## 7 Conclusions  
Through the simulation test bed of a composite rock stratum, the distribution law of the prestress field of bolt support under different surrounding rock lithology and anchorage lengths is obtained, and the optimization of the anchoring method and anchoring position is proposed. The main conclusions are as follows.  
(1) The main action area of anchor bolt prestress on surrounding rock is in the range of the free section of bolt body. Shortening the anchorage length properly and setting a certain length of free section is conducive to the full effect of pretightening in the surrounding rock. However, if the length of anchoring section is too small, it is not conducive to the  
Figure 11: Mine pressure monitoring of roadway: (**a**) roadway deformation monitoring; (**b**) bolt stress monitoring.  
Figure 10: Dynamic pressure coal roadway with soft intercalated composite roof.  
transmission of compressive stress in the axial direction of the anchor bolt, and the reliability of anchoring will also be reduced.  
(2) In the composite rock stratum, the anchorage section should be arranged in hard rock as a priority, which is beneficial to the enhancement and diffusion of the stress peak value in the upper compressive stress zone of the free section of the bolt body and, to a certain extent, increases the restraint ability of the free section on the surrounding rock, further improving the surrounding rock's control of the free section area.  
(3) The relative position between the anchorage section of the anchor bolt and the structural plane should be reasonably controlled in the composite rock stratum. If the effect of horizontal stress on the surrounding rock is not considered, the structural plane can be in the range of high compressive stress by shortening the anchorage length; if the influence of horizontal stress on the interlayer dislocation of the composite rock stratum is considered and the anchorage section is needed to improve the overall shear capacity of the bolt, the anchorage length should be appropriately extended to ensure that the structural surface is located at the middle and back of the anchorage section so as to avoid the area of concentrated tensile stress and reduce the influence of tensile stress on the structural plane.  
(4) These conclusions apply to the \"hard intercalated\" and \"soft intercalated\" composite roofs in Qinyuan Mining Area; they may better ensure the stress state of the bolt and effectively control the deformation of the roadway, achieving good results.  
Software, J.Y. and C.Z.; Formal analysis, Y.Z.; Investigation, Y.Z., D.L. and B.H.; Data curation, Y.Z. and D.L.; Writing--original draft, Y.Z.; Writing--review and editing, J.Y. All authors have read and agreed to the published version of the manuscript.  
This study was supported by the Special Project of Science and Technology Innovation and Entrepreneurship Fund of Tiandi Science and Technology Co., Ltd. (2023-2-TD-RC005). This study was also supported by the National Natural Science Foundation of China (52304141) and the Natural Science Foundation of China (U2106203).  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the data involving trade secrets.  
Thanks to the Yongqing Branch of China Coal Technology and Engineering Group for providing the test site, and to Qinxin Coal Mine of Shanxi Qinxin Coal Industry Co., Ltd. for providing the on-site industrial test site.  
Authors [PERSON], [PERSON] and [PERSON] were employed by the company China Coal Research Institute. Authors [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] were employed by the company CCTEG Coal Mining Research Institute. The authors declare that the research was conducted in the absence of any commercial or financial relation-ships that could be construed as a potential conflict of interest.