Experimental and Theoretical Analysis of the Pullout Characteristics of Inclined-Anchor Short-Pile Foundations

In response to the challenges of steep terrain, complex composite strata, and demanding foundation requirements for power transmission towers in mountainous regions of Southwest China, a composite foundation system of inclined-anchor short piles is proposed to enhance the pullout resistance of pile foundations. This study investigates the vertical displacement of the pile top, axial force distribution in the anchors, and the load-sharing characteristics of the inclined-anchor short pile under uplift loading through full-scale field tests, numerical simulations, and theoretical analyses. Results demonstrate that the proposed system significantly improves the uplift bearing capacity, with inclined anchors contributing up to 48% of the total load and effectively participating in load transfer and distribution. Parametric analyses reveal that increasing pile length reduces the load borne by the anchors, whereas increasing anchor diameter enhances their bearing role in the later stages of loading. Additionally, the load ratio of the anchor structure gradually decreases as the anchor angle increases. A theoretical model is developed based on elastic theory and pile–anchor deformation compatibility, accurately predicting internal forces and displacements, as validated by test data. A corresponding formula for calculating the load distribution coefficient of the anchors is also proposed. The findings provide a theoretical basis for foundation design in mountainous terrains, enabling full utilization of bedrock bearing capacity, reducing excavation depth and construction difficulty, and offering significant economic benefits.