# Stability Control of Multilayer Roof Strata in the Large Mining Height Gob-Side Entry: A Case Study
## 5 Conclusions  
A systematic study was conducted on the mechanical mechanisms of roof failure and delamination in the large mining height gob-side entry, and implemented in the 22301 working face in Tunlan Mine. The following conclusions were drawn:  
1. The 22301 working face exhibits typical characteristics of a compound roof. Within a 40-m range ahead of the working face, the development of internal fractures and the state of roof fragmentation in the surrounding rock decrease as the distance away from the working face increases. Shallow fractures primarily present circumferential damage characteristics, while deeper fractures predominantly show longitudinal damage characteristics. The area within 1.2 m of the shallow roof layer is identified as a high-frequency location for roof delamination.
2. By mechanically analyzing the interaction between the side cemented backfill and roof structure, the key points of the supporting scheme have been derived, e.g., ensuring the stability of immediate roof above the filling area, transferring the resistance from the cemented backfill to the roof structure and maintaining self-supporting capacity. Correspondingly, control techniques for stabilizing the roof structure have been proposed: (a) Employing high-prestressed, high-stiffness anchor cable support to enhance the bearing capacity of the anchorage structure above the fill area, ensuring roof integrity and load transfer capability; (b) Controlling the reasonable length of initial filling backfill to recover the three-dimensional stress state; (c) Using hydraulic support to facilitate pressure transfer in the filling area.  
Figure 13: On-site supporting results of the 22301 gob-side entry.  
3. The industrial application of the gob-side entry retaining technique in Tunlan Mine has shown that the surrounding rock deformation ahead of the working face was minimal. The roof subsidence primarily occurred within 10 to 70 m behind the working face, with a maximum roof-to-floor convergence within the range of 440 mm, side convergence within the range of 270 mm and roof delamination within the range of 40 mm. The anchors and cables performed well, effectively controlling the gob-side entry deformation and meeting the safety requirements for coal extraction in the 22301 working face.  
Conceptualization, Y.C.; Methodology, Y.C. and Y.W.; Software, Y.W. and Z.Q.; Investigation, Z.Q.; Resources, Y.C.; Data curation, F.Y.; Writing--original draft, Z.Q.; Writing--review & editing, V.A. and Z.Q. All authors have read and agreed to the published version of the manuscript.  
This research was financially supported by the National Natural Science Foundation of China (No. 52174135, 52174136) and Key Research and Development Projects for University-Enterprise Cooperation in Lvliang City (No. 2022 XDHZ16).  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author upon reasonable request.  
Author [PERSON] was employed by the company China Coal Consultant International. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.