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

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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.