超长桩施工中桩身稳定性的三维非线性有限元分析

随着海洋油、气开发活动逐渐由近海向深海发展，出现了大直径、超长、深贯入的打入桩，打桩施工中采用的桩锤也随之加重．由于桩的直径大，桩壁薄，在打桩施工前或施工中更换桩锤时，伸出海底面的接桩段在自重、锤重和环境荷载的共同作用下容易产生失稳破坏．借助三维有限元分析方法，考虑桩身变形的几何非线性特性，对实际工程进行了桩的自由站立稳定性模拟分析．研究了线性算法与非线性算法在结果上的差异，并对不同的桩身倾斜度、自由站立长度以及桩顶作用水平荷载等工况进行对比分析，总结规律性。研究结果表明，线弹性算法的计算结果偏于危险，桩身倾斜度、自由站立长度以及水平荷载的大小对桩的自由站立稳定性均有较大的影响．

Nonlinear 3D Finite Element Method Analysis for Stability of Pile Stick-Up During Driving

Pile foundations are widely used substructure for platform in ocean engineering. Since the exploitation of oil and gas is developing from shallow to deep water, many large diameter, super length and deep penetration piles have been adopted. Accordingly, heavier driving hammers have to be selected. Before driving a pile, the driving hammer has to be placed on the pile head, which will cause the pile to penetrate into the soil for about 10 m. The segment stick-up on the seabed may suffer buckle failure under the action of the self-weight of the pile, the weight of the hammer and the environmental loads. Considering the geometrical nonlinear deformation of the pile numerical stimulation analysis for stability of pile stick-up is performed with 3 D finite element method in pile foundations of ocean platform. The effects of nonlinear behavior, the gradient of pile, the length of pile stick-up, and the horizontal load on the stability of pile stick-up are studied in details. The results show that the ultimate load calculated with nonlinear analysis is about 10% smaller than that calculated with the conventional elastic analysis. The stability of pile stick-up is also sensitive to the gradient, stick-up length and the ho-rizontal load.