Liquefaction and dynamic poroelasticity in soft sediments

In this paper we present a model that can explain earthquake-induced dynami c liquefaction in unconsolidated sediments without the need for irreversibl e compaction. We study the behavior of a poroelastic layer subjected to a p eriodic cyclic stress using dynamic poroelasticity formulation. We show tha t in such a layer pore pressure may increase due to a resonant mode of Blot 's type II wave, an attenuated mode whose wavelength is short and can reson ate inside a layer of few meters thickness. We show that in sediments such as sand, where the shear modulus is less than 0.3 GPa, pore pressure can ex ceed the total stress. This will cause unconsolidated material to liquefy. We also show that as the elastic coefficient of the sediment decreases, the pore pressure induced by Blot's type II wave increases. Thus, in a materia l where the elastic moduli are pressure dependent (e.g., Hertzian material) the increased pore pressure reduces the stiffness and thus liquefaction is more likely to occur.