Impact of flooding on the bearing capacity of a preloaded single piled raft in collapsible soils

This study investigates the performance of a preloaded single piled raft foundation built in collapsible soil and subjected to surface flooding, focusing on changes in load-bearing behavior. A full-scale field test was conducted in Uberlândia (MG), Brazil, complemented by three-dimensional finite element modeling using RS3 software. The novelty lies in jointly evaluating preloading and flooding effects on a real-scale piled raft foundation, a scenario rarely addressed in the literature. Results showed a significant reduction in bearing capacity under flooding (≈35%), causing a clear failure, whereas preloading effectively mitigated settlements by densifying the soil and increasing stiffness beneath the pile cap. Load transfer analysis indicated that the pile shaft carried the largest share of the load (50–80%), followed by the raft (10–30%) and pile tip (<20%). These findings provide new insights into the design of mixed foundations in tropical regions under extreme moisture conditions.