Effect of foundation flexibility on consolidation gains in undrained capacity

Subsea mudmats are extensively deployed to support subsea infrastructure such as inline structures, pipeline end terminations and manifolds. In fine-grained seabeds, consolidation during the delay between mudmat installation and operation of the associated pipelines increases the geotechnical capacity of the mudmat compared to that immediately following mudmat set down. Gain in consolidated undrained capacity has previously been investigated by assuming the mudmat behaves as a rigid body. However, rigidity index decreases with increasing mudmat size, and mudmats are becoming larger to resist increasingly large and complex loads and due to developments on softer seabeds. The enhancement in undrained shear strength of the seabed around a mudmat due to consolidation under self-weight is affected by foundation rigidity, due to the dependence of the stress distribution in the soil domain underneath the mudmat on the flexibility of the mudmat. In this paper, the effect of rigidity index of mudmats on post-installation consolidation, the associated increase in strength of the subsoil and consolidated, undrained capacity is presented.