Analysis of Vertical Earth Pressure Acting on Box Culverts through Centrifuge Model Test

Round 1

Reviewer 1 Report

This manuscript attempted to analyze the vertical earth pressure acting on box culverts through a centrifuge model test. The topic seems interesting and the manuscript has been very well written and organized. However, I have a couple of comments to the authors. The main comments are as follows:

1. The authors should cite more recent references related to this research.
2. In the introduction part, the gaps of your study are missing.
3. How to choose the best probability density functions according to KS test ? For a certain amount of data, there should be a KS threshold.
4. This manuscript lacks in-depth discussion and no appropriate conclusion to summarize.

Comments for author File: Comments.docx

Author Response

Point 1: The authors should cite more recent references related to this research.

 

Response 1: The contents were added using recent references, and are as follows.

 

“Recently, scale model tests and numerical analysis were conducted according to the structural form (flat seam, round hinged, integral, and mortise) of the prefabricated reinforced concrete box culverts, stress–strain self-sensing precast-box culvert smart element design and experimental verification under loading conditions were analyzed [15-16]. In addition, studies on the effect of load and the use of box culverts in tunnels or railway tracks are being actively conducted [17-19].”

 

Point 2: In the introduction part, the gaps of your study are missing.

 

Response 1: The research part was added at the end of the introduction part to explain the process and method of this manuscript.

 

“Therefore, in this study, the variability of vertical earth pressure acting on a box culvert is measured by conducting repetitive centrifuge model tests. For this purpose, a uniform sand ground was composed through sand pluviation using funnel, and at the same time, a box culvert was installed as an embankment installation method. After the ground was composed, loading and unloading conditions are simulated through gravitational acceleration, and the test parameters are height of backfill soil above the box culvert. Afterwards, the measured results are compared with the predicted results, and finally, the variability analysis is performed through the goodness-of-fit test.

”

 

Point 3: How to choose the best probability density functions according to KS test ? For a certain amount of data, there should be a KS threshold.

 

Response 1: We did not determine the best probability density functions using only the KS test. As a result of considering both the KS test and the AS test, it was determined that the lognormal distribution was appropriate. The number of data for the KS threshold is not clear, but as the number of data increases, the accuracy including convergence is expected to increase. The current number of data is 30, which may or may not be sufficient. For this reason, statistical analysis is performed for the predictive model, and the following has been added to ‘Discussion [2]’ according to the opinion of the reviewers.

 

“[1] The optimal probability distribution of variability of vertical earth pressure was determined according to the goodness-of-fit test. The lognormal distribution was selected as a result of considering both the KS and AS test results, because it is necessary to select a normal or lognormal distribution in terms of geotechnical uncertainty. Although the calculated COV cannot be said to be a small value, it is judged to be meaningful in that it is the selection of a predictive model for the corresponding result.”

 

Point 4: This manuscript lacks in-depth discussion and no appropriate conclusion to summarize.

 

Response 1: The discussion part was subdivided, and a final conclusion was drawn according to the manuscript.

 

“In this study, the variability and uncertainty of vertical earth pressure on box culvert through geocentrifuge model test were evaluated. The contents and results of the experiment and statistical analysis were carried out in the main text, and the discussion accordingly is as follows.

 

[1] The optimal probability distribution of variability of vertical earth pressure was determined according to the goodness-of-fit test. The lognormal distribution was selected as a result of considering both the KS and AS test results, because it is necessary to select a normal or lognormal distribution in terms of geotechnical uncertainty. Although the calculated COV cannot be said to be a small value, it is judged to be meaningful in that it is the selection of a predictive model for the corresponding result.

[2] As a result of the variability analysis, the vertical earth pressures under the loading and unloading state were measured to be 1.251 to 1.430 times greater than the existing theoretical earth pressure. This is considered an interaction problem between the top of the box culvert and the backfill soil, and AASHTO [43] defines it as a soil–structure interaction. In this case, the value of soil–structure interaction is used to conservatively compute the vertical earth pressure during the design process, and the value of soil–structure interaction is multiplied by the theoretical earth pressure. The soil–structure interaction should not exceed 1.15 for embankment installations and 1.40 for trench installations.

