The traditional method of subsea mudmat foundation stability analysis is to calculate the bearing capacity factor of safety using the classical approach given in the API RP 2GEO (2011, updated 2A). This classical approach can be overly conservative for foundations under complex loading conditions with multiple interacting loads. For example, pipeline end termination (PLET) structures, which can be subjected to combinations of self-weights, structure-soil interactions, and multiple interface loads from the flowline and jumpers during operating conditions.
In this paper, a rigorous 3D-FEA based assessment approach is described that can overcome such complex loading conditions and interactions to achieve a more accurate bearing capacity estimates of subsea structure mudmats. The approach is demonstrated by an example application to a subsea flowline sled support system with mudmat foundation. The approach features fully integrated finite element analysis using comprehensive 3-D modeling of all critical system components and their physical interactions.
The use of this approach improves the calculated mudmat bearing capacity factor of safety, and can be critical in situations where the mudmat size is restricted, or where new loadings will be applied to existing mudmats in brown field developments. On the other hand, it uses elaborate numerical procedures and hence requires much larger effort.