Research on stress release for the gob-side roadway using the roof-cutting technology with a chainsaw arm

The narrow pillar mining method is widely adopted for working faces in coal mines. However, in cases of an overlying hard roof, a suspended triangle roof plate or a cantilever will be formed near the goaf. At this point, the coal pillar extrusion and serious deformation will occur in the gob-side roadway. In order to mitigate the problem, the roof-cutting technology with a chainsaw arm and its equipment have been developed. In this paper, based on the analysis of deformation and failure characteristics of 2312 roadway, which is close to the goaf of 2311 working face in Tashan Coal, the roof-cutting technology with a chainsaw arm was chosen to be applied in 2311 roadway. Then, the roof-cutting process and the load acting on the coal pillar were discussed and analysed. A numerical model was established to analyse the stress releasing effects after roof cutting. Moreover, the roof-cutting height and the support parameters of the roadway were optimized through numerical analysis and the results manifested that the roof cutting was the most effective when the roof-cutting height was 6.4 m. After roof cutting, the vertical stresses within the coal pillars were lowered by about 25.0%. Finally, the roof-cutting experiment was carried out in the 2311 roadway in Tashan Coal Mine. The on-site roof-cutting depth was 6.4 m and the roof-cutting width was 42 mm guided by the numerical analysis. To verify the stress-relieving effects, the borehole stress meters were applied to monitor the peak advancing stresses of narrow pillars at various depths. The measured results indicated that the peak advancing stresses decreased by 22.8% on average, and therefore, roof cutting and stress releasing effects were achieved.

chainsaw arm proposed by the author can effectively form continuous cutting cracks and effectively solve the problem of coal pillar pressure relief. In this paper, the numerical calculation method is mainly used to give the rule of stress change of coal pillar before and after pressure relief, and optimize the roof-cutting height and anchor cable support parameters. On the whole, the paper structure is reasonable and detailed, which is a good academic paper. Therefore, I suggest that the article can be accepted after revision. At the same time, there are also the following problems that the authors need to consider: 1. In Chapter 5.1.1 of this paper, the author describes the relationship between the stope rock mass and the rock mass in the experiment, but mechanical parameters needed to reduce should be given, firstly. Is whether the mechanical parameters correspond to the formula (4) -(5). 2. The roof-cutting technology with chainsaw arm is an innovative technology. Does it also have other engineering application or application prospect in the field of coal mine, such as floor pressure relief or non-pillar mining technology? 3. The author gives the reasonable roof-cutting height and the corresponding supporting parameters. These parameters are aimed at the special geological conditions of Tashan Coal Mine of the same coal group. Are they worth popularizing and applying? 4. It is an important parameter that coal pillar on the boundary in numerical simulation. Please give the specific value in the paper and explain the basis of selecting the value? 5. Figure 7 shows the vertical stresses and the failure areas of surrounding rock after the roadway excavation, after mining without roof cutting and after mining with the roof cutting. Meanwhile, the vertical stresses on top of narrow pillars were extracted。 There are some inaccuracies in the author's statement. Please check it carefully and give corresponding modifications. 6. Hoek Brown criterion is a common rock criterion in recent years. The value of D is a core parameter affecting rock strength. The author chooses 0 here, and please give a reason.

Dear Dr Tai
On behalf of the Editors, I am pleased to inform you that your Manuscript RSOS-191663 entitled "Research on Stress Release for Gob-Side Roadway Using Roof-Cutting Technology with Chainsaw Arm" has been accepted for publication in Royal Society Open Science subject to minor revision in accordance with the referee suggestions. Please find the referees' comments at the end of this email.
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Reviewer comments to Author: Reviewer: 1 Comments to the Author(s) In the narrow pillar mining technology, the deformation and failure of the free roadway is one of the common problems in the coal mine. In this paper, Research on Stress Release for Gob-Side Roadway Using Roof-Cutting Technology with Chainsaw Arm, the roof-cutting technology with chainsaw arm can solve the above problems well and has outstanding engineering value. At the same time, the key of roof cutting is optimized by theoretical derivation, numerical calculation and engineering test. The structure of the paper is reasonable, the chart processing is exquisite and the discussion is detailed, which reflects the author's good scientific research ability. Therefore, this paper suggests that the paper should be accepted after revision. At the same time, the paper also has the following small problems: 1) There are some punctuation problems in some parts of the article, such as page 2 line 46. Floor weave, two ended anchor cable failure, the coal wall failure, coal pillar failure and etc take place in the roadway.
2) Why the numerical simulation is adopted after the theoretical calculation in this paper. What is the relationship between the both method? Is it mutual verification or theoretical calculation has some shortcomings? Please give an explanation.
3) There are some unclear expressions about formula (4) and (5) in this paper. Please give some explanations. Are σcm and Ecm the corresponding reduced uniaxial compressive strength and elastic modulus in the stope? 4) In Page5 Line 29, the author uses load to replace the effect of overlying surrounding rock on the working face. Is this simplification reasonable? Is there any reference to use this method? Please give a detailed explanation. 5) In Page 5 Line 36-38, the author's statement is not accurate. Please check it carefully and give corresponding modification. 6) Whether the chainsaw arm machine can cut the roof at a certain angle, and whether the rock collapse angle is considered, please give some explanation.
Reviewer: 2 Comments to the Author(s) The narrow pillar mining technology in this paper "Research on Stress Release for Gob-Side Roadway Using Roof-Cutting Technology with Chainsaw Arm" is one of the commonly used mining methods in China, and the problem of gob-side roadway described in this paper is also a prominent problem in the narrow pillar mining technology. The roof-cutting technology with chainsaw arm proposed by the author can effectively form continuous cutting cracks and effectively solve the problem of coal pillar pressure relief. In this paper, the numerical calculation method is mainly used to give the rule of stress change of coal pillar before and after pressure relief, and optimize the roof-cutting height and anchor cable support parameters. On the whole, the paper structure is reasonable and detailed, which is a good academic paper. Therefore, I suggest that the article can be accepted after revision. At the same time, there are also the following problems that the authors need to consider: 1. In Chapter 5.1.1 of this paper, the author describes the relationship between the stope rock mass and the rock mass in the experiment, but mechanical parameters needed to reduce should be given, firstly. Is whether the mechanical parameters correspond to the formula (4) -(5).
2. The roof-cutting technology with chainsaw arm is an innovative technology. Does it also have other engineering application or application prospect in the field of coal mine, such as floor pressure relief or non-pillar mining technology?
3. The author gives the reasonable roof-cutting height and the corresponding supporting parameters. These parameters are aimed at the special geological conditions of Tashan Coal Mine of the same coal group. Are they worth popularizing and applying? 4. It is an important parameter that coal pillar on the boundary in numerical simulation. Please give the specific value in the paper and explain the basis of selecting the value? 5. Figure 7 shows the vertical stresses and the failure areas of surrounding rock after the roadway excavation, after mining without roof cutting and after mining with the roof cutting. Meanwhile, the vertical stresses on top of narrow pillars were extracted。 There are some inaccuracies in the author's statement. Please check it carefully and give corresponding modifications.

6.
Hoek Brown criterion is a common rock criterion in recent years. The value of D is a core parameter affecting rock strength. The author chooses 0 here, and please give a reason.

03-Feb-2020
Dear Dr Tai, It is a pleasure to accept your manuscript entitled "Research on Stress Release for Gob-Side Roadway Using Roof-Cutting Technology with Chainsaw Arm" in its current form for publication in Royal Society Open Science. The comments of the reviewer(s) who reviewed your manuscript are included at the foot of this letter.
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