An Experimental Investigation on the Benefits of a Hybrid Pile/Footing System on Sand-PPT Presentation

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The study experimentally investigated a hybrid pile/footing system in loose, dry Leighton Buzzard sand. Small open-ended steel pipe piles were fitted with square bearing plates of either 2D or 3D width (where D is the pile diameter). Tests measured load and penetration as the pile and plate were driven, with repeated trials and controls intended to maintain consistent sand density and test conditions.<br /><br />The plate-equipped piles showed stiffer load–settlement responses than the pile alone. The 3D plate produced the greatest increase in stiffness and capacity, along with more pronounced post-peak softening, which the authors associate with greater soil densification. The measured response was relatively consistent across trials, although manual pile installation and soil-preparation variability caused some differences.<br /><br />Conventional bearing-capacity theory substantially underestimated the observed capacity. The authors proposed an iterative back-calculation method that accounts for changes in soil density during loading. It produced critical friction angles of 34.5° for the 2D plate and 35.5° for the 3D plate, broadly consistent with published values for the sand.<br /><br />A hypothetical full-scale example suggested that, for a 2 MN capacity, a 2D plate could reduce pile penetration from 7.8 m to 6.5 m, while a 3D plate could reduce it to 3 m. Such reductions could save steel, costs, and embodied carbon. Potential applications include loose sand, limiting settlement, and increasing resistance to scour. However, the benefits may diminish for longer piles, and settlement, test variability, and the performance of different pile types require further consideration.

Keywords

hybrid pile footing system

loose dry sand

open-ended steel pipe piles

bearing plates

load-settlement response

soil densification

bearing capacity

friction angle

pile penetration reduction

embodied carbon savings