Abstract

Two platforms, about 125m apart, supported on piled foundations were successfully installed recently offshore Vietnam. Extensive pile driving and monitoring data were collected with the objective of performing post-installation analysis in order to evaluate and infer the most applicable site-specific methods for axial pile capacity and Soil Resistance to Driving (SRD).

The approach for assessing the most applicable axial pile capacity computation method involves firstly extrapolating long term axial capacity based on Soderberg, L. O. (1962) radial consolidation model with spot capacities obtained from CAPWAP analyses performed on selected hammer-blows at End Of Driving (EOD) and Beginning Of Restrike (BOR). The extrapolated long term axial capacity is then compared with predicted axial pile capacity based on different methods to evaluate the site- specific most applicable method for axial pile capacity computation.

The approach for assessing the most applicable SRD computation method involves firstly back analyzing SRD using the global (bearing graph) method for every 25cm driving, as well as CAPWAP analyses at selected hammer-blows near end of driving of each add-on. The back-analyzed SRDs are then compared with predictive SRD methods to evaluate suitable SRD computation methods.

From this study, the most applicable SRD were assessed to be Alm & Hamre (2001) method, whereas the extrapolated ultimate axial pile capacity is comparable with ultimate pile capacity computed based Kolk & Van der Velde (1996) in cohesive soils and lowest of the four recommended CPT based methods in frictional soils.

This improved understanding of the most applicable predictive engineering methods will be very beneficial when applied to future development in the vicinity to the assessed location. However, it should be noted that the extrapolated capacity is based on CAPWAP of a blow which likely did not mobilize the full capacity, also the set-up model is based on past literatures and not site specific.

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