Centrifuge modelling on tetrapod jacket foundation subjected to lateral loads

Jacket foundation is widely applied in development of offshore wind power, oil and gas. The failure of a jacket foundation is mainly caused by the lateral loads of wind, wave, current, earthquake, etc. Two groups of centrifugal model tests on a jacket foundation loaded along the border and the diagonal respectively are carried out in saturated sand to investigate the distribution of internal forces, difference of soil resistance and deformation characteristics for piles. The test results show that the piles of a jacket foundation will be pulled out more easily under diagonal loading. Moreover, compared with the up-lifted pile, the downward-pushed pile bears larger shear force and the maximum negative bending moment at the top, and larger maximum positive bending moment of the pile shaft, and shows basically the same lateral deflection. As for a 5.8-diameter spaced jacket foundation, because of the pile group effect and the up-lifting force which reduces the effective stress in soil around the pile, the resistance of shallow layer soils around the up-lifted pile is 60% of that around the downward-pushed pile within the depth of 2.5-diameter below mudline under diagonal loading, which is only 40% of that under diagonal loading. These differences of shear force, the maximum negative bending moment, axial force at the top and the maximum positive bending moment of the pile shaft between the downward-pushed pile and the up-lifted pile under diagonal loading are also more obvious than those under diagonal loading. In comparison with these results of centrifugal model tests on a large-diameter single pile under lateral loads, it is found that the soil resistance for a single pile is between that for the up-lifted pile and the downward-pushed pile of a jacket foundation at the same depth.