Optimization of steel anchor pile configurations for enhanced pullout resistance in expansive soil foundations

This study aims to predict the pullout behavior of steel anchor piles in saturated expansive soil using finite element method-based PLAXIS 3D CONNECT Edition V22 software. It inspects the effects of varying pile parameters and spacings for a displacement of 10% of the pile diameter. The study evaluates the performance of single and group anchor piles by comparing square configurations (2 × 2, 3 × 3, and 4 × 4) at varying centre-to-centre (c/c) spacings of 2.5D, 3D, and 3.5D, where D is the pile diameter. The numerical analysis reveals that increasing the pile length (L) and diameter (D) significantly improves the uplift (pullout) capacity of the piles. Furthermore, the group efficiency-defined as the ratio of the total uplift capacity of a pile group to the sum of individual pile capacities-was assessed to understand the interaction effects among piles at different spacings. Results indicate that optimal spacing enhances efficiency by minimizing negative group interaction and maximizing load resistance. The pullout force in pile groups increases with the number of piles, but group efficiency decreases as the number of piles rises. The efficiency of the anchor pile system showed minimal variation when spacing increased from 3 D to 3.5 D, suggesting that 3 D is the optimum spacing for group anchor pile systems. The findings contribute to a better understanding of how pile configuration and spacing influence uplift resistance in expansive soils, aiding in the practical design and optimization of foundation systems.