Research on Reducing Mining-Induced Disasters by Filling in Steeply Inclined Thick Coal Seams
Round 1
Reviewer 1 Report
Authors did put effort into reviewing the manuscript and resubmitting it.
However, as stated in first review, presented case deals with the problem in unusual way that conflicts reviewer experience and is possibly highly dangerous for the work environment.
It is therefore recommended that this manuscript is rejected.
Author Response
Point: However, as stated in first review, presented case deals with the problem in unusual way that conflicts reviewer experience and is possibly highly dangerous for the work environment.
Response: Conventional methods used to solve dynamic mine disasters include water injection, destressing blasting, pressure relief grooves, and pressure relief holes. When horizontal sublevel caving, as the upper layer of the coal seam is continuously mined out, the roof strata loses bearing capacity, which would lead to the collapse of roof strata and cause impact disaster. Goaf filling is an important method to control the movement of roof strata and the surface. In fact, destressing blasting is occasionally used at stress concentration area. In general, filling is the main control method to control power disasters. So, currently filling technology is one of the most effective way to control the dynamic disasters of mines.
Reviewer 2 Report
In general, this paper is a good contribution to Sustainability. I found the subject match interesting and representing a valuable contribution to the existing body of work on the behavior of backfilling of underground coal mining. Some minor comments/suggestions follow:
The language requires professional editing or check by a native speaker. The method to determine the filling strength (Section 2.2) is confusing. Based on the statement in L213-214, the roof would not fail when the strength of the filling material meets the requirement of Eq. (1.9), but roof failure occurred both on field observation and numerical simulation. This means the theatrical analysis to determine the filling strength was wrong. The authors did not take the confining pressure into account when determining the strength of the filling material. Rock (or rock-like materials) strength would increase when apply confining stress to it, so the strength (in Eq. (1.9)) may be conservative since the confining pressure was not taken into account. The backfilling technology presented in this work is quite different from the conventional method used in underground longwall mining, but is similar to ore mining, so literature review on this point should pay much attention in the Introduction section. At the same time, the backfilling method is also a little different from the ore mining, since all the backfilling was carried out on the surface. I think this is a highlight for this study, which should be well introduced in this manuscript. How to use the hydraulic tamper to compact the filling material can be more elaborate. For the numerical simulation, there exist several queries.5a. It seems that the author did not consider the retreating distance (i.e., the direction perpendicular to the current model) of the shortwall mining. It is significant to use a 3D model to simulate mining-induced roof strata behaviors.
5b. How the backfilling was simulated? Did the model simulate the filling materials caving and the re-compaction?
5c. The backfilling material in the gob plays a significant role in rock responses by mining. The gob compaction behavior is very important when simulating longwall mining, and should be well considered. There are seveal works regarding this issue and can be helpful, e.g., Majdi (2012); Cun Zhang et al (2019); Yavuz (2004);Bai et al (2016,2017), etc.
Author Response
Point 1:The method to determine the filling strength (Section 2.2) is confusing. Based on the statement in L213-214, the roof would not fail when the strength of the filling material meets the requirement of Eq. (1.9), but roof failure occurred both on field observation and numerical simulation. This means the theatrical analysis to determine the filling strength was wrong.
Response 1: With the release of coal seams, cracks and joints in the roof cause the expansion of fractures. Parts of the roof lose its support and fail. Filling is used to lessen the impact of roof fail. Therefore, in the theoretical calculation, it is assumed that the roof is complete for the calculation of the strength of filling material.
Point 2: The authors did not take the confining pressure围压 into account when determining the strength of the filling material. Rock (or rock-like materials) strength would increase when apply confining stress to it, so the strength (in Eq. (1.9)) may be conservative since the confining pressure was not taken into account.
Response 2: The strength of filling material is more related to the mining depth. Steeply inclined coal seams are rigid rock with good stability. After filling, the stable structure of “roof-filling material-floor” can prevent movement of the roof. Therefore, determining the strength of filling material according to roof can guarantee the power of controlling roof movement.
Point 3: The backfilling technology presented in this work is quite different from the conventional method used in underground longwall mining, but is similar to ore mining, so literature review on this point should pay much attention in the Introduction section. At the same time, the backfilling method is also a little different from the ore mining, since all the backfilling was carried out on the surface. I think this is a highlight for this study, which should be well introduced in this manuscript.
Response 3: Authors have added statements about filling in section 4 Engineering practice as follows:
Filling material is obtained through blending fully aggregates, adhesives, and dusts on the ground, and is then pumped into the total goaf from its top under its own gravity.
As observed in the field, there should be about one week for filling material to reach a steady status; the advanced distance of the working face is 45 m per month.
Point 4: It seems that the author did not consider the retreating distance (i.e., the direction perpendicular to the current model) of the shortwall mining. It is significant to use a 3D model to simulate mining-induced roof strata behaviors.
