Numerical Simulation on Pillar Design for Longwall Mining under Weak Immediate Roof and Floor Strata in Indonesia

Round 1

Reviewer 1 Report

Comment

This study discusses the design of safety pillar width in longwall mining under weak geological conditions by using FLAC3D. And the proposed scheme outperforms the state of the arts.

There are some problems, which must be solved before it is considered for publication. If the following problems are well-addressed, this reviewer believes that the essential contribution of this paper are important for pillar design for longwall mining under weak immediate roof and floor strata, mainly:

(1) We find that there are some unnecessary contents in the abstract, which seems to be of little help to the thesis. It is recommended to delete and modify the abstract appropriately.

(2) The structure of the numerical model in the second paragraph is not reasonable. It is suggested to introduce the general situation of the project and then put forward the numerical simulation, the logical sequence is more smooth.

(3) In line 139-140 of the paper, the load setting is 6000kN, 8000kN and 10000kN respectively. Please confirm whether the setting load is reasonable and whether references are quoted.

(4) The analysis method and description in the part of model validation are simple, and the validity verification of the model is not sufficient, so please improve the author.

(5) There are many errors in the document citation format in the article, such as lines 139, 328 and 332. Please modify.

(6) In the process of reading, we find that there are grammatical errors in English writing. Please view and view the full text.

(7) Please read the manuscript carefully to polish the language Please read the manuscript carefully to polish the language.

Author Response

Thank you very much for your valuable comments.

 

1. We find that there are some unnecessary contents in the abstract, which seems to be of little help to the thesis. It is recommended to delete and modify the abstract appropriately.

 

Removed unnecessary content from the abstract.

 

2. The structure of the numerical model in the second paragraph is not reasonable. It is suggested to introduce the general situation of the project and then put forward the numerical simulation, the logical sequence is more smooth.

 

Added a site overview as follows:

The coal mine under study is located in the Kutai basin of East Kalimantan province. The coal seam in the study area is a monocline structure with a maximum dip of 13 °. The mining area is composed of a series of parallel panels consisting of one working face, two entries, and one pillar between the panels. Panel sizes range from 130m to 150m in width and 500m to 1000m in length. The gate-entry is 3 m wide by 5 m high, and the roof is supported at 1 m spacing by steel arches with a maximum yield strength of 540 MPa. A numerical model was created in FLAC3D based on actual field conditions.

 

3. In line 139-140 of the paper, the load setting is 6000kN, 8000kN and 10000kN respectively. Please confirm whether the setting load is reasonable and whether references are quoted.

 

The powered support used in the studied coal mines can vary the setting load from approximately 5000 kN to 8000 kN. The setting load of 10,000 kN is also applied to confirm whether an increase in the setting load improves the stability of the longwall face. The following research on the same mine is also used as a reference for the selection of the setting load.

 

Mao, P., Hashikawa, H., Sasaoka, T., Shimada, H., Wan, Z., Hamanaka, A., & Oya, J. (2022). Numerical Investigation of Roof Stability in Longwall Face Developed in Shallow Depth under Weak Geological Conditions. Sustainability, 14(3), 1036.

 

4. The analysis method and description in the part of model validation are simple, and the validity verification of the model is not sufficient, so please improve the author.

 

The results of in-situ monitoring data show the relationship between the number of days since the gate entry is excavated and the roof displacement. On the other hand, the analytical results show the relationship between the simulation step and the roof displacement. The horizontal axis is different for the results of in-situ monitoring data and the analysis results. There is no method to convert this simulation step to an actual time for comparison. Therefore, some deviations are observed from those curves. However, the simulation results are intended to illustrate the state of the model at equilibrium. The roof displacement in the field is also approximately constant at equilibrium. The roof displacement is 7 mm in the field data and 6.6 mm in the analytical results, which are approximately the same values when the stresses are considered to have converged. The error between the field data and the analysis results is less than 5%, indicating the validity of the model. We consider this error to be acceptable.

 

5. There are many errors in the document citation format in the article, such as lines 139, 328 and 332. Please modify.

 

The errors in the document citation format in the article are corrected.

 

6. In the process of reading, we find that there are grammatical errors in English writing. Please view and view the full text.

 

Our manuscript was checked and modified by a native English speaker.

 

7. Please read the manuscript carefully to polish the language.

 

Our manuscript was revised in phrasing by a native English speaker.

Author Response File: Author Response.pdf

Reviewer 2 Report

Reviewer:

Comments to the Author

This study discusses the design of safety pillar width in longwall mining under weak geological conditions by using FLAC3D, which is innovative. I think this article should be modified as follows:

1 In formulas 1 and 3, the characters are not italicized, which is inconsistent with the following.

2 The statements in some parts of the paper are not very accurate, such as ' The coal production in Indonesia is increasing and the demand for coal is also increasing significantly '. Please ask the author to think it over.

