7. According to Reviewer’s comment, information of the dimensions and boundary conditions added to the Figs. 10 and 11. Also the modeled geogrid is shown as below.
Figure 10. Very coarse mesh and boundary conditions for a strip anchor (H/B=5)
Figure 11. Very fine mesh and boundary conditions for a strip anchor (H/B=5)
Point 8. According to Table 5, the value of Qu descends as the meshing is finer. More detailed explanations are needed for why mesh density level of “fine mesh” is chosen in the numerical simulations.
Response 8. The change in uplift capacity due to the coarseness of the mesh mentioned by the Reviewer is a problem encountered in finite element analysis. As a result of the analyzes made to prevent the results from being affected by the mesh structure, it was observed that the results in fine and very fine mesh cases changed negligibly, and a finite element mesh was selected by using the fine mesh option, taking into account the solution time.
Point 9. What is the innovation of this manuscript as compared with the previous studies, such as references [5], [7] [12] and [26].
Response 9. In all of the mentioned studies ([5], [7], [12] and [26]), the behavior of the anchors was investigated in unreinforced soil conditions. The most important innovation that distinguishes this study from other studies is the reinforcement of the soil with geogrid and the determination of the optimum geogrid placement combinations.
Point 10. The conclusions indicate that the inclination angle of 45 degrees for the geogrid gave a better result. Please discuss the applicability of the findings in the geotechnical constructions. What are the limitations of the investigation work of this manuscript?
Response 10. In practical applications, the excavation to be carried out for the placement of the anchor plate can be done in accordance with the geogrid placement angle and the system can be applied. The limitations of the study are that no test was performed for the intermediate values of the geogrid placement angle. For example, it can be investigated whether higher uplift capacity values can be obtained at 30°, 35° or any other angle value.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I suggest accepting this paper
Reviewer 3 Report
The comments has been responded and revisions were made in the manuscript.
