LIQUEFACTION-INDUCED FLOW, LATERAL SPREAD, AND GROUND OSCILLATION

Failures generated by liquefaction that involve lateral ground displacement are divided into three types: flow-failure, lateral-spread, and ground-oscillation. Primary factors that control the type of failure that develops, if any, include ground slope, density and continuity of the liquefiable layer, and the depth of that layer. Flow failures occur on relatively steep slopes (generally greater than 3 degrees) and require loose or contractive sediment within zones of shear deformation. The liquefiable layer must be continuous over a distance several times the thickness of the mobilized flow. Lateral spreads form beneath gentle slopes (0.3 to 3 degrees) or near free faces, such as incised river channels. The density state of granular sediment within the shear zone may be loose (contractive) to medium dense (slightly dilative). If the liquefiable layer is discontinuous or lays at a depth greater than about twice the height of a free face, for free face conditions, lateral spread is not likely to develop. Ground oscillation commonly develops on slopes that are too flat to generate lateral spread (slopes less than 0.3 degrees). As with lateral spread, ground oscillation requires a continuous liquefiable layer over a distance of tens of meters or more. Examples of these failure type and the conditions under which they developed are presented.