Numerical Study on Evaluation of Countermeasure Effects on Liquefaction Resistance in a Reclamation Dike

1997年鹿儿岛-北塞武大地震造成各种建筑物受损，农业设施也遭到破坏。尤其是泉水市的围垦堤防遭受了液化破坏。河道底部和水田中的沙子沸腾，围垦堤防路面出现裂缝和坍塌，护岸发生液化变形。本文采用非线性动力有效应力分析的有限元方法，模拟了地震作用下加筋填海堤防及其周围地基的液化行为。从地基应力历史的角度阐明了超孔隙水压力的发展机理，验证了液化对策施工的效果。在液化对策分析中，抑制了孔压的发展，与破坏情况分析结果相比，计算变形值也有所减小。地震过程中的应力路径在很大程度上取决于初始应力条件，即初始剪应力和覆岩压力分布，由于采取相应措施而增加的初始应力抑制了液化的发生。2000年托托里肯-斯耶布地震和2001年庆应地震袭击了围垦土地和堤防，液化破坏了稻田和堤防。对影响液化的因素进行了现场调查。

The 1997 Kagoshimaken-Hokuseibu Earthquake brought about damage to various structures, and agricultural facilities also suffered damage. Especially, damage by liquefaction was inflicted on the reclamation dikes in Izumi City. Sand boils at the bottom of water channels and in paddy fields, cracks and collapses in the pavement of the reclamation dikes, and deformation of revetments by liquefaction occurred at that time. In this study, liquefaction behavior of the reinforced reclamation dike and the surrounding ground during the earthquake is simulated by the finite element method with nonlinear dynamic effective stress analysis. The development mechanism of excess pore water pressure is clarified from the viewpoint of stress history of the ground, and the effect of the countermeasure construction against liquefaction is verified. In the analysis of countermeasures for liquefaction, the development of the pore water pressure is suppressed, and the computed deformation values also decrease in comparison with the result of the analysis on the damage situation. Also, it is found that the stress path during earthquake depends largely on the initial stress condition, that is, the initial shear stress and the overburden pressure distribution, and the initial stress increase due to the countermeasures restrains the occurrence of liquefaction.The 2000 Tottoriken-Siebu Earthquake and the 2001 Geiyo Earthquake hit the reclamation land and dikes, and damage by liquefaction was inflicted on paddy fields and dikes. The in-situ investigation was carried out to research factor of liquefaction.