Floor Heave Control in Gob-Side Entry Retaining by Pillarless Coal Mining with Anti-Shear Pile Technology

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, the anti-shear pile technology to control floor heave in gob-side entry retaining was investigated by using numerical simulation and field monitoring. The obtained conclusions have reference value for related research. However, the following points raised by the reviewers need further explanation and clarification:

1. The introduction should be expanded, and its logic needs to be reorganized.

2. Domestic and foreign scholars have done a lot of research on the ground settlement of tunnels. Therefore, the literature review in this paper is insufficient. Many papers on this topic have not explained.

3. The authorship of this paper encompasses an excessive number of affiliations; therefore, it is recommended to eliminate authors and their affiliated units that are less pertinent to the study.

4. The language of this article requires additional refinement.

5. The picture quality of the paper needs to be improved.

6. Please explain how the results of this paper can be used to guide engineering practice.

7.The conclusions need to be further refined.

Comments on the Quality of English Language

In this paper, the anti-shear pile technology to control floor heave in gob-side entry retaining was investigated by using numerical simulation and field monitoring. The obtained conclusions have reference value for related research. However, the following points raised by the reviewers need further explanation and clarification:

1. The introduction should be expanded, and its logic needs to be reorganized.

2. Domestic and foreign scholars have done a lot of research on the ground settlement of tunnels. Therefore, the literature review in this paper is insufficient. Many papers on this topic have not explained.

3. The authorship of this paper encompasses an excessive number of affiliations; therefore, it is recommended to eliminate authors and their affiliated units that are less pertinent to the study.

4. The language of this article requires additional refinement.

5. The picture quality of the paper needs to be improved.

6. Please explain how the results of this paper can be used to guide engineering practice.

7.The conclusions need to be further refined.

Author Response

Reviewer 1

1. Summary

Thank you very much for taking the time to review this manuscript. We appreciate the constructive suggestions, which have been valuable and helpful for revising and improving our paper. We have seriously considered all the questions/comments from Reviewers #1, and revised the manuscript as possible as we can, in which the new analysis is highlighted in the text. The part modified according to the reviewer 's Comments is highlighted in red.

2. Point-by-point response to Comments and Suggestions

Comments1. The introduction should be expanded, and its logic needs to be reorganized.

The introduction section has been expanded. The revised content was added in Introduction section, and highlighted in red.

Comments2. Domestic and foreign scholars have done a lot of research on the ground settlement of tunnels. Therefore, the literature review in this paper is insufficient. Many papers on this topic have not explained.

The literature review was expanded.

Zhu et al. [32] proposed the control method of “bottom lifting + bottom angle bolt + floor bolt ” based on results of numerical simulation. Wang et al. [33] proposed asymmetric floor heave control scheme of “floor leveling + anchor cable support + concrete hardening” on the base of control principle of “roof + two sides + floor”. Wei et al. [34] used the 3DEC discrete-element software to simulate and analyze the characteristics and evolution of the asymmetric roadway floor heave under dynamic-load disturbance, and proposed the asymmetric control scheme of “slurry anchor reinforcement + top cutting and pressure relief”. Zhang et al. [35] used UDEC software to study the floor failure mechanism under the influence of superimposed dynamic and static loads. Full-section anchor cables and inverted arches were proposed to maintain the stability of the surrounding rock. Qin et al. [36] proposed the zonal reinforcement scheme of “fix cable to shed, floor pressure relief, deep-shallow composite grouting” and implemented into practice, with good results.

5 references were added to literature.

32. Zhu, L.; Liu, C.; Gu, W.; Yuan, C.; Wu, Y.; Liu, Z.; Song, T.; Sheng, F. Research on Floor Heave Mechanisms and Control Technology for Deep Dynamic Pressure Roadways. Processes2023, 11, 467. https://doi.org/10.3390/pr11020467.
33. Wang, D.; Zheng, Y.; He, F.; Song, J.; Zhang, J.; Wu, Y.; Jia, P.; Wang, X.; Liu, B.; Wang, F.; et al. Mechanism and Control of Asymmetric Floor Heave in the Gob-Side Coal Roadway under Mining Pressure in Extra-Thick Coal Seams. Energies2023, 16, 4948. https://doi.org/10.3390/en16134948.
34. Wei, W.; Zhang, G.; Li, C.; Zhang, W.; Shen, Y. Mechanism and Control of Asymmetric Floor Heave in Deep Roadway Disturbed by Roof Fracture. Sustainability2023, 15, 6357. https://doi.org/10.3390/su15086357.
35. Zhang, D.; Bai, J.; Yan, S.; Wang, R.; Meng, N.; Wang, G. Investigation on the Failure Mechanism of Weak Floors in Deep and High-Stress Roadway and the Corresponding Control Technology. Minerals2021, 11, 1408. https://doi.org/10.3390/min11121408.
36. Qin, D.; Wang, X.; Zhang, D.; Chen, X. Study on Surrounding Rock-Bearing Structure and Associated Control Mechanism of Deep Soft Rock Roadway Under Dynamic Pressure. Sustainability2019, 11, 1892. https://doi.org/10.3390/su11071892.