3 The expression of ' The size of the panel width in the numerical model is 75 m, half of the 150 m length because the model is a half-section model. ' is somewhat cumbersome, please restate.

4 Figure 4 shows that the two results have large errors. The author considers whether to show the subsequent data to avoid misunderstanding, or to correct the simulation test to reduce the error.

5 in the fourth line of the third paragraph ‘;’ using errors, ask the author to correct similar errors elsewhere in the text.

6 Please ask professional institutions to modify the language of the manuscript.

Comments for author File: Comments.pdf

Author Response

Thank you very much for your valuable comments.

 

1. In formulas 1 and 3, the characters are not italicized, which is inconsistent with the following.

 

Formulas 1 and 3 have been changed to italics.

 

2. The statements in some parts of the paper are not very accurate, such as ' The coal production in Indonesia is increasing and the demand for coal is also increasing significantly '. Please ask the author to think it over.

 

Added explanation of Indonesia's coal production and coal demand.

 

3. The expression of ' The size of the panel width in the numerical model is 75 m, half of the 150 m length because the model is a half-section model. ' is somewhat cumbersome, please restate.

 

Corrected " The size of the panel width in the numerical model is 75 m, half of the 150 m length because the model is a half-section model." as follows:

“For our half-section model, the size of the panel width is 75 m, half of the 150 m.”

 

4. Figure 4 shows that the two results have large errors. The author considers whether to show the subsequent data to avoid misunderstanding, or to correct the simulation test to reduce the error.

 

The results of in-situ monitoring data show the relationship between the number of days since the gate entry is excavated and the roof displacement. On the other hand, the analytical results show the relationship between the simulation step and the roof displacement. The horizontal axis is different for the results of in-situ monitoring data and the analysis results. There is no method to convert this simulation step to an actual time for comparison. Therefore, some deviations are observed from those curves. However, the simulation results are intended to illustrate the state of the model at equilibrium. The roof displacement in the field is also approximately constant at equilibrium. The roof displacement is 7 mm in the field data and 6.6 mm in the analytical results, which are approximately the same values when the stresses are considered to have converged. The error between the field data and the analysis results is less than 5%, indicating the validity of the model. We consider this error to be acceptable.

 

5. in the fourth line of the third paragraph ‘;’ using errors, ask the author to correct similar errors elsewhere in the text.

 

Corrected ";" in the text.

 

6. Please ask professional institutions to modify the language of the manuscript.

 

Our manuscript was checked and modified by a native English speaker.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments for author File: Comments.pdf

Author Response

Thank you very much for your valuable comments.

 

1. During the numerical analysis in Lines 112-113, the authors describe that the properties of rocks are obtained from the laboratory tests from actual site. The reviewer suggests that the photos of rock specimens and the test curves should be added if possible.

 

The data used in this study were provided by an Indonesian mining company. For various reasons, detailed data are secret. Therefore, the photos of rock specimens and the test curves cannot be added.

 

2. In the line of 139, how to determine the setting load during the numerical simulation.

 

The powered support used in the studied coal mines can vary the setting load from approximately 5000 kN to 8000 kN. The setting load of 10,000 kN is also applied to confirm whether an increase in the setting load improves the stability of the longwall face. The following research on the same mine is also used as a reference for the selection of the setting load.

 

Mao, P., Hashikawa, H., Sasaoka, T., Shimada, H., Wan, Z., Hamanaka, A., & Oya, J. (2022). Numerical Investigation of Roof Stability in Longwall Face Developed in Shallow Depth under Weak Geological Conditions. Sustainability, 14(3), 1036.

 

3. Figure 4 gives the comparison of field data and analysis results. Some deviations could be observed from those curves, the authors should illustrate what accounts for this difference.

 

In Figure 4, the results of in-situ monitoring data show the relationship between the number of days since the gate entry is excavated and the roof displacement. On the other hand, the analytical results show the relationship between the simulation step and the roof displacement. The horizontal axis is different for the results of in-situ monitoring data and the analysis results. There is no method to convert this simulation step to an actual time for comparison. Therefore, some deviations are observed from those curves. However, the simulation results are intended to illustrate the state of the model at equilibrium. The roof displacement in the field is also approximately constant at equilibrium. The roof displacement is 7 mm in the field data and 6.6 mm in the analytical results, which are approximately the same values comparing the results after October 7, 2019, when the stresses are considered to have converged, Therefore, it can be concluded that the validation of the numerical model is confirmed.

 

4. In line 139, the remark for reference 14 should be revised according to the journal template.

 

In line 139, the remark for reference 14 has been corrected.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The author has carefully revised and answered the questions mentioned in the manuscript.

Author Response

Thank you for your valuable comments concerning our manuscript entitled "Numerical Simulation on Pillar Design for Longwall Mining under Weak Immediate Roof and Floor Strata in Indonesia". We appreciate for your chariness and warm work. Your suggestions not only improved my manuscript, but also gave me a deeper understanding on the research. Again, thank you very much.