The paper reports the design, installation, and back-analysis of six 54-inch driven steel piles in dense sands and gravels at the Wiriagar Deep A platform in Berau Bay, Papua Barat, Indonesia. Pile design required to incorporate the presence of thick gravel layers and the potential interaction of the piles with adjacent well conductors during installation or during drilling activities. Installation design required to consider the lack of industry recommendations for the derivation of Soil Resistance during Driving (SRD) in gravel and selection of fit for purpose piling equipment. Dedicated site investigations were carried out to acquire data that would enable pile capacity and drivability predictions. Geological analysis of the origin and distribution of the gravels provided additional context that was incorporated to the installation engineering studies. Pile design mitigation measures included setting the conductor tip below the proposed pile tip depth and strengthening the tip of the piles. Installation mitigations included full instrumentation and monitoring of the piles during driving and the mobilization of a pile top drilling spread. The pile driving instrumentation data enabled efficient management of the installation programme and limited the requirement to implement the installation mitigations available. A companion paper (Pua et al, 2020) provides a detailed description of the instrumentation programme for the Wiriagar Deep A platform adopted during installation. The data acquired also confirmed the uncertainties previously published for pile driving in gravels and the challenges to characterize their in-situ relative density and behaviour during driving. The pile driving monitoring data suggests degradation of shaft resistance during driving in a similar way to friction fatigue effects. The pile instrumentation data also enabled evaluation of the change of pile capacity with time as re-strikes were performed at selected time intervals and confirm the pile design suitability.
Hugo Galanes-Alvarez, Achmad Makmur, Philippe Jeanjean and Chee Peng Pua
Keywords: piles, gravel, drivability, instrumentation, Tangguh
Publisher: DFI