The revised content was added in Introduction section, and highlighted in red.

Comments 3. The authorship of this paper encompasses an excessive number of affiliations; therefore, it is recommended to eliminate authors and their affiliated units that are less pertinent to the study.

Response 3: Thank you very much for this important suggestion. Number of affiliations was reduced to three. Due to the fact that the participation of each co-author was included in the article, in accordance with editorial requirements, we kindly ask you to take this fact into account: Author Contributions: Conceptualization, Ivan Sakhno and Svitlana Sakhno; Methodology, Ivan Sakhno and Oleksandr Isaienkov; Software, Krzysztof Skrzypkowski; Validation, Ivan Sakhno, Krzysztof Skrzypkowski, Krzysztof Zagórski and Anna Zagórska; Formal analysis, Svitlana Sakhno; Investigation, Ivan Sakhno; Resources, Krzysztof Zagórski and Anna Zagórska; Writing – original draft, Ivan Sakhno; Writing – review & editing, Svitlana Sakhno and Krzysztof Skrzypkowski; Visualization, Oleksandr Isaienkov; Supervision, Ivan Sakhno; Project administration, Ivan Sakhno; Funding acquisition, Krzysztof Skrzypkowski, Krzysztof Zagórski and Anna Zagórska.

Comments4. The language of this article requires additional refinement.

Response 4: Thank you for your suggestion. The article has undergone additional language editing. Corrections are highlighted in yellow.

Comments5. The picture quality of the paper needs to be improved.

Response 5: Thank you very much for your offer. The quality of pictures has been improved.

Comments6. Please explain how the results of this paper can be used to guide engineering practice.

Response 6: Thank you for your suggestion. The implementation of the proposed floor heave control method with anti-shear pile leads to the significant reduction of heaving in gob-side entry retaining. The results of this study can be used for designing the support system in gob-side entry retaining. The revised content was added in (2) point of Conclusion section, and highlighted in red.

Comments 7.The conclusions need to be further refined.

Thank you for your suggestion. Sections (2) and (3) of conclusion have been refined. Changes are highlighted in red.

 

Reviewer 2 Report

Comments and Suggestions for Authors

Floor heave is very difficult to control in long wall mining and this paper proposes a very novel control technology, which, though not commonly seen, should be quite interesting. Here are some questions and suggestions regarding the technology, for your reference only.

（1）Could the authors please elaborate on the approximate cost of implementing this technology, including any upfront investments, maintenance costs, and other relevant expenses?

（2）Does this technology take a long time to implement? Can it match the production schedule of the working face?

（3）Has this technology been applied in the field? How is the effect? Can the authors provide some monitoring data?

Author Response

Reviewer 2

1. Summary

Thank you very much for taking the time to review this manuscript. We appreciate the constructive suggestions, which have been valuable and helpful for revising and improving our paper. We have seriously considered all the questions/comments from Reviewers #2, and revised the manuscript as possible as we can, in which the new analysis is highlighted in the text. The part modified according to the reviewer 's Comments is highlighted in red.

2. Point-by-point response to Comments and Suggestions

Floor heave is very difficult to control in long wall mining and this paper proposes a very novel control technology, which, though not commonly seen, should be quite interesting. Here are some questions and suggestions regarding the technology, for your reference only.

（Comment 1）Could the authors please elaborate on the approximate cost of implementing this technology, including any upfront investments, maintenance costs, and other relevant expenses?