[3] In the centrifuge model test conducted in this study, embankment installation was adopted in the process of box culvert and ground formation. Therefore, the soil–structure interaction should not exceed 1.15 according to the existing AASHTO theory. However, the actual soil–structure interaction exceeded the prescribed value according to the loading and unloading conditions, and it exhibited considerable variability. This means that the previously set theoretical values ​​do not reflect the actual environment, and it is necessary to check the variability of the actual ground during the design process.

[5] This study analyzed only the vertical earth pressure acting on the box culvert, and the effect on the horizontal earth pressure should be reviewed in the future. This is because it can calculate an important coefficient of earth pressure (K0) in the field of geotechnical engineering. Therefore, when horizontal earth pressure is analyzed in the same way, it is judged that detailed evaluation of earth pressure considering uncertainty is possible.”

 

 

Thank you for your review.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear Editor and Authors,

Analysis of Vertical Earth Pressure Acting on Box Culverts through Centrifuge Model Test by Woo et al. is an interesting manuscript that uses a geotechnical centrifuge model test to measure the vertical earth pressure on a box culvert.  The abstract is the weak spot given does not effectively describe the importance of the study.  This in no way takes away from the manuscript.  Because of this, I recommend the manuscript be accepted with minor revisions.  Below are detailed recommendations for the authors. 

Abstract

Abstract provides a good overview of the project and informs the reader of the topic.  I do feel the abstract undersells the importance of the study and should demonstrate the importance of the study.

Keywords

Keywords are strong and fitting of the paper. 

Introduction
The introduction provided all of the necessary background information on the topic. 

Vertical Earth Pressure Acting on Box Culverts

This section provides excellent information on why this study is important.  It demonstrates the soil pressures that are present on box culverts and the impacts vertical pressure from the earth can have on these structures.  Excellent addition to this paper.

Centrifuge Model Tests

Section was well thought out and provides great information on the model test that is being conducted within this study including information on the device itself and box culverts.

Ground Composition

Another important section as it demonstrates the properties of soil and how it impacts the box culvert.  The graphics are well thought out in this section and provide good input into the importance of the study.

Test Cases

The section provides great insight into the box culverts and the testing which was performed on them.  The diagrams of the boxes add to the manuscript!

Measurement Results of Vertical Earth Pressure Acting on Box Culvert

The results section was well written and reported all of the results necessary from the methodology.  Excellent use of graphics and description of them.  Overall, this is a great section and very well written.

Discussion

The discussion went full circle and wrapped up the analysis and the results.  Very short section, but it was direct and provided all of the important information.

Comments for author File: Comments.docx

Author Response

Point 1: Abstract provides a good overview of the project and informs the reader of the topic.  I do feel the abstract undersells the importance of the study and should demonstrate the importance of the study.

 

Response 1: The importance of the study was explained in the abstract part. The changes are as follows.

 

“Due to the lack of surface space, most structures are heading to underground. The box culvert is one of the underground infrastructures and serves to protect the buried underground from the underground environments, but it has a different characteristic from other structures in that the inner space is empty. Therefore, in this study, the vertical earth pressure which is most significant effective stress acting on a box culvert was measured by conducting a geotechnical centrifuge model test. A box culvert was installed following the embankment installation method, and the vertical earth pressure acting on it was measured considering the cover depth, gravitational acceleration, and loading and unloading conditions. The soil pressure measured was greater than the existing theoretical value under a high cover depth and the unloading condition, which is considered the variability of many soils or the residual stress acting under the loading condition. Finally, a through the goodness-of-fit test was conducted as a part of variability analysis. The measured earth pressure was found to be considerably larger than the existing theoretical value, and the variability was large as well. This means the existing theoretical equation is under-designed, which should be reflected in future designs.”

 

 

Thank you for your review.

Author Response File: Author Response.docx