REVIEW OF TOPOGRAPHIC AND SOIL CONDITIONS FOR LIQUEFACTION-RELATED DAMAGE INDUCED BY THE 2007 OFF MID-NIIGATA EARTHQUAKE

The 2007 Niigata-ken Chuetsu-oki (Off Mid-Niigata) earthquake caused the liquefaction of the sandy soil distributed near the coast of the Japan Sea in the middle of Niigata Prefecture. The liquefaction-induced damage occurring in many residential areas was investigated in detail by means of victim interviews, visual inspections, Swedish Weight Sounding tests, Standard Penetration Tests, old topographical map examinations, etc. Based on in situ soil investigations, the liquefied soil layers were estimated for each area. As a result, it was confirmed that the liquefied areas were mainly sand dune hinterlands, flood plains, reclaimed old river channels and sandy fills with high groundwater table. Among them, damage was especially serious on land having an inclined ground surface due to the flow of foundations, on the cut-fill borders of artificially developed land due to landslides and at the toes of sand dune slopes due to the thrust of the sliding soil and/or the collision of the sliding soil with objects. These investigation results also revealed that soil improvement by cement mixed columns is an effective countermeasure against liquefaction-induced damage unless lateral spreading of the subsoil arises.