Response 1: According to the authors, the proposed anti-shear pile technology does not require significant investment. Investments are required to purchase an SBG-1M type drilling machine. The approximate cost of such equipment in Ukraine, taking into account transportation costs, is 15 thousand euros. Taking into account the service life, residual value and average monthly depreciation, downtime, depreciation expense will be 205 euros/month. The machine repairs and maintenance expense, taking into account planned repairs, is 0.012 man-hour. Taking into account wages in Ukraine, monthly maintenance expense will be 119 euros/month. Electricity consumption and the salary of a worker on drilling machine depend on local wages and the quantities of drilling work. Three workers per shift are involved in the implementation of the proposed technology. Material costs are shown in Table 4.

The revised content was added in section 4.3, and highlighted in red.

（Comment 2）Does this technology take a long time to implement? Can it match the production schedule of the working face?

Response 2: Thank you for your suggestion. The piles installation must be carried out after roadway excavation stage, and before the longwall mining stage. Therefore, production schedule of the working face does not affect the schedule of pile installation. The estimated pace of installation of piles in gateroad in a 3-shift operating mode is 819 m/month. The revised content was added in section 4.3, and highlighted in red.

（Comment 3）Has this technology been applied in the field? How is the effect? Can the authors provide some monitoring data?

Response 3: Thank you for your suggestion. The anti-shear pile technology is at the stage of elaboration and justification of parameters. In-situ tests are planned for the future. Therefore, the described above effect is based only on the results of numerical simulation so far. The revised content was added in (3) point of Conclusion section, and highlighted in red.

 

Reviewer 3 Report

Comments and Suggestions for Authors

This paper mainly deals with the numerical modelling of floor heave in underground hard coal mines.

The first part of the article discusses floor uplift in coal mines in light of the mining system used.

The second part briefly describes the geological and mining conditions in one of the Ukrainian underground mines. It also briefly discusses the exploitation system and the phenomenon of floor uplift.

The genesis of the floor heave phenomenon was not discussed, and the time factor was not considered, only its maximum values (1.04 m—line 198). This chapter requires development and supplementation.

The relatively high cohesion values assumed/calculated in Table 1 also raise some doubts. For example, for sandy mudstone (using the RocLab program for paper data), a cohesion of 1.395 MPa is obtained, not 2.45 MPa.

I understand that the grey zones in Fig. 5, 6, 8-14, and 16, 17 mean exceedances of strains of the order of -0.02 to + 0.02. If so, it must be marked and commented on. Should this be the main criterion for destruction? This requires a broader comment.

What do the ranges of plasticity zones look like?

The numerical model used in the calculations is 3D, but with such assumptions, a flat model (2D) would also be sufficient - there is no variability in the x-axis direction.

Steel arches are permanently connected to the rock mass (there are no contact elements) and modelled using beam elements. Their deformability was not taken into account.

We can agree with the model's calibration regarding the amount of floor uplift (approximately 0.98 m in Figs. 10 and 14). However, the use of structural elements (piles) is not calibrated in any way. There is no detailed description of the modelling of structural elements, adopted contact data, etc.

Finally, the most serious note — to my surprise, no in situ verification of any proposed method of strengthening the footwall rocks exists. Yes, there is even a simplified financial analysis, but no verification.

Technological problems are described only from a hypothetical point of view.

This work is missing a very important part: verifying the modelling results by installing any of the proposed construction schemes (Table 3) in the underground pavement.

Statements such as "The implementation of the proposed floor heave control method with anti-shear pile leads to the reduction of heaving by 2.47 times." require in situ verification. Without it, unfortunately, they have no coverage.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Minor editorial errors are highlighted in yellow in the attached text.

Author Response

Reviewer 3

1. Summary

Thank you very much for taking the time to review this manuscript. We appreciate the constructive suggestions, which have been valuable and helpful for revising and improving our paper. We have seriously considered all the questions/comments from Reviewers #3, and revised the manuscript as possible as we can, in which the new analysis is highlighted in the text. The part modified according to the reviewer 's comments is highlighted in red.

2. Point-by-point response to Comments and Suggestions for Authors

Comment 1. This paper mainly deals with the numerical modelling of floor heave in underground hard coal mines.The first part of the article discusses floor uplift in coal mines in light of the mining system used.

The second part briefly describes the geological and mining conditions in one of the Ukrainian underground mines. It also briefly discusses the exploitation system and the phenomenon of floor uplift. The genesis of the floor heave phenomenon was not discussed, and the time factor was not considered, only its maximum values (1.04 m—line 198). This chapter requires development and supplementation.

