Amplification Properties of Developed Residential Land for Main Shock and Three Aftershocks

Abstract eng:
Takamachi developed residential land was damaged in Niigata Chuetsu Earthquake in 2004. The maximum magnitude of acceleration of main shock is 818 gal and three big aftershocks took place within 40 minutes after the main shock. The magnitudes of aftershocks were 6.3,6.0 and 6.5. It was observed that many houses and soil structures failed progressively by the repeats of aftershocks. To make clear the influences of repeated aftershocks, two dimensional equivalent linear simulations were performed against damaged and undamaged area. The reduction tendencies of shear modulus of filled soils were measured by laboratory tests. The results of simulation for main shock could not express the generation of earthfill slope failure enough. However, the considering aftershocks gives more reasonable results, because the aftershocks has different predominant period. Of course, the slope angle of natural ground and fill thickness are influenced to the vibration behavior of development land. On the other hand, the maximum acceleration, velocity and relevant displacement were not enough for expression the slope failures, it is found that the average acceleration during principal motion is available index. In another static back analysis, the slopes of earthfills are failed when the horizontal seismic coefficient is over 0.25, this result corresponds with consequences of numerical analysis. This shows we have possibility of conversion between dynamic force to static force using the average acceleration, since the static force is adopted widely in the design for earthquake-proof.

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