Response 4: The distance advanced during each shift is 6.4 m, representing the filling amount each day.
Point 5: How the backfilling was simulated? Did the model simulate the filling materials caving and the re-compaction?
Response 5:The numeral calculations process is as follows: first step is evacuation. After the evacuation is stable, filling the material and then calculating. And the cycle is repeated.
The purpose of this manuscript is to study the surrounding rock and surface movement after filling, so we didn’t simulate the filling materials caving and the re-compaction.
Point 6: The backfilling material in the gob plays a significant role in rock responses by mining. The gob compaction behavior is very important when simulating longwall mining, and should be well considered.
Response 6: In the caving, the development of the roof crack helps the stability of filling material. We added the effect of roofs rocks have on filling in Section 1, and four related references.
Reviewer 3 Report
The authors corresponded well to my comments and I think the manuscript can be accepted now.
Author Response
We would like to express our great appreciation to you for comments on our paper.
Reviewer 4 Report
The revised manuscript has improved significantly. Minor grammar checks and proofreading are needed.
Author Response
Point: The revised manuscript has improved significantly. Minor grammar checks and proofreading are needed.
Response: We tried our best to improve the manuscript and have it checked by a native English speaking colleague. We hope it will meet with approval.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
Manuscript presents analysis of how two coal seams with dip of 45 degrees could be mined using later backfilling, while being primarily excavated by sublevel caving. Authors utilize analytical approach to determine necessary strength of the backfilling material, as well as numerical 3D model for the sequenced analysis of mining process.
Major flaw that is found here is that modelled case is not achievable in practice, since authors anlyzed open underground space that is significantly larger than possible for such rock formations. This means that mined stope is to be under collapse before backfilling could take place. Most of the rocks are reported to be 25-30 MPa (compressive strength), while rocks in the middle of the coal seams are reported to be extraordinary strong for such formations (up to 98MPa). Authors do not provide results of rock mechanics testing to support these values nor explain them. On the other side, backfilling methodology is not explained with enough details, so it remains unclear how is backfilling material installed. Authors should report data and foundations for research in clear and easily understandable way. Overall terminology and language check is required.
Having in mind above statements it is recommended that manuscript is rejected in its current form.
Reviewer 2 Report
Please see the comments for editors
Reviewer 3 Report
This paper exhibited the design, the numerical simulation of the filling-mining process, and some detection results of the Wudong Coal Mine. However, the scientific significance is not strong. The authors are suggested to greatly improve the writing, organization, and details of the paper for the publication of the current work. The following are some suggestions:
(1) There are so many grammatical errors and the English expression is poor. The writing should be improved significantly.
(2) The authors are suggested to highlight the significance of their work.
(3) In section 1.2, the symbols in equations and sentences should be in a unified format, such as M1(x) and M3(x).
(4) In section 2.1, why the author used FLAC3D as the numerical tool? During the FLAC3D simulation, what constitutive model and rock failure models were used?
(5) Could the author explain the six sublevels mining process in detail?
Reviewer 4 Report
The paper titled: “Research on Reducing Mining-induced Disaster by Filling in Steeply Inclined Thick Coal Seam” was reviewed. The manuscript must be completely reviewed for the proper use of punctuations. Also several typos were observed that should be corrected in the text.
The authors should respond to the following comments and submit the revised version of the manuscript for the second round of review.
Please respond to the following comments:
Line 113: Based on the Figure 1, the dip angle is 40 degree and should be measured with respect to the horizontal plane. Please correct the figure and text. Text need extensive punctuation edits. Line 194: what is “gaped goaf”? Any filling method adopted needs to be explained in the text. Line 206, Table 1: how soil parameters are calculated? Has any lab testing completed on the filling materials? How the initial stress condition has been implemented in the model? Please add. Figure 6: It would recommend presenting a 3D shape of the model in the text. What is the hydrostatic pressure in mine and how this has been modeled? Line 217: What is “S” type stress distribution feature? What are the shear strength parameters used in the model for the backfill and bedrock interface? Please add. Figure 7: what is the unit used in the legend? All Figures containing the results should have vertical and horizontal axes showing the distance and ground elevation. Figure 8: what is the level unit used in the figure? Line 229 and 320: check the grammar/structure. Line 240: check the grammar. Line 261: The stress transfer mechanism from the backfill to the side walls in a narrow mine stope is called arching effect. This needs to be understood from the results and discussed further in the text as the this is the main stress distribution in the backfill and surrounding rocks. Line 272: repetitive sentence. Lines 203 and 281: repetitive information. Figure 14: Please add the color legend? Line 354: Can you validate the accuracy of the proposed equation using the results of the numerical model? There are different analytical solution and numerical model, as well as the radar technique, but the results were not considered in unison to analysis the data and to derive conclusion from the current study. For that reason the connection and idea floe between the Sections and their results are missing. This needs to be improved in the text.
