Liquefaction Analysis of Reclamation Dike during Earthquake

第二次世界大战后，在中国、四国和九州地区建成了88个填海堤坝。其中28个堤坝和41个地基由桑迪组成。利用建设部科学研究院建立的衰减方程，对所有建筑场地进行了地震危险性分析。在此基础上，计算了百年地震运动，并提出了三个地区（宫崎、三池、德岛）有价值超过100加仑的五个地区（竹原、小岛、约纳戈、国分、西国崎）的值不超过100 gal但不低于80 gal，其他的值不超过80 gal。利用百年一遇的地震动、标准贯入值（N值）、图纸、土壤勘探和地下水位资料，进行了建设部的方法。首先对不同N值、不同地下水位、不同粒径和不同比重的地基模型进行了分析，然后对由桑迪组成的堤坝进行了计算，得出了堤坝的安全系数。当土壤和地面条件变差时，很少有小于1.0的。但由于这些堤顶发生液化的深度均在6.0m以上，而且实际工程中这些堤身和地基土必须由较细的土组成，因此，根据百年一遇地震作用下的液化分析结果，这些堤身是安全的。最后，在这40年中，没有堤坝被地震破坏。

There are eighty-eight reclamation dikes in the Chugoku,Shikoku and Kyushu region which have been completed after the Second World War. Twenty-eight of these dikes and forty-one of these foundation grounds consist of sandy soil. Seismic risk analysis were carried out for all construction sites by making use of the attenuation equations which were established by Research Institute,Ministry of Construction. From this analysis, the 100-year earthquake motion was calculated and three district(Miyazaki,Miike,Tokushima) had the value more than 100 gal, five districts (Takehara,Kojima,Yonago,Kokubu,Nishikunisaki) had the value no more than 100 gal but no less than 80 gal and the others had the value no more than 80 gal.Liquefaction analysis by Research Institute,Ministry of Construction's method were carried out by using the 100-year earthquake motion,stamdard penetration value(N-value), blueprins, soil explorations and groundwater level. First, this cnalysis was applied to ground models which have different N-vaiues, groundwater levels, grain sizes and specific gravities, then, to each dikes which consist of sandy soil and safty factors were calucated. When the condition of soil and ground become worse,few of them were less than 1.0. But, these happening depths from dike crests were deeper than 6.0m and,moreover,these dikes and foundation ground must consit of more fine soil in practical ploblems,accordingly from these results of liquefaction analysis for the 100-year earthquake motion, it was concluded that these dikes will be in safety. Finally,there was no dikes which was damaged by earthquake during these forty years.