Liquefaction and dynamic poroelasticity in soft sediments

In this paper we present a model that can explain earthquake-induced dynamic liquefaction in unconsolidated sediments without the need for irreversible compaction. We study the behavior of a poroelastic layer subjected to a periodic cyclic stress using dynamic poroelasticity formulation. We show that in such a layer pore pressure may increase due to a resonant mode of Biot's type II wave, an attenuated mode whose wavelength is short and can resonate 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 exceed 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 Biot's type II wave increases. Thus, in a material 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.