Response 1: Thank you for your suggestion. An analysis of the floor heave dynamic monitoring showed that this phenomenon evolved with different intensity at different stages of the gateroads life. This is generally consistent with previously known studies [15, 17, 27, 42]. The gateroad, that was an object of study, had no water inflows. Therefore, the swelling mechanism of heaving is not typical for it. The greatest increase in gateroad floor heave was associated with the longwall face influence. The abutment pressure changes the equilibrium state of rock masses, increases vertical stress concentration and leads to post-elastic deformation of rocks. In this case, the immediate floor loses its continuity and becomes discontinued. This is visually confirmed after rock excavation during floor restoration, similar to previous studies [42]. Post-elastic deformation (pseudoplastic flow) and dilatancy are the main causes of floor heave. Floor heave in the gob-side entry is complicated by the asymmetrical stress-strain state. In this case, the heaving mechanism is close to bearing capacity failure cases. However, due to the stress asymmetry, failures of the floor strata underneath the coal body and filling wall body are different.

The revised content was added in 2.2. section, and highlighted in red.

Comment 2. The relatively high cohesion values assumed/calculated in Table 1 also raise some doubts. For example, for sandy mudstone (using the RocLab program for paper data), a cohesion of 1.395 MPa is obtained, not 2.45 MPa.

Response 2. Thank you for your suggestion. The authors based their calculations on The Hoek-Brown Failure Criterion. Section 3 describes the procedure of choosing the parameters. The calculation procedure was described in more detail in previous studies of authors [18, 51]. The calculation results are presented in Table 1.

Immediate floor (mudstone)
47	0.5	0.87	0.04	0.50	0.3	1.61	22	22

For example, the cohesion of immediate floor (mudstone) is 1.61 MPa. The authors did not use RocLab program, therefore perhaps the parameters are different from the reviewer's parameters.

Comment 3. I understand that the grey zones in Fig. 5, 6, 8-14, and 16, 17 mean exceedances of strains of the order of -0.02 to + 0.02. If so, it must be marked and commented on. Should this be the main criterion for destruction? This requires a broader comment.

Response 3. Thank you very much for your offer. Gray zones in Fig. 5, 6, 8-14, and 16, 17 show an excess of strain value "+0.05". The positive strain scale in the figures are limited by "+0.05". All strains that are greater than +0.05 are indicated in gray.

In this paper, authors do not study the failure of rocks in detail. The authors understand that in a triaxial stress field, failure will depend on the ratio of stress components and can vary. In the context of this study, it is important to recognize the post-elastic stage. Therefore the post-peak strain is analyzed. In the Drucker-Prager model, pseudoplastic deformation is accepted for analyse the behavior of rock mass beyond the elastic stage, including discontinues rock. In numerical simulation the post-peak limit was accepted in the range of "-0.02" - "+0.02", according to the results of laboratory tests, references to which [53-56] are given in the paper. However, these limits are important for evaluating of rock deformations and are, strictly speaking, the limits of plasticity/pseudoplasticity in the model.

Text about  gray areas has been added to the article in section 3.2. A comment about the plasticity/pseudoplasticity limits has been added to the article, and highlighted in red.

Comment 4. What do the ranges of plasticity zones look like?

Response 4. A detailed answer to this question is given in the previous answer. Short answer: The elasticity limit was accepted in the range of "-0.02" - "+0.02". Beyond these limits, the deformation in the model is pseudoplastic.

Comment 5. The numerical model used in the calculations is 3D, but with such assumptions, a flat model (2D) would also be sufficient - there is no variability in the x-axis direction.

Response 5. It is absolutely correct comment. It’s very nice that the reviewer is a high-level expert that understands this. The negative experience of submitting previous articles showed that it is easier to make a more complex 3D model than to receive negative feedback from a reviewer about a reject to publish because of a 2D model or a simpler 3D model. Therefore, the authors believe that the 3D model is more accurate, although it requires more resources

Comment 6. Steel arches are permanently connected to the rock mass (there are no contact elements) and modelled using beam elements. Their deformability was not taken into account.

Response 6. Steel arches are modeled with beam elements. This is correct. The steel arches have no yielding nodes. It is quite difficult to model yielding nodes, and impossible on a model scale. Therefore, this simplification was applied. The authors believe that such simplification does not cause large errors, since the object of study is floor.

