Mechanism for postliquefaction water film generation in layered sand

Soil investigations at two sites demonstrate that layered structure or stratification in sand deposits is prevalent not only in reclaimed ground but also in natural alluvial ground. One-dimensional liquefaction tests in a lucite tube are then carried out for models of several types of layered sand, indicating that water films will develop under most circumstances beneath or within less-permeable sublayers. A basic mechanism for the water film generation is discussed based on the measurements of soil settlement and excess pore pressure. The development of the water film and the associated soil settlement are numerically simulated by a simple sedimentation analysis and a rational explanation of the test results is found. Thus a significant involvement of water films in liquefied sand deposits and their basic mechanism are clarified. It is highly probable that water films are involved as a part of a sliding surface and play a significant role in a seismically induced flow failure in loose and layered sand deposits during liquefaction.