考虑桩基弱化的导管架平台横向振动特性试验研究

导管架平台桩身循环往复运动将使桩周土体超孔隙水压增加、横向土抗力降低，从而导致桩基弱化。泥面以下6倍桩径处嵌固桩身的等效桩简化理论没有考虑桩基弱化对平台基础自然频率的影响，计算结果与实测值有一定差距。为研究桩基弱化对平台结构横向振动特性的影响，进行了比例尺为1:10的导管架平台模型试验，测量不同循环荷载作用之后导管架平台模型水平方向的振动特性。由试验结果可知，桩基横向土抗力在不同循环荷载作用过程中出现不同程度的衰减，桩基土抗力的衰减与桩身往复运动的幅值和次数有关。考虑桩-土相互作用时导管架平台模型两个水平方向的基础自然频率（基频）比等效桩理论计算值分别低15.5%和6.0%。桩基弱化后，实测值与计算值的差距增大到22.0%和13.4%。假设导管架-桩-土系统阻尼为比例阻尼，通过试验结果发现，桩基弱化对系统阻尼影响较小。

Experiment study of horizontal vibration characteristics of fixed jacket platform considering degradation of pile foundation

The piles of jacket platform move in cycles, so as to increase excess pore pressure of soil, decrease the lateral soil resistance and weaken pile foundation. The basic natural frequency that based on equivalent simplified pile theory not considering the degradation of pile foundation which fixing the pile at 6 pile diameters below mudline still has some difference with the test result. In a simulation experiments, cyclic environmental loading impose in jacket platform, a 1:10 scale model, and measure the vibration characteristics in x and y directions of jacket platform model after different cyclic loadings. The experiments aim to study the relation between pile foundation weakening and platform horizontal vibration characteristics. According to experiment results, lateral soil resistance show different degrees of decay in different cycle loadings; and the degradation of pile foundation is related to the amplitude and frequency of reciprocating motion of piles. Because of the effect of pile foundation weakening, the basic natural frequency of jacket platform decreases when lateral soil resistance decay. The test values of fundamental natural frequency are lower than the calculated values by 15.5% in x direction and 6% in y direction. And the differences increase to 22% and 13.14% after the degradation of pile foundation occurred. Assuming system damping is proportional damping, the degradation of pile foundation has a small impact on system damping.