Design procedures for embedded structure considering seabed gonging of deformed sea ice

本文提出了一种考虑各种环境参数概率分布的冰冲事件模拟方法。根据各种条件下的计算结果，发现了与现场观测资料相似的量级--冲刷长度为几十米到几公里，冲刷深度为几十厘米到几米。实际冲刷事件的综合趋势/特性（再现性），获得了与现场观察结果相比有利的结果。利用模拟结果，我们可以估计的概率，结构的故障（结构和冰龙骨之间的接触概率），根据埋深。在此基础上，提出了管道等海底结构物抗冰冲刷最优埋深的估算方法。可以推测，上述概念是基于可靠性设计，通过可靠性设计，可以对周围环境的不确定性突出的情况进行安全评估。此外，我们还进行了中尺度模型试验，以及去年进行的与“底冲变形”相关的小尺度试验，这意味着海冰下方海床内的应力传递或土壤变形。从中小比例模型试验结果中，我们阐明了与海底反力和应力分布相关的尺度效应/相似性。同时，我们针对海底应力建立了简单的管道响应分析模型，我们证实模型的计算结果与实测结果几乎相符。利用这种方法，可以计算考虑尺度效应的管道响应。本文还尝试在实际海域中考虑海底冲刷变形的情况下，估算管道的最佳埋深。因此，我们发现，将管道埋深为冲刷深度的1.6倍就足够了。

We developed a simulation method of Ice Scour Event considering probability distributions of various environmental parameters. As a result of calculations made under various conditions, order similar to those in the field observation data -the scour length of several tens of meters to several kilometers and the scour depth of several tens of centimeters to several meters -were found. Furthermore, due to the similarity to (reproducibility of) the comprehensive tendency/property of actual scour events, results that compared favorably with field observation results were obtained. Using the simulation results we then can estimate the probability of failure of structures (probability of contact between structure and ice keel) according to burial depth. From the basis, we finally proposed an estimation method of optimal burial depth of seabed structures such as pipeline against ice scour event. It can be presumed that the above concept is based on a reliability design through which safety assessment for the case in which uncertainties surrounding the environment are prominent is possible.Also, we made a medium-scale model experiment as well as the small-scale experiment in the last year related to "sub-scour deformation", which means stress transmission or soil deformation within the seabed below the sea ice. From the small-and medium scale model test results, we clarified the scale effects/similarities related to reaction forces and stress distributions within seabed While we made a simple pipeline-response analysis model due to the stress within seabed, we confirmed that calculation results by the model were almost corresponded to measured results. Using this method, we can calculate pipeline-response considering the scale effects. We also attempted to estimate the optimal burial depth of a pipeline considering the sub-scour deformation in an actual sea area. As a result, we found that it would be enough to bury a pipeline at 1.6 times deep as the scour depth.