Occurrence of spanning of a submarine pipeline with initial embedment

For better understanding the mechanism of the occurrence of pipeline span for a pipeline with initial embedment, physical and numerical methods are adopted in this study. Experimental observations show that there often exist three characteristic phases in the process of the partially embedded pipeline being suspended: (a) local scour around pipe; (b) onset of soil erosion beneath pipe; and (c) complete suspension of pipe. The effects of local scour on the onset of soil erosion beneath the pipe are much less than those of soil seepage failure induced by the pressure drop. Based on the above observations and analyses, the mechanism of the occurrence of pipeline spanning is analyzed numerically in view of soil seepage failure. In the numerical analyses, the current-induced pressure along the soil surface in the vicinity of the pipe (i.e. the pressure drop) is firstly obtained by solving the N-S equations, thereafter the seepage flow in the soil is calculated with the obtained pressure drop as the boundary conditions along the soil surface. Numerical results indicate that the seepage failure (or piping) may occur at the exit of the seepage path when the pressure gradient gets larger than the critical value. The numerical treatment provides a practical tool for evaluating the potentials for the occurrence of pipe span due to the soil seepage failure.

近海岩土工程

<正>本组的主要内容是围绕近海(Offshore)(又称“离岸”)的勘探、开发和建设中所涉及的岩土力学和基础工程的问题。除了考虑海洋资源的提取(矿物、生物、化学等)、能源的利用(潮汐、风力和海水温差发电、太阳能利用等)以及各种沿海的工程建设外,当前我国正在大力开展近海石油和天然气的勘探和开发工作。