Offshore Open End Steel Tubular Piles-A Case History

Steel piles of 1,219 and 1,016 mm diameter were driven open end in 16 to 20 m of water, to 36 to 44 m depth in marine soils of variable, but generally silty sand composition. The 308 piles support marine structures requiring maximum compression and tension service loads of 5,702 kN and 2,650 kN. The piles drove easily without soil plug development and driving resistances did not mirror the SPT profiles. Dynamic tests and CAPWAP analyses indicated soil set-up was essential to achieve pile capacities, but no clear trend emerged regarding required set-up duration. A pile subjected to static tension and dynamic compression tests indicated the static tension resistance was equivalent to 72 % of the dynamic shaft resistance and to K = 0.5. A static compression test on an unplugged pile indicated the average external/internal unit shaft resistance was 75 % of the unit tension resistance and about 50 % of the API predicted unit shaft resistance. External and internal friction was not equal and was grossly overestimated by the API method. Static and dynamic tests on another test pile indicated plugging had developed, as at this location internal shaft resistance was greater than toe end bearing.