Effect of seabed instability on fixed offshore platforms

Storms, hurricanes, and earthquakes may cause seabed instability, especially if the seabed is weak. The seabed instability, manifested in movement of soil layers, exerts lateral forces that may cause large stresses in offshore foundations. The induced stresses may compromise the stability of the foundation and supported structure. The effect of seabed instability on a fixed offshore structure is examined in this study. The method used accounts for soil nonlinearity, dynamic soil resistance, and pile–soil–pile interaction within the stable soil layer. Dynamic p–y curves, dynamic t–z curves and q–z curves have been used to simulate the soil resistance in the lateral and axial directions. The effect of different parameters that influence the response of offshore structures to seabed instability is evaluated. The parameters considered include the value of soil movement, the sliding layer depth, the wave loading, the pile flexibility, the soil movement profile, and the axial loading at the pile head. The response predicted using the proposed analysis compared well with that calculated using a boundary element solution for a case history of a failed offshore platform.