This research program addresses fundamental concepts for understanding the behavior of granular material (usually sand) saturated with water (below the ground water table) when subjected to the strong ground motions resulting from earthquake shaking. Under these conditions, such soils have the potential to "liquefy", that is to lose shear strength and undergo large deformations, resulting in damage to building foundations, tunnels and pipelines built on or passing through such liquefied soil. This phenomenon is related to the response of saturated loose sands strained sufficiently to result in flow slides. A devastating landslides is an example of such a flowslide. The relation between the steady state (flow slide) and the cyclic (earthquake) behavior is being addressed by fundamental experimental studies. A key element to be investigated is the concept of structural collapse of the sand fabric. The concept of "collapse" is associated with the fact that the structure of contractive sands is metastable. In a collapsive skeleton, small shear strains may be sufficient to produce a sudden rearrangement of grains with an associated loss of contact points between neighboring grains, accompanied by a large increase in pore water pressure. Consequently, the shear strength of the sand is reduced to a small value and the sand becomes susceptible to large deformations. The results of this investigation are expected to contribute to an improved understanding of liquefaction phenomena and associated instabilities, and to result in an improved ability to predict their occurrence.
