Break-Out Resistance of Offshore Pipelines Buried in Inclined Sandy Seabed

Submarine pipelines are highly susceptible to lateral buckling failure under service conditions of high temperature and pressure. While existing bearing capacity evaluation methods mainly focus on flat seabeds, research on the ultimate bearing capacity of pipelines buried in sloping seabeds is limited. This study applies the FELA method to analyze the ultimate bearing capacity of pipelines buried in inclined sandy seabeds under various loading directions. The results reveal that in sloping seabeds, the minimum ultimate bearing capacity (Pu,b) does not occur in the vertical direction, but rather deviates toward the outward normal direction of the seabed surface, moving toward the foot of the slope. The Pu,b is only 57% of the uplift bearing capacity in the extreme case. A predictive model was proposed to accurately determine the direction of Pu,b. The results also indicated that increasing the seabed slope angle leads to a significant reduction of bearing capacity, while increases in the internal friction angle of the seabed and the pipeline–soil interface friction angle enhance the bearing capacity. Moreover, the design code of DNV (2017) was identified as unsafe due to its omission of seabed inclination effects, and the Pu,b is only 75% of the best estimate of DNV (2017) in the extreme case. A reduction factor model was developed to mitigate this gap, offering a more reliable framework for evaluating the bearing capacity of pipelines.