Comment 7. We can agree with the model's calibration regarding the amount of floor uplift (approximately 0.98 m in Figs. 10 and 14). However, the use of structural elements (piles) is not calibrated in any way. There is no detailed description of the modelling of structural elements, adopted contact data, etc.

Response 7. Thank you very much for your offer. Unfortunately, it is impossible to calibrate the piles at this study stage, since in-situ studies of the proposed technology have not been carried out yet. The piles were modeled as beam elements. In this case, the deformation modulus was calculated as a weighted average between steel and concrete for each pile type structure separately according to the theory of elasticity.

The revised content was added in 4.1 section, and highlighted in red.

Comment 8. Finally, the most serious note — to my surprise, no in situ verification of any proposed method of strengthening the footwall rocks exists. Yes, there is even a simplified financial analysis, but no verification.

Technological problems are described only from a hypothetical point of view.

This work is missing a very important part: verifying the modelling results by installing any of the proposed construction schemes (Table 3) in the underground pavement.

Statements such as "The implementation of the proposed floor heave control method with anti-shear pile leads to the reduction of heaving by 2.47 times." require in situ verification. Without it, unfortunately, they have no coverage.

Response 8. Thank you for your suggestion. The anti-shear pile technology is at the stage of elaboration and justification of parameters. In-situ tests are planned for the future. Therefore, the described above effect is based only on the results of numerical simulation so far. The revised content was added in (3) point of Conclusion section, and highlighted in red.

The implementation of the proposed floor heave control method with anti-shear pile leads to the significant reduction of heaving in gob-side entry retaining.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have modified the paper according to the review comments. I suggest that the paper be published.

Comments on the Quality of English Language

The Quality of English Language is OK.

Author Response

Thank you very much for taking the time to review this manuscript. 

Reviewer 3 Report

Comments and Suggestions for Authors

C1 + C2. I hoped that the measurement material would be supplemented in addition to the genesis, but unfortunately, we still only have the maximum value. It is difficult to discuss the parameter values here since the calibration comes down to only one maximum floor height value.

C3-C6 - I am satisfied with the answers.

C7+C8 are still unanswered, but there will be no answers because there is no in situ verification. According to the authors, it is planned for the near future.

Author Response

1. Summary

Thank you very much for taking the time to review this manuscript. We appreciate the constructive suggestions, which have been valuable and helpful for revising and improving our paper. We have seriously considered all the questions/comments from Reviewers #3, and revised the manuscript as possible as we can, in which the new analysis is highlighted in the text. The part modified according to the reviewer 's Comments is highlighted in red.

2. Point-by-point response to Comments and Suggestions

Comment 1. C1 + C2. I hoped that the measurement material would be supplemented in addition to the genesis, but unfortunately, we still only have the maximum value. It is difficult to discuss the parameter values here since the calibration comes down to only one maximum floor height value.

Response 1: Thank you for your suggestion. The measurement material was added in section 2.2 of paper and highlighted in red. Please also look at Fig. 3c.

Added: The floor heave monitoring was held in the headgate of 12 panel. Measurements were carried out at three monitoring station. The distance between stations was 9.6 m. Each station consisted of 4 marker points installed in the roof, floor, and both wall sides of the gateroad. The measurements were carried out over 4 months. The graphs of floor heave evolution in the center of the headgate span in advance of the longwall face and behind it are presented in Figure 3c. The floor uplift in advance of the longwall influence zone was 95 mm (9% of the total floor heave) and occurred during the roadway excavation stage. The monitoring results show that the main part of the floor uplift occurred at a distance of +40 m in advance of the longwall face and -50 m behind it. 35% of the floor uplift occurred at a distance of “+40” m in advance of the longwall face to the intersection of headgate with the face. Another 28% of floor uplift appears in the section of the headgate “0” - “-50” m behind the longwall face. The floor uplift has a damping tendency and stabilizes at a distance of 260-300 m behind the longwall face. At the stage of maintaining the headgate behind the longwall face, 56% of the total floor uplift occurs.

 

Comment 2. C7+C8 are still unanswered, but there will be no answers because there is no in situ verification. According to the authors, it is planned for the near future.

Response 2: Thank you for your comment. No doubt, the paper would have been better with in-situ verification of the proposed technology. However, unfortunately, the authors have not yet been able to organize such an experiment. Our efforts are aimed at finding and implementing such an opportunity.