Research on the Correlation Between Overburden Rock Fracture Development and High-Energy Events During Deep Mining in Extremely Thick and Weakly Consolidated Strata for Regional Coal Mining Safety

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

The article considers issues related to the study of the relationship between the development of cracks in overburden rocks and high-energy events during deep mining.

The extraction of solid minerals at present and, to a large extent, in the future, is associated with the development of deposits at great depths. With an increase in the depth of development, the problem of the stability of workings becomes especially relevant. Great depths are characterized by high rock pressure, at which the mechanical stress of the massif near the workings exceeds the strength of the rock. As a result, a natural physical (geomechanical) process of rock destruction develops in the massif, complicating the operation of the workings. In brittle rocks, destruction is expressed in the formation of new, man-made (otherwise, induced) micro- and macrocracks. Induced cracks significantly change the natural fracture structure of the rock mass near the workings and the reaction of the massif to natural and man-made impacts. In particular, the appearance of induced cracks reduces the resistance of the rock mass to explosive loads, leads to a more intense displacement of rocks in mine workings up to the detachment of rock plates from the rock mass, as occurs during rock shooting and sudden outbursts. Despite the great practical importance of the problem of workings stability and the availability of in-kind data, the mechanism of crack formation in rocks under the action of rock pressure, in particular the mechanism of formation of rupture cracks (rock detachment), has been poorly studied theoretically. Therefore, there are good reasons to expect that fundamental studies of the conditions for the origin, propagation and manifestation of induced cracks can contribute to the emergence of new ideas in the development of measures to improve the stability of workings, prevent dangerous dynamic manifestations of rock pressure, and create new mining methods that take into account the geomechanical features of great depths. A feature of modern urgent problems on the stability of workings and rock masses is their focus on studying the natural process of massif destruction. In this case, destruction is understood not only as the division of a massif into parts or the collapse of rock, but in a broader sense, as an irreversible qualitative transition of a certain area of the massif to a new mechanical state, accompanied by a change in its structure (development of cracks or other damage), as a result of which the ability of this area to withstand natural or man-made loads changes qualitatively.

The results obtained in the article are of interest to readers in the field under consideration.

 

However, there are the following issues that should be clarified:

1. The introduction could provide a list of the most significant high-energy events and the corresponding development of fractures in the considered area of China, as well as a comparative analysis with similar situations in other regions of the world. It would also be possible to provide the values of the indicators characterizing the environmental situation at the time of these events and compare them with the standard indicators.

2. Has a comparative analysis of the coal mine under consideration been carried out with similar mines in other regions in terms of hydrogeological conditions, overburden content, etc. (section "2.1. Geographical Location of the Mining Area and Mining Status of the Working Face")?

3. It is necessary to add the sections "Materials and Methods" and "Discussion" to ensure that the structure of the article complies with the IMRAD requirements. Perhaps the section can be added by listing the methods from section "3.1. Analysis of the Observation Results of Overburden Fracture Development Height in the Working Face". In addition, the main methods used in coal mining could be given, in particular, the hydraulic fracturing method (https://doi.org/10.1016/j.ijrmms.2024.105840, https://doi.org/10.31897/PMI.2022.98).

4. It is necessary to present a generalized methodology for conducting experimental studies in the form of an algorithm based on the materials of the section "3.1. Analysis of the Observation Results of Overburden Fracture Development Height in the Working Face", for which a corresponding patent could be obtained.

5. It is necessary to explain how the monitoring was carried out, on the basis of which the diagram shown in Figure 2 was constructed.

6. Were random energy characteristics determined during the statistical analysis of energy data monitored during the mining process. Was the distribution law of random variables determined?

7. It is necessary to provide the values of the correlation coefficients according to the data in Figure 2.

8. What software was used to process the results of the experimental studies?

9. According to the data in Tables 4 and 5, it is necessary to provide specific mathematical models that allow the calculation and forecasting of the output values under consideration during the correlation and regression analysis.

10. The analysis of Figure 5 is not presented in sufficient detail.

11. It is necessary to explain whether the experimental planning method was used during the simulation (section “4.2. Simulation Excavation Plan”).

12. The conclusions should focus on the prospects for further research on the presented topic.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article contains original research on the influence of rock mass tremors on the development of fractures in the roof. The obtained dependencies of overburden fracture development before and after high energy events are interesting from a scientific point of view and may be helpful at the stage of rock burst prevention in longwall excavations during the exploitation of hard coal deposits. Below are a few minor comments and suggestions:
1. In the introduction, it should be added informations that monitoring in the longwall excavation can be carried out using a powered support (doi:10.2478/sgem-2018-0007), thanks to which it is possible to predict interruptions in operation caused by additional dynamic load; 2. In the subsection 2.1 for the first Figure, please write what is the width of the pillar between two longwall excavations and whether the roadways are additionally reinforced behind the longwall face, if so, please write what type of support is used;
3. In the subsection 2.2, please write whether there are faults in the considered area and what their throws and angles of inclination are; 4. In the subsection 3.2, please add a few sentences regarding the influence of the energy of tremors on the occurrence of collapses of roof rocks in the longwall or roadways - is there a certain correlation;
5. In the subsection 4.1, please write what values ​​of vertical and horizontal stresses were assumed, how the energy of tremors was modeled and whether the goaf zone was modeled;
6. In the subsection 4.3 for Figure 8, please write whether the values ​​of maximal subsidence exceeded the permissible values ​​of terrain deformations - was this compared; 7. In the subsection 5.3 in Figures 11-16 there is a layer called: "weak cemented overlaying rock", please write how thick it is;
8. In the subsection 5.3, please add a table with a summary of the results of the range of fracutes in the roof for the conditions without tremors and with tremors, in relation to the results presented in Figures 11-16;
9. The conclusions cover the scope of the analyses and are sufficient.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The comments have been corrected. I recommend the article for publication in its presented form.