Numerical Insights into Mechanisms of Earthquake-Induced Catastrophic Landslides on Gentle Slopes in Liquefiable Soils

Abstract

Catastrophic landslides characterized by large and extremely rapid movements are among the most destructive phenomena associated with failure of slopes during earthquakes. An understanding of the mechanism involved in the occurrence of catastrophic slope failures is of major importance in the process of developing effective mitigation strategies against such geohazards. This paper employs numerical analysis to illustrate two major concepts addressing the geomechanics of catastrophic landslides on gentle slopes in liquefiable soils due to earthquakes. For slope angles less than 20º but greater than about 10º, results from laboratory geotechnical research indicate that the mechanism controlling the high mobility of the slide mass after failure appears to be the gradual loss in shear strength with progressive shear displacement, culminating in ultimate steady state strengths smaller than the static (gravitational) driving shear stress. Numerical results from a dynamic sliding block analysis addressing the seismic performance of a well-documented earthquake-induced catastrophic landslide in Japan are used to illustrate this failure mechanism. Slopes characterized by very mild gradients approaching horizontal ground conditions may experience large landslide movements due to earthquake-induced ground liquefaction as a result of void redistribution and formation of water films in liquefied deposits with continuous low permeability interlayers. A numerical example employing a finite-element scheme for transient seepage coupled with changes in volumetric strains due to excess pore pressure dissipation is used to illustrate the evolution of the water film developed beneath a low permeability interlayer in a liquefied sand deposit.