Offshore jacket foundations may fail under lateral loads of wind, wave, current, earthquake, etc. This paper describes centrifuge model tests carried out to investigate the pile-soil interaction of a tetrapod jacket foundation subjected to laterally monotonic and cyclic loads in the diagonal direction. The monotonic loading test results show that the maximum bending moment of the up-lifted pile is smaller than that of the down-pushed pile. Moreover, within the depth of 2.5 times the pile diameter, the static soil reaction on the up-lifted pile per unit length is only approximately 40% of that of the down-pushed pile at the same depth, since the axial force on the up-lifted pile decreases the effective stress on the soil around the pile. In the cyclic loading test, the maximum bending moments of both up-lifted and down-pushed piles decrease and the latter one decreases more. The soil reactions on piles per unit length were derived from the measured bending moments of the pile shaft. Degradation of these soil reactions occur during laterally cyclic loading, and the cyclic degradation factor of the up-lifted pile is almost half of that of the down-pushed pile of the jacket foundation.
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