Soil Plug Behaviour of Open-Ended Pipe Piles During Installation-Article

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Seo and Kim experimentally examined how soil plugs form and change during the driving of open-ended pipe piles. They drove vertically split model piles with inner diameters of 15 and 34.5 mm through loose and dense fine sand in a transparent tank, recording the process with high-resolution images. Alternating coloured sand layers enabled measurements of plug length, vertical strain and changes in density.<br /><br />The results show that plugging was not a steady, one-way process. Incremental filling ratios rose and fell during driving, indicating repeated transitions between more plugged and less plugged conditions. Plug length ratios generally declined as penetration increased. At the same penetration depth, larger piles and piles in denser sand generally had longer plugs.<br /><br />Soil within the plug was compressed as the pile advanced. Compressive strain typically increased with distance from the top of the plug, peaked around its middle, and decreased toward the pile base. The soil near the plug’s top also became denser with penetration. This densification was especially pronounced for small piles in loose sand: estimated relative density increased 8.8-fold, compared with 3.7-fold for larger piles. In initially dense sand, the corresponding increases were 1.5- and 1.2-fold.<br /><br />The findings provide visual evidence that plug state, strain and density evolve throughout installation, with implications for estimating inner shaft resistance and predicting pile capacity. The authors caution that model-test results are not directly transferable quantitatively to field piles because of tank boundaries, low stress levels and differences between PVC and steel interfaces.

Keywords

open-ended pipe piles

soil plugs

pile driving

sand

incremental filling ratio

plug length ratio

compressive strain

relative density

inner shaft resistance

pile capacity