Seismic liquefaction, lateral spreading, and flow slides: a numerical investigation into void redistribution

Abstract

Experience from past earthquakes indicates that seismically induced large lateral spreads and flow slides in alluvial sand deposits have taken place in coastal and river areas in many parts of the world. The ground slope in these slides was often not very steep, gentler than a few percent. Recent research indicates that the presence of low-permeability silt or clay sublayers within the sand deposits is responsible for this behaviour. Such layers form a barrier to upward flow of water associated with earthquake-generated pore pressures. This causes an accumulation of pore water at the base of the layers, resulting in greatly reduced strength and possible slope instability. This paper uses an effective stress coupled stress-flow dynamic analyses procedure to demonstrate the effects of a low-permeability barrier layer on ground deformations from an earthquake event. The analyses show that an expansion zone develops at the base of barrier layers in stratified soil deposits under seismic loading which can greatly reduce shear strength and result in large deformations and flow failure. Without such a layer or layers, the slope may undergo significant displacements, but not a flow slide. Slopes with a barrier layer can be stabilized by drains.Key words: liquefaction, lateral spreads, stratification, flow failure, dynamic analysis, UBCSAND model, drain.