Pile Design, Installation and Backanalysis of 54 in. Piles in Gravels at the Wiriagar Deep Platform in Berau Bay, Indonesia-Paper

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The paper describes the design, installation, and performance assessment of six 54-inch open-ended steel piles supporting the Wiriagar Deep A offshore platform in Berau Bay, Indonesia. The piles were driven approximately 72.5 m through dense sands, gravels, and hard clays in a geologically variable setting.<br /><br />Thick gravel layers created uncertainty in predicting both axial capacity and soil resistance during driving, since standard design methods may overestimate gravel strength and site investigations cannot reliably establish its in-situ density. Geological analysis suggested the deposits formed in braided river channels and were unlikely to contain large boulders. The design ultimately avoided relying on gravel for pile toe capacity. Conductors were set at least 7 m below the pile tips to reduce the potential effects of drilling on foundation capacity, and the pile tips were strengthened. A drilling spread was also available as a contingency.<br /><br />All piles and conductors were instrumented during installation. Monitoring showed broadly consistent pile behaviour and helped manage the driving programme without needing the planned drilling mitigation. Driving resistance was generally lower than design predictions, particularly in the gravel between about 51 and 62 m. Resistance also decreased with continued penetration, consistent with driving-induced loosening or degradation of shaft friction. Most piles behaved as expected for open-ended piles during driving, with some partial plugging observed.<br /><br />Restrike tests assessed capacity gain over time. After approximately 30 days, CAPWAP analysis estimated a pile resistance of 48 MN, close to the API RP 2GEO design capacity of 47 MN. The results supported the design’s suitability and demonstrated the value of comprehensive instrumentation for managing uncertainty, optimizing installation, and verifying pile capacity in gravelly ground.

Keywords

offshore platform

steel piles

pile driving

gravel strata

axial capacity

driving resistance

instrumentation

CAPWAP analysis

open-ended piles

pile capacity