Axial Capacity Evaluation of Open-Ended Pipe Piles in Medium Dense Silty Sand Using Soil Plugging Length Ratio-Paper

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The study evaluates how soil plugging affects the axial capacity of open-ended steel pipe piles driven into medium-dense silty sand. Unlike many earlier studies based on laboratory model piles, it uses field data: plug lengths from 1,303 piles and PDA/CAPWAP capacity estimates for 110 piles. The piles were 406–914 mm in diameter and generally penetrated 15–40 m.<br /><br />Average plug length ratio (PLR) increased with pile diameter, from about 0.65 for 406-mm piles to about 0.79 for 914-mm piles. The authors propose a field-based relationship for estimating PLR from pile inner diameter.<br /><br />Back-calculated shaft friction and end-bearing factors both increased as PLR decreased. In other words, piles with less-developed soil plugs generally showed higher unit shaft friction and end bearing. The paper presents empirical relationships linking these capacity factors to PLR and, for shaft friction, penetration depth.<br /><br />Compared with API RP 2GEO recommendations, the measured factors suggest API may underestimate shaft friction and end bearing for smaller-diameter piles in medium-dense silty sand. API values were more appropriate for the largest piles studied. The findings provide field-based guidance for incorporating plugging effects into pile capacity estimates, within the tested soil conditions and PLR range.

Keywords

soil plugging

open-ended steel pipe piles

axial capacity

medium-dense silty sand

plug length ratio

pile diameter

shaft friction

end bearing

PDA/CAPWAP

API RP 2GEO