水平循环荷载下桩基变形特性的离心模型试验研究

波浪、船舶等长期水平循环荷载作用下，桩基将不可避免地产生附加应力和变形。针对饱和黏土地层，开展离心模型试验研究了船舶系泊水平荷载作用下单桩和群桩的变形特性。发现水平循环加-卸载诱发了桩周土体的塑性变形，进而导致桩身产生了不可恢复的水平位移和弯曲变形。随着循环荷载的增加，单桩和群桩的桩顶最大水平位移和残余水平位移均同时增加，但残余水平位移明显小于最大水平位移。单桩的桩顶残余水平位移与最大位移比值介于0.17～0.22；群桩的桩顶残余水平位移与最大水平位移比值介于0.30～0.84。水平循环加-卸载作用下，桩身残余弯曲应变明显小于最大弯曲应变。单桩的残余弯曲应变与最大弯曲应变比值介于0.13～0.50；群桩的桩身残余弯曲应变与最大弯曲应变比值介于0.23～0.82。群桩前桩的残余和最大弯曲应变明显大于后桩，前桩与后桩的最大弯曲应变、残余应变比值分别高达3.2和3.1。因此，前桩要采取合理的加固和保护措施，以确保桩基长期服役的安全性。

Centrifuge studies of pile deformation mechanisms due to lateral cyclic loading

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.