Effect of Installation Method on the Ratio of Tensile to Compressive Unit Shaft Resistance of Piles in Dense Sand-Paper

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The study examines how pile installation method affects the ratio of tensile to compressive shaft resistance in dense sand. Researchers tested model piles in a half-cylindrical calibration chamber: piles were either monotonically jacked into the sand, representing displacement piles, or pre-installed before the sand was placed, representing non-displacement piles. Load measurements and digital image correlation (DIC) were used to assess shaft resistance and surrounding-soil movements.<br /><br />For pre-installed piles, tensile and compressive limit shaft resistances were both about 70 kPa, giving a tension-to-compression ratio of 1. For jacked piles, the corresponding resistances were 125 kPa in tension and 250 kPa in compression, giving a ratio of 0.5. Thus, jacked piles developed greater resistance overall, but their tensile resistance was substantially lower than their compressive resistance.<br /><br />DIC observations help explain this difference. Around pre-installed piles, soil displacement patterns and magnitudes were similar in tension and compression, with soil moving radially away from the pile. Around jacked piles, movements were localized; soil response was dilative during compression but contractive during tension. The findings indicate that installation history strongly influences tensile capacity and should be considered when estimating pile shaft resistance. The experiments used model piles in dense silica sand, so their resistance values should not be directly transferred to full-scale piles.

Keywords

pile installation

shaft resistance

dense sand

tensile capacity

compressive resistance

model piles

jacked piles

pre-installed piles

digital image correlation

soil displacement