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

1997年的鹿儿岛北西部大地震造成了各种建筑物的破坏，农业设施也受到了破坏。特别是泉市的围垦堤坝遭受了液化破坏。当时，河道底部和稻田中的泥沙沸腾，围垦堤坝路面出现裂缝和坍塌，护岸因液化而变形。本研究利用有限单元法，结合非线性动有效应力分析，模拟地震作用下围堤及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，验证了抗液化对策措施的效果。在液化对策分析中，孔隙水压力的发展受到抑制，计算的变形值也比破坏情况分析的结果有所减小。此外，地震时的应力路径主要取决于初始应力条件，即初始剪应力和上覆压力分布，由于采取了对策，初始应力的增加抑制了液化的发生。2000年鸟取县地震和2001年的嘉余地震都对填海造地和堤坝造成了冲击。水田和堤防遭受液化破坏。通过现场调查，研究了液化影响因素。

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.