Seabed stiffness model for steel Catenary risers
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2015 Taylor & Francis Group, London. The stress ranges used in the fatigue analysis of Steel Catenary Risers (SCRs) are calculated from changes in riser stresses caused by wave motions. The Touchdown Zone (TDZ) - the region where the riser comes into contact with the seabed - is often the critical location from the standpoint of fatigue life of the riser. Relatively minor variations in seabed stiffness can have a significant effect on estimated fatigue life; therefore, the seabed stiffness model must realistically portray actual non-linear behavior. Riser interaction with the seabed involves a number of complexities including plastic deformation during virgin penetration, nonlinear load-displacement response, softening during cyclic loading, reconsolidation and thixotropic strength gain during rest periods, and suction-induced tensile resistance during breakaway. Physical model testing has been an important tool for characterizing these features of seabed behavior. This paper first presents an analysis of single-element riser model tests that measured soil resistance for different conditions of cyclic displacement magnitude and rest intervals. These data are then used to develop an equivalent soil spring model.
