Takehisa HOSAKA

Study on Damages of Land Reclamation for Housing Lots in the Mid Niigata Prefecture Earthquake in 2004

Satoru OHTSUKA

Mid Niigata prefecture earthquake of magnitude 6.8 occurred on October 23 in 2004. The seismic intensity was recorded as 7 at Kawaguchi and corresponds to the revel 2 vibration directly above its epicenter. Earth structures were severely damaged in comparison with the Hanshin great earthquake disaster since the earthquake occurred in the middle mountain area. The disaster got greater by the rainstorm just before earthquake and the repeated aftershocks. Lots of embankments were destroyed and damage of land reclamation for housing lots was remarkable. In this study the Takamachi land for housing lots were studied in detail by field investigation. The followings were obtained:
(1)There was observed a strong relationship between the land damage and the borderline for cutting and filling.
(2)Large collapse of fills occurred at the geographical corner and convex points where water concentrated.
(3)Anchor prevented the retaining wall from lateral movement.
(4)Drainage facilities will work to reduce the observed damage of landfill.
(5)Retaining wall was laterally moved a long distance due to shear strength reduction of bearing strata. Talus is not proper for bearing strata for retaining wall.
(6)Landfill failed along the borderline of cutting and filling. Bench cut construction is necessary to combine the fill and the basin.
(7)Risk management of land reclamation for housing lots is required to prevent from earthquake disaster.