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

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The study evaluates whether API-based design parameters underestimate shaft friction for offshore piles driven into Arabian Gulf sands. It compares API geotechnical estimates with Dynamic Monitoring System (DMS) measurements for 40 piles at five major fields—Manifa, Zuluf, Marjan, Safaniya, and Karan—with pile depths reaching 86 m.<br /><br />The investigation focused on marine calcareous and carbonate sands. Soil samples were characterized by carbonate content and mineral composition, and sand layers were grouped by relative density. Shaft friction values from API and DMS reports were compared for silica and carbonate sands across density groups. Shaft friction represented about 77% of total pile capacity, versus 23% from end bearing.<br /><br />Overall, API shaft-friction estimates were lower than measured DMS values. Statistical testing found the API and DMS capacities to differ significantly at the 0.05 level, except for very loose sand. The study quantified this conservatism using an adjusted overconservative factor (OCF). For carbonate sand, the adjusted factors were 1.79 for loose-to-medium-dense layers and 2.00 for dense-to-very-dense layers. Corresponding factors for silica sand were much smaller: 1.20 and 1.06.<br /><br />The findings indicate that API shaft-friction predictions are particularly conservative for carbonate sand. The authors conclude that API shaft-friction values for piles in sand may be increased using the adjusted OCF, with the applicable factor depending on sand type and density.

Keywords

API design

shaft friction

offshore piles

Arabian Gulf sands

Dynamic Monitoring System

carbonate sand

silica sand

pile capacity

overconservative factor

geotechnical estimates