NUMERICAL ANALYSIS ON MECHANISM OF LIQUEFACTION NOT ONLY IN MAIN EARTHQUAKE BUT ALSO IN AFTER SHOCK

Abstract

During the 2011 Great East Japan Earthquake, liquefaction occurred in the reclaimed ground in
the wide area of east Japan. In some areas, liquefaction happened in the aftershock was even more serious than
what happened in the main shock. For this reason, the liquefaction that happened a long time after the
earthquake caused not only by the main shock but also the multiple aftershocks within a short period of time,
is intensively investigated in recent years. In this paper, particular attention is paid to the characteristic features
of the liquefaction and its consequent consolidation-induced settlement. Based on the observed data, a series
of dynamic-static analyses, considering not only the earthquake loading but also static loading during the
consolidation after the earthquake shocks, are conducted in a sequential way just the same as the scenario of
the earthquake. The calculation is conducted with 3D soil-water coupling finite element-finite difference (FE-
FD) analyses based on a rotating-hardening elastoplastic constitutive model. From the analyses, it is recognized
that small sequential earthquakes, which cannot cause liquefaction of a ground in an independent earthquake
vibration, cannot be neglected when the ground has already experienced the liquefaction after a major shock.
In addition, the aftershocks have great influence on the long-term settlement of the soil layers with low
permeability. It is confirmed that the numerical method used in this study can describe the ground behavior
correctly under repeated earthquake shocks.