## 6 Conclusions  
This study performs an optimized design to simplify construction while maintaining reliable connection performance based on the prevailing form of corrugated pipe-restrained grout anchor lap connections. It conducts mechanical performance tests on the corrugated pipe-restrained grout anchor lap connections to evaluate the influence of grouting material strength, anchorage length, and U-shaped stirrup spacing on grout anchor lap joints' bond strength and failure modes. From the experimental data, several conclusions can be drawn:  
(1) The specimens predominantly underwent two failure modes: anchorage failure, characterized by the steel bar being pulled out, and tensile failure, where the steel bar fractured. Specimens experiencing anchorage failure had shorter anchorage lengths; at the time of failure, the grout channel was entirely penetrated, and the corrugated pipe was dislodged. In addition, no noticeable surface cracks were observed, indicating that the specimen's overall integrity was largely preserved. Conversely, specimens experiencing tensile failure of the steel bar had longer anchorage lengths and showed no significant surface cracks, maintaining overall structural integrity.  
(2) The bond anchorage performance correlates positively with the strength of the grouting material and the anchorage length of the grout steel bar. Specimens with medium and low-strength grouting materials failed to meet the performance criteria specified. As the strength of the grouting material increased, so did the bonding force of the steel bar, leading to improved bond anchorage performance.  
(3) The anchorage length of the grout steel bar markedly influences the specimens' anchorage performance. For a given grout strength, a longer anchorage length results in a higher strain value for the steel bar under identical loads. Once a specimen's anchorage length reaches the basic length stipulated in the relevant codes, it can progress through the complete stages of elasticity, yielding, strengthening, and necking of the steel bar. The failure mode is marked by the tensile failure of the steel bar, indicative of robust bond anchorage performance.  
(4) The placement of U-shaped stirrups external to the corrugated pipe augments the confinement effects on the corrugated pipe and the grouting material while modestly enhancing the bonding force on the anchoring reinforcement.  
Conceptualization, F.L.; methodology, H.Q. and F.L.; software, F.L. and H.Q.; validation, F.L., H.Q., Z.Z. and H.Z.; formal analysis, F.L., H.Q. and Z.Z.; investigation, F.L. and H.Q.; resources, H.Q.; data curation, H.Q.; writing--original draft preparation, F.L.; writing--review and editing, F.L., H.Q., Z.Z. and H.Z.; supervision, H.Q. funding acquisition, H.Q. and H.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (No. 51978631), Program for Innovative Research Team (in Science and Technology) in University of Henan Province (Grant no. 23 IRTSTHN006), and Key Scientific Research Project in University of Henan Province (No. 23A560009).  
Not applicable.  
**Acknowledgments:** The authors appreciate the financial support provided by the National Natural Science Foundation of China (No. 51978631), Program for Innovative Research Team (in Science and Technology) in University of Henan Province (Grant no. 23 IRTSTHN006), and Key Scientific Research Project in University of Henan Province (No. 23A560009).  
**Conflicts of Interest:** Author [PERSON] was employed by the company SCSCEC Zhongyuan Architectural Design Institute Co., Ltd. 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.