## 7 Conclusions  
(1) Six rock bolts at the roadway roof were selected on site to analyze their deformation characteristics. It was found that the bending and shear deformation of the rock bolts in the middle of the roadway roof was relatively small, and slight shear deformation occurred at the interface between the roof and the coal seam, with the lateral shear dislocation being 3.7 cm and 3.3 cm, respectively. However, the rock bolts at the two top corners of the roadway showed obvious shear deformation at the interface between the roof and the coal seam, with the lateral shear dislocation being 16.2 cm and 15.6 cm, respectively.  
(2) A \"break-tension-suture\" method for applying the pretension force of the pile unit simulation rock bolt was proposed. The interface was used to simulate the weak surface of the layered composite roof structure, and a reasonable calculation sequence of the stress field of the surrounding rock before and after the rock bolt was invented. Using the above simulation method to invert the deformation characteristics of the on-site rock bolts, it was found that the simulated deformation form and degree of the rock bolts were relatively consistent with the on-site situation. The lateral dislocations of 1\({}^{\#}\) and 3\({}^{\#}\) rock bolts on site and in the simulation were 16.2 cm, 13.3 cm, 3.7 cm, and 4.1 cm, respectively, indicating that the simulation method was reliable, the parameter selection was reasonable, and the calculation sequence was consistent with the actual excavation process.  
(3) A unified model of deformation and stress evolution of rock bolts in the layered composite roof roadway was constructed. The influences of the strength of the surrounding rock and the strength of the structural plane on the shear and bending deformation of the rock bolts were analyzed. It was found that the influencing factors of the rock bolt deformation were the strength of the structural plane > the strength of the surrounding rock. When the strength of the structural plane was low, the strength difference between the upper and lower rock layers was large, and the weak rock layer was located below the structural plane, the rock bolts were most prone to lateral dislocation.  
(4) This study found that the deformation of the top corner bolt was the largest, and on-site measurements were conducted to strengthen the top corner bolt monitoring. Furthermore, regarding the impact of structural deformation on bolts, grouting reinforcement can be adopted on site to ensure the integrity of the roadway roof. This article did not change the pretension force of the bolts in the simulation. However, on-site practice has shown that the active restraining force provided by high pretensioning bolts can not only limit the opening of weak surfaces in the structure, but also increase the shear strength of the structural surface and suppress its activity. Thus, future research will focus on the influence of pretension on bolt deformation.  
[PERSON] and [PERSON] conceived and designed the study. [PERSON] and [PERSON] were involved in the numerical simulation and analysis. [PERSON] was involved in the field measurement and prepared all figures. All authors have read and agreed to the published version of the manuscript.  
Financial support for this work is provided by the National Key R&D Program of China (2023 YFC2907602), the Science and Technology Innovation and Entrepreneurship Fund of Tiandi Science and Technology Co., Ltd. (2023-TD-ZD011-001), the National Natural Science Foundation of China (52104155), and the Fundamental Research Funds for the Central Universities (2024 ZKPYNY01).  
All data used to support the findings of this study are available from the corresponding author upon request.  
The authors declare no conflicts of interest.