浅层地基上管道轴向运动的阻力研究

Study of axial resistance of subsea pipe on shallow foundation

铺设于深海浅层地基上的海底管道在运行期间受高温高压等的作用易产生轴向膨胀和收缩,间歇性的往复剪切管道周围浅层地基土,对这种管道轴向运动过程中管-土相互作用机制需深入研究。基于修正剑桥模型建立了浅埋式管道在运行期间的轴向运动过程的小变形有限元分析(SSFE),采用有效应力指标,得到了不同初始埋深的管道在轴向运动过程中地基土在临界塑性剪切固结阶段的轴向阻力随时间发展规律(S形管-土轴向阻力发展曲线),探究了不同剪切速度下剪切带内地基土的超孔隙水压力、管-土界面摩擦系数、反映管-土接触面形状的楔形变形因子ζ以及管-土之间轴向阻力等的发展变化规律,研究发现轴向剪切产生的超孔压是速度和时间的函数,随着轴向运动速度减小,峰值超孔压的值减小且出现峰值超孔压的时间推迟。管道轴向运动过程中地基土由不排水条件向排水条件过渡的内在机制做出了较完整的阐述。

The submarine pipeline laid on the shallow foundation of the deep sea is prone to axial expansion and contraction under the action of high temperature and high pressure during operation,and this movement will intermittently shear the shallow soil around the pipe.Therefore,it is necessary to investigate the mechanism of tube-soil interaction during the axial movement of the pipeline.In this paper,a small strain finite element analysis of the axial motion of a shallowly buried pipeline during operation is established based on the modified Cambridge model.In the process of axial movement of pipelines with different initial depths,the development curve of axial resistance(S-shaped consolidation curve)in critical plastic shear consolidation stage is fitted.The variations of the excess pore water pressure,the friction coefficient of the pipe-soil interface,the wedging factorζand the axial resistance between pipes and soils are discussed.It is found that the peak excess pore pressure generated by axial shear is a function of velocity and time.As the axial velocity decreases,the value of the peak excess pore pressure decreases and the time point of the peak pore pressure is delayed.The internal mechanism of the transition from undrained condition to drained condition in the process of axial movement is expounded.