A review on Pedestal Piles-Paper

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This paper reviews experimental, numerical, and analytical research on pedestal (belled) piles, which have enlarged bases and are used to support structures exposed to substantial uplift, lateral, and vertical loads, including transmission towers and offshore facilities. Their enlarged bases mobilize more surrounding soil than straight-shaft piles, potentially improving resistance and reducing effects such as negative skin friction.<br /><br />Research reviewed includes small- and full-scale load tests, field studies, finite-element analysis, and the Material Point Method. Findings show that uplift capacity depends on pile geometry, embedment, soil properties, and installation conditions. In sand, bells placed near the ground surface provide little uplift benefit, while increasing bell angle can reduce uplift resistance. Denser sand generally improves uplift capacity; longer embedment and, in sloping ground, greater distance from the slope edge also increase resistance. Geocell reinforcement can further improve uplift capacity, although increasing its height beyond about 100 mm showed little additional benefit in the cited tests. The benefit of increasing the bell-to-shaft diameter ratio becomes less pronounced above approximately 1.67.<br /><br />For lateral loading, belled piles generally outperform straight piles, with resistance increasing with sand density. One reviewed study found the best lateral performance at a bell angle of 45°. Under oblique loading, uplift capacity decreases as load inclination increases; soil stiffness can have a stronger influence than friction angle. For vertical loading in sand and gravel, full-scale tests reported belled piles with capacities up to about 5.5 times those of straight piles, provided the base was properly cleaned.<br /><br />Overall, the reviewed evidence indicates that pedestal piles can substantially improve foundation capacity, but performance depends on soil type, pile dimensions, loading direction, and construction quality.
Keywords
pedestal piles
belled piles
uplift capacity
lateral loading
finite element analysis
Material Point Method
soil reinforcement
sand density
bell angle
foundation capacity