Numerical Analysis of Pillar Stability in Longwall Mining of Two Adjacent Panels of an Inclined Coal Seam
, Alexey Peryshkin 1, Gabriel Esterhuizen 2, Larisa Pavlova 3 and Victor Fryanov 3Round 1
Reviewer 1 Report
This research investigated the pillar stability in longwall mining of two adjacent panels of an inclined coal seam. Actually, there are many references performed in this region. This paper proposed a new modification of the damage accumulation kinetic equation in this study to simulate the stress strain of the rock mass. The stresses in pillars in the inclined coal seam may be complex, how do the authors consider the shear-compressive stress in the model?
Author Response
Thank you very much for the question. We used the finite-difference method which is described exhaustively in [Wilkins, 1999] and is similar to the method employed in FLAC3D. Method allows for calculating the six components of Cauchy stress tensor in each step of numerical integration. Further we analyze the hydrostatic pressure and equivalent stress in each point of continuum to determine the stress state of the point with respect to the yield surface. Therefore, either shear-compressive or shear-tensile stresses and other types of stress are automatically considered within the model.
Reviewer 2 Report
1. I suggest the authors provide more details about the model they proposed.
2. The proposed method might need to be calibrated before to be implemented for their research. Please celibate the method or explain it.
Author Response
- Thank you very much for the question. We added an additional paragraph to appendix explaining some further details of the model. We also provided a reference to our previous work wherein the basic equations of the model are discussed. We decided not to repeat them here to avoid self-plagiarism.
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Thank you very much for the question. We added an additional paragraph to the manuscript wherein the results of numerical modeling are discussed regarding calibration against the field data.
Reviewer 3 Report
The paper is interested to apply the finite-difference continuum damage mechanics in modeling stress-strain evolution of the rock mass during the mining activities. The numerical modeling results are available to provide reliable basis reference for pillar stability assessment. It is valuable for readers in the related research and can be considered revised. Here are comments in details.
1 How do you consider the trade-off between the safety and economic efficiency of mining in details. Or what are your suggestion from your experience in mining activities.
2 Figures are fuzzy, please revise them, especially Figure 1.
3 In the further study, it is suggested to consider more complex three-dimensional geo-mechanical model with anisotropy and heterogeneity view on rock materials based the achieved results.
4 The distinction between tenses should be strictly treated in various sections of this manuscript, especially the simple present tense and the simple past tense.
5 The font and font size of words should be uniform in the same figure, while these items should be close to each other in different pictures, to meet better reading result.
6 In Line 345, "factor of safety" has the capitalized first letter, which is confused.
7 How have you achieved the field data, to compare with the numerical modeling data? The reliability is the key.
8 For the surrounding rock in the coal mine, it is of complex elastic-plastic characteristics, which is relatively rough to evaluate the protective pillar stability only based on the curve change of the stress-strain. It is suggested to deepen the research in this item in the future.
9 In Line 355, as the compromise solution, the 11 is selected for the W/H ratio of 11 considering the production safety and economic benefits. It is biased only based on the research results in this paper. More analysis is needed in this regard.
10 The language needs to be polished to enhance the effect of expression.
Author Response
1 How do you consider the trade-off between the safety and economic efficiency of mining in details. Or what are your suggestion from your experience in mining activities.
Answer: Thank you very much for the question. Analysis presented in a current study represents the part of a general stability calculations made by the project institute prior to the mining activities. Based on these calculations, we estimate the W/H ratio which should not fall below the obtained value. A final decision is undertaken by the executive engineer group in-situ with respect to some other factors disregarded in theoretical calculations. These factors are generally taken into account by the means of increasing coefficients from mine field statistics and experience. Each coefficient yields the economic losses. Therefore, starting from theoretical estimation and taking into account increasing coefficients based on the in-situ analysis, we finally get the trade-off between safety and economic efficiency.
2 Figures are fuzzy, please revise them, especially Figure 1.
Answer: Thank you very much for the comment. Some figures were revised to make them clearer for the reader.
3 In the further study, it is suggested to consider more complex three-dimensional geo-mechanical model with anisotropy and heterogeneity view on rock materials based the achieved results.
Answer: Thank you very much for the suggestion.
4 The distinction between tenses should be strictly treated in various sections of this manuscript, especially the simple present tense and the simple past tense.
Answer: Thank you very much for the comment. The manuscript was additionally proofread.
5 The font and font size of words should be uniform in the same figure, while these items should be close to each other in different pictures, to meet better reading result.
Answer: Thank you very much for the comment. The font and font size were revised as much as possible.
6 In Line 345, "factor of safety" has the capitalized first letter, which is confused.
Answer: Thank you very much for the comment. Fixed
7 How have you achieved the field data, to compare with the numerical modeling data? The reliability is the key.
Answer: Thank you very much for the question. According to the field data in this particular mine, in a considered mining depth the width of protective pillars varied in the range of 40-60 m depending on the conditions. Therefore, the model results give the low border of this range (see answer to the first question).
8 For the surrounding rock in the coal mine, it is of complex elastic-plastic characteristics, which is relatively rough to evaluate the protective pillar stability only based on the curve change of the stress-strain. It is suggested to deepen the research in this item in the future.
Answer: Thank you very much for the comment. Our model takes account of complex elastic-plastic state of surrounding rock. Therefore, the stability calculations based on the stress change implicitly take account of complex elastic-plastic state of surrounding rock. But we agree that additional elastic-plastic characteristics will benefit to the analysis.
9 In Line 355, as the compromise solution, the 11 is selected for the W/H ratio of 11 considering the production safety and economic benefits. It is biased only based on the research results in this paper. More analysis is needed in this regard.
Answer: Thank you very much for the question. We agree that additional data might be used in stability calculations, however in this work we considered the “ideal” case, to some extent, as the first approximation and suggestion for the mine. The last conclusion was re-drawn according to your question.
10 The language needs to be polished to enhance the effect of expression.
Answer: Thank you very much for the comment. The manuscript was additionally proofread.
Reviewer 4 Report
This paper propose an intersting method to evaluate the stability of pillar, and the it can be applied to the similar geologic condtion. there are still some places that can be improved.
(1) there may be no immediate roof, since the rock is siltstone, and it is so hard that can be known as basic roof.
(2) the paper should be take some modification about the format.
this paper can be pulished when make some minor revision.
Author Response
1. Thank you very much for the comment. Yes, in some cases the layer of siltstone is quite large, which makes impossible to distinguish in from the main roof since they are prone to cave mutually. This fact generally does not have an impact to the stability calculations proposed in this work.
2. Thank you very much for the comment. We made corrections according to the journal template.
Round 2
Reviewer 3 Report
I am pleased to review the revised version submitted by the authors. In the review of the manuscript v1 I put forward several comments. In the revised version v2 manuscript, it is found that the authors have responded to and modified the mentioned questions one by one. Their attitude is serious and the v2 revision of the paper is meticulous. I recommend that it can be accepted for publication.
