In Situ Tests and Numerical Simulation Study on the Tensile Bearing Capacity of Large-Anchor-Plate Helical Anchors for 500 kV Transmission Towers

Compared with multi-helix small-diameter anchor group foundations, the single large-diameter helical anchor foundation exhibits superior mechanical behavior and construction convenience, and has therefore been progressively promoted and applied in transmission tower construction. In this study, in situ static load tests on the tensile capacity of four single large-diameter helical anchors were conducted at a 500 kV transmission tower construction site in the Songyuan area, and 19 finite element models were established to analyze their mechanical behavior. Based on the cylindrical shear failure model of soils and the Mohr–Coulomb strength criterion, analytical formulae for the ultimate tensile capacity were derived. The research results indicate that no apparent failure occurred in the soil surrounding the helical anchors. The load–displacement and loading time–displacement curves obtained from the tests are characterized by stable and reliable data, and the trends among different specimens are generally consistent. The ultimate tensile capacity of the helical anchors is 1260 kN. When the helix spacing ratio S/D = 3, the uplift capacity is 1063 kN, which is 46% higher than that at S/D = 1. When the number of helix plates is 3, the uplift capacity is 1314 kN, which is approximately 2.2 times that of the single-helix-plate case (593 kN). Therefore, the influence of the helix plates on the uplift displacement is more significant than that of the anchor shaft. The discrepancies between the theoretically derived tensile capacity and the experimental values and numerical simulation results are relatively small, indicating that the theoretical results have good accuracy and may reflect the load-bearing characteristics of large-diameter helical anchors.