Influence of Backfill Soil on the Uplift Bearing Capacity of Prefabricated Foundations for Temporary Transition Towers

In response to the non-reusable nature and prolonged construction period of traditional foundations for temporary and transitional towers, this paper designs a fully reusable all-metal prefabricated foundation for 35 kV–110 kV transmission lines. The uplift bearing capacity of the fully metallic prefabricated foundation was investigated through a series of eight reduced-scale model tests (scale 1:3). Weathered sand and silty clay were selected as backfill materials, with relative density and foundation embedment depth as test variables. The load–displacement curves were plotted, and the ultimate uplift capacity was determined based on the load corresponding to the onset of a sharp transition in these curves. The test results demonstrated that the ultimate uplift capacity of foundations with weathered sand backfill was significantly superior to that of counterparts with silty clay under comparable conditions. Specifically, at an embedment depth of 1.2 m and high relative density, the ultimate load of the weathered sand backfill was 33.3% higher than that of the silty clay backfill. The ultimate uplift capacity increased markedly with higher relative density. When the degree of compaction increased from 0.7 to 0.9, the ultimate capacity of the weathered sand backfill increased by 100.0%, substantially exceeding the 30.4% increase observed for the silty clay backfill. Furthermore, the ultimate capacity exhibited greater sensitivity to the embedment depth in weathered sand. As the embedment depth increased from 0.5 m to 1.2 m, the ultimate capacity of the weathered sand backfill increased by 191%, far surpassing the 114% increase for the silty clay backfill. This study provides experimental evidence and theoretical references for the design and construction of assembled foundations for temporary tower structures. The conclusions of this study are based on model test conditions and require further verification through prototype tests and numerical simulation.