PIV analysis of the ground behavior at pile tip by vertical load test of model piles with and without expanded bottom as a variable.-Paper

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This study used particle image velocimetry (PIV) to examine soil behavior around the tips of straight and belled piles under vertical loading. Tests were conducted in dense Toyoura sand using a transparent, pressurized tank, with single piles and two-pile groups. The researchers varied overburden pressure (100 or 300 kPa), pile geometry, and pile spacing.<br /><br />For single piles, soil displacement extended roughly 2.5–3 pile-tip diameters below the tip. In both pile types, downward movement formed a wedge beneath the tip, with soil outside the wedge moving diagonally downward. Lower overburden pressure generally produced greater horizontal displacement. Shear-strain patterns developed similarly for straight and belled piles as settlement increased.<br /><br />For pile groups, the deformation patterns reflected the overlap of the individual piles’ failure zones. At close spacing, the soil between the piles was constrained, and the group behaved more like a single, wider pile. At wider spacings, horizontal movement occurred between the piles. Under low overburden pressure, this movement was greater for belled piles than for straight piles; the difference was smaller under higher pressure. Vertical displacement showed little sensitivity to pile geometry or spacing.<br /><br />These findings indicate that pile shape, spacing, and overburden pressure affect soil interaction within a group, and suggest that group-pile effects may differ between belled and straight piles. Further testing is needed to determine how these deformation differences influence bearing capacity.

Keywords

particle image velocimetry

PIV

soil deformation

straight piles

belled piles

vertical loading

pile groups

overburden pressure

Toyoura sand

bearing capacity