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Well fatigue assessment is an important aspect of the design and integrity assurance of deepwater riser-well systems. Fatigue damage arises from stress changes in a conductor due to cyclic loading. In practice, the lateral cyclic soil response is typically modeled using Winkler type springs known as the soil resistance-displacement (p-y) springs. An appropriate soil model for conductor-soil interaction analysis should predict the absolute and incremental magnitudes of stresses and the resulting impact on fatigue. Monotonic p-y relationships (backbone curves) which were originally developed for piled foundations are not appropriate for well conductor fatigue analysis. To determine the appropriate soil response an extensive study involving physical model testing in a geotechnical centrifuge and numerical analyses was initiated. The intent was to develop a robust and comprehensive approach to cover a wide range of seabed soils and loading conditions specifically for conductor fatigue analysis. Soil p-y models were developed for conductors installed in normally consolidated to lightly overconsolidated clays, medium-dense sands and over-consolidated clays. The models rely on the cyclic response of degraded soil at the steady-state condition and provide fatigue life predictions with high accuracy. This paper provides an overview of the past and recent studies that led to development of the fatigue p-y models. It presents the results of two centrifuge test series conducted in normally consolidated clay and medium dense sand. Ultimately, the paper provides recommendations for developing p-y springs specifically for well conductor fatigue analysis.

Submarine landslides and debris flows are among the most destructive geohazards, economically and environmentally, for installations on the seafloor. Estimating the drag forces caused by these geohazards is an important design consideration in offshore engineering. A summary of the major methods available for estimating the drag forces on pipelines and piles caused by a mass gravity soil movement has been presented and compared with one another. The methods available are limited in terms of the application and provide a wide range of estimates. There is significant room for improvement and new research to advance the state-of-the-art.