Conceptual Axial Stress-Strain Behavior Assessment of Drilled Displacement Piles Using Full-Scale Load Tests Database-Paper

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The study evaluates the axial load–displacement behavior of drilled displacement (DD) piles using a database of 40 full-scale static load tests. The cases cover six pile types, diameters of approximately 350–650 mm, embedment depths of 7–19.5 m, and clay, sand, and mixed soil deposits.<br /><br />To compare results across different pile sizes, the researchers converted load–displacement records into pressure versus displacement-to-diameter curves. They assessed ultimate pressure using the 5% and 10% displacement-to-diameter criteria and the Brinch-Hansen 80% method. The analysis focused on embedment depth, pile breadth, and surrounding soil, examining initial stiffness and pressure at 5% relative displacement.<br /><br />Longer piles generally showed greater initial stiffness and higher pressures, while narrower piles tended to perform better than wider piles. Soil conditions also mattered: piles in mixed deposits generally had the highest stiffness, ultimate pressure, and energy absorption; clay cases tended to have the lowest performance, with sand typically intermediate.<br /><br />The study also proposes using toughness—the area beneath the pressure–relative displacement curve up to 1 inch of displacement—to represent the pile–soil system’s capacity to absorb deformation energy. Toughness was greatest for piles that were more deeply embedded, narrower, and installed in mixed soils.<br /><br />The authors conclude that normalized load–displacement analysis and toughness can support comparisons between DD pile configurations and inform foundation design. These findings may be particularly useful where energy dissipation under dynamic or seismic loading is important.

Keywords

drilled displacement piles

axial load-displacement

full-scale static load tests

ultimate pressure

embedment depth

initial stiffness

soil conditions

pressure-displacement curves

toughness

foundation design