Numerical investigation on the pull-out capacity of suction anchors in sand considering torsional and mooring line effects

Torsional pullout of suction anchors may occur during installation due to improper positioning or deviations caused by current forces, but less attention has been paid to the effect of torsion on the pull-out capacity of suction anchor in existing literatures. This paper therefore numerically investigates the pull-out capacity and failure mechanism of suction anchors in sand considering both torsional and mooring line effects using the advanced SIMSAND constitutive model. It is found that considering torsional influence causes a significant reduction in the pull-out capacity of suction anchor in sand under horizontal and inclined loading. The case with the optimal padeye depth of 0.7L produces the largest pull-out capacity and the greatest reduction in the pull-out capacity due to torsion. The dimensionless pull-out capacity for the case without mooring line is approximately 24% higher than or almost twice that of the case with mooring line in scenarios without or with torsional condition. Based on the findings, a new framework for estimation of the pull-out capacity of the suction anchor at the optimal padeye depth in sand considering torsional and mooring line effects is finally proposed which may benefit the design of suction anchor in scenarios with torsion in the real practice.