A new hysteretic seabed model for riser-soil interaction

Several models for the simulation of soil-riser interaction have been developed and used in practice. The models range from the extreme of a rigid seabed to springs that are either linear elastic or provide more sophisticated nonlinear response to simulate the seabed behaviour in the touchdown zone. The main goal of this study is to review the positive points and limitations of existing nonlinear models and introduce a new hysteretic model to simulate the seabed response more realistically for practical application. The new model uses a unified mathematical approach for different modes of the soil-riser interaction and incorporates an explicit degradation model for the soil behaviour. Development of a trench is simulated, together with incremental penetration of the riser into intact soil. The model can also incorporate variable parameters (e.g. depending on riser penetration rates and depth). The new model has been calibrated against existing data from model tests and found to provide good agreement for a range of test conditions.