Liquefaction traces on the Shinano River left bank after the 1964 Niigata Earthquake – Liquefaction research issues suggested by geoslicer survey results –

抄録

The 1964 Niigata earthquake and the 1964 Alaska earthquake led to extensive research investigating liquefaction. The Niigata earthquake is well known to have caused lateral flow movement of about 20 m in the Shinano River mouth’s left bank, leading to the Showa Bridge collapse. The authors conducted an investigation of liquefaction traces at that site using “geoslicer” methods, undisturbed soil sampling (GS sampling), and the surface wave survey (MASW) several decades after the earthquake. Results indicated numerous traces of sand boiling induced by ground liquefaction. Some findings present possible evidence elucidating lateral flow mechanisms. According to eyewitness testimony, the lateral flow occurred after the seismic motion had ceased. Therefore, seepage failure induced by the migration of excess pore water pressure presents the main issue. Furthermore, the residual deformation characteristics of liquefied ground are important because the liquefaction damage can be evaluated using the amount of residual ground deformation. Therefore, for performance-based design, residual deformation characteristics during liquefaction must receive greater emphasis than the occurrence of liquefaction.