Screw and Straight Pile Behavior under Cyclic Compressive Loading in Dense Sand-Paper

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The study compares the compressive performance of single-helix screw piles and straight pipe piles in dense sand under monotonic and rapid cyclic loading. Model tests used closed-ended steel piles with the same 60 mm tip diameter in Toyoura sand compacted to 80% relative density. To ensure comparable ground conditions, piles were placed in the prepared soil rather than installed using their usual methods. Cyclic tests applied 15 loading–unloading cycles at 50% of each pile’s monotonic ultimate capacity, followed by loading to failure.<br /><br />Cyclic loading changed the load–settlement response and reduced ultimate capacity for both pile types. Capacity fell by 8.6% for the screw pile and 14.5% for the straight pile. Despite this greater cyclic reduction, the straight pile had 27.9% higher ultimate capacity than the screw pile in monotonic tests. The authors suggest that rapid cycling may loosen dense sand around the pile tip, though this mechanism requires further investigation.<br /><br />Helix bending also affected performance: piles with a deformed, thin helix experienced larger capacity reductions under cyclic loading than non-deformed piles, and settlement during cycles was greater. Overall, the findings show that cyclic loading and helix deformation can reduce pile capacity, with helix deflection becoming more consequential under repeated loading. The results are based on model-scale tests and should be validated in further research.

Keywords

compressive performance

single-helix screw pile

straight pipe pile

dense sand

monotonic loading

rapid cyclic loading

ultimate capacity

load-settlement response

helix deformation

model tests