Large Scale Soil-riser Model Testing on High Plasticity Clay
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Offshore projects frequently use Steel Catenary Risers (SCRs) to connect floating production facilities (e.g. FPSOs) and their respective seabed systems. The fatigue life of these risers is typically lowest at the hang-off point and in the Touchdown Zone (TDZ). However, behavior in the TDZ is not fully understood and the complex soil behavior may not be accurately captured by models used within the industry. This uncertainty can have significant implications for the design and resulting project costs. Large-scale physical model testing has been used to investigate soil-riser interaction in the TDZ, although little data is available in the public domain. The Norwegian Geotechnical Institute (NGI) and Texas A&M University (TAMU) recently cooperated on a project involving large scale model testing of vertical soil-riser interaction using high plasticity clay. This paper presents key data from cyclic penetration tests together with important conclusions reached. Initial penetration shows good agreement with existing models. Strength degradation occurs rapidly during cyclic penetration, which can reduce seabed-riser stiffness. Copyright 2008 by The International Society of Offshore and Polar Engineers (ISOPE).
