Liquefaction and cyclic mobility model for saturated granular media

Abstract

SUMMARYA new constitutive law for the behaviour of undrained sand subjected to dynamic loading is presented. The proposed model works for small and large strain ranges and incorporates contractive and dilative properties of the sand into the unified numerical scheme. These features allow to correctly predict liquefaction and cyclic mobility phenomena for different initial relative densities of the soil. The model has been calibrated as an element test, by using cyclic simple shear data reported in the literature. For the contractive sand behaviour a well-known endochronic densification model has been used, whereas a plastic model with a new non-associative flow rule is applied when the sand tends to dilate. Both dilatancy and flow rule are based on a new state parameter, associated to the stiffness degradation of the material as the shaking goes on. Also, the function that represents the rearrangement memory of the soil takes a zero value when the material dilates, in order to easily model the change in the internal structure. Proceeding along this kind of approach, liquefaction and cyclic mobility are modelled with the same constitutive law, within the framework of a bi-dimensional FEM coupled algorithm developed in the paper. For calibration purposes, the behaviour of the soil in a cyclic simple shear test has been simulated, in order to estimate the influence of permeability, frequency of loading, and homogeneity of the shear stress field on the laboratory data.

Undrained monotonic and cyclic simple shear behaviour of carbonate sand. D. PORCINO, G. CARIDI and V. N. GHIONNA (2008). Géotechnique 58, No. 8, 635–644

“…Therefore, the dilative behaviour of this sand is independent of its initial density, which is a rather particular behaviour, even for carbonate sand. The cyclic liquefaction or cyclic mobility failure type usually depends on the phase transformation line location in the ó9-ô plane, for cyclic simple shear tests results: the smaller the slope, the denser the sand, and the more dilative behaviour would be expected, closer to cyclic mobility failure type (López-Querol & Blázquez, 2006). The discussion focuses on two major issues.…”

An Endochronic-based approach for simulating pore water pressure variation during liquefaction of sand

“…It is appropriate to define this cumulative rearrangement of grain configurations by a suitable parameter, ξ , called "rearrangement measure", that is a function of deviatoric component of the strain tensor [1]. In the mathematical form we have…”

“…In addition, employing an appropriate constitutive law for simulating sand behavior under complex loading conditions is very important. Numerical models require constitutive laws which predict the stress-strain relationship, the soil stiffness degradation, and the changes in the pore water pressure [1]. Numerical modeling of soil liquefaction using advanced constitutive laws and numerical techniques has been the subject of many investigations in recent years.…”

“…In this case, the intrinsic time parameter represents the length of the path traced by the states of the material in strain space [6,7,8]. Lopez and Blazquez improved the Endochronic model to simulate the behavior of undrained sand under dynamic loading [1]. Their proposed model works for both small and large strains and incorporates contractive and dilative properties of the sand into a unified numerical scheme.…”

Performance of heterogeneous earthfill dams under earthquakes: optimal location of the impervious core

“…1) was derived by López-Querol and Blázquez (2006). It is based on the calculation of the plastic volumetric strains of dry sandy soil under vibrations (densification), which are related to the changes in the effective stress of the saturated soil.…”