Pullout Behavior of Suction Piles in Saturated Sand Subjected to Combined Vertical and Horizontal Loading – Centrifuge and Finite Element Analysis

Suction piles have increasingly been considered as foundations for offshore facilities. In this study, the pullout behaviors of suction piles embedded in saturated sand subjected to combined vertical and horizontal loading at various inclination angles and pad-eye positions are investigated carrying out centrifugal tests and finite element (FE) analyses. The ultimate pullout capacities obtained from the model tests and FE analyses both increased as the inclination angle was close to 0° and the pad-eye position approached 75% of the pile length from the lid. This is associated with the increase of the passive earth pressure and friction between the soil and suction pile while the pile is pulled out. The failure envelopes were suggested depending on pad-eye positions to improve the design approach for offshore foundations. The optimal pad-eye positions for catenary and taut-leg mooring systems were then investigated by additional FE analyses to demonstrate the practical implications. For both mooring systems, the largest ultimate pullout capacity was obtained when the pad-eye was located at 75% of the suction pile length below the lid. The ultimate pullout capacity of the catenary mooring system was determined to be 1.94 times that of the taut-leg mooring system under the same conditions.