Recent Advances in Soil Response Modeling for Well Conductor Fatigue Analysis and Development of New Approaches

摘要

Well fatigue assessment is an important aspect of the design and integrity assurance of deepwaterrnriser-well systems. Fatigue damage arises from stress changes in a conductor due to cyclic loading. Inrnpractice, the lateral cyclic soil response is typically modeled using Winkler type springs known as the soilrnresistance-displacement (p-y) springs. An appropriate soil model for conductor-soil interaction analysisrnshould predict the absolute and incremental magnitudes of stresses and the resulting impact on fatigue.rnMonotonic p-y relationships (backbone curves) which were originally developed for piled foundations arernnot appropriate for well conductor fatigue analysis. To determine the appropriate soil response anrnextensive study involving physical model testing in a geotechnical centrifuge and numerical analyses wasrninitiated. The intent was to develop a robust and comprehensive approach to cover a wide range of seabedrnsoils and loading conditions specifically for conductor fatigue analysis. Soil p-y models were developedrnfor conductors installed in normally consolidated to lightly overconsolidated clays, medium-dense sandsrnand over-consolidated clays. The models rely on the cyclic response of degraded soil at the steady-staterncondition and provide fatigue life predictions with high accuracy. This paper provides an overview of thernpast and recent studies that led to development of the fatigue p-y models. It presents the results of tworncentrifuge test series conducted in normally consolidated clay and medium dense sand. Ultimately, thernpaper provides recommendations for developing p-y springs specifically for well conductor fatiguernanalysis.