离岸深水全直桩码头承载性能有限元分析

Finite element analysis on bearing capacity of all-vertical-piled wharf in offshore deep-water

全直桩码头是适于软土地基上离岸深水海域的新型高桩码头结构型式,其承载机理与传统高桩码头存在较大差异,且软土地基循环软化效应显著。建立全直桩码头结构与地基相互作用三维弹塑性有限元模型,基于二次开发采用拟静力法对土体循环软化效应进行模拟。通过有限元模型研究全直桩码头的承载特性与破坏模式,并探讨水平极限承载力的影响因素。研究表明水平荷载作用下,基桩的塑性破坏是结构失稳的控制因素,地基土体的承载力对结构水平极限承载力不起决定性作用;竖向荷载作用下,结构竖向极限承载力由地基土体强度决定。研究范围内入土深度对结构水平极限承载力影响不大,但桩壁厚度减小或考虑土体软化后,结构水平极限承载力明显降低。设计中,增加入土深度可有效减小土体软化引起的水平极限承载力降低程度,且应考虑结构腐蚀和土体软化对水平极限承载力的双重降低效应,为钢管桩预留足够的腐蚀富裕量。

All-vertical-piled wharf is a new type of high-pile wharf suitable for offshore deep sea on soft soil foundation, but its bearing behavior is quite different from the traditional high-pile wharf, and cyclic-softening effect of soft soil foundation is remarkable. A 3D e- lastic-plastic finite element model of all-vertical-piled wharf and soil foundation is established, and pseudo-static method is used to sim- ulate cyclic-softening effect based on secondary development. With the finite element model, the bearing behavior and failure mode are studied, and the influence factors of the horizontal ultimate bearing capacity are analyzed. The results show that under the horizontal loads, plastic failure of pile foundation is the key to the buckling damage, while the bearing capacity of foundation soil is not a control- ling factor; and under the vertical loads, the vertical ultimate bearing capacity is decided by the strength of foundation soil. The resuhs also show that the horizontal ultimate bearing capacity is hardly affected by the embedded depth of piles within the scope of research, but the decrease of the thickness of piles or the cyclic-softening effect of soil will obviously reduce the horizontal ultimate bearing capac- ity. In the design, increasing the embedded depth of piles can effectively reduce the decrement of the horizontal ultimate bearing capac- ity caused by cyclic-softening effect of soil. Double abate effect of structure corrosion and cyclic-softening effect on the horizontal ulti- mate bearing capacity should be considered, and enough corrosion depth for pile should be reserved.