Water Films Involved in Post-Liquefaction Flow Failure in Niigata City During the 1964 Niigata Earthquake

Natural sand deposits are in most cases heterogeneous and layered in the horizontal direction due to stratification. If such deposits are liquefied during earthquakes, water films are likely to develop beneath less permeable sublayers leading to destabilization of a sloping ground. In Niigata city, large lateral flow displacements were reported during the Niigata earthquake in almost flat areas. Possible involvement of the water films in lateral flow failure in liquefied ground during the earthquake is examined in this research based on various site investigation data of Niigata city. Soil profiles in the area estimated from many bore-hole logging data indicate that there exists a continuous sublayer of silt or clay capping liquefiable loose sand. The elevation contours of 0.1 m pitch are drawn based on insitu leveling survey and local maps. The flow displacements during the earthquake seem to head downward normal to the contours and show a clear correlation with ground slope. This suggests that the large flow deformation in this area was driven by the slight ground surface inclination of less than 1% and that was made possible due to the formation of water films, which will considerably reduce the shear resistance of the soil against flow