Study on the Pullout Performance and Failure Mechanism of the UHPC-Grouted Helical Anchor Rod-Prefabricated Cap Connection Joint

During the construction process of prefabricated helical anchor foundations, eccentricity and inclined installation of anchor rods may alter the stress distribution and interfacial load-transfer mechanism within the UHPC grouting connection zone, resulting in the inability of performance evaluation methods established under ideal installation conditions to fully capture the joint response under actual construction scenarios. In this study, five full-scale pullout tests and three-dimensional nonlinear finite element analyses were conducted to investigate the load-transfer behavior, damage evolution process, and failure modes of UHPC-grouted helical anchor-prefabricated cap connection joints subjected to construction deviations. The results demonstrate that eccentricity primarily induces local stress redistribution and has a limited influence on the bearing capacity, whereas inclination introduces additional bending moments that accelerate the initiation of interfacial damage. With the incorporation of shear keys, the damage-control load under non-eccentric conditions increased from 429 kN to 800 kN, representing an enhancement of approximately 86.5%. Based on the experimental and analytical results, a pullout performance evaluation method considering interfacial load-transfer characteristics and the influence of construction deviations was proposed. The maximum error was 7.5% under the single eccentricity condition and 18.0% under the combined eccentricity-inclination condition. The findings provide valuable references for the design optimization and performance evaluation of prefabricated helical anchor foundation connection joints under non-ideal construction conditions.