Influence of local scour on the evolution of the failure envelope for suction caisson foundation

Local scouring significantly undermines the load-bearing capacity of suction caisson foundations and poses a daunting challenge to the integrity of offshore structures. This study numerically addresses the impact that the size and shape of the local scour hole have on both the monotonic bearing capacities and failure envelopes of suction caisson embedded in sandy soil. Different loading conditions - individually and combined - by integrating local scour parameters such as scour depth (S_d), scour width (S_w) and scour angle (φ) while maintaining realistic scour proportions are carefully evaluated. The obtained results show that (1) scour depth has a stronger influence on the ultimate bearing capacity than the influences of scour width and angle; (2) the horizontal bearing capacity shows increased sensitivity to variations in scour depth; and (3) both the horizontal bearing capacity and the moment bearing capacity reach a plateau and a steady state manifest itself when the relative scour depth exceeds a threshold value of 0.9. An empirical formulation to characterize the failure envelope within the horizontal force-moment (H-M) plane is finally proposed, which properly considers the effect of scour depth. These findings provide a valuable reference for ensuring structural resilience to local scour phenomena.