Recently proposed theoretical models and relationships for prediction of pile set-up effects in cohesive soils are assessed by comparison with a compiled data base consisting of load tests on piles in clays covering a range of geotechnical properties and stress history. The results indicate that reasonable predictions can be made with simplified relationships although this is dependent on the clay's stress history. Consolidation parameters are needed for set-up predictions, and these were deduced from the measured time-dependent friction gain for some of the tests. The deduced parameters were compared with values calculated empirically, and the results showed reasonable agreement.
The majority of the pile capacity calculation models are intended to predict the ultimate capacity of a pile more or less at full set-up conditions; i.e. after the soil has fully reconsolidated following the pile driving process. However the immediate and short-term capacities of a pile have several important applications in the offshore environment; as there are several critical situations when the period between installation and loading of the pile is rather short. These could arise, for example, from mating of the topside with the jacket shortly after the piles have been driven, or from impact loading of so-called underleg piles during docking of the jacket. These piles are used in indexing of a jacket against a pre-installed template and/or to reduce mudmat requirements in soft seabed. Upon docking of the jacket, the pile heads could experience large vertical forces, and if the soil has not fully recovered from the installation process; with the consequence that the pile capacity is inadequate, the pile could be redriven into the seabed by the applied weight of the jacket. On the other hand if a reasonable amount of set-up can be assured to have occurred shortly after pile driving.