## 6 Conclusions
For example, in soft clay with an unconfined compressive strength below 50 kPa, 0.8 m close-packing is used to offset the rapid attenuation of stress, while in sandstone with strength exceeding 60 MPa, it can be relaxed to 1.5 m to balance costs and support effects. In order to ensure that the shear adhesion force of the bolt-soil interface is not less than 1.2 MPa, the grouting construction needs to strictly control the water-cement ratio (\(\leq\)0.45) and realize the complete wrapping of the expansion pipe. The field test shows that the ratio can reduce the slurry porosity in silty clay (cohesion 30 kPa) by 25% and significantly improve the interface bonding performance. 5. On-site performance verification scheme: In order to systematically evaluate and optimize the engineering applicability of the anchor rod, a three-stage on-site performance verification process is proposed: firstly, the pull-out test requires incremental loading (rate 10 \(\mathrm{kN/min}\)) on 5% (no less than 15) of the installed anchor rod until it reaches 90% of the theoretical maximum pull-out force (432.8 MPa) to verify its short-term bearing capacity; secondly, the durability assessment should be combined with an accelerated aging test (such as 500 h of salt spray exposure) and half-year on-site inspection to monitor the corrosion rate and prestress loss of the anchor rod to ensure its long-term stability in the eroded environment; finally, the clamping force of the bolt-soil interface is monitored in real time by embedding a pressure sensor and the clamping force is required to maintain more than 80% of the initial value (120-150 kN) within 24 months, so as to quantify the cooperative working performance of the bolt and the surrounding rock. The comprehensive test framework can provide data-driven decision support for bolt support design in complex strata. The optimized bolt is verified by numerical simulation. The results show that the optimized hollow grouting bolt with an umbrella-shaped expansion head with an expansion pipe has significantly improved the pull-out bearing capacity, shear resistance, and reinforcement effect on the surrounding soil. The specific performance is as follows: (1) The maximum drawing force of the umbrella-shaped expansion head can be increased by up to 35%, and the load transfer is more uniform; (2) The fixed range of the expansive body section compared to the loose circle is expanded by 45%, which effectively inhibits the loosening and deformation of the soil. (3) The cooperative working performance of the bolt and the soil is significantly enhanced, and the overall stability is significantly improved. The numerical simulation results are in good agreement with the theoretical analysis and experimental data, which verifies the rationality and reliability of the optimization. Conceptualization, J.X. and Y.L. ([PERSON]); methodology, T.W., Y.L. ([PERSON]) and J.X. ; software, T.W. and Y.W. ([PERSON]); validation, T.W. and Y.L. ([PERSON]); formal analysis, Y.W. ([PERSON]); investigation, Y.W. ([PERSON]) and B.Z. ; resources, J.X. ; data curation, T.W. and Y.W. ([PERSON]); visualization, T.W. and Y.G. ; supervision, Y.G. ; writing--original draft preparation, T.W. ; writing--review and editing, Y.L. ([PERSON]), Y.L. ([PERSON]) and B.Z. ; funding acquisition, J.X. and [PERSON]. ([PERSON]). All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author. The authors declare no conflicts of interest.