Evaluation of Degree of Overconservatism in API Shaft Friction of Piles in Marine Sand of the Arabian Gulf-Paper

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The study evaluates whether API design guidance underestimates shaft friction in offshore piles driven into Arabian Gulf sands. The authors compiled geotechnical and dynamic pile monitoring (DMS) reports for 40 piles, up to 86 m deep, at more than five locations. They compared API estimates with DMS measurements from restrike tests, grouping sands by composition and density. A Mann–Whitney nonparametric test was used to assess differences and derive adjusted overconservatism factors (OCFs).<br /><br />Shaft friction contributed about 75–77% of total pile capacity, making it the focus of the comparison. API estimates were generally lower than DMS measurements. For silica sand, adjusted OCFs were modest: 1.20 for loose-to-medium-dense sand and 1.06 for dense-to-very-dense sand. For carbonate sand, the factors were substantially higher: 1.79 and 2.00, respectively. No adjusted factor was established for very loose sand because the data did not show a statistically significant difference.<br /><br />The authors conclude that API guidance provides a reasonable estimate for silica sands but is notably conservative for carbonate sands. For the studied conditions, API shaft-friction values for carbonate sand could be adjusted using the reported factors. The findings are limited to the investigated sites and dataset; the authors recommend further research by sand classification and relative density, and revision of API design parameters. They also note that restrike measurements were taken about 12 hours after installation, whereas capacity may increase with time.

Keywords

API design guidance

shaft friction

offshore piles

Arabian Gulf sands

dynamic pile monitoring

restrike tests

carbonate sand

silica sand

overconservatism factors

Mann-Whitney test