海洋黏土超固结性和结构性对沉垫基础离底吸附力的影响

Influence of over-consolidated and structural marine clay on off-bottom suction force of mat foundation

我国近海区域海床表面广泛存在一层深厚软黏土,具有一定的超固结性与结构性。自升式海洋平台沉垫基础的离底吸附力对海上平台的起浮回收影响显著。通过数值方法模拟了沉垫基础的作业工况,将可以描述土体超固结性和结构性的弹塑性本构模型通过UMAT子程序嵌入有限元软件ABAQUS中,采用可以描述材料强度破坏和刚度衰减的黏结接触模型模拟基础底与海床的相互作用,并通过现场模型试验对数值模型进行了验证。在此基础深入探讨了黏土海床超固结性和结构性对基础离底吸附力的影响规律。研究结果表明:沉垫基础上拔时,底部会产生负孔隙水压力,随上拔时间先减后增,且沉垫基础边缘位置率先发生离底;黏土超固结性越强,离底吸附力越大;黏土结构性越强,离底吸附力越小。

A layer of deep soft clay which exists widely on the surface of the seabed in the offshore area of China is over-consolidated and structural to some extent.The mat foundation off-bottom suction force of jack-up offshore platforms has a significant impact on the extraction of the offshore platform.We simulated the working conditions of the mat foundation through a numerical method.The elastoplastic constitutive model that can describe the structural property and over-consolidation of the soil was embedded in the finite element software ABAQUS through the UMAT subroutine.The cohesive contact model which can describe the strength failure and stiffness attenuation was adopted to stimulate the interaction between the foundation bottom and the seabed.The model was verified by field test.The influence of clay seabed over-consolidation and structural property on the off-bottom suction force was deeply discussed on the base of the proposed model.The results show that negative pore pressure is generated when the mat foundation is pulled up,which first decreases and then increases with the uplift time.The edge of the mat foundation is off from the seabed first.The off-bottom suction force is larger with stronger over-consolidation,and smaller with stronger structural property.