Because of long-term cyclic loads resulting from waves and ships

additional stress and deformation are inevitably induced in existing piles. Centrifugal model tests are conducted in this study to investigate deformation mechanisms of single piles and pile group embedded in saturated clay due to lateral cyclic loading. It is found that the horizontal cyclic loading-unloading induces plastic deformation of the soil around the pile

which in turn leads to unrecoverable horizontal displacement and bending deformation of the pile. As the cyclic loading increases

the maximum pile head horizontal displacement and residual pile head horizontal displacements increase as well

but the residual pile head horizontal displacement is much smaller than maximum pile head horizontal displacement. For single piles and a pile group

ratios of the residual lateral displacements to the maximum lateral displacements range from 0.17–0.22 and 0.30–0.84

respectively. The residual bending strains are also much smaller than the maximum bending strains. For single piles and a pile group

ratios of the residual to the maximum bending strains induced in the piles vary from 0.13 to 0.50 and 0.23 to 0.82

respectively. The maximum and residual bending strains induced in the front piles are up to 3.2 and 3.1 times as large as those in the rear piles. Thus

protection measures should be used for the front piles to ensure long-term serviceability of pile foundations.