Author(s): Miguel Ferreira, Ana Sousa, João Martins and Beatriz Oliveira

Abstract: Expansive soils pose significant challenges to foundation engineering due to their pronounced shrink-swell behavior, which induces considerable structural distress through uplift forces, heave pressures, and reduced load-bearing capacity. This study investigates the behavior of pile foundations embedded in expansive soils subjected to cyclic wetting and drying, focusing on variations in axial capacity, uplift displacement, and load transfer mechanisms. A series of controlled laboratory experiments were conducted using mild steel model piles of varying diameters and lengths. Load-displacement and uplift tests were performed across multiple moisture cycles to evaluate the effects of pile geometry and environmental conditions on performance. Results revealed a progressive reduction in pile capacity with successive moisture cycles, accompanied by an increase in uplift displacement and a redistribution of shaft resistance from the toe to upper segments. Larger diameter and deeper piles consistently exhibited superior performance, retaining a higher percentage of their initial capacity and resisting heave-induced uplift more effectively. Statistical analysis confirmed that pile diameter was the dominant factor influencing capacity, while moisture cycling contributed significantly to performance degradation. The study concludes that integrating geometric optimization, moisture management, and depth-dependent shaft behavior modeling can significantly improve the design and durability of pile foundations in expansive soil environments. These findings provide valuable guidance for designing safer and more resilient infrastructure in regions affected by expansive